Internet Info 1997 December/Internet_Info_CD-ROM_Walnut_Creek_December_1997.iso/faqs/alt/www/hotjava/comp.lang.java_FAQ

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Archive-name: computer-lang/java-faq/part1
Posting-Frequency: weekly
Last-modified: 1997/10/06
Version: 1.6
URL: http://sunsite.unc.edu/javafaq/javafaq.html

                         THE COMP.LANG.JAVA FAQ LIST

   This is a Java FAQ list for the comp.lang.java newsgroups. If you're
   reading the text version via Usenet, I do apologize that parts of it
   may be less intelligible than possible in HTML. Please refer to the
   HTML version at http://sunsite.unc.edu/javafaq/javafaq.html.

   The only official mirrors of this site are at the other sunsites. If
   the URL where you found this file is not a sunsite, then this is an
   illegal mirror copy and is likely to be out of date. Please refer to
   the official site instead.

   This document is Copyright 1995-1997 by Elliotte Rusty Harold. For
   information about reproduction, redistribution and other such rights
   please see the end of this file.

What's New



   Question 4.10: How do I load and display formatted HTML?

   I've added some info about Sun's HotJava HTML bean.

   Question 8.4: How do I format numbers like C's printf()?

   I've added some info about the java.text package.

   I've also added the following two questions:

     * 5.5: How can I make my applets work well on multiple browsers and
       virtual machines?
     * 14.3: Disassembly, Decompilation, and Obfuscation

   For the most part, this FAQ list covers Java 1.0.2. I have begun the
   slow process of converting this list over to Java 1.1. I am aware of
   the changes in Java 1.1 and will incorporate them as time permits.
   Please don't send me email pointing out errors or omissions that are
   only relevant to 1.1. I am fully cognizant of these.

Table of Contents

     * What's New
     * Table of Contents
     * 1: What is Java?
          + 1.1: Where did Java come from?
          + 1.2: Doesn't the World Wide Web have something to do with
            this?
          + 1.3: What platforms does Java run on?
          + 1.4: Do I need to know C++ to learn Java?
          + 1.5: Where does Javascript fit in?
          + 1.6: What's the difference between an application and an
            applet?
     * 2: What other Java Resources are available?
          + 2.1Web Sites
          + 2.2: Mailing Lists
          + 2.3: Newsgroups
          + 2.4: Books
     * 3: Java for C++ programmers
          + 3.1: Data Types
          + 3.2: Control Statements
          + 3.3: Command Line Arguments
          + 3.4: Comments
          + 3.5: Classes
          + 3.6: How is Java unlike C++?
     * 4: How Do I...
          + 4.1: Make a linked list without pointers?
          + 4.2: How do I scanf, readln, etc. in Java?
          + 4.3: How do I convert strings to numbers?
          + 4.4: How Do I Call C Code from Java?
          + 4.5: How Do I Call Java from C?
          + 4.6: How do you do multiple inheritance?
          + 4.7: Can I write objects to and read objects from a file or
            other stream?
          + 4.8: How do I call the native API from Java?
          + 4.9: How do I pass a function pointer to a method?
          + 4.10: How do I load and display formatted HTML?
          + 4.11: How do I play a sound in an application?
     * 5: Programming Applets
          + 5.1: Can applets communicate with each other?
          + 5.2: Can applets launch programs on the server?
          + 5.3: Can applets launch programs on the client?
          + 5.4: Can I record audio from an applet?
          + 5.5: How can I make my applets work well on multiple browsers
            and virtual machines?
     * 6: Language Issues
          + 6.1: What does it mean that a class or member is "final"?
          + 6.2: What does it mean that a method or field is "static"?
          + 6.3: What does it mean that a method or class is abstract?
          + 6.4: What's an interface?
          + 6.5: Why doesn't Java include insert your favorite feature
            here?
          + 6.6: Is Java CORBA compliant?
          + 6.7: Can I cast an int to an Integer? a float to a Float?
          + 6.8: How do I version a class?
          + 6.9: Why isn't there operator overloading?
          + 6.10: Does Java have pointers?
          + 6.11: Does Java pass method arguments by value or by
            reference?
          + 6.12: Are there parameterized types (templates)?
          + 6.13: How does garbage collection work?
          + 6.14: PERFORM and BECOME
     * 7: java.awt
          + 7.1: What Does AWT Stand For?
          + 7.2: What are peer "classes"?
          + 7.3: Can you explain how events are passed?
          + 7.4: Clipping
          + 7.5: How do I change the thickness of the line?
          + 7.6: What fonts does Java support?
     * 8: java.io
          + 8.1:How do I read data from a file?
          + 8.2: How do I write data to a file?
          + 8.3: How do I append data to a file?
          + 8.4: How do I format numbers like C's printf()?
     * 9: java.net
          + 9.1: How do I convert a numeric IP address like 199.1.32.90
            into a host name like star.blackstar.com?
          + 9.2: How can a Java program talk to a CGI program?
          + 9.3: How can an applet send email?
          + 9.4: How can I use ICMP in Java?
          + 9.5: How do I make Java work with a proxy server?
     * 10: java.util
          + 10.1: How random is Random()?
          + 10.2: How do I generate a random integer between a and b?
     * 11: Common Errors and Problems
          + 11.1: How Can I Avoid Flicker in an Applet?
          + 11.2: Can you explain CLASSPATH?
          + 11.3: Why won't my audio clip play?
          + 11.4: When I load the page Netscape gives me a
            java.lang.ClassFormatError.
          + 11.5: Netscape gives me "Applet Not Initialized Error"
          + 11.6: Other Netscape Problems
          + 11.7: I keep getting access privilege violations, " Java
            tried to read file foo.class in directory bar."
          + 11.8: javac keeps insisting that it can't find the right
            constructor function in my class, but I'm sure it's in a
            file I imported. Why is it even looking in my class instead
            of the imported file?
          + 11.9: NullPointerExceptions with arrays of objects
          + 11.10: Can't make static reference to method type myMethod in
            class myClass
          + 11.11: Why do I have trouble when using == to compare
            Strings?
     * 12: Security
          + 12.1: System Level Security
          + 12.2: User Level Security
     * 13: Tools
          + 13.1: IDE
          + 13.2: Debugger
          + 13.3: Editors
          + 13.4: YACC grammar
          + 13.5: Profilers
     * 14: The Java Virtual Machine and Byte Code
          + 14.1: Can I program directly in byte code?
          + 14.2: Optimizing Java
          + 14.3: Disassembly, Decompilation, and Obfuscation
     * 15: Legal Issues
     * 16: FAQ's about the FAQ
          + 16.1: Who is this Elliotte guy, and just what qualified him
            to write a Java FAQ anyway?
          + 16.2: Why don't you include X in your FAQ?
          + 16.3: This is really cool. Can I republish or translate it?

1: What is Java?

   Java, formerly known as oak, is an object-oriented programming
   language developed by Sun. It shares many superficial similarities
   with C, C++, and Objective C (for instance for loops have the same
   syntax in all four languages); but it is not based on any of those
   languages, nor have efforts been made to make it compatible with them.

   Java is sometimes referred to as C++ ++ --. The language was
   originally created because C++ proved inadequate for certain tasks.
   Since the designers were not burdened with compatibility with existing
   languages, they were able to learn from the experience and mistakes of
   previous object-oriented languages. They added a few things C++
   doesn't have like garbage collection and multithreading; and they
   threw away C++ features that had proven to be better in theory than in
   practice like multiple inheritance and operator overloading. (There's
   still argument over whether they made the right choices. I tend to
   think they were correct to throw out operator overloading and probably
   correct to throw out multiple inheritance. For now let's just say that
   neither choice is likely to be reviewed soon.)

   Even more importantly Java was designed from the ground up to allow
   for secure execution of code across a network, even when the source of
   that code was untrusted and possibly malicious. This required the
   elimination of more features of C and C++. Most notably there are no
   pointers in Java. Java programs cannot (at least in theory) access
   arbitrary addresses in memory.

   Furthermore Java was designed not only to be cross-platform in source
   form like C, but also in compiled binary form. Since this is frankly
   impossible across processor architectures, Java is compiled to an
   intermediate byte-code which is interpreted on the fly by the Java
   interpreter. Thus to port Java programs to a new platform all that is
   needed is a port of the interpreter and a few native code libraries.

    Finally Java was designed to make it a lot easier to write bug free
   code. Shipping C code has, on average, one bug per 55 lines of code.
   About half of these bugs are related to memory allocation and
   deallocation. Thus Java has a number of features to make bugs less
   common:
     * Strong Typing
     * No unsafe constructs
     * The language is small so its easy to become fluent.
     * The language is easy to read and write. Obfuscated Java isn't
       nearly as common as obfuscated C.
     * There are no undefined or architecture dependent constructs.
     * Java is object oriented so reuse is easy.
     * Java has concurrency.

  1.1: WHERE DID JAVA COME FROM?

   In the late 1970's Bill Joy thought about doing a language that would
   merge the best features of MESA and C. However other projects (like
   cofounding Sun) intervened. In the late 1980's he got Sun's engineers
   started on a complete revision of the UNIX operating system that
   involved merging SunOS4.x with AT&T's SYSVR4.

   In 1989 Joy sold his Sun stock, invested heavily in Microsoft and
   moved out of mainstream Sun to Aspen, Colorado. By the early 90's Bill
   was getting tired of huge programs. He decided that he wanted to be
   able to write a 10,000 line program that made a difference. In late
   1990 Bill wrote a paper called Further which outlined his pitch to Sun
   engineers that they should produce an object environment based on C++.
   Today Joy freely admits that C++ was too complicated and wasn't up to
   the job.

   Around this time James Gosling (of emacs fame) had been working for
   several months on an SGML editor called "Imagination" using C++. The
   Oak language (now Java) grew out of Gosling's frustration with C++ on
   his "Imagination" project.

   Patrick Naughton, then of Sun, now vice-president of technology at
   StarWave, started the Green Project on December 5th, 1990. Naughton
   defined the project as an effort to "do fewer things better". That
   December he recruited Gosling and Mike Sheridan to help start the
   project. Joy showed them his Further paper, and work began on graphics
   and user interface issues for several months in C.

   In April of 1991 the Green Project (Naughton, Gosling and Sheridan)
   settled on smart consumer electronics as the delivery platform, and
   Gosling started working in earnest on Oak. Gosling wrote the original
   compiler in C; and Naughton, Gosling and Sheridan wrote the
   runtime-interpreter, also in C. Oak was running its first programs in
   August of 1991. Joy got his first demos of the system that winter,
   when Gosling and Naughton went skiing at Joy's place in Aspen.

   By the fall of 1992 "*7", a cross between a PDA and a remote control,
   was ready This was demoed to Scott McNealy, Sun's president, in
   October. He was blown away. Following that the Green Project was set
   up as First Person Inc., a wholly owned Sun subsidiary.

   In early 1993 the Green team heard about a Time-Warner request for
   proposal for a settop box operating system. First Person quickly
   shifted focus from smart consumer electronics (which was proving to be
   more hype than reality) to the set-top box OS market, and placed a bid
   with Time-Warner.

   Fortuitously, Sun lost the bid. The Time-Warner project went nowhere,
   the same place it probably would have gone if Sun had won the bid.
   First Person continued work on settop boxes until early 1994, when it
   concluded that like smart consumer electronics settop boxes were more
   hype than reality.

   Without a market to be seen First Person was rolled back into Sun in
   1994. However around this time it was realized that the requirements
   for smart consumer electronics and settop box software (small,
   platform independent secure reliable code) were the same requirements
   for the nascent web.

   For a third time the project was redirected, this time at the web. A
   prototype browser called WebRunner was written by Patrick Naughton in
   one weekend of inspired hacking. After additional work by Naughton and
   Jonathan Payne this browser became HotJava. The rest, as they say, is
   history.

   Information in this section is primarily based on the first hand
   accounts of Bill Joy and Patrick Naughton (which don't always agree).
   No doubt other people have still different memories of what occurred.
   If you've got any more first hand information about what went on in
   the Green project I'd like to hear from you.

  1.2: DOESN'T THE WORLD WIDE WEB HAVE SOMETHING TO DO WITH THIS?

   Not necessarily. Java is a programming language. When work began on
   what has become Java, the World Wide Web was just getting started at
   CERN; and Mosaic wasn't even a glint in Marc Andreesen's eye. The
   original use of the Java language (settop boxes) required security and
   the ability to execute code from untrusted hosts. It turns out these
   are virtually the same requirements for allowing people to download
   and run programs from the Web. No other language has the built-in
   security of Java. The key here is the security features. The
   object-oriented nature of Java is secondary, and mainly reflects the
   preferences and prejudices of the developers who set out to write a
   secure language. The C-like syntax of the language is even less
   crucial.

   At the lowest level the advantage of Java to the web is that it
   provides a secure, cross-platform way for code to be executed. At a
   somewhat higher level Java adds several features to existing web
   sites:

   Arbitrary Graphics
          Java lets the server draw pictures in a window on the client.
          In theory this allows a web page to do anything a regular
          program can do by drawing in a window.

   Arbitrary Data Types
          In practice rather than using graphics primitives to create
          your desired web page you'd use a graphics program to draw the
          page and then write a program that could read and display the
          file formats of that program. Java lets you write content
          handlers that display any particular data format. This way you
          can download your data and your data display program rather
          than downloading a bitmapped snapshot of the display. People
          are already using this to add sound and animation to web pages.
          Rather than having to download a file and spawn an external
          viewer, the viewer is included with the data; and the data is
          displayed right on the page.

   Less Load On The Server
          CPU intensive cgi-bin scripts place a large load on a server,
          particularly at busy sites. With Java you can off-load the
          calculations to the client's PC. I've written an applet that
          calculates all possible ram configurations for a given Mac
          model. However on models with many memory slots the sheer
          number of permutations can tie up even a fast machine for
          several hours. Publishing this as a cgi-bin would bring my
          server to its knees, but by publishing it as a Java applet I
          can distribute the load across all the machines that want to
          run it.

   More User Interaction
          Finally Java allows for more interaction with the user. Java
          not only allows you to paint arbitrary data on the screen. It
          also allows you to collect input from the user in the form of
          mouse clicks, keystrokes and the like. This lets you put almost
          any application on your web page that doesn't require disk
          access.

  1.3: WHAT PLATFORMS DOES JAVA RUN ON?

   Sun has made a Java Development Kit (JDK) available for Sparc and X86
   Solaris, Windows NT and Windows 95 Intel. The JDK is free, and most
   third party ports are based on this.

   Sun also published a 1.0.2 JDK for MacOS 7.5 on PowerMacs and 68030
   (25 MHz and faster) and 68040 Macs. However it's dropped development
   for Macs in favor of Apple's own Macintosh Runtime for Java (MRJ)
   which is a better option for Mac users. Currently MRJ supports Java
   1.0. Java 1.1 support is promised soon.

   SGI's port of Sun's JDK 1.1.x to IRIX 5.3, 6.2, 6.3, and 6.4 is
   available at http://www.sgi.com/Fun/Free_webtools.html. An IRIX port
   of JDK 1.0 has mostly been completed by Simon Leinen.

   A Linux port is in fairly good shape. See
   http://java.blackdown.org/java-linux.html.

   IBM has ported Java to Windows 3.1, OS/2, and AIX. It is working on
   ports for MVS and OS/400. See
   http://ncc.hursley.ibm.com/javainfo/hurindex.html .

   The OSF has ported the JDK 1.0.2 to Unixware, the Bull Estrella or
   other PowerPC running AIX4.1, X86 running DASCOM OSF/1 , the Digital
   Alpha running Digital UNIX 3.2, the HP700 series running HPUX 10.x,
   the NCR Globalyst (Pentium) running UNIX SysV, and Sony NEWS (MIPS)
   running Sony NEWS 6.1.1. See http://www.osf.org/mall/web/JDK/.

   Other ports are underway for Nextstep, SunOS 4.1, the Amiga and
   possibly other platforms.

   In the past new versions of Java have most often been made available
   first for Solaris. If you have to have the latest version as soon as
   it's released, or if you're developing "Bet your company" applications
   with Java, you should probably be running Solaris on a SparcStation.
   Otherwise, if you just want to learn the language, you can get away
   with an Intel based Windows 95 or NT machine with a lot of RAM.

   Netscape 2.0 and later plays Java 1.0 applets on Windows NT, Windows
   95, Solaris, SunOS 4.1, Linux and most other Unix platforms. Netscape
   3.0 for the Mac also supports Java 1.0. Netscape 4.0 and earlier and
   Internet Explorer 3.0 and earlier do not support Java 1.1 to any
   significant extent, only Java 1.0. The only web browser that really
   supports Java 1.1 is Sun's HotJava.

   Netscape 2.0 can even compile Java programs. (Netscape 3.0 cannot).

   First download the classes.zip file from the Solaris distribution of
   the JDK. (You have to download the entire JDK. You can't get just the
   classes.zip file.) Next set your CLASSPATH environment variable to
   include the classes.zip file. For example, on Unix, if you put the
   file in /usr/local/lib/classes.zip, then you would set it like this:

sh: % CLASSPATH=$CLASSPATH:/usr/local/lib/classes.zip
csh: % setenv CLASSPATH "$CLASSPATH:/usr/local/lib/classes.zip"

   You'll probably want to put this line in your .login or .cshrc file.
   Of course you'll need to adjust this to match where you've installed
   these files and to add any other classes you use. Finally you compile
   programs from the command line like this:

% netscape -java sun.tools.javac.Main HelloWorld.java

   You can always alias netscape -java sun.tools.javac.Main to just javac
   to make this more transparent.

   You can also run command-line programs that don't use the AWT in the
   same way, like this:

% netscape -java HelloWorld.class

   You can't use netscape -java to run programs that use the AWT, but you
   can of course play applets in Netscape..

  1.4: DO I NEED TO KNOW C++ TO LEARN JAVA?

   No. Java is in fact a much easier language to learn than C++.

   A little further out in left field, it isn't even necessary to know
   Java to write Java programs. Intermetrics is beta testing an ADA-95 to
   Java byte code compiler. Other such cross-compilers are probably
   possible including ANSI Fortran-77, COBOL, and Basic. However the one
   most people probably want, a C/C++ to Java byte code compiler, is
   probably not possible due to Java's lack of pointers.

  1.5: WHERE DOES JAVASCRIPT FIT IN?

   To quote from p. 31 of my book, The Java Developer's Resource,

     Java and JavaScript are about as closely related as the Trump Taj
     Mahal in Atlantic City is to the Taj Mahal in India. In other words
     Java and JavaScript both have the word Java in their names.
     JavaScript is a programming language from Netscape which is
     incorporated in their browsers. It is superficially similar to Java
     in the same way C is similar to Java but differs in all important
     respects.

  1.6: WHAT'S THE DIFFERENCE BETWEEN AN APPLICATION AND AN APPLET?

   This question can be answered on many levels. Technically an
   application is a Java class that has a main() method. An applet is a
   Java class which extends java.applet.Applet. A class which extends
   java.applet.Applet and also has a main() method is both an application
   and an applet.

   More generally and less technically an application is a stand-alone
   program, normally launched from the command line, and which has more
   or less unrestricted access to the host system. An applet is a program
   which is run in the context of an applet viewer or web browser, and
   which has strictly limited access to the host system. For instance an
   applet can normally not read or write files on the host system whereas
   an application normally can.

   The actions of both applets and applications, however, can be
   controlled by SecurityManager objects. If you can change the
   SecurityManager that's used you can change what an applet or an
   application is and is not allowed to do. Thus these are not hard and
   fast differences, though this is normally how they separate out in
   practice.

2 What other Java Resources are available?

  2.1WEB SITES

   The key site for Java information is http://www.javasoft.com/. This is
   Sun's official site for Java, and contains the latest published
   version of all official Java information. The most important page on
   this site is the Documentation page at http://www.javasoft.com/doc/.
   Most of the other pages are linked off of this page or its children.

   For many more web sites see the Cafe au Lait links page at
   http://sunsite.unc.edu/javafaq/links.html.

  2.2: MAILING LISTS

   There are over sixty different Java related mailing lists. A
   more-or-less complete list is at the Cafe Au Lait mailing list page at
   http://sunsite.unc.edu/javafaq/mailinglists.html.

  2.3: NEWSGROUPS

   alt.www.hotjava
          A newsgroup for the discussion of the HotJava browser.

   comp.lang.java.announce
          A newsgroup for announcements that may be of interest to Java
          developers. See
          http://www.cs.latrobe.edu.au/~leachbj/clj.announce/guidelines
          .html for the ridiculously complicated submission guidelines
          and submission address.

   comp.lang.java.programmer
          A newsgroup for the discussion of the Java language.

   comp.lang.java.machine
          Technical issues about Java not related directly to
          programming, including virtual machines, byte code, classfile
          format, performance and optimization, possible extensions,
          porting, native methods and interfacing Java with other
          languages.

   comp.lang.java.security
          Discussion concerning any of Java's security features such as
          byte code verification, SecurityManagers, class loaders,
          public-key encryption and authentication of classes, holes in
          the security model, and similar topics.

   comp.lang.java.help
          This group is for end-users of Java systems, not programmers.
          It deals with installation problems, CLASSPATH problems, the
          availability of ports to specific platforms, and the like.
          Subject lines should include the platform that the problem
          occurs on, and the browser version, for example MacOS 7.5
          Netscape 3.0.

   comp.lang.java.beans
          The JavaBeans component software API

   comp.lang.java.databases
          Java and databases, including middleware like java.sql, JDBC,
          ODBC, and Java based databases like jDB.

   comp.lang.java.gui
          The AWT and other GUI enrvironments: windows, dialogs, menus,
          components, buttons, radio buttons, printing, cut and paste,
          etc.

   comp.lang.java.softwaretools
          Integrated Development Environments (IDEs), web browsers,
          compilers, applet viewers, Rapid Application Development (RAD)
          tools, class browsers, visual interface builders, and other
          tools.

  2.4: BOOKS

   As of March, 1997 I recommend four books in particular for those
   learning the language. The first is my own book, The Java Developer's
   Resource, ISBN: 0-13-570789-7, $26.95 from Prentice Hall. This is an
   introduction to Java 1.0 for programmers, regardless of previous
   experience with C or OOP. It should be available in most bookstores
   that stock computer books as well as from amazon.com,
   http://www.amazon.com/exec/obidos/ISBN=0135707897/

   The second book I recommend is Java in a Nutshell: A Desktop Quick
   Reference for Java Programmers by David Flanagan from O'Reilly &
   Associates, Inc., ISBN: 1-56592-262-X, $19.95 (the tiger book). This
   is an excellent introduction to Java for C and C++ programmers and an
   excellent reference for everyone.

   For people with no prior experience in programming I recommend Kris
   Jamsa's Java Now!, ISBN: 1-884133-30-4, $16.95, Jamsa Press.

   None of these books cover Java 1.1. In fact as of this writing, few
   books truly cover Java 1.1 though several claim to. The best of the
   lot as of this writing seems to be Rogers Cadenhead's Teach Yourself
   Java 1.1 Programming in 24 Hours from Sams.net, ISBN 1-57521-270-6.
   This is a decent book introducing Java 1.1 programming to
   non-programmers. However it's quite basic, and coverage of the AWT is
   very limited.

   For details about these and many more books see the Cafe au Lait books
   page at http://sunsite.unc.edu/javafaq/books.html

3: Java for C++ programmers

   In the large Java looks like Smalltalk. In the small it looks like C.
   The syntax of Java is deliberately similar to C. If you know C you
   already know large chunks of Java. Here, in brief, is Java syntax for
   C programmers:

  3.1: DATA TYPES

   Java's primitive data types are very similar to those of C. (The
   boolean type has been added.) However the implementation of the data
   types has been substantially cleaned up in several ways.

    1. Where C and C++ leave a number of issues to be machine and
       compiler dependent (for instance the size of an int) Java
       specifies everything.

    2. Java prevents casting between arbitrary variables. Only casts
       between numeric variables and between sub and superclasses of the
       same object are allowed.

    3. All numeric variables in Java are signed.



   Here are the detailed primitive data types:

   boolean
          1-bit. May take on the values true and false only.

          true and false are defined constants of the language and are
          not the same as True and False, TRUE and FALSE, zero and
          nonzero, 1 and 0 or any other numeric value. Booleans may not
          be cast into any other type of variable nor may any other
          variable be cast into a boolean.

   byte
          1 signed byte (two's complement). Covers values from -128 to
          127.

   short
          2 bytes signed (two's complement), -32,768 to 32,767

   int
          4 bytes, signed (two's complement). -2,147,483,648 to
          2,147,483,647. Like all numeric types ints may be cast into
          other numeric types (byte, short, long, float, double). When
          lossy casts are done (e.g. int to byte) the conversion is
          done modulo the length of the smaller type.

   long
          8 bytes signed (two's complement). Ranges from
          -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807.

   float
          4 bytes, IEEE 754. Covers a range from 1.40129846432481707e-45
          to 3.40282346638528860e+38 (positive or negative).

          Like all numeric types floats may be cast into other numeric
          types (byte, short, long, int, double). When lossy casts to
          integer types are done (e.g. float to short) the fractional
          part is truncated and the conversion is done modulo the length
          of the smaller type.

   double
          8 bytes IEEE 754. Covers a range from 4.94065645841246544e-324d
          to 1.79769313486231570e+308d (positive or negative).

   char
          2 unsigned bytes, Unicode.

          Chars are not the same as bytes, ints, shorts or Strings.

          sizeof isn't necessary in Java because all sizes are precisely
          defined. i.e. an int is always 4 bytes. This may not seem to be
          adequate when dealing with objects that aren't base data types.
          However even if you did know the size of a particular object,
          you couldn't do anything with it anyway. You cannot convert an
          arbitrary object into bytes and back again.

          Strings are a reference or object type, that is a instances of
          the class java.lang.String. They are not null terminated and
          are not the same as an array of chars.

          Arrays are also objects. Multidimensional arrays are created
          via arrays of arrays.

  3.2: CONTROL STATEMENTS

   Java contains if, else, for, while, do while and switch statements.
          The syntax is identical to C's. However all condition tests
          must return boolean values. Since non-boolean assignment
          statements and arithmetic statements do not return a boolean
          value, some of the more obfuscated condition tests in C are
          prohibited.

  3.3: COMMAND LINE ARGUMENTS

   Command line arguments are like C's except that argv has become a
          string array commonly called args and args[0] is the first
          command line argument, not the name of the program. The other
          arguments are all shifted one to the left from where they'd be
          in C or C++.

  3.4: COMMENTS

   Java supports both the /* This is a comment */ comment from C and the
          // This is a C++ comment
          comment from C++.

          However comments that begin with a /** are special. These
          comments should only be used before a method or class
          declaration. They indicate that the comment should be included
          in automatically generated documentation for that declaration.

  3.5: CLASSES

   Java does not support multiple inheritance.

          Superclasses of a class are indicated with the extends keyword
          rather than with a :.

          Methods must be defined inside the class to which they belong.
          They may not be declared inside the class and defined outside
          the class as is common in C++.

  3.6: HOW IS JAVA UNLIKE C++?

   Two classes of language features have been removed from C++ to make it
          Java. These are those language features which make C++ unsafe
          and those which make it hard to read.

          Features removed that make Java easier to read and understand
          than C++ include #define, typedef, operator overloading, enum,
          unions and structs.

          The main feature removed to make Java safer and more robust
          than C++ is pointer arithmetic.

          Other features removed include global variables, standalone
          functions (everything is a method), friend functions
          (Everything in a package is a friend of everything else in the
          package.) and non-virtual functions.

          A number of features have been added to Java to make it safer
          including true arrays with bounds checking, garbage collection,
          concurrency, interfaces (from Objective C) and packages. There
          is no need to explicitly allocate or free memory in Java.

4: How Do I...

  4.1: MAKE A LINKED LIST WITHOUT POINTERS?

   Short answer: Use the Vector class in java.util. It can do anything a
          linked list can do and a little more and saves you a lot of
          coding which, after all, is the point of OOP and the class
          library. However it is array based so insertions or deletions
          from the middle of a Vector are not as efficient as with a true
          linked list.

          Long answer: Object variables in Java are all references. A
          reference acts like a pointer in most other languages. (Though
          they're handles, not pointers, in most Java implementations.
          The notable exception is Microsoft's.) The main difference is
          that you can't do pointer arithmetic on references. Therefore
          wherever you'd use a pointer to an object in C++, in Java you
          should just use the object itself.

          On the other hand the primitive data types (int, float, double,
          char, byte, short, long and boolean) are not references. If you
          want to get a reference to one of these you need to wrap it in
          a class first. Java provides ready-made type-wrapper classes in
          the java.lang package for Boolean, Character, Integer, Double,
          Float, and Long. Bytes and shorts can be stored in the Integer
          class as well. Java 1.1 adds Byte, Short, and Void classes too.

  4.2: HOW DO I SCANF, READLN, ETC. IN JAVA?

   Java has no exact equivalent to C's scanf(), fscanf() and sscanf()
          functions, Pascal's read() and readln() function, or Fortran's
          READ* function. In particular there's no one method that lets
          you get input from the user as a numeric value.

          However, roughly equivalent functionality is scattered across
          several classes. You first read an input line into a String
          using DataInputStream.readline() or BufferedReader (in Java
          1.1)

          Next use the StringTokenizer class in java.util to split the
          String into tokens. By default StringTokenizer splits on white
          space (spaces, tabs, carriage returns and newlines), but this
          is user definable.

          For example,

import java.util.StringTokenizer;

class STTest {

  public static void main(String args[]) {

    String s = "9 23 45.4 56.7";

    StringTokenizer st = new StringTokenizer(s);
    while (st.hasMoreTokens()) {
      System.out.println(st.nextToken());
    }

  }

}

   prints the following output:


9
23
45.4
56.7

   Finally you convert these tokens into numbers using the type wrapper
          classes as described in the next question.

  4.3: HOW DO I CONVERT STRINGS TO NUMBERS?

   You can convert strings into numbers using the Integer, Float, Double
          and Long type wrapper classes as indicated by the following
          code snippet:

class ConvertTest {

  public static void main (String args[]) {

    String str;

    str = "25";

    int i = Integer.valueOf(str).intValue();
    System.out.println(i);
    long l = Long.valueOf(str).longValue();
    System.out.println(l);

    str = "25.6";

    float f = Float.valueOf(str).floatValue();
    System.out.println(f);
    double d = Double.valueOf(str).doubleValue();
    System.out.println(d);

  }

}

   There are no equivalent Short and Byte classes in Java 1.0. There are
          in Java 1.1. For shorts and bytes use the Integer class but use
          the byteValue() or shortValue() methods instead.

  4.4: HOW DO I CALL C CODE FROM JAVA?

   First of all for security reasons you can only call external code from
          an application. You cannot call external code from an applet.
          (Otherwise all the security would go out the window.)
          Furthermore all code you write in this way will be
          non-portable. If these aren't problems for you, check out javah
          in the JDK 1.0 or the Java Native Interface in JDK 1.1.

          Chapter 19 of my book Java Secrets discusses the Java Native
          Interface in depth. (IDG Books, 1997, ISBN 0-764-58007-8,
          http://www.amazon.com/exec/obidos/ISBN=0764580078/cafeaulaitA
          /)

  4.5: HOW DO I CALL JAVA FROM C?

   Since Java is not as of yet a true compiled language, the only way to
          call Java code from C in Java 1.0 is by using the system() call
          (or your OS's equivalent) to execute the java interpreter with
          appropriate command line arguments.

          In Java 1.1 the Java Native Method Interface in combination
          with the Invocation API allows native applications to load and
          access the Java virtual machine.

  4.6: HOW DO YOU DO MULTIPLE INHERITANCE?

   Java does not support multiple inheritance. Instead declare interfaces
          for each additional class you want to inherit from, and
          implement those interfaces in your subclass. For more details,
          see question 6.1 below.

  4.7: CAN I WRITE OBJECTS TO AND READ OBJECTS FROM A FILE OR OTHER STREAM?

   In theory yes, but once again all the coding is up to you. There is no
          general method for doing this in Java 1.0. The problem is made
          harder by Java's security features that don't let you forge
          arbitrary byte streams into objects.

          In Java 1.1 a serialization interface has been added to the
          language. However only objects that explicitly implement the
          java.io.Serializable interface can be serialized.

  4.8: HOW DO I CALL THE NATIVE API FROM JAVA?

   You can do this only in an application, not in an applet. You will
          need to write some intermediary code in C or another
          traditional language and call your C code from Java.

  4.9: HOW DO I PASS A FUNCTION POINTER TO A METHOD?

   Methods are not first class objects in Java. Only objects and
          primitive data types can be passed to methods.

          Instead you should declare an interface which declares the
          function you want to pass; for example

public interface Comparable {

  public abstract int compare(Object o1, Object o2);

}

   Then declare that your method takes an object of this type. For
          example,

  public void sort(Object[] o, Comparable c) {

    boolean done = false;
    while (!done) {
      done = true;
      for (int i = 0; i < o.length - 1; i++) {
      if (c.compare(o[i], o[i+1]) < 0) {
        swap(o[i], o[i+1]);
        done = false;
      }

    }

  }

   Each class you want to compare then needs its own class which
          implements Comparable. For example,

public class StringCompare implements Comparable {

  public int compare(Object o1, Object o2) {

    String s1 = (String) o1;
    String s2 = (String) o2;
    return s1.compareTo(s2);

  }

}

   It helps that Object is a superclass for all object types.

  4.10: HOW DO I LOAD AND DISPLAY FORMATTED HTML?

   If you need to do this, you should probably be looking at JavaScript
          instead of Java. It's possible in Java, but only with GREAT
          difficulty. There is no simple answer at this point in time.
          The problem is that Java does not contain a built-in HTML
          rendering engine. You either need to generate the file on the
          server, then load the URL of that file into the browser; or you
          need to write a complete HTML parser and display engine.

          Recently Sun released the $195 payware HotJava HTML Component.
          This is a Java bean which parses and renders HTML. In requires
          Java 1.1 or later.

          There is at least one semi-free third party solution. Data
          Technology's Ice Browser
          (http://www.bgnett.no/datatech/ICEBrowser/index.html) can
          handle most HTML 3.2 constructs, though I haven't had a chance
          to test it personally yet. Ice Browser also requires Java 1.1.

  4.11: HOW DO I PLAY A SOUND IN AN APPLICATION?

   Java's audio support comes from the AppletContext class and the
          AudioClip interface. Since applications don't have applet
          contexts, they have no easy way to play audio clips. This is
          supposed to be fixed in Java 1.2. In the meantime you have to
          use undocumented classes in the sun packages. The following
          example demonstrates:

import sun.audio.*;
import java.awt.*;
import java.io.*;


public class SoundPlayer extends Frame implements FilenameFilter {

  Button openButton = new Button("Open");
  Button playButton = new Button("Play");
  Button loopButton = new Button("Loop");
  Button stopButton = new Button("Stop");
  Label filename = new Label("                   ");
  File theFile = null;
  AudioData theData = null;
  InputStream nowPlaying = null;

  public SoundPlayer() {
    super("Sound Player");
    resize(300, 200);
    Panel north = new Panel();
    north.setLayout(new FlowLayout(FlowLayout.LEFT));
    north.add(new Label("File: "));
    north.add("North", filename);
    add("North", north);
    Panel south = new Panel();
    south.add(openButton);
    south.add(playButton);
    south.add(loopButton);
    south.add(stopButton);
    add("South", south);
  }

  public static void main(String[] args) {
    SoundPlayer sp = new SoundPlayer();
    sp.show();
  }

  public void open() {
    FileDialog fd = new FileDialog(this, "Please select a .au file:");
    fd.setFilenameFilter(this);
    fd.show();
    try {
      theFile = new File(fd.getDirectory() + "/" + fd.getFile());
      if (theFile != null) {
        filename.setText(theFile.getName());
        FileInputStream fis = new FileInputStream(theFile);
        AudioStream as = new AudioStream(fis);
        theData = as.getData();
      }
    }
    catch (IOException e) {
      System.err.println(e);
    }
  }

  public void play() {
    stop();
    if (theData == null) open();
    if (theData != null) {
      AudioDataStream ads = new AudioDataStream(theData);
      AudioPlayer.player.start(ads);
      nowPlaying = ads;
    }
  }

  public void stop() {
    if (nowPlaying != null) {
      AudioPlayer.player.stop(nowPlaying);
      nowPlaying = null;
    }
  }

  public void loop() {
    stop();
    if (theData == null) open();
    if (theData != null) {
      ContinuousAudioDataStream cads = new ContinuousAudioDataStream(theData);
      AudioPlayer.player.start(cads);
      nowPlaying = cads;
    }
  }

  public boolean action(Event e, Object what) {

    if (e.target == playButton) {
      play();
      return true;
    }
    else if (e.target == openButton) {
      open();
      return true;
    }
    else if (e.target == loopButton) {
      loop();
      return true;
    }
    else if (e.target == stopButton) {
      stop();
      return true;
    }

    return false;

  }

  public boolean accept(File dir, String name) {

    name = name.toLowerCase();
    if (name.endsWith(".au")) return true;
    if (name.endsWith(".wav")) return true;
    return false;

  }

}

   This example is taken from Chapter 10 of Java Secrets, available from
          amazon
          (http://www.amazon.com/exec/obidos/ISBN=0764580078/cafeaulait
          A/) and various independent bookstores. It's published by IDG
          Books, ISBN number 0-764-58007-8. Chapters 8-17 cover various
          of the sun packages including sun.audio. (Chapters 1-7 cover
          the internals of Java like byte code and class files. Chapter
          19 and 20 cover platform dependent Java including native
          methods.)

5: Programming Applets

  5.1: CAN APPLETS COMMUNICATE WITH EACH OTHER?

   At this point in time applets may communicate with other applets
          running in the same virtual machine. If the applets are of the
          same class, they can communicate via shared static variables.
          If the applets are of different classes, then each will need a
          reference to the same class with static variables. In any case
          the basic idea is to pass the information back and forth
          through a static variable.

          An applet can also get references to all other applets on the
          same page using the getApplets() method of
          java.applet.AppletContext. Once you've got a reference to an
          applet, you can communicate with it by using its public
          members.

          It is conceivable to have applets in different virtual machines
          that talk to a server somewhere on the Internet and store any
          data that needs to be serialized there. Then, when another
          applet needs this data, it could connect to this same server.
          Implementing this is non-trivial.

  5.2: CAN APPLETS LAUNCH PROGRAMS ON THE SERVER?

   Yes, using CGI. Any other implementation would be server dependent. Of
          course this requires a lot of coding and is non-trivial. A
          simple way to do this is not built into Java because that would
          require a special server. One of Java's strengths is that it is
          web server independent.

          A number of organizations have developed special http servers
          that allow applets or other clients to run Java programs on the
          server in a secure environment. Most notably Sun's Java Web
          Server implements a servlet interface for this purpose. The
          W3C's JigSaw implements a similar idea called resource objects.

  5.3: CAN APPLETS LAUNCH PROGRAMS ON THE CLIENT?

   Absolutely not. This would be a security hole big enough to walk three
          herds of elephants, two marching bands and at least one quarter
          of the people AT&T laid off through.

  5.4: CAN I RECORD AUDIO FROM AN APPLET?

   This is what is known as "a third-party opportunity". In other words
          not this year and probably not next year either. This would
          make a neat Java plug-in if anyone cares to write one in C.

  5.5: HOW DO I MAKE MY APPLETS WORK WELL ON MULTIPLE BROWSERS AND VIRTUAL
  MACHINES?

   Java is cross-platform, but that doesn't mean all platforms, browsers,
          and virtual machines operate identically. However, there are a
          number of steps a developer can take to ensure that their
          applet works reasonably well on most browsers.

         1. Use Java 1.0 only. Use a Java 1.0 compiler and a Java 1.0
            environment to test in. Do not use Java 1.1.

         2. From day 1, run your tests in Netscape Navigator 3.0 and
            earlier. Of browsers that support Java, Navigator's probably
            the buggiest so if you can get something to work there it's
            more likely to run elsewhere. In particular, do not develop
            your applets using the appletviewer. The appletviewer's too
            reliable and too stable to accurately model real user
            experience.

         3. From day 1, include multiple platforms in your tests and
            development. You may not be able to test on every platform
            Java supports, but Windows 95 and the Mac are a must. The Mac
            VMs in Navigator are some of the worst around so it's
            important to write for them. Windows NT is also a nice test,
            but I'd stay away from Solaris unless I had lots of time.
            It's too stable and reliable. However, Linux makes a very
            nice test since it's a stable OS (which you're not testing
            against) combined with a buggy VM and a strange GUI (which
            you are testing against). If you've got multiple people
            working on the project, have them work on different platforms
            and report bugs to each other. Better yet have them switch
            development environments daily so programmers are forced to
            make sure their code works in all browsers.

         4. Learn to love layout managers. Provide plenty of extra white
            space in your user interfaces. Learn to hate absolute
            positioning. If you must use it, be sure to check font
            metrics. Don't just eyeball it.

         5. Avoid filename filters, multiple window interfaces, and other
            GUI features that don't translate well across platforms.

   I know this sounds a little perverted. I'm telling you to work with
          the worst tools rather than the best. But right now Sun's
          promise of "write once/run anywhere" translates into "write
          once/debug everywhere". And the fact is, users are far more
          likely to be using the buggy platforms like Mac/Netscape rather
          than stable ones like Solaris/appletviewer. Working around a
          bug in one VM generally doesn't cause problems on other VMs. In
          fact it will probably make your code more portable to platforms
          you haven't tested. However, assuming that your development
          environment is bug-for-bug compatible with users' runtime
          environments does cause problems. It is much easier to work
          with multiple platforms from the beginning, rather than
          developing a great app on Windows or Solaris and then porting
          it to all the other platforms.

6: Language Issues

  6.1: WHAT DOES IT MEAN THAT A CLASS OR MEMBER IS FINAL?

   A final class can no longer be subclassed. Mostly this is done for
          security reasons with basic classes like String and Integer. It
          also allows the compiler to make some optimizations, and makes
          thread safety a little easier to achieve.

          Methods may be declared final as well. This means they may not
          be overridden in a subclass.

          Fields can be declared final, too. However, this has a
          completely different meaning. A final field cannot be changed
          after it's initialized, and it must include an initializer
          statement where it's declared. For example,

          public final double c = 2.998;

          It's also possible to make a static field final to get the
          effect of C++'s const statement or some uses of C's #define,
          e.g.

public static final double c = 2.998;


  6.2: WHAT DOES IT MEAN THAT A METHOD OR FIELD IS "STATIC"?

   Static variables and methods are instantiated only once per class. In
          other words they are class variables, not instance variables.
          If you change the value of a static variable in a particular
          object, the value of that variable changes for all instances of
          that class.

          Static methods can be referenced with the name of the class
          rather than the name of a particular object of the class
          (though that works too). That's how library methods like
          System.out.println() work. out is a static field in the
          java.lang.System class.

  6.3: WHAT DOES IT MEAN THAT A METHOD OR CLASS IS ABSTRACT?

   An abstract class cannot be instantiated. Only its subclasses can be
          instantiated. You indicate that a class is abstract with the
          abstract keyword like this:

          public abstract class Container extends Component {

          Abstract classes may contain abstract methods. A method
          declared abstract is not actually implemented in the current
          class. It exists only to be overridden in subclasses. It has no
          body. For example,

          public abstract float price();

          Abstract methods may only be included in abstract classes.
          However, an abstract class is not required to have any abstract
          methods, though most of them do.

          Each subclass of an abstract class must override the abstract
          methods of its superclasses or itself be declared abstract.

          For more details, see section 8.1.2.1 of the Java Language
          Specification.

  6.4: WHAT'S AN INTERFACE?

   An interface is an idea taken from Objective C. It describes the
          public methods that a class implements and their calling
          conventions without saying anything about how those methods are
          implemented. It is the responsibility of each class that
          implements an interface to provide code to handle the cases
          where the methods of the interface are called.

          For example suppose you're writing an inventory database. The
          inventory may include many different items of many different
          types and classes. However each item in the warehouse needs to
          be able to tell you its price. Normally you would implement
          this by having each class extend a common superclass. However
          that's not always convenient. Instead you can declare an
          interface called Price with a price() method like this:

public interface Price {

  public float price();

}

   Any class which implements the Price interface must contain a method
          with the signature public float price(). The code of the
          price() method is included separately in each separate class
          which implements Price, not in the Price interface itself.

          Different classes in your warehouse can each implement the
          Price interface like this:

public class Monopoly extends BoardGame implements Price {

  // other methods

  public float price() {
    return 14.95;
  }

}

   When other code is passed an object, it can test whether the object
          implements Price with the instanceof operator. For example,

          if (o instanceof Price) System.out.println("Subtotal is " +
          o.price());

          In fact, interfaces can be used to tag objects. The
          java.rmi.Remote interface declares no methods. Its sole purpose
          is to indicate that an object is a remote object. In general,
          sub-interfaces of java.rmi.Remote will declare remote methods,
          however. For example,

public interface Hello extends java.rmi.Remote {

  public String sayHello();

}
public class HelloImpl extends UnicastRemoteServer implements Hello {

  public String sayHello() {
    return "Hello";
  }

}

   For more information about the java.rmi package, see
          http://chatsubo.javasoft.com/current/rmi/index.html or
          Chapter 14 of my book, Java Network Programming, from O'Reilly
          & Associates.

  6.5: WHY DOESN'T JAVA INCLUDE INSERT YOUR FAVORITE FEATURE HERE?

   The Java language has been extensively debated and argued about within
          Sun. Almost every language construct of existing languages has
          already been considered for inclusion in Java. While there may
          still be room for addition, it is very unlikely that your pet
          feature will be added to the language spec if it isn't already
          there. In a couple of years parameterized types (i.e.
          templates) may be added to the language. Otherwise the spec is
          pretty much frozen except for minor changes and bug fixes.

          Extensions are planned for the class library though. In
          particular Sun is working on extensions for 3D, multimedia,
          telephony, and improved graphics.

  6.6: IS JAVA CORBA COMPLIANT?

   Not yet. However work is underway for a Java ORB and IDL.
          http://splash.javasoft.com/JavaIDL/pages/index.html.

  6.7: CAN I CAST AN INT TO AN INTEGER? A FLOAT TO A FLOAT?

   No, you cannot promote a base data type like int or float to an object
          such as an Integer or a Float. However the proper way to do
          this isn't very hard. Instead do

int x = 5;
myInteger = new Integer(x);

  6.8: HOW DO I VERSION A CLASS?

   There is no support for versioning classes in Java 1.0. However in
          Java 1.1 the serialver tool provides a serialVersionUID for one
          or more classes you can add to your class as a field. This is
          used in object serialization.

  6.9: WHY ISN'T THERE OPERATOR OVERLOADING?

   Because C++ has proven by example that operator overloading makes code
          almost impossible to maintain. In fact there very nearly wasn't
          even method overloading in Java, but it was thought that this
          was too useful for some very basic methods like print(). Note
          that some of the classes like DataOutputStream have
          unoverloaded methods like writeInt() and writeByte().

  6.10: DOES JAVA HAVE POINTERS?

   No, no, a thousand times no. Java does not have pointers, no way, no
          how, the daily email I get from people who think differently
          not withstanding.

          Java does have references. A reference is an abstract
          identifier for an object. It is not a pointer. A reference tags
          a particular object with a name in the Java virtual machine so
          that the programmer may refer to it. How exactly the virtual
          machine implements references at the level of machine code is
          VM-dependent and completely hidden from the programmer in any
          case. Most VMs including Sun's use handles, not pointers. A
          handle is a pointer to a pointer. At the level of machine code
          in the CPU a reference is an address in memory where the
          address of the object is stored. This way the objects can be
          moved around in memory and only the master pointer needs to be
          updated rather than all references to the object. This is
          completely hidden from the Java programmer, though. Only the
          implementer of the virtual machine needs to worry about it.
          Indeed, this is not the only way references can be implemented.
          Microsoft's VM actually does use pointers rather than handles.
          Other schemes are possible.

  6.11: DOES JAVA PASS METHOD ARGUMENTS BY VALUE OR BY REFERENCE?

   Java passes all arguments by value, not by reference. However this is
          one of the few places where the distinction between an object
          and a reference to an object becomes important. Object and
          array variables in Java are really references to the object or
          array. This can make it look like an object is passed by
          reference if you only modify the fields of the object or array,
          but do not change the reference itself. For example, consider
          this program:

import java.awt.Point;

class changePoint {

  public static void main(String args[]) {

    Point p1 = new Point(0, 0);
    changePoint(p1);
    System.out.println(p1);

  }

  static void changePoint(Point p) {

    p.x = 38;
    p.y = 97;

  }

}

   It prints:

java.awt.Point[x=38,y=97]

   Therefore the point has been changed. However the reference, which is
          what was really passed, has not been changed. To see that
          consider the following program.

import java.awt.Point;


class dontChangePoint {

  public static void main(String args[]) {

    Point p1 = new Point(0, 0);
    dontChangePoint(p1);
    System.out.println(p1);

  }

  static void dontChangePoint(Point p) {

    p = new Point(38, 97);

  }

}

   It prints:


java.awt.Point[x=0,y=0]

   What happened in this example was that a copy of the reference p1 was
          passed to the dontChangePoint() method. A new Point object was
          then assigned to that copy. However this did not change the old
          reference in the main method. In the previous example the
          reference p in the changePoint() method and p1 in the main()
          method both referred to the same object. In this example p and
          p1 refer to different objects after the new Point is assigned
          to p.

  6.12: ARE THERE PARAMETERIZED TYPES (TEMPLATES)?

   Not in Java 1.0 or 1.1. However this is being seriously considered for
          future versions.

  6.13: HOW DOES GARBAGE COLLECTION WORK?

   Current implementations of Java use a mark and sweep garbage
          collector. Reference counting is not used. Thus circular linked
          lists do not lead to memory leaks. It is theoretically possible
          that future versions of Java will use some other garbage
          collection algorithm.

  6.14: PERFORM AND BECOME

   Sorry Smalltalkers. There's no equivalent for PERFORM or BECOME in
          Java 1.0. These would probably open security holes. There are
          workarounds for some things you might want to do using
          interfaces.

          In Java 1.1 the Core Reflection API and the java.lang.reflect
          package provides most of the functionality you need. However
          this API is partially unavailable to applets due to security
          issues.

7: java.awt

  7.1: WHAT DOES AWT STAND FOR?

   So far I've heard it claimed that AWT stands for:

          + Abstract Window Toolkit
          + Advanced Window Toolkit
          + Another Window Toolkit
          + Applet Window Toolkit
          + Awkward Window Toolkit
          + Annoying Window Toolkit

   I do not know which if any of these are correct, but Abstract Window
          Toolkit seems to be the most popular.

  7.2: WHAT ARE PEER "CLASSES"?

   Peer classes exist mainly for the convenience of the people who wrote
          the Java environment. They help in translating between the AWT
          user interface and the native (Windows, OpenWindows, Mac etc.)
          interfaces. Unless you're porting Java to a new platform you
          shouldn't have to use them.

  7.3: CAN YOU EXPLAIN HOW EVENTS ARE PASSED?

   The following applies to Java 1.0 only. The event mechanism has
          changed completely in Java 1.1, though the following is
          retained for backwards compatibility.

          Components are subclasses of java.awt.Component. Examples of
          components include buttons, scrollbars, text fields, frames,
          windows, dialogs, panels, canvases, and checkboxes. One
          subclass of java.awt.Component is java.awt.Container. A
          container is a component which can hold other components.
          Examples of containers include Frames, Windows, Dialogs, Panels
          and Applets. An applet is a subclass of Panel. Panel is a
          subclass of Container. Container is a subclass of Component.
          Therefore an applet is both a container and a component.

          When the user clicks the mouse, types on the keyboard, drags
          and drops, or does any of a few other things, the operating
          system produces an event. This event is passed to Java, and the
          Java runtime tries to figure out which component the event was
          intended for.

          The Java runtime then passes that event to the
          handleEvent(Event e) method of some Component. The Component's
          handleEvent() method contains a big if-else statement to look
          at the type of event and respond appropriately. What the
          handleEvent() method does depends on the type of component.
          Generally some events are ignored and other events are passed
          to methods that know how to respond to those events. For
          instance a MOUSE_DOWN event is passed to mouseDown(). The table
          below shows the events the default handleEvent() can deal with.
          When one of these events occurs, handleEvent() passes it and
          various other information to the specified method.


Event                      Method Called
--------------------------------------------------------
Event.MOUSE_ENTER:         mouseEnter(evt, evt.x, evt.y)
Event.MOUSE_EXIT:          mouseExit(evt, evt.x, evt.y)
Event.MOUSE_MOVE:          mouseMove(evt, evt.x, evt.y)
Event.MOUSE_DOWN:          mouseDown(evt, evt.x, evt.y)
Event.MOUSE_DRAG:          mouseDrag(evt, evt.x, evt.y)
Event.MOUSE_UP:            mouseUp(evt, evt.x, evt.y)
Event.KEY_PRESS:           keyDown(evt, evt.key)
Event.KEY_ACTION:          keyDown(evt, evt.key)
Event.KEY_RELEASE:         keyUp(evt, evt.key)
Event.KEY_ACTION_RELEASE:  keyUp(evt, evt.key)
Event.ACTION_EVENT:        action(evt, evt.arg)
Event.GOT_FOCUS:           gotFocus(evt, evt.arg)
Event.LOST_FOCUS:          lostFocus(evt, evt.arg)

   By default each of these methods does nothing. Furthermore, by default
          all other events do nothing. If you want to do something when
          one of the above events occurs in your component, subclass the
          component and override the appropriate method. For example, to
          create a Canvas that prints the message "Don't Tread on Me!"
          every time the user clicks on it, use the following subclass of
          Canvas:

public class noTread extends Canvas {

  public boolean mouseDown(Event e, int x, int y) {
    System.out.println("Don't Tread on Me!");
    return true;
  }

}

   Button, Choice, TextField, and Checkbox are special because of how
          they're implemented as native widgets. They do not see
          MOUSE_DOWN, MOUSE_UP, KEY_PRESS, and other such events. Rather
          they receive one event and one event only: Event.ACTION_EVENT.
          When a Button is pressed, the user hits return in a TextField,
          the user double clicks on a List item, clicks a Checkbox, or
          selects from a Choice, an ACTION_EVENT is generated. If you
          haven't overridden handleEvent(), this is passed to the
          action() method of the component's container. These four
          components are the only things which generate ACTION_EVENTs. No
          other component will generate an ACTION_EVENT. (Menu items,
          which are not components but are implemented as native peers,
          also generate action events.)

          Each event handler method, including handleEvent(), returns
          true if the event was completely handled and false if it was
          not. If false is returned, then the event is passed to the
          component's container to see if the container wants to process
          the event.

          If you want to respond to a different set of events, you must
          override handleEvent(). You can either completely replace it or
          just add the extra events you want to handle and then return
          super.handleEvent() for other types of events. For example to
          print all the events as they happen in your applet you might
          use this handleEvent() method:

public boolean handleEvent(Event e, int x, int y) {
  System.out.println(e);
  return super.handleEvent(e, x, y);
}

   mouseDown(), mouseUp(), keyDown(), and all the other event methods
          would still be called by the superclass. If you don't handle an
          event in the handleEvent() method, return super.handleEvent(e)
          to give your superclass an opportunity to process the event. In
          this case, we've handled the event but not completely so we
          still let the superclass process it by returning
          super.handleEvent(e, int x, int y).

          The return value of handleEvent() is important. If
          handleEvent() returns true, that means the event has been fully
          digested and no further processing is needed. On the other hand
          if handleEvent() returns false, then the event is passed to the
          component's container to be handled.

          Note that this all works for any component at all. You'll most
          commonly override these methods in a subclass of Applet or
          perhaps Frame. However the same methods and techniques apply to
          all subclasses of Component.

          The API documentation confuses the issue because of the
          ambigious use of the word parent. In object-oriented circles
          the word parent usually refers to the superclass. However in
          the context of the AWT, the word parent refers to the container
          that contains a component. Thus in the statement:

     return true if the event has been handled and no further action is
     necessary; false if the event is to be given to the component's
     parent

   the word parent means the component's container, not its superclass.

          You must distinguish between the container/component hierarchy
          and the inheritance hierarchy. By default, the way an event
          travels has nothing to do with the inheritance hieararchy. If
          you override an event handling method, then events passed to
          that method will not be passed to a component's superclass
          unless you specifically ask them to be. However, in most cases
          your handleEvent() method will return super.handleEvent() to
          give the superclass a crack at handling the event rather than
          simply returning false.

          To sum up, when you write a subclass of Component, you can
          either respond to specific events by overriding the methods
          that correspond to those events, such as mouseDown(); or you
          can respond to all events by overriding handleEvent(). Each of
          your event handling methods must return a boolean. Return true
          when an event has been completely processed, and return false
          when you want the component's container to try to handle the
          event. When overriding handleEvent(), you also have an option
          to return super.handleEvent() to ask the superclass to handle
          the event and decide whether or not to pass it along to the
          component's container.

  7.4: CLIPPING

   java.awt.Graphics.clipRect(int, int, int, int) and related methods are
          hopelessly flawed, at least as of 1.0. Ignore them completely.

          Instead if you need to do clipping, create separate offscreen
          Images for each clipping region. Each Image should be the
          size of the clipping region you desire. Draw into those
          offscreen images, and then copy them onto the appropriate
          section of the of your applet window using
          java.awt.Graphics.drawImage(). Some coordinate conversion
          will almost certainly be necessary.

          If the background image isn't a simple color then you'll first
          need to copy the appropriate part of that image to your
          offscreen clipping Image. You can do this by drawing your
          background Image into your offscreen region with
          Graphics.drawImage() and a suitable shifting of coordinates.

          This all works for rectangular regions only since all Images
          are rectangular. More complicated geometries can be faked if
          all but one section contains only simple colors.

  7.5: HOW DO I CHANGE THE THICKNESS OF THE LINE?

   Java 1.1 and earlier only support 1 pixel wide lines. There's no easy
          way around this. You can, however, draw multiple, parallel
          lines offset from each other by one pixel:

  public void paint(Graphics g) {

    int x1=5;
    int x2=278;
    int y1=8;
    int y2=93;


    // Draw a ten pixel thick line
    for (int i = -5; i < 5; i++) {
      g.drawLine(x1+i,y1+i,x2+i,y2+i);
    }

  }

   This isn't perfect. The ends of the line are excessively tapered. You
          really need to take the slope of the line into account when
          incrementing x and y, but this should give you the idea. If
          you're doing a lot of this, you can write a class or method to
          do it for you.

          There are other hacks you can use. For example, a thick line is
          essentially a filled rectangle. Therefore you can calculate the
          endpoints of the rectangle and use fillPolygon() to draw it.

          The real solution is going to have to wait for a more complete
          graphics API for Java, possibly in Java 1.2.



  7.6: WHAT FONTS DOES JAVA SUPPORT?

   Java 1.0 implementations are guaranteed to have the fonts Helvetica,
          Courier, TimesRoman, and Symbol or some reasonable facsimile
          thereof.

          These names are deprecated in Java 1.1. In Java 1.1 you should
          use SansSerif, Serif, and Mono instead which will be mapped to
          an appropriate font like Helvetica, Times, or Courier.

          Whether fonts installed on the client are available to Java is
          implementation depenedent. You can get a String array of the
          names of the available fonts by calling the getFontList()
          method from java.awt.Toolkit. For example,

          String[] fonts = Toolkit.getDefaultToolkit().getFontList()

8: java.io

  8.1:HOW DO I READ DATA FROM A FILE?

   There are a number of ways to read data from a file. If you're reading
          a file as raw binary data, you open a file using a
          FileInputStream(String) constructor and use one of the various
          read() methods to read the data into an array of bytes. For
          example the following program reads raw data from a file
          specified on the command line. It then writes the same data to
          the standard output.

import java.io.*;

class ReadRawData {

  public static void main (String args[]) {

    boolean done = false;
    byte b[] = new byte[1024];
    int num_bytes = 0;

    FileInputStream fin = null;
    try {
      fin = new FileInputStream(args[0]);
    }
    catch(ArrayIndexOutOfBoundsException e) {
      System.out.println("You have to give me the name of a file to open.");
      System.exit(0);
    }
    catch (FileNotFoundException e) {
      System.out.println("Could not open input file " + args[0]);
      System.exit(0);
    }
    catch(IOException e) {
      System.out.println("Error while opening input file" + args[0]);
      System.exit(0);
    }
    catch (Exception e) {
      System.out.println("Unexpected exception: " + e);
      System.exit(0);
    }

    try {
      num_bytes = fin.read(b);
    }
    catch(IOException e) {
      System.out.println("Finished Reading: " + e);
      done = true;
    }
    catch (Exception e) {
      System.out.println("Unexpected exception: " + e);
      System.exit(0);
    }

    while(!done) {
      System.out.write(b, 0, num_bytes);
      try {
        num_bytes = fin.read(b);
      }
      catch(IOException e) {
        System.out.println("Finished Reading: " + e);
        done = true;
      }
      catch (Exception e) {
        System.out.println("Unexpected exception: " + e);
        System.exit(0);
      }
      if (num_bytes == -1) done = true;
   }  // end while

 }  // end main

} // end ReadRawData

   On the other hand if you're reading a text file in Java 1.0 you'll
          probably want to use a DataInputStream which gives you a
          readLine() method that returns successive lines of the file as
          Java Strings. You can then process each String as you see fit.

// Implement the Unix cat utility in java

import java.io.*;

class cat  {

  public static void main (String args[]) {

    String thisLine;

   //Loop across the arguments
   for (int i=0; i < args.length; i++) {

     //Open the file for reading
     try {
       FileInputStream fin =  new FileInputStream(args[i]);

       try {
         DataInputStream myInput = new DataInputStream(fin);

         try {
           while ((thisLine = myInput.readLine()) != null) {  // while loop beg
ins here
             System.out.println(thisLine);
           } // while loop ends here
         }
         catch (Exception e) {
           System.out.println("Error: " + e);
         }
      } // end try
      catch (Exception e) {
        System.out.println("Error: " + e);
      }

    } // end try
    catch (Exception e) {
      System.out.println("failed to open file " + args[i]);
      System.out.println("Error: " + e);
    }
  } // for ends here

} // main ends here

}

   This code emulates the Unix "cat" command. Given a series of filenames
          on the command line it concatenates the files onto the standard
          output.

          In Java 1.1 DataInputStream.readLine() is deprecated. You
          should use a BufferedReader instead as in this class:

// Implement the Unix cat utility in java

import java.io.*;

class cat {

  public static void main (String args[]) {

    String thisLine;

   //Loop across the arguments
   for (int i=0; i < args.length; i++) {

     //Open the file for reading
     try {
       FileReader fr =  new FileReader(args[i]);
       BufferedReader myInput = new BufferedReader(fr);

       while ((thisLine = myInput.readLine()) != null) {  // while loop begins
here
         System.out.println(thisLine);
       } // while loop ends here

     } // end try
     catch (IOException e) {
       System.out.println("Error: " + e);
     }

  } // for ends here

} // main ends here

}

  8.2: HOW DO I WRITE DATA TO A FILE?

   You should only assume you'll be able to write to a file from an
          application. Although it may be possible to write data into a
          file from an applet if the browser viewing the applet is
          HotJava, this ability will generally be disabled. From within
          Netscape there is no way for an applet to write to a file on
          the local hard drive.

          Within an application, however, file access is
          straight-forward. There are several ways but here is a simple
          example using formatted output streams:

import java.io.*;

class PrintToAFile  {

  public static void main (String args[]) {

    //First open the file you want to write into
    try {
      FileOutputStream fout =  new FileOutputStream("test.out");

      // now convert the FileOutputStream into a PrintStream

      PrintStream myOutput = new PrintStream(fout);

      // Now you're able to use println statements just as if you were using Sy
stem.out.println
      // to write to the terminal

      myOutput.println("Hello There!");
      myOutput.println(1 + " + " + 1 + " = " + (1+1));
    }
    catch (IOException e) {
      System.out.println("Error opening file: " + e);
      System.exit(1);
    }

  } // main ends here

}

   There are a number of other things to note about writing data to a
          file. This program creates or opens a file called "test.out" in
          the same directory as the running program. However you could
          pass it a full pathname to a file in a different directory
          instead.

          You should also learn about the DataOutputStream class and the
          write() method when you get a chance. DataOutputStreams and
          DataInputStreams are used for moving data between Java programs
          in a portable way. The various incarnations of the write()
          method are used for writing and reading arbitrary byte streams.
          What I've demonstrated here is more suitable for human
          consumption.

          In Java 1.1 you should probably use a PrintWriter instead of a
          PrintStream.

  8.3: HOW DO I APPEND DATA TO A FILE?

   In Java 1.1 you can just pass true as the second argument to this
          FileOutputStream constructor to indicate that you want to
          append data to the file:

public FileOutputStream(String name, boolean append)
 throws IOException

   In Java 1.0, however, you must use the java.io.RandomAccessFile class
          that lets you read and write bytes from arbitrary locations in
          a file. This class implements DataInput and DataOutput so you
          have all the methods of DataInputStream and DataOutputStream
          available to you.

           To create a new random access file pass the name of the file
          and the mode to the constructor. The mode is either "r"
          (read-only) or "rw" (read and write). The length() method
          returns a long that tells you how many bytes there are in a
          file and the seek(long p) method lets you position the file
          pointer at a particular point in the file. Thus to start
          writing at the end of a RandomAccessFile raf, you first
          raf.seek(raf.length()). The following example demonstrates by
          appending the string "Kilroy was here!" to every file specified
          on the command line.

import java.io.*;

class AppendToAFile  {

  public static void main (String args[]) {

    for (int i = 0; i < args.length; i++) {
      //First open the file you want to append to

      try {
        RandomAccessFile raf =  new RandomAccessFile(args[i], "rw");
        // Position yourself at the end of the file
        raf.seek(raf.length());

       // Write the String into the file. Note that you must
       // explicitly handle line breaks.
       raf.writeBytes("\nKilroy was here!\n");

      }
      catch (IOException e) {
        System.out.println("Error opening file: " + e);
      }

    }

  }

}

  8.4: HOW DO I FORMAT NUMBERS LIKE C'S PRINTF()?

   Java does not have any built in equivalent to C's
          printf/sprintf/fprintf family of functions that specify the
          width and precision of numbers converted into strings. Since
          Java does not support variable length argument lists, it's not
          possible to write exact equivalents for these functions.
          Instead the approach that must be taken is to convert one
          number at a time into a string according to a format
          specification, then write the resulting string onto the
          appropriate output stream. This is a more flexible solution,
          but it's far from obvious.

          In Java 1.1, the java.text package contains classes that format
          numbers according to particular needs. In particular it's worth
          getting to know the java.text.NumberFormat and
          java.text.DecimalFormat classes, though these can't handle
          exponential notation. I've begun work on my own formatting
          class that does handle exponential and other notations
          available through printf(). It can be found at
          http://sunsite.unc.edu/javafaq/formatter/. Gary Cornell and
          Cay Horstmann's popular book Core Java also includes such a
          class. You can probably find more at Gamelan.

9: java.net

   Network programming in Java is covered in much more detail in my book,
          Java Network Programming from O'Reilly & Associates. Most of
          what is new and exciting about Java centers around the
          potential for new kinds of dynamic, networked applications; and
          Java Network Programming shows you how to write them. Topics
          covered include sockets, URLs, InetAddresses, UDP, TCP/IP,
          multicasting, applets, servlets, RMI, and more.

          Manning Publications has also recently published a book titled
          Java Network Programming. It's not a bad book, and is
          surprisingly orthogonal to mine. About 2/3 of that book is
          streams and encryption which I only touch on. My book covers
          servlets, applets, RMI, multicast sockets, and Java 1.1 which
          that book doesn't discuss. The matching titles appear to be
          just unlucky choices. Both publishers went with the most
          obvious title they could think of. However the cover of the
          Manning book has a big fish, and looks suspiciously like an
          O'Reilly book. Don't be fooled. The real O'Reilly book has a
          gyroscope on the cover.

          You can buy Java Network Programming at any bookstore that
          stocks computer books, or you can order it from amazon.com or
          Computer Literacy.



  9.1: HOW DO I CONVERT A NUMERIC IP ADDRESS LIKE 199.1.32.90 INTO A HOSTNAME
  LIKE STAR.BLACKSTAR.COM?

   Unfortunately due to an unintended side effect (i.e. a bug) in Java's
          caching of IP addresses and hostnames, Java 1.0 can't convert
          numeric IP addresses into hostnames. However this is
          straightforward in Java 1.1. For example,

          String hostname =
          InetAddress.getByName("199.1.32.90").getHostName()

  9.2: HOW CAN A JAVA PROGRAM TALK TO A CGI PROGRAM?

   Web browsers display forms, read user input, encode that input into a
          standard format called a "query string", and send that data to
          CGI programs that live on the web server. When you write an
          applet that talks to a CGI program, you have to do all this
          yourself.

          The first thing to know is that there are two ways a CGI
          program can accept data from a web browser, GET and POST. CGIs
          that use GET take their arguments from the URL. Programs that
          use POST read their arguments from standard input.

          The second thing to know is that when you submit data to a form
          through a web browser, the web browser encodes the data for
          you. In an applet, however, you need to encode the data
          yourself. The data is encoded like this: Each form entry is a
          name-value pair. Names and values are separated from each other
          by equals signs (=). Pairs are separated from each other by
          ampersands (&). For example, consider this form:

<Form method=GET action="http://sunsite.unc.edu/javafaq/cgi-bin/getform.pl">
Email: <Input NAME="email" size=40>
Name: <Input NAME="realname" size=40>
<Input TYPE="submit" VALUE="Subscribe">
</Form>

   You see that this uses the GET method to communicate with a cgi-bin
          program at http://sunsite.unc.edu/javafaq/cgi-bin/getform.pl.
          It sends two fields to the CGI program, email and realname.
          Let's say you want to send the string "[e-mail]"
          for the email address, and the string "Elliotte Harold" for the
          real name. Then the query string would look like this:

          String qs =
          "email=elharo%40sunsite.unc.edu&realname=Elliotte%20Harold";

          The spaces in "Elliotte Harold" and the @ in
          "[e-mail]" have been converted into percent
          escapes. All non-alphanumeric characters in the values must be
          replaced with a % followed by their ASCII value. Thus a space
          becomes %20 and the @ becomes %40.

          To send this data to the server, append a question mark (?) and
          the query string to the URL of the CGI program, and request
          that URL from the server. Thus the URL you want is:

http://sunsite.unc.edu/javafaq/cgi-bin/getform.pl?email=elharo%40sunsite.unc.ed
u;realname=Elliotte%20Harold";

   In Java terms this requires constructing a URL object from this
          string, and opening that URL's InputStream to read the
          response. The following code fragment demonstrates:

try {
  String thisLine;
  String qs = ""email=elharo%40sunsite.unc.edu&realname=Elliotte%20Harold";
  URL u = new URL("http://sunsite.unc.edu/javafaq/cgi-bin/getform.pl?" + qs);
  DataInputStream theHTML = new DataInputStream(u.openStream());
  while ((thisLine = theHTML.readLine()) != null) {
    System.out.println(thisLine);
  }
}
catch (Exception e) {
  System.err.println(e);
}

   Communicating with CGI programs that use POST is somewhat more
          complex, and it doesn't work very well in Java 1.0.2. It may be
          improved in Java 1.1. When POSTing to a CGI, you encode the
          query string exactly as you do for GET requests. However
          instead of merely requesting a URL's InputStream, you open a
          URLConnection to the CGI program.

          Do not append the query string to the URL as you did with GET.
          Instead set the URLConnection's doOutput and doInput fields to
          true and set AllowUserInteraction to false. Chain the
          URLConnection's OutputStream to a DataOutputStream and use the
          DataOutputStream's writeBytes() method to send the query string
          to the server.

          If you want to read the response, then chain the
          URLConnection's InputStream to a DataInputStream, and use the
          DataInputStream's readLine() method to read the response in a
          while loop. The following code fragment demonstrates:

String query = "email=elharo%40sunsite.unc.edu;realname=Elliotte%20Harold";

try {

  // open the connection and prepare it to POST
  URL u = new URL("http://sunsite.unc.edu/javafaq/cgi-bin/postform.pl");
  URLConnection uc = u.openConnection();
  uc.setDoOutput(true);
  uc.setDoInput(true);
  uc.setAllowUserInteraction(false);
  DataOutputStream dos = new DataOutputStream(uc.getOutputStream());

  // Send the data
  dos.writeBytes(query);
  dos.close();


  // Read the response
  DataInputStream dis = new DataInputStream(uc.getInputStream());
  String nextline;
  while((nextline = dis.readLine()) != null) {
   System.out.println(nextline);
  }
  dis.close();

}
catch (Exception e) {
  System.err.println(e);
}

   As you see, posting forms is considerably more complex than using the
          GET method. However on some platforms, GET has an annoying
          habit of failing once the query string grows past 200
          characters. The exact point where GET fails varies depending on
          the operating system and the web server.

  9.3: HOW CAN AN APPLET SEND EMAIL?

   The simplest way to answer this question is to tell you to write a CGI
          program which sends email, and then refer you to the previous
          question to learn how to communicate with the CGI program.
          There really isn't any other reliable, cross-platform way to
          send email. The problem is that email programs are platform
          dependent.

          The Simple Mail Transport Protocol is an Internet standard that
          you may be able to use some of the time. The basic idea is to
          open a socket to the SMTP port, 25, on the web server, and send
          your email through the server. However not all web servers,
          especially those based on Macs or Windows NT, run SMTP servers,
          and an applet can't open sockets to other hosts. Even if you do
          have SMTP software running on your web server, the applet may
          be behind a firewall that disallows outgoing connections to
          port 25 on hosts outside the firewall.

  9.4: HOW CAN I USE ICMP IN JAVA?

   Java does not support ICMP, the Internet Control Message Protocol, at
          this time; nor does it allow you to send raw IP packets. You
          must use TCP or UDP. Therefore protocols that rely on ICMP like
          ping and traceroute cannot yet be implemented in Java.

  9.5: HOW DO I MAKE JAVA WORK WITH A PROXY SERVER?

   The socksProxyHost, socksProxyPort, http.proxyHost, and http.proxyPort
          system properties define the proxy server used to support SOCKS
          v4 and HTTP proxy functionality:

socksProxyHost // for socks v4
socksProxyPort
http.proxyHost // standard HTTP proxy
http.proxyPort

   This is documented in the HotJava documentation, but applies to the
          JDK too. You can set system properties from the command line
          like this

java -DsocksProxyHost=utopia.poly.edu -DsocksProxyPort=9087  MyClass

   Of course you have to change it to use your proxy host and port.

          These can also be set by any other convenient means to set
          system properties, such as including them in the
          appletviewer.properties file like this:

# caching
proxySet=true
proxyHost=proxy.mysite.com
proxyPort=8080

# ftp
ftpProxySet=true
ftpProxyHost=ftpprxy.mysite.com
ftpProxyPort=7070

10: java.util

  10.1: HOW RANDOM IS RANDOM()?

   It's good enough for games. I wouldn't use it for cryptography.

          Unlike most random functions in other libraries the
          Math.random() method seeds itself with the current time in
          milliseconds. Thus you do not need to seed it explicitly at the
          start of your program. If you require a non-random Random() for
          test purposes or you need more randomness than the current time
          in milliseconds can provide, then you can use
          java.util.Random() which has a constructor that lets you
          specify a seed.

  10.2: HOW DO I GENERATE A RANDOM INTEGER BETWEEN A AND B?

   Generate a random double between 0.0 and 1.0, multiply by the number
          of int values you want to choose from, add the smallest int
          value you want, round it down to the nearest integer using
          Math.floor(), and cast the result to an int. For example, the
          following class simulates a six-sided die by producing random,
          uniformly distributed ints between 1 and 6.

public class Die {

  Random generator = new Random();

  public static int roll() {

    // get a rcandom number between 0 and 1
    double r = generator.nextDouble();

    // multiply by 6 so it's now between 0 and 6
    r *= 6.0;

    // add 1
    r += 1.0;

    //truncate it to an int
    r = Math.floor(r);

    // handle one special if unlikely case
    if (r == 7.0) r = 6.0;

    // convert to an int and return
    return (int) r;

  }

}

11: Common Errors and Problems

  11.1: HOW CAN I AVOID FLICKER IN AN APPLET?

   The key to fixing flicker is realizing that the screen isn't actually
          painted in the paint() method. The pixels get put on the screen
          in the update() method which most applets don't override.
          However by overriding the update() method you can do all your
          painting in an offscreen Image and then just copy the final
          Image onto the screen with no visible flicker.

          The cookbook approach is simple. Add the following three
          private fields to your applet and the public update() method.
          Flicker will magically disappear.


  private Image offScreenImage;
  private Dimension offScreenSize;
  private Graphics offScreenGraphics;

  public final synchronized void update (Graphics g) {

    Dimension d = size();
    if((offScreenImage == null) || (d.width != offScreenSize.width) ||  (d.heig
ht != offScreenSize.height)) {
      offScreenImage = createImage(d.width, d.height);
      offScreenSize = d;
      offScreenGraphics = offScreenImage.getGraphics();
    }
    offScreenGraphics.clearRect(0, 0, d.width, d.height);
    paint(offScreenGraphics);
    g.drawImage(offScreenImage, 0, 0, null);

  }

  11.2: CAN YOU EXPLAIN CLASSPATH?

   A path specifies the name and location of a file on the file system.
          It starts with the name of the disk or the root of the
          filesystem and works its way down through various directories
          until reaches the file. File, directory, and path naming
          conventions are platform specific. For example a Unix path
          looks like /home/users/elharo/html/javafaq.html. A DOS/Windows
          path looks like C:\html\javafaq.htm. A Macintosh path looks
          like My Hard Drive:html:Java FAQ List v1.1. All three of these
          examples point to a file. Paths can also point to a directory.
          For example, /home/users/elharo/html, C:\html, or My Hard
          Drive:html:.

          The character that separates one directory from the next in a
          path is called the separator character. It is a slash (/) on
          Unix, a backslash (\) in Windows and a colon (:) on the Mac.
          You can get its value on a particular platform by looking at
          the static variable java.io.File.separatorCharacter.

          If you actually check this on the Mac, you'll note something
          funny. java.io.File.separatorCharacter appears to be a slash
          (/) like on Unix, not a colon like a Mac programmer would
          expect. Why Java had to be different from every other Mac
          program in the universe I don't know. This is problematic
          because Mac file names can include slashes.

          The CLASSPATH is an environment variable that contains a list
          of directories where Java looks for classes referenced in a
          program. If the CLASSPATH isn't set properly no program written
          in Java will be able to run, and the compiler won't be able to
          compile. Each entry in this list is separated from the other
          entries by the java.io.File.pathSeparatorChar. This is
          semicolon (;) on Windows and a colon (:) on Unix and the Mac.
          For example


Unix: ~/classes:/usr/local/netscape/classes
Windows: C:\java\classes;C:\netscape\classes
Mac: My Hard Drive/JDK/classes:My Hard Drive/My Project:My Hard Drive/classes



          On most platforms, the JDK's java interpreter appends some
          directories to the CLASSPATH you set manually. These are set
          relative to where the java interpreter itself is. For example,
          if the java program is installed in /usr/local/java/bin, then
          it will append /usr/local/java/classes and
          /usr/local/java/lib/classes.zip to the CLASSPATH. Another way
          of thinking about it: if the directory where the java
          interpreter is installed is $JAVA, then $JAVA/../classes and
          $JAVA/../lib/classes.zip are automatically in your CLASSPATH.

          Java applets and applications aren't self-contained. They need
          access to other classes to do their work. For instance when you
          call System.out.println() Java needs to know where to look to
          find the file that includes the System class.

          The directories in the CLASSPATH are where Java starts
          searching for classes. To find a class Java first changes the
          periods in the full package-qualified name of the class (e.g.
          java.util.Date and not just Date) into directory separators (/
          on Unix, \ on Windows, : on the Mac). Thus if it wants the
          java.awt.GridBagLayout class, it looks for the file
          java/awt/GridBagLayout.class in each of the root directories
          listed in the CLASSPATH variable from left to right until it
          finds the file. With the Unix CLASSPATH listed above, Java
          first looks for ~/classes/java/awt/GridBagLayout.class Then
          for, /usr/local/netscape/classes/java/awt/GridBagLayout.class.

          The specification of the CLASSPATH is somewhat platform
          dependent. For instance ~ means the home directory on Unix but
          has no meaning on the Mac.

          Under Unix you set CLASSPATH variables like this:

csh: % setenv CLASSPATH my_class_path
sh: % CLASSPATH=my_class_path

   You'll probably want to add one of these lines to your .login or
          .cshrc file so it will be automatically set every time.

          Under Windows you set the CLASSPATH environment variable with a
          DOS command like

C:\> SET CLASSPATH=C:\JDK\JAVA\CLASSES;c:\java\lib\classes.zip

   You can also add this to your autoexec.bat file. You should of course
          point it at whichever directories actually contain your
          classes.

          The CLASSPATH variable is also important when you run Java
          applets, not just when you compile them. It tells the web
          browser or applet viewer where it should look to find the
          referenced .class files. If the CLASSPATH is set improperly,
          you'll probably see messages like "Applet could not start."

          Since large packages can contain many, many .class files Sun
          has built the capability to read zip archives into Java.
          Therefore an entire directory structure of class files can be
          zipped to save space. If you want to see what's inside the zip
          file, unzip it. Java doesn't care whether or not a directory
          has been zipped. You just need to make sure that the .zip file
          is named the same as the directory it replaces plus the .zip
          extension and that it is in the same location.

          In Netscape you should make sure that the first directory in
          the CLASSPATH is the directory that contains Netscape's class
          files (The defaults are /usr/local/netscape/java/classes on
          Unix and C:\NETSCAPE\NAVIGATOR\Program\java\classes in
          Windows.)

          Finally note that if you install additional packages such as
          Jeeves or any third party package, you need to add the
          directory where the package is installed to your CLASSPATH. For
          example let's say you buy a package of statistics classes from
          SPSS, and you put those classes in /opt/classes/stats. Then you
          you need to add /opt/classes/stats to the end of your
          CLASSPATH.

          You can temporarily add a directory to the CLASSPATH by giving
          the -classpath option to the java interpreter or the javac
          compiler. For example,

javac -classpath $CLASSPATH:/opt/classes/stats

   To use just the classes in /opt/classes/stats and not the classes
          normally found in your CLASSPATH, omit $CLASSPATH like this:

javac -classpath /opt/classes/stats

   Finally if the CLASSPATH environment variable has not been set, and
          you do not specify one on the command line, then Java sets the
          CLASSPATH to the default:


Unix: .:$JAVA/classes:$JAVA/lib/classes.zip
Windows: .:$JAVA\classes:$JAVA\lib\classes.zip
Mac: ./$JAVA:classes/$JAVA:lib:classes.zip

   Here . is the current directory and $JAVA is the main Java directory
          where the different tools like javac were installed.

  11.3: WHY WON'T MY AUDIO CLIP PLAY?

   It's probably in the wrong format. Java 1.1 and earlier only
          understand 8 bit, mulaw-encoded, 8000 Hz, one-channel files.
          Many sound conversion programs will convert various formats to
          .au files but not necessarily to 8 bit, mulaw-encoded, 8000 Hz,
          one-channel files.

  11.4: WHEN I LOAD THE PAGE NETSCAPE GIVES ME A JAVA.LANG.CLASSFORMATERROR.

   Something is mangling the .class file. Most likely the .class files
          were uploaded to the server as text or MacBinary rather than as
          raw binary data. Make sure you put your ftp program in binary
          mode before sending the files to the server.

          The other possibility is that the web server is sending the
          file to clients as text rather than binary data. Make sure the
          web server is configured to send files that end in ".class"
          with a MIME type of application/octet-stream. Many web servers
          send files as type text/plain which often works but causes
          problems on a few servers. In particular, WebStar needs to
          change the action to "binary" and the MIME type to
          "application/octet-stream".

          It's also possible on some platforms that Netscape just can't
          find the .class file; that is, it isn't in the directory where
          Netscape is looking for it. Technically, this isn't really a
          ClassFormatError, but this is how Netscape reports it on some
          platforms and versions.

  11.5: NETSCAPE GIVES ME "APPLET NOT INITIALIZED ERROR"

   This is almost always means Netscape can't find one of the classes it
          needs to run the applet. Check to make sure that the classes
          your program uses are in the CODEBASE, the CLASSPATH, or
          somewhere else Netscape can find them. It's not uncommon to get
          this error when you first test a new package or class you've
          written with Netscape. If you've only tested it with the applet
          viewer or an IDE, then the applet viewer or the IDE may have
          included the current directory in the CLASSPATH where Netscape
          does not. Therefore the applet viewer can find the right class,
          but Netscape can't. Explicitly add the path containing your
          class or package to the CLASSPATH as specified in the previous
          question.

  11.6: OTHER NETSCAPE PROBLEMS

   As of version 3.0, Netscape has many problems handling Java applets.In
          no particular order they are:

          + Netscape can only run applets that are compiled with the Java
            1.0 beta compilers through the Java 1.0.2 compiler. It cannot
            handle .class files compiled for the various alpha versions
            of Java or Java 1.1. As a general rule, make sure you're
            using Sun's javac 1.0.2 to compile all applets you
            distribute. (Microsoft and Natural Intelligence's compilers
            have non-trivial bugs of their own.)

          + Not all versions of Netscape support Java. Notably the
            Windows 3.1 version does not, though a beta version that does
            has recently become available.

          + Netscape will not import any user-defined packages from the
            local CLASSPATH.

          + Netscape does not flush classes when you reload a page. If
            you need to reload a changed applet, for instance if you made
            a change to the applet source code and regenerated the .class
            file, there are a number of things you can try. On some
            platforms holding down the shift key and pressing the reload
            button will get Netscape to reload the .class file. You can
            also try manually clearing both the memory and disk caches,
            in order to reload an applet. Turning Java off and then on
            again in the Options/Security Preferences... menu may also do
            the trick. If none of these work, you'll simply have to quit
            and relaunch Netscape.

          + Netscape calls your init() method many times more than the
            appletviewer will. In particular Netscape calls init()
            anytime your reload, resize or otherwise restart your applet.
            I am not sure whether or not this is a bug, but it does
            indicate that you should try to keep your init() methods as
            small and quick as possible. Similarly it may call destroy()
            when the applet viewer would only call stop().

          + Netscape won't run any applet that calls Object.clone().

          + Netscape can't print applets.

  11.7: I KEEP GETTING ACCESS PRIVILEGE VIOLATIONS, " JAVA TRIED TO READ FILE
  FOO.CLASS IN DIRECTORY BAR."

   This happens when you try to load a class from a local hard disk
          instead of a server, the class is not a subclass of Applet, and
          the directory where the class resides is not in the HotJava
          read path. The solution is to move the class file into a
          directory in the HotJava read path. On Unix one such directory
          is ~/public_html/classes (where ~ is your home directory).
          Alternatively you can change the HOT_JAVA_READPATH environment
          variable to point to the directory containing your classes
          directory.

  11.8: JAVAC KEEPS INSISTING THAT IT CAN'T FIND THE RIGHT CONSTRUCTOR FUNCTION
  IN MY CLASS, BUT I'M SURE IT'S IN A FILE I IMPORTED. WHY IS IT EVEN LOOKING
  IN MY CLASS INSTEAD OF THE IMPORTED FILE?

   You cannot construct instances of a class on the fly using syntax like

          System.out.println(Double(0.56).toString());

          You must use the new operator like:

Double myDouble = new Double(0.56);
System.out.println(myDouble.toString());

   or


System.out.println((new Double(0.56)).toString());

   In other words, constructors are only called after a new operator.

  11.9: NULLPOINTEREXCEPTIONS WITH ARRAYS OF OBJECTS

   When you allocate an array of objects, each component of the array is
          initialized to null. The individual components of the array
          must still be initialized with a constructor or an assignment
          statement. For example, consider this statement:

Integer[] scores = new Integer[10];
int m = scores[5].intValue(); // throws NullPointerException

   This creates an array called scores containing ten references to
          Integer objects. Then it tries to get the value of the fifth
          component. However, each of those references is initially set
          to null. Thus when you try to call a method on one of the
          components of the array or pass the component to a method that
          expects a non-null argument, a NullPointerException is thrown.

          To fix this, you need to initialize the components of the
          array, either with constructors or with assignment statements
          For example:

Integer[] scores = new Integer[10];
for (int i = 0; i < scores.length; i++) scores[i] = new Integer(i);
int m = scores[5].intValue();

   You do not need to initialize all the components of the array though
          it's a good idea to do so. You can initialize just those you'll
          use, or you can make sure you catch and handle
          NullPointerExceptions in the appropriate places.

          This is different from how Java handles uninitialized non-array
          reference variables. By way of contrast when you write,

Integer score;
int m = score.intValue();

   the compiler catches the null reference in score and complains. You
          have to fix the problem before you can compile the program.
          However in general the compiler has no way to know whether an
          array component has or has not been initialized. Therefore the
          check for the non-nullness of an array component is deferred
          till runtime when the NullPointerException may be thrown.

  11.10: CAN'T MAKE STATIC REFERENCE TO METHOD TYPE MYMETHOD IN CLASS MYCLASS

   This common error occurs when you attempt to call an instance method
          from a static method, most commonly main(). For example,

class StaticTest {

  public static void main(String[] args) {

    int i = getX();

  }

  public int getX() {

    return 3;

  }

}

   The static method, main(), belongs to the class. However, getX()
          belongs to an object in the class. The compiler doesn't know on
          which object it's invoking the getX() method.

          There are a couple of ways around this problem. You could
          declare that getX() is also static; that is:

          public static int getX() {

          Alternately, you can instantiate an object in the StaticTest
          class in the main() method and invoke that object's getX()
          method, like this:

  public static void main(String[] args) {

    StaticTest st = new StaticTest();
    int i = st.getX();

  }

  11.11: WHY DO I HAVE TROUBLE WHEN USING == TO COMPARE STRINGS?

   When used on objects, == tests whether the two objects are the same
          object, not whether they have the same value. Consider this
          code fragment:

        String s1 = new String("Hello World");
        String s2 = new String("Hello World");
        if (s1 == s2) {
          System.out.println("The strings are the same.");
        }
        else {
          System.out.println("The strings are different.");
        }

   This prints "The strings are different."

          To compare to objects for equality, rather than identity, you
          should use the equals() method, like this:

        String s1 = new String("Hello World");
        String s2 = new String("Hello World");
        if (s1.equals(s2)) {
          System.out.println("The strings are the same.");
        }
        else {
          System.out.println("The strings are different.");
        }

   This prints "The strings are the same." The default equals() method
          all objects inherit from java.lang.Object just tests for object
          identity with ==. However many classes, including
          java.lang.String, override equals() to test the state of the
          object.

          However, the issue is a little confused when string literals
          are considered. Consider this code fragment:

        String s1 = "Hello World";
        String s2 = "Hello World";
        if (s1 == s2) {
          System.out.println("The strings are the same");
        }
        else {
          System.out.println("The strings are different");
        }

   This prints "The strings are the same". The compiler recognizes that
          the two string literals have the same value and it performs a
          simple optimization of only creating one String object. Thus s1
          and s2 both refer to the same object and are therefore equal.
          The Java Language Specification requires this behavior.
          However, not all compilers get this right so in practice this
          behavior here is implementation dependent.

12: Security

  12.1: SYSTEM LEVEL SECURITY

   On a system level Java applets live in a cage. They can do pretty much
          anything they want inside their cage, but they cannot get
          outside the cage and do damage unless the user unlocks the door
          to the cage. Even then they wear shackles that prevent them
          from doing things like writing to arbitrary addresses in
          memory.

          In Netscape the user doesn't even get the keys to the cage so
          you can't let the applets out into your system even if you
          wanted to. With the Applet Viewer it is possible to give your
          applets more access to the network. However they still can't do
          everything a C program can do.

          Specifically a Java applet cannot write anything to a hard
          drive. It cannot write directly to memory, and it cannot
          introduce a virus into your system. A Java applet can use a lot
          of your CPU time though not 100% of it. It cannot crash your
          system (though a Java enabled browser can).

  12.2: USER LEVEL SECURITY

   A Java applet can trick the user into doing something stupid such as
          revealing their root password though there are efforts to avoid
          this. A Java applet can also send this information back to the
          applet's server.

          Finally an applet can display pictures or text or play sounds
          which the user may find annoying or offensive, but this hardly
          qualifies as a security flaw and is not unique to Java enabled
          browsers.

13: Tools

  13.1: IDE

   Symantec publishes Cafe and Visual Cafe, an applet development
          environment for Windows 95, NT and the Mac. It includes a
          source code editor and a class browser, and a just-in-time
          compiler. It is still beta quality at best. I do not recommend
          it.

          Natural Intelligence's Roaster is a Macintosh hosted applet
          development environment. It is also still beta quality. I do
          not recommend it.

          Metrowerks includes Java support in Code Warrior Gold.
          Metrowerks has licensed Sun's source code. The Java support is
          alpha quality, and is not by itself worth the price of Code
          Warrior, even the $99 Java only edition. However if you also
          need a C compiler it doesn't cost you anymore to get Java
          support.

          Sun publishes a payware IDE called Java Workshop. It is fairly
          cheap, ($99) but again not yet worth the download time. Java
          Workshop is similar to Sun's existing Workshop products for
          Fortran and C++. However it is written entirely in Java. You'll
          need at least a Pentium Pro to squeeze adequate performance out
          of this system.

          Microsoft's Visual J++ is one of the faster VM/JIT combinations
          available. However the compiler has some bugs that prevent it
          from compiling certain legal Java code. Once again this is beta
          software at best, and is not worth spending money on.

          Borland's JBuilder has gotten some nice reviews, but I've yet
          to try it personally. Furthermore, their lawyers seem to be out
          of control.

          The bottom line is that you should use Sun's JDK (or your local
          platform's equivalent) and the text editor of your choice. None
          of the available IDEs are worth what they cost. All will cause
          you more problems than they solve. Unless you enjoy paying to
          beta test products, there's no reason to purchase any of these
          products at this time.

  13.2: DEBUGGER

   A preliminary jdb is available with Java Developer's Kit from Sun.
          Various payware IDEs include debuggers of beta quality at best.

  13.3: EDITORS

   I use BBEdit 4.0 on the Mac. The free, light version works well too
          although it doesn't include syntax coloring. See

          http://www.barebones.com/bbedit.html

          However, in general any normal text or programmer's editor
          should be fine.

          The Windows Notepad program, however, is not fine. It appends
          the extension ".txt" to all files it saves. Java source code
          files must end in ".java". If you must use Notepad, enclose the
          filename in double quotes when you save it; that is don't just
          type HelloWorld.java but rather "HelloWorld.java". This will
          force Notepad not to append a ".txt" extension to the file.

  13.4: YACC GRAMMAR

   An LALR grammar for Java is included in The Java Language
          Specification.

  13.5: PROFILERS

   Using the -prof option to the java interpreter produces basic profile
          information in a file called java.prof. That is,

          % java -prof HelloWorld.class

14: The Java Virtual Machine and Byte Codes

   The most recent Java Class File / Java Virtual Machine specs are
          available in various formats from
          http://www.javasoft.com/java.sun.com/newdocs.html

  14.1: CAN I PROGRAM DIRECTLY IN BYTE CODE?

   Yes, you can. Jonathan Meyer's Jasmin Java assembler is a small
          assembler for Java byte code, and would be of great assistance
          to you in such an endeavor. The Java interpreter will check
          your byte codes to make sure they don't violate security. If
          you write security violating byte codes the interpreter won't
          run them.

14.2: Optimizing Java

         1. Make your classes final.

         2. Use the -O flag to the compiler.

         3. If you're reading data off a disk read it in as large a chunk
            as possible. Do not read it a byte at a time. If you need to
            process the data a byte at a time read it into a temporary
            buffer first.

         4. Creating objects is expensive. Try to reuse objects rather
            than creating new ones, especially for temporary objects that
            exist only to support a calculation.

         5. Avoid synchronization where possible.



14.3: Disassembly, Decompilation, and Obfuscation

   Compiled Java byte code is comparatively trivial to disassemble, and
          it's not that much harder to decompile. The javap program
          included in the JDK disassembles .class files into reasonably
          legible, assembly like code. For example,

% javap -c HelloWorld
Compiled from HelloWorld.java
class HelloWorld extends java.lang.Object {
    public static void main(java.lang.String[]);
    public HelloWorld();
}


Method void main(java.lang.String[])
   0 getstatic #7 <Field java.io.PrintStream out>
   3 ldc #1 <String "Hello World!">
   5 invokevirtual #6 <Method void println(java.lang.String)>
   8 return


Method HelloWorld()
   0 aload_0
   1 invokespecial #8 <Method java.lang.Object()>
   4 return


   While this isn't the original source code, it's enough for experienced
          programmers to understand, especially if they have a copy of
          the Java Virtual Machine Specification in hand.

          There are also third party decompilers that go a step further
          and produce something very close to the actual source code. The
          first was Mocha by the late HanPeter van Vliet, although this
          is beginning to show its age. (In yet another tale of lawyers
          run wild, Borland is trying to retroactively change the Mocha
          license agreement.) SourceTec's Jasmine is a $29.80 shareware
          decompiler. Wingsoft's WingDIS is a $39.95 payware decompiler.
          A free copy of WingDIS 2.0.3 is included in the CD with my book
          Java Secrets (IDG Books, 1997).

          Obfuscator or shrouder tools play various tricks with the
          compiled byte code in a .class file, especially with private
          field and method names, to attempt to confuse these tools.
          However Java's late binding places severe limits on how much
          these tools can do, especially in class libraries and other
          component software.

          To the best of my knowledge the first such tool developed was
          HanPeter van Vliet's payware Crema, though there's evidence
          that IBM may have developed a similar tool internally around
          the same time but never released it to the public. A version of
          Crema has been incorporated into Borland's JBuilder.

          Other obfuscators include K.B. Sriram's Hashjava (distributed
          under the GNU Library General Public License (LGPL).), Eron
          Jokipii's Jobe (free for non-commercial use), and Eastridge
          Technology's $45 payware Jshrink.

15: Legal Issues

   Some portions of Java and HotJava are neither in the public domain nor
          copylefted. However no license is required to write and
          distribute most Java applications and applets. Nor is any
          license from Sun is required to distribute the Java or HotJava
          in binary form.

          The source code for Java is freely available for non-commercial
          use though a license must be signed. Source code for the java
          packages is included with the various versions of the JDK,
          including 1.1. However, if you want to license the Java source
          code for commercial use, you will need to negotiate a source
          code license with Sun. Complete details are at
          http://www.javasoft.com/java.sun.com/source.html.

          Furthermore whether your product is commercial or
          non-commercial you may not use the trademark "Java" to describe
          your product unless you pass an as yet unreleased verification
          and test suite.

16: FAQ's about the FAQ

  16.1: WHO IS THIS ELLIOTTE GUY, AND JUST WHAT QUALIFIED HIM TO WRITE A JAVA
  FAQ ANYWAY?

   He was willing to do it. Seriously, months on the Java mailing lists
          made it obvious that a FAQ was needed and since none seemed to
          be forthcoming from those more qualified than I, I boldly and
          with a complete disregard for my absolute lack of
          qualifications stepped forward and volunteered. I do have some
          hope that my previous experience with FAQ lists, the World Wide
          Web and a variety of programming languages may somehow cover up
          the fact that I have no idea what I'm doing. You've read the
          FAQ list by now. Did I succeed?

          Why am I taking on such a Herculean task? It's often said that
          you never really understand a subject until you teach it. I'm
          going to endeavor to learn Java and understand it by teaching
          it. The result should be interesting at least. Since I'm very
          new to Java and clearly do not yet understand the language,
          I'll have a perspective on the issues that should be helpful to
          newcomers.

          Are there mistakes here? Absolutely. I hope people here and
          elsewhere will correct me gently and help lead me on the path
          to true Java enlightenment when I err. And if they aren't so
          gentle, well, I've developed a pretty thick skin after six
          years of Usenet.

          My companion tutorial in how to write Java is going to reflect
          the programs I'm actually writing. As I learn to do a Hello
          World program, I'll write about Hello World. (OK, I've actually
          already gotten beyond Hello World but not much beyond.) How
          fast the FAQ list grows will depend in large part on how fast
          my skills grow. You'll get to watch me learn, make mistakes,
          correct mistakes and so on.

          There may be an advantage to this approach. People who want to
          learn Java will be coming from almost identical places as me. I
          always hate having to write down or talk down to people, and I
          don't do it very well. Similarly I find it frustrating to try
          to communicate with people who are way beyond me (as obviously
          some people on the Java mailing lists are). This means that I
          can write for people without much prior experience without
          boring myself or, hopefully, my audience, to tears.

          Finally I'll emphasize that I'm not trying to prevent anyone
          else or any other team of people from taking on a similar
          project. I hope someone does. I'll probably learn from what
          they do, and they'll learn from what I do, even if it's only to
          learn the sorts of things novices are confused about. And of
          course not everyone shares the same learning style so while
          some people may enjoy my approach to Java I am sure others will
          find it dense, incoherent, and ultimately incomprehensible.
          More choices are better.

          Ultimately I'm doing this because I think Java is very, very
          cool and I am convinced I need to learn it sooner rather than
          later. I think this project will propel my Java knowledge
          forward, and if it does that I'll consider my project a
          success. If I can help a few other lost souls to climb out of
          the pit with me at the same time, so much the better.

  16.2: WHY DON'T YOU INCLUDE X IN YOUR FAQ?

   Please do make suggestions about topics for FAQ list inclusion. You
          can email them to [e-mail]. I do follow the
          various comp.lang.java groups as best I can, and have a pretty
          good idea of what's discussed there.

  16.3: THIS IS REALLY COOL. CAN I REPUBLISH OR TRANSLATE IT?

   This FAQ list and its entire contents are copyright 1995-1997 by
          Elliotte Rusty Harold. If you have specific desires to
          republish it in whole or part contact me at
          [e-mail] and tell me exactly what you want to
          do. I'm generally receptive to non-profits that want to make it
          available to the public at no charge and to anyone who's
          willing to make reasonable payment arrangements.

          However I do not allow the FAQ list, either the text or HTML
          version, to be placed on any web or ftp sites but my own.
          Mirroring HTML files is a fundamentally bad idea that is at
          cross-purposes with the design of the web. Among other problems
          it makes maintaining up-to-date copies phenomenally difficult.
          If you think this file would be a useful addition to your web
          site, then link to it. That's the way the web is designed. Not
          all information needs to reside in one central location. No
          permission is needed to link to this or any other of my HTML
          files. In fact I'd prefer it if you'd not ask me, since then I
          don't have to spend time answering you.

          Although there's more reason to want to translate the document
          rather than merely mirror it, I regret that I do not have the
          time or resources to support any translation efforts, and
          therefore do not currently allow this FAQ list to be translated
          into other languages. This document will be available in
          English only for the foreseeable future.

          If you want to use the source code samples included here,
          please do. I consider the source code (though not the FAQ list
          itself!) to be public domain. No permission is necessary to
          reuse, edit, modify or publish any of the source code contained
          in this FAQ list.

--
          Copyright 1995-1997 Elliotte Rusty Harold
          [e-mail]
          Last Modified October 6, 1997
--
Elliotte Rusty Harold
[e-mail]
[e-mail]