Mac OS Runtime for Java (MRJ) 2.0 is a software package that includes Apple’s implementation of the Java Virtual Machine (VM) and related libraries. It is based on software created by the JavaSoft business unit of Sun Microsystems, Inc. and implements version 1.1.3 of Sun’s Java specification.
With MRJ installed, you are able to run Java applets within the Microsoft Internet Explorer web browser or the Apple Applet Runner, both of which are included with Mac OS 8.1.
Microsoft Internet Explorer
The most convenient way to locate Java applets on the World Wide Web and to run them is to use a web browser such as Microsoft Internet Explorer. To configure Internet Explorer to use MRJ so that you can run Java applets, first use the Preferences command in the Internet Explorer Edit menu to bring up the Internet Explorer Preferences dialog. Click the triangle next to “Web Browser” in the box on the left side of the dialog to show its subcategories. Then click the “Java” subcategory to see the Java Options pane on the right side of the dialog:
Check the “Enable Java” box so you will be able to run Java applets; then use the “Java virtual machine” popup menu to select “Apple MRJ”. To confirm the selections, click OK to dismiss the dialog. You must then quit Internet Explorer and run it again for the new selections to take effect.
Apple Applet Runner
You can also use Apple Applet Runner to run Java applets. It is located in the “Mac OS Runtime for Java” folder in the “Apple Extras” folder of your startup disk.
Each Java applet on the Internet has a unique URL (Uniform Resource Locator), or address, that the Apple Applet Runner uses to locate it. If you know the URL of an applet you want to run, use the “Open URL” command (in the File Menu) to add it to a list of saved URLs, choose the new applet from the list, then click the Open button to run it.
You can also run an applet that is stored on your local hard disk. To do this, use the “Open Local HTML File” command (in the File menu) to select the HTML (Hypertext Markup Language) file used to identify and run the applet. This file, whose name usually has a “.html” suffix, is most often located inside the folder on your hard disk where the applet is stored. You can also drag and drop an applet’s HTML file onto the Apple Applet Runner icon in the Finder.
Note: If you run applets using the Apple Applet Runner you will see only the applet window itself. If you run the applet inside a Java-enabled web browser like Internet Explorer, you will usually see other information displayed on your web page around the portion used to show the applet. This information comes from the same HTML file used to run the applet, but is intended for use only by browsers and is ignored by Apple Applet Runner.
Several demonstration applets can be run from the Applets menu in Apple Applet Runner even if you do not have an active Internet connection. These applets are stored locally in the Applets folder inside the “Mac OS Runtime for Java” folder in the “Apple Extras” folder. Note that these demonstration applets were created by Sun Microsystems, Inc., not by Apple Computer, Inc., and may not follow Apple’s guidelines for user interaction.
Where to Find Applets to Run
There are thousands of applets available on the Internet, most of them for no charge. Three good starting points for finding applets are:
• <http://www.gamelan.com/>
• <http://www.jars.com/>
• <http://trp.research.apple.com/>
System requirements
MRJ 2.0 works on PowerPC and 68040 computers running Mac OS 8.0 or later. At least 8 MB of free RAM is recommended and at least 30 MB of free disk space is required to run MRJ. The amount of RAM needed depends on the applets being run; larger applets will need more than 8MB of RAM. If you are running MRJ in a Web browser, you’ll need at least 8MB of free RAM after the browser has launched. To see how much RAM you have available, choose “About this Computer” from the Apple menu in the Finder. See the Memory Usage section below for more information.
To run Java applets over the Internet you must have an active Internet connection.
Note: MRJ 2.0 may be installed on System 7.6.1 by doing a Custom Install and choosing the software components appropriate for that System.
What’s Installed with MRJ?
The MRJ 2.0 installer places the following software components on your hard disk:
On all computers:
• “Mac OS Runtime for Java” folder in the Apple Extras folder at the top level of the startup drive; this folder holds the Apple Applet Runner and many demonstration applets.
• “MRJ Libraries” folder in the Extensions folder of the active System Folder
• “Text Encoding Converter” file in the Extensions folder of the active System Folder (if needed)
• “Text Encodings” folder in the active System Folder (if needed)
On 68040 computers only:
• “CFM-68K Runtime Enabler” file in the Extensions folder of the active System Folder (if needed)
When you run the Apple Applet Runner, a preferences file named “Apple Applet Runner Prefs” is saved in the Preferences folder of the active System Folder.
What’s New in MRJ 2.0?
MRJ 2.0 supports Sun’s Java version 1.1.3 specification, which has added or improved support in the following areas:
• Internationalization
• Security and Signed Applets
• AWT Enhancements
• JavaBeans™
• JAR File Format
• Networking Enhancements
• I/O Enhancements
• Math Package
• Remote Method Invocation
• Object Serialization
• Reflection
• JDBC™ - Connecting Java and Databases
• Inner Classes
• Java Native Interface
• Performance Enhancements
• The demonstration applets have been updated and/or replaced with new examples
For detailed technical information on these new features, visit Sun’s web site at
<http://java.sun.com/products/jdk/1.1/docs/>.
MRJ 2.0 also contains a just-in-time compiler (JITC) for both PowerPC and 68040 Macintoshes that greatly enhances the speed of many operations in Java.
MRJ Software Development Kit
If you are a software developer and you want to learn more about programming with Java on a Macintosh, visit our web site at <http://applejava.apple.com/> for information on how to obtain a software development kit (SDK) to facilitate your development efforts using MRJ. The MRJ SDK includes utilities and documentation that allow software developers to:
• run Java applets and applications within a Macintosh application
• access the Java runtime from a Macintosh application
• call Java methods from C and C++
• call native methods from Java
• build standalone Java applications
Troubleshooting
Memory Usage
If there is not enough random-access memory (RAM) in your computer, you may have trouble running Java applets or applications. If you see an error message that contains one of terms below, the problem might be that you do not have enough memory to run:
• OutOfMemoryError
• OutOfMemoryException
• java.lang.NoClassDefFoundError
• java.lang.NullPointerException
Note: These error messages may happen for reasons other than low memory. You might try running the applet or application on another computer to see if the same error messages occur there.
MRJ uses system memory to run Java applets and applications. Applications allocate their own application memory, leaving less memory available to the rest of the system. If an application that uses MRJ (such as Apple Applet Runner or Internet Explorer) is using an especially large amount of memory, you may have trouble running large Java applets or applications.
To make more memory available try quitting applications that you aren’t using. If you still cannot run the applet or application, try reducing the amount of memory used by the application that is using MRJ; this will free up more system memory for MRJ to use. To reduce an application’s memory size, first quit the application, then select the application’s icon and choose Get Info from the Finder’s File menu. Enter a smaller number in the Preferred Size field, but do not set the preferred size smaller than the indicated minimum size.
You may also wish to turn on Virtual Memory to allow applications to use some of your disk space as if it were RAM. This allows you to run more memory-intensive programs, but your computer may run more slowly as a result. You can turn Virtual Memory on with the Memory control panel.
Known Problems
• MRJ may display error messages, fail to load images or fail to play sounds if there is not enough memory available to run, as described in the Memory Usage section above. In rare cases, MRJ may crash or hang if it cannot get enough memory to run. Try the techniques described in the Memory Usage section if you are having trouble running MRJ.
• Microsoft Internet Explorer may fail to load or run applets if there is not enough memory available to run. Try the techniques described in the Memory Usage section if you are having trouble running applets in Internet Explorer.
• Some applets may cause MRJ to hang. If your browser or Apple Applet Runner appears to be frozen, wait a few minutes to see if the problem corrects itself. If the problem continues, try force-quitting the application by typing -option-escape and choosing “Force Quit” when the dialog appears. If the problem reproduces every time you visit a particular applet, please send email describing the problem to the bug-reporting address listed at our Web site, <http://applejava.apple.com/>.
• Some Java applets (such as the Clock example) or applications that are processor intensive may cause other applets to open or run slowly, or may cause them not to open at all. To improve performance, try closing applets or applications that you are not using.
• Marimba’s Castanet Tuner 1.0 (distributed with Mac OS 8.0) is only compatible with MRJ 1.0.2 (also provided with Mac OS 8.0) and MRJ 1.5.1. It does not work with MRJ 2.0. Contact Marimba for information on how to upgrade to a newer version that does work with MRJ 2.0. Marimba’s web address is <http://www.marimba.com/>.
• MRJ may fail to run or give an error message saying that it can’t find required Java Classes if an empty folder has been created or placed in the MRJClasses folder (located in the MRJ Libraries folder, which is in the Extensions folder of the active System Folder).
• If you have an extension called PPCExceptionEnabler in the Extensions folder of your active System Folder you must remove it and restart before running MRJ. This extension was installed by early versions of Macintosh Common Lisp (MCL); the latest version of MCL does not require this extension. If you have MCL 3.9 or earlier, upgrade to version 4.0 or later.
• Serialized objects created by MRJ are currently created as type 'TEXT'. Many utilities for transferring files from Mac OS systems to other systems (such as PC Exchange or Fetch) may automatically manipulate text files, effectively corrupting the serialized object. To avoid this problem, you must make sure that the objects are transferred as raw or binary data, rather than being interpreted as a text file. Most transfer utilities provide a method for specifying how the data is transferred.
• If you have Personal Web Sharing on and are trying to share applets, you may see a problem if the applet’s class files contain a “$”. Personal Web sharing incorrectly interprets the “$”, resulting in the applet failing to run. The applet will work correctly if its class files are packaged in .zip or .jar format.
• JDK 1.1.3 performs more complete bytecode verification than earlier versions of Java. If you see an error of the form “java.lang.ClassFormatError: Arguments can't fit into locals...” you may need to obtain a newer version of the applet or application.
Further Information
Visit our Web site at <http://applejava.apple.com/> to find out about future releases of MRJ, fixes to problems, and other related news and information.
Java not Fault-tolerant
The Java technology is not fault-tolerant and is not designed, manufactured or intended for use or resale as on-line control equipment in the operation of nuclear facilities, aircraft navigation or communication systems, or air traffic control machines in which the failure of the Java technology or Mac OS Runtime for Java could lead directly to death, personal injury, or severe physical or environmental damage.
Apple, the Apple logo, and Mac are trademarks of Apple Computer, Inc., registered in the U.S. and other countries. PowerPC is a trademark of International Business Machines Corporation, used under license therefrom. Java and all Java-based trademarks and logos are either trademarks or registered trademarks of Sun Microsystems, Inc. in the U.S. and other countries. Microsoft and Internet Explorer are either trademarks or registered trademarks of Microsoft Corporation, in the U.S. and/or other countries. All other product and company names may be trademarks or registered trademarks of their respective owners. Mention of non-Apple products is for information purposes and constitutes neither an endorsement nor a recommendation. Apple assumes no responsibility with regard to the selection, performance, or use of these products.
