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DataInputStream.java
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/*
* @(#)DataInputStream.java 1.39 98/07/01
*
* Copyright 1995-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
package java.io;
/**
* A data input stream lets an application read primitive Java data
* types from an underlying input stream in a machine-independent
* way. An application uses a data output stream to write data that
* can later be read by a data input stream.
* <p>
* Data input streams and data output streams represent Unicode
* strings in a format that is a slight modification of UTF-8. (For
* more information, see X/Open Company Ltd., "File System Safe
* UCS Transformation Format (FSS_UTF)", X/Open Preliminary
* Specification, Document Number: P316. This information also
* appears in ISO/IEC 10646, Annex P.)
* <p>
* All characters in the range <code>'\u0001'</code> to
* <code>'\u007F'</code> are represented by a single byte:
* <center><table border="3">
* <tr><td><i>0</i></td> <td>bits 0-7</td></tr>
* </table></center>
* <p>
* The null character <code>'\u0000'</code> and characters in the
* range <code>'\u0080'</code> to <code>'\u07FF'</code> are
* represented by a pair of bytes:
* <center><table border="3">
* <tr><td>1</td> <td>1</td> <td>0</td> <td>bits 6-10</td></tr>
* <tr><td>1</td> <td>0</td> <td colspan=2>bits 0-5</td></tr>
* </table></center><br>
* Characters in the range <code>'\u0800'</code> to
* <code>'\uFFFF'</code> are represented by three bytes:
* <center><table border="3">
* <tr><td>1</td> <td>1</td> <td>1</td> <td>0</td> <td>bits 12-15</td</tr>
* <tr><td>1</td> <td>0</td> <td colspan=3>bits 6-11</td></tr>
* <tr><td>1</td> <td>0</td> <td colspan=3>bits 0-5</td></tr>
* </table></center>
* <p>
* The two differences between this format and the
* "standard" UTF-8 format are the following:
* <ul>
* <li>The null byte <code>'\u0000'</code> is encoded in 2-byte format
* rather than 1-byte, so that the encoded strings never have
* embedded nulls.
* <li>Only the 1-byte, 2-byte, and 3-byte formats are used.
* </ul>
*
* @author Arthur van Hoff
* @version 1.39, 07/01/98
* @see java.io.DataOutputStream
* @since JDK1.0
*/
public
class DataInputStream extends FilterInputStream implements DataInput {
/**
* Creates a new data input stream to read data from the specified
* input stream.
*
* @param in the input stream.
*/
public DataInputStream(InputStream in) {
super(in);
}
/**
* Reads up to <code>byte.length</code> bytes of data from this data
* input stream into an array of bytes. This method blocks until some
* input is available.
* <p>
* The <code>read</code> method of <code>DataInputStream</code>
* calls the <code>read</code> method of its underlying input stream
* with the three arguments <code>b</code>, <code>0</code>, and
* <code>b.length</code> and returns whatever value that method returns.
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end
* of the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
* @see java.io.InputStream#read(byte[], int, int)
*/
public final int read(byte b[]) throws IOException {
return in.read(b, 0, b.length);
}
/**
* Reads up to <code>len</code> bytes of data from this data input
* stream into an array of bytes. This method blocks until some input
* is available.
* <p>
* The <code>read</code> method of <code>DataInputStream</code>
* calls the <code>read</code> method of its underlying input stream
* with the same arguments and returns whatever value that method returns.
*
* @param b the buffer into which the data is read.
* @param off the start offset of the data.
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end
* of the stream has been reached.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
* @see java.io.InputStream#read(byte[], int, int)
*/
public final int read(byte b[], int off, int len) throws IOException {
return in.read(b, off, len);
}
/**
* Reads <code>b.length</code> bytes from this data input stream
* into the byte array. This method reads repeatedly from the
* underlying stream until all the bytes are read. This method blocks
* until all the bytes are read, the end of the stream is detected,
* or an exception is thrown.
*
* @param b the buffer into which the data is read.
* @exception EOFException if this input stream reaches the end before
* reading all the bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final void readFully(byte b[]) throws IOException {
readFully(b, 0, b.length);
}
/**
* Reads exactly <code>len</code> bytes from this data input stream
* into the byte array. This method reads repeatedly from the
* underlying stream until all the bytes are read. This method blocks
* until all the bytes are read, the end of the stream is detected,
* or an exception is thrown.
*
* @param b the buffer into which the data is read.
* @param off the start offset of the data.
* @param len the number of bytes to read.
* @exception EOFException if this input stream reaches the end before
* reading all the bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final void readFully(byte b[], int off, int len) throws IOException {
InputStream in = this.in;
int n = 0;
while (n < len) {
int count = in.read(b, off + n, len - n);
if (count < 0)
throw new EOFException();
n += count;
}
}
/**
* Skips exactly <code>n</code> bytes of input in the underlying
* input stream. This method blocks until all the bytes are skipped,
* the end of the stream is detected, or an exception is thrown.
*
* @param n the number of bytes to be skipped.
* @return the number of bytes skipped, which is always <code>n</code>.
* @exception EOFException if this input stream reaches the end before
* skipping all the bytes.
* @exception IOException if an I/O error occurs.
*/
public final int skipBytes(int n) throws IOException {
InputStream in = this.in;
for (int i = 0 ; i < n ; i += (int)in.skip(n - i));
return n;
}
/**
* Reads a <code>boolean</code> from this data input stream. This
* method reads a single byte from the underlying input stream. A
* value of <code>0</code> represents <code>false</code>. Any other
* value represents <code>true</code>. This method blocks until
* either the byte is read, the end of the stream is detected, or an
* exception is thrown.
*
* @return the <code>boolean</code> value read.
* @exception EOFException if this input stream has reached the end.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final boolean readBoolean() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return (ch != 0);
}
/**
* Reads a signed 8-bit value from this data input stream. This
* method reads a byte from the underlying input stream. If the byte
* read is <code>b</code>, where
* 0 <= <code>b</code> <= 255, then the
* result is:
* <ul><code>
* (byte)(b)
* </code></ul>
* <p>
* This method blocks until either the byte is read, the end of the
* stream is detected, or an exception is thrown.
*
* @return the next byte of this input stream as a signed 8-bit
* <code>byte</code>.
* @exception EOFException if this input stream has reached the end.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final byte readByte() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return (byte)(ch);
}
/**
* Reads an unsigned 8-bit number from this data input stream. This
* method reads a byte from this data input stream's underlying input
* stream and returns that byte. This method blocks until the byte is
* read, the end of the stream is detected, or an exception is thrown.
*
* @return the next byte of this input stream, interpreted as an
* unsigned 8-bit number.
* @exception EOFException if this input stream has reached the end.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final int readUnsignedByte() throws IOException {
int ch = in.read();
if (ch < 0)
throw new EOFException();
return ch;
}
/**
* Reads a signed 16-bit number from this data input stream. The
* method reads two bytes from the underlying input stream. If the two
* bytes read, in order, are <code>b1</code> and <code>b2</code>,
* where each of the two values is between <code>0</code> and
* <code>255</code>, inclusive, then the result is equal to:
* <ul><code>
* (short)((b1 << 8) | b2)
* </code></ul>
* <p>
* This method blocks until the two bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @return the next two bytes of this input stream, interpreted as a
* signed 16-bit number.
* @exception EOFException if this input stream reaches the end before
* reading two bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final short readShort() throws IOException {
InputStream in = this.in;
int ch1 = in.read();
int ch2 = in.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (short)((ch1 << 8) + (ch2 << 0));
}
/**
* Reads an unsigned 16-bit number from this data input stream. This
* method reads two bytes from the underlying input stream. If the
* bytes read, in order, are <code>b1</code> and <code>b2</code>,
* where <code>0 <= b1</code>,
* <code>b2 <= 255</code>, then the result is equal to:
* <ul><code>
* (b1 << 8) | b2
* </code></ul>
* <p>
* This method blocks until the two bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @return the next two bytes of this input stream, interpreted as an
* unsigned 16-bit integer.
* @exception EOFException if this input stream reaches the end before
* reading two bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final int readUnsignedShort() throws IOException {
InputStream in = this.in;
int ch1 = in.read();
int ch2 = in.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (ch1 << 8) + (ch2 << 0);
}
/**
* Reads a Unicode character from this data input stream. This
* method reads two bytes from the underlying input stream. If the
* bytes read, in order, are <code>b1</code> and <code>b2</code>,
* where 0 <= <code>b1</code>,
* <code>b1</code> <= 255, then the result is equal to:
* <ul><code>
* (char)((b1 << 8) | b2)
* </code></ul>
* <p>
* This method blocks until either the two bytes are read, the end of
* the stream is detected, or an exception is thrown.
*
* @return the next two bytes of this input stream as a Unicode
* character.
* @exception EOFException if this input stream reaches the end before
* reading two bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final char readChar() throws IOException {
InputStream in = this.in;
int ch1 = in.read();
int ch2 = in.read();
if ((ch1 | ch2) < 0)
throw new EOFException();
return (char)((ch1 << 8) + (ch2 << 0));
}
/**
* Reads a signed 32-bit integer from this data input stream. This
* method reads four bytes from the underlying input stream. If the
* bytes read, in order, are <code>b1</code>, <code>b2</code>,
* <code>b3</code>, and <code>b4</code>, where
* 0 <= <code>b1</code>, <code>b2</code>,
* <code>b3</code>, <code>b4</code> <= 255, then the
* result is equal to:
* <ul><code>
* (b1 << 24) | (b2 << 16) + (b3 << 8) +b4
* </code></ul>
* <p>
* This method blocks until the four bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @return the next four bytes of this input stream, interpreted as an
* <code>int</code>.
* @exception EOFException if this input stream reaches the end before
* reading four bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final int readInt() throws IOException {
InputStream in = this.in;
int ch1 = in.read();
int ch2 = in.read();
int ch3 = in.read();
int ch4 = in.read();
if ((ch1 | ch2 | ch3 | ch4) < 0)
throw new EOFException();
return ((ch1 << 24) + (ch2 << 16) + (ch3 << 8) + (ch4 << 0));
}
/**
* Reads a signed 64-bit integer from this data input stream. This
* method reads eight bytes from the underlying input stream. If the
* bytes read, in order, are <code>b1</code>, <code>b2</code>,
* <code>b3</code>, <code>b4</code>, <code>b5</code>,
* <code>b6</code>, <code>b7</code>, and <code>b8</code>, where
* <ul><code>
* 0 <= b1, b2, b3, b4, b5, b6, b7, b8 <= 255,
* </code></ul>
* <p>
* then the result is equal to:
* <p><blockquote><pre>
* ((long)b1 << 56) + ((long)b2 << 48) +
* ((long)b3 << 40) + ((long)b4 << 32) +
* ((long)b5 << 24) + (b6 << 16) +
* (b7 << 8) + b8
* </pre></blockquote>
* <p>
* This method blocks until the eight bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @return the next eight bytes of this input stream, interpreted as a
* <code>long</code>.
* @exception EOFException if this input stream reaches the end before
* reading eight bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.FilterInputStream#in
*/
public final long readLong() throws IOException {
InputStream in = this.in;
return ((long)(readInt()) << 32) + (readInt() & 0xFFFFFFFFL);
}
/**
* Reads a <code>float</code> from this data input stream. This
* method reads an <code>int</code> value as if by the
* <code>readInt</code> method and then converts that
* <code>int</code> to a <code>float</code> using the
* <code>intBitsToFloat</code> method in class <code>Float</code>.
* This method blocks until the four bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @return the next four bytes of this input stream, interpreted as a
* <code>float</code>.
* @exception EOFException if this input stream reaches the end before
* reading four bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.DataInputStream#readInt()
* @see java.lang.Float#intBitsToFloat(int)
*/
public final float readFloat() throws IOException {
return Float.intBitsToFloat(readInt());
}
/**
* Reads a <code>double</code> from this data input stream. This
* method reads a <code>long</code> value as if by the
* <code>readLong</code> method and then converts that
* <code>long</code> to a <code>double</code> using the
* <code>longBitsToDouble</code> method in class <code>Double</code>.
* <p>
* This method blocks until the eight bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @return the next eight bytes of this input stream, interpreted as a
* <code>double</code>.
* @exception EOFException if this input stream reaches the end before
* reading eight bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.DataInputStream#readLong()
* @see java.lang.Double#longBitsToDouble(long)
*/
public final double readDouble() throws IOException {
return Double.longBitsToDouble(readLong());
}
private char lineBuffer[];
/**
* Reads the next line of text from this data input stream. This
* method successively reads bytes from the underlying input stream
* until it reaches the end of a line of text.
* <p>
* A line of text is terminated by a carriage return character
* (<code>'\r'</code>), a newline character (<code>'\n'</code>), a
* carriage return character immediately followed by a newline
* character, or the end of the input stream. The line-terminating
* character(s), if any, are not returned as part of the string that
* is returned.
* <p>
* This method blocks until a newline character is read, a carriage
* return and the byte following it are read (to see if it is a
* newline), the end of the stream is detected, or an exception is
* thrown.
*
* @deprecated This method does not properly convert bytes to characters.
* As of JDK 1.1, the preferred way to read lines of text is via the
* <code>BufferedReader.readLine()</code> method. Programs that use the
* <code>DataInputStream</code> class to read lines can be converted to use
* the <code>BufferedReader</code> class by replacing code of the form
* <ul>
* <code>DataInputStream d = new DataInputStream(in);</code>
* </ul>
* with
* <ul>
* <code>BufferedReader d
* = new BufferedReader(new InputStreamReader(in));
* </code>
* </ul>
*
* @return the next line of text from this input stream, or
* <tt>null</tt> if no bytes are read before end-of-file
* is reached.
* @exception IOException if an I/O error occurs.
* @see java.io.BufferedReader#readLine()
* @see java.io.FilterInputStream#in
*/
public final String readLine() throws IOException {
InputStream in = this.in;
char buf[] = lineBuffer;
if (buf == null) {
buf = lineBuffer = new char[128];
}
int room = buf.length;
int offset = 0;
int c;
loop: while (true) {
switch (c = in.read()) {
case -1:
case '\n':
break loop;
case '\r':
int c2 = in.read();
if (c2 != '\n') {
if (!(in instanceof PushbackInputStream)) {
in = this.in = new PushbackInputStream(in);
}
((PushbackInputStream)in).unread(c2);
}
break loop;
default:
if (--room < 0) {
buf = new char[offset + 128];
room = buf.length - offset - 1;
System.arraycopy(lineBuffer, 0, buf, 0, offset);
lineBuffer = buf;
}
buf[offset++] = (char) c;
break;
}
}
if ((c == -1) && (offset == 0)) {
return null;
}
return String.copyValueOf(buf, 0, offset);
}
/**
* Reads in a string that has been encoded using a modified UTF-8
* format from this data input stream. This method calls
* <code>readUTF(this)</code>.
* See <code>readUTF(java.io.DataInput)</code> for a more
* complete description of the format.
* <p>
* This method blocks until all the bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @return a Unicode string.
* @exception EOFException if this input stream reaches the end before
* reading all the bytes.
* @exception IOException if an I/O error occurs.
* @see java.io.DataInputStream#readUTF(java.io.DataInput)
*/
public final String readUTF() throws IOException {
return readUTF(this);
}
/**
* Reads in a string from the specified data input stream. The
* string has been encoded using a modified UTF-8 format.
* <p>
* The first two bytes are read as if by
* <code>readUnsignedShort</code>. This value gives the number of
* following bytes that are in the encoded string, not
* the length of the resulting string. The following bytes are then
* interpreted as bytes encoding characters in the UTF-8 format
* and are converted into characters.
* <p>
* This method blocks until all the bytes are read, the end of the
* stream is detected, or an exception is thrown.
*
* @param in a data input stream.
* @return a Unicode string.
* @exception EOFException if the input stream reaches the end
* before all the bytes.
* @exception IOException if an I/O error occurs.
* @exception UTFDataFormatException if the bytes do not represent a
* valid UTF-8 encoding of a Unicode string.
* @see java.io.DataInputStream#readUnsignedShort()
*/
public final static String readUTF(DataInput in) throws IOException {
int utflen = in.readUnsignedShort();
char str[] = new char[utflen];
int count = 0;
int strlen = 0;
while (count < utflen) {
int c = in.readUnsignedByte();
int char2, char3;
switch (c >> 4) {
case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
// 0xxxxxxx
count++;
str[strlen++] = (char)c;
break;
case 12: case 13:
// 110x xxxx 10xx xxxx
count += 2;
if (count > utflen)
throw new UTFDataFormatException();
char2 = in.readUnsignedByte();
if ((char2 & 0xC0) != 0x80)
throw new UTFDataFormatException();
str[strlen++] = (char)(((c & 0x1F) << 6) | (char2 & 0x3F));
break;
case 14:
// 1110 xxxx 10xx xxxx 10xx xxxx
count += 3;
if (count > utflen)
throw new UTFDataFormatException();
char2 = in.readUnsignedByte();
char3 = in.readUnsignedByte();
if (((char2 & 0xC0) != 0x80) || ((char3 & 0xC0) != 0x80))
throw new UTFDataFormatException();
str[strlen++] = (char)(((c & 0x0F) << 12) |
((char2 & 0x3F) << 6) |
((char3 & 0x3F) << 0));
break;
default:
// 10xx xxxx, 1111 xxxx
throw new UTFDataFormatException();
}
}
return new String(str, 0, strlen);
}
}