datainputstream.java

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/*
 * @(#)DataInputStream.java	1.38 97/08/22
 * 
 * Copyright (c) 1995, 1996 Sun Microsystems, Inc. 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.
 * 
 * SUN MAKES NO REPRESENTATIONS OR WARRANTIES ABOUT THE SUITABILITY OF THE
 * SOFTWARE, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, OR NON-INFRINGEMENT. SUN SHALL NOT BE LIABLE FOR ANY DAMAGES
 * SUFFERED BY LICENSEE AS A RESULT OF USING, MODIFYING OR DISTRIBUTING
 * THIS SOFTWARE OR ITS DERIVATIVES.
 * 
 * CopyrightVersion 1.1_beta
 * 
 */

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>'&#92;u0001'</code> to 
 * <code>'&#92;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>'&#92;u0000'</code> and characters in the 
 * range <code>'&#92;u0080'</code> to <code>'&#92;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>'&#92;u0800'</code> to 
 * <code>'&#92;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>'&#92;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 1.38, 08/22/97
 * @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&nbsp;&lt;=&nbsp;<code>b</code>&nbsp;&lt;=&nbsp;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 &lt;&lt; 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&nbsp;&lt;=&nbsp;b1</code>, 
     * <code>b2&nbsp;&lt;=&nbsp;255</code>, then the result is equal to:
     * <ul><code>
     *     (b1 &lt;&lt; 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);
    }

    /**