datainputstream.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 700 行 · 第 1/2 页

/*
 * @(#)DataInputStream.java	1.59 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

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.) Note that in the 
 * following tables, the most significant bit appears in the
 * far left-hand column.
 * <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" summary="Bit values and bytes">
 *        <tr>
 *            <td></td>
 *            <th id="bit" colspan=2><P ALIGN="LEFT">Bit Values</P></th>
 *        </tr>
 *        <tr> 
 *            <th id="byte1">Byte 1&nbsp;</th>
 *            <td headers="bit byte1"><i>0</i></td>
 *            <td>bits 6-0</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" summary="Bit values and bytes">
 *        <tr>
 *            <td></td>
 *            <th id="bit" colspan=4><P ALIGN="LEFT">Bit Values</P></th>
 *        </tr>
 *         <tr>
 *             <th id="byte1">Byte 1&nbsp;</th>
 *             <td headers="bit byte1">1</td>
 *             <td headers="bit byte1">1</td>
 *             <td headers="bit byte1">0</td>
 *             <td headers="bit byte1">bits 10-6</td>
 *         </tr>
 *         <tr>
 *             <th id="byte2">Byte 2&nbsp;</th>
 *             <td headers="bit byte2">1</td>
 *             <td headers="bit byte2">0</td>
 *             <td headers="bit byte2" colspan=2>bits 5-0</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" summary="Bit values and bytes">
 *        <tr>
 *            <td></td>
 *            <th id="bit" colspan=5><P ALIGN="LEFT">Bit Values</P></th>
 *        </tr>
 * 
 *        <tr>
 *            <th id="byte1">Byte 1&nbsp;</th>
 *            <td headers="bit byte1">1</td>
 *            <td headers="bit byte1">1</td>
 *            <td headers="bit byte1">1</td>
 *            <td headers="bit byte1">0</td>
 *            <td headers="bit byte1">bits 15-12</td>
 *        </tr>
 *        <tr>
 *            <th id="byte2">Byte 2&nbsp;</th>
 *            <td headers="bit byte2">1</td>
 *            <td headers="bit byte2">0</td>
 *            <td headers="bit byte2" colspan=3>bits 11-6</td>
 *        </tr>
 *        <tr>
 *            <th id="byte3">Byte 3&nbsp;</th>
 *            <td headers="bit byte3">1</td>
 *            <td headers="bit byte3">0</td>
 *            <td headers="bit byte3" colspan=3>bits 5-0</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>
 *
 * @version 1.52 10/17/00
 * @see     java.io.DataOutputStream
 * @since   JDK1.0
 */
public
class DataInputStream extends FilterInputStream implements DataInput {

    /**
     * Creates a DataInputStream that uses the specified
     * underlying InputStream.
     *
     * @param  in   the specified input stream
     */
    public DataInputStream(InputStream in) {
	super(in);
    }

    /**
     * Reads some number of bytes from the contained input stream and 
     * stores them into the buffer array <code>b</code>. The number of 
     * bytes actually read is returned as an integer. This method blocks 
     * until input data is available, end of file is detected, or an 
     * exception is thrown. 
     * 
     * <p>If <code>b</code> is null, a <code>NullPointerException</code> is 
     * thrown. If the length of <code>b</code> is zero, then no bytes are 
     * read and <code>0</code> is returned; otherwise, there is an attempt 
     * to read at least one byte. If no byte is available because the 
     * stream is at end of file, the value <code>-1</code> is returned;
     * otherwise, at least one byte is read and stored into <code>b</code>. 
     * 
     * <p>The first byte read is stored into element <code>b[0]</code>, the 
     * next one into <code>b[1]</code>, and so on. The number of bytes read 
     * is, at most, equal to the length of <code>b</code>. Let <code>k</code> 
     * be the number of bytes actually read; these bytes will be stored in 
     * elements <code>b[0]</code> through <code>b[k-1]</code>, leaving 
     * elements <code>b[k]</code> through <code>b[b.length-1]</code> 
     * unaffected. 
     * 
     * <p>If the first byte cannot be read for any reason other than end of 
     * file, then an <code>IOException</code> is thrown. In particular, an 
     * <code>IOException</code> is thrown if the input stream has been closed. 
     * 
     * <p>The <code>read(b)</code> method has the same effect as: 
     * <blockquote><pre>
     * read(b, 0, b.length) 
     * </pre></blockquote>
     *
     * @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 the contained 
     * input stream into an array of bytes.  An attempt is made to read 
     * as many as <code>len</code> bytes, but a smaller number may be read, 
     * possibly zero. The number of bytes actually read is returned as an 
     * integer.
     *
     * <p> This method blocks until input data is available, end of file is
     * detected, or an exception is thrown.
     *
     * <p> If <code>b</code> is <code>null</code>, a
     * <code>NullPointerException</code> is thrown.
     *
     * <p> If <code>off</code> is negative, or <code>len</code> is negative, or
     * <code>off+len</code> is greater than the length of the array
     * <code>b</code>, then an <code>IndexOutOfBoundsException</code> is
     * thrown.
     *
     * <p> If <code>len</code> is zero, then no bytes are read and
     * <code>0</code> is returned; otherwise, there is an attempt to read at
     * least one byte. If no byte is available because the stream is at end of
     * file, the value <code>-1</code> is returned; otherwise, at least one
     * byte is read and stored into <code>b</code>.
     *
     * <p> The first byte read is stored into element <code>b[off]</code>, the
     * next one into <code>b[off+1]</code>, and so on. The number of bytes read
     * is, at most, equal to <code>len</code>. Let <i>k</i> be the number of
     * bytes actually read; these bytes will be stored in elements
     * <code>b[off]</code> through <code>b[off+</code><i>k</i><code>-1]</code>,
     * leaving elements <code>b[off+</code><i>k</i><code>]</code> through
     * <code>b[off+len-1]</code> unaffected.
     *
     * <p> In every case, elements <code>b[0]</code> through
     * <code>b[off]</code> and elements <code>b[off+len]</code> through
     * <code>b[b.length-1]</code> are unaffected.
     *
     * <p> If the first byte cannot be read for any reason other than end of
     * file, then an <code>IOException</code> is thrown. In particular, an
     * <code>IOException</code> is thrown if the input stream has been closed.
     *
     * @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);
    }

    /**
     * See the general contract of the <code>readFully</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @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);
    }

    /**
     * See the general contract of the <code>readFully</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @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 {
	if (len < 0)
	    throw new IndexOutOfBoundsException();
	int n = 0;
	while (n < len) {
	    int count = in.read(b, off + n, len - n);
	    if (count < 0)
		throw new EOFException();
	    n += count;
	}
    }

    /**
     * See the general contract of the <code>skipBytes</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @param      n   the number of bytes to be skipped.
     * @return     the actual number of bytes skipped.
     * @exception  IOException   if an I/O error occurs.
     */
    public final int skipBytes(int n) throws IOException {
	int total = 0;
	int cur = 0;

	while ((total<n) && ((cur = (int) in.skip(n-total)) > 0)) {
	    total += cur;
	}

	return total;
    }

    /**
     * See the general contract of the <code>readBoolean</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @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);
    }

    /**
     * See the general contract of the <code>readByte</code>
     * method of <code>DataInput</code>.
     * <p>
     * Bytes
     * for this operation are read from the contained
     * input stream.
     *
     * @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();