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From-SVN: r102074
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Tom Tromey
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384
libjava/classpath/java/io/PushbackReader.java
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384
libjava/classpath/java/io/PushbackReader.java
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/* PushbackReader.java -- An character stream that can unread chars
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Copyright (C) 1998, 2000, 2001, 2003, 2005 Free Software Foundation, Inc.
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This file is part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2, or (at your option)
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any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; see the file COPYING. If not, write to the
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Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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02110-1301 USA.
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.io;
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/**
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* This subclass of <code>FilterReader</code> provides the ability to
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* unread data from a stream. It maintains an internal buffer of unread
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* data that is supplied to the next read operation. This is conceptually
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* similar to mark/reset functionality, except that in this case the
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* position to reset the stream to does not need to be known in advance.
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* <p>
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* The default pushback buffer size one char, but this can be overridden
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* by the creator of the stream.
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*
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* @author Aaron M. Renn (arenn@urbanophile.com)
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* @author Warren Levy (warrenl@cygnus.com)
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*/
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public class PushbackReader extends FilterReader
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{
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/**
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* This is the default buffer size
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*/
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private static final int DEFAULT_BUFFER_SIZE = 1;
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/**
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* This is the buffer that is used to store the pushed back data
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*/
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private char[] buf;
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/**
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* This is the position in the buffer from which the next char will be
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* read. Bytes are stored in reverse order in the buffer, starting from
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* <code>buf[buf.length - 1]</code> to <code>buf[0]</code>. Thus when
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* <code>pos</code> is 0 the buffer is full and <code>buf.length</code> when
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* it is empty
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*/
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private int pos;
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/**
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* This method initializes a <code>PushbackReader</code> to read from the
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* specified subordinate <code>Reader</code> with a default pushback buffer
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* size of 1.
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*
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* @param in The subordinate stream to read from
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*/
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public PushbackReader(Reader in)
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{
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this(in, DEFAULT_BUFFER_SIZE);
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}
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/**
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* This method initializes a <code>PushbackReader</code> to read from the
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* specified subordinate <code>Reader</code> with the specified buffer
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* size
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*
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* @param in The subordinate <code>Reader</code> to read from
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* @param bufsize The pushback buffer size to use
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*/
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public PushbackReader(Reader in, int bufsize)
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{
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super(in);
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if (bufsize < 0)
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throw new IllegalArgumentException("buffer size must be positive");
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buf = new char[bufsize];
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pos = bufsize;
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}
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/**
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* This method closes the stream and frees any associated resources.
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*
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* @exception IOException If an error occurs.
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*/
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public void close() throws IOException
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{
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synchronized (lock)
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{
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buf = null;
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super.close();
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}
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}
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/**
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* This method throws an exception when called since this class does
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* not support mark/reset.
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*
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* @param read_limit Not used.
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*
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* @exception IOException Always thrown to indicate mark/reset not supported.
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*/
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public void mark(int read_limit) throws IOException
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{
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throw new IOException("mark not supported in this class");
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}
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/**
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* This method returns <code>false</code> to indicate that it does not support
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* mark/reset functionality.
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*
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* @return This method returns <code>false</code> to indicate that this
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* class does not support mark/reset functionality
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*
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*/
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public boolean markSupported()
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{
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return(false);
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}
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/**
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* This method always throws an IOException in this class because
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* mark/reset functionality is not supported.
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*
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* @exception IOException Always thrown for this class
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*/
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public void reset() throws IOException
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{
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throw new IOException("reset not supported in this class");
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}
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/**
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* This method determines whether or not this stream is ready to be read.
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* If it returns <code>false</code> to indicate that the stream is not
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* ready, any attempt to read from the stream could (but is not
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* guaranteed to) block.
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* <p>
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* This stream is ready to read if there are either chars waiting to be
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* read in the pushback buffer or if the underlying stream is ready to
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* be read.
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*
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* @return <code>true</code> if this stream is ready to be read,
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* <code>false</code> otherwise
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*
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* @exception IOException If an error occurs
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*/
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public boolean ready() throws IOException
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{
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synchronized (lock)
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{
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if (buf == null)
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throw new IOException ("stream closed");
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if (((buf.length - pos) > 0) || super.ready())
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return(true);
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else
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return(false);
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}
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}
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// Don't delete this method just because the spec says it shouldn't be there!
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// See the CVS log for details.
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/**
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* This method skips the specified number of chars in the stream. It
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* returns the actual number of chars skipped, which may be less than the
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* requested amount.
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* <p>
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* This method first discards chars from the buffer, then calls the
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* <code>skip</code> method on the underlying <code>Reader</code> to
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* skip additional chars if necessary.
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*
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* @param num_chars The requested number of chars to skip
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*
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* @return The actual number of chars skipped.
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*
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* @exception IOException If an error occurs
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*/
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public long skip(long num_chars) throws IOException
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{
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synchronized (lock)
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{
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if (num_chars <= 0)
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return(0);
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if ((buf.length - pos) >= num_chars)
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{
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pos += num_chars;
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return(num_chars);
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}
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int chars_discarded = buf.length - pos;
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pos = buf.length;
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long chars_skipped = in.skip(num_chars - chars_discarded);
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return(chars_discarded + chars_skipped);
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}
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}
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/**
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* This method reads an unsigned char from the input stream and returns it
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* as an int in the range of 0-65535. This method also will return -1 if
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* the end of the stream has been reached. The char returned will be read
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* from the pushback buffer, unless the buffer is empty, in which case
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* the char will be read from the underlying stream.
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* <p>
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* This method will block until the char can be read.
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*
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* @return The char read or -1 if end of stream
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*
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* @exception IOException If an error occurs
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*/
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public int read() throws IOException
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{
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synchronized (lock)
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{
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if (buf == null)
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throw new IOException("stream closed");
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if (pos == buf.length)
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return(super.read());
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++pos;
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return((buf[pos - 1] & 0xFFFF));
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}
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}
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/**
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* This method read chars from a stream and stores them into a caller
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* supplied buffer. It starts storing the data at index <code>offset</code>
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* into
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* the buffer and attempts to read <code>len</code> chars. This method can
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* return before reading the number of chars requested. The actual number
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* of chars read is returned as an int. A -1 is returned to indicate the
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* end of the stream.
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* <p>
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* This method will block until some data can be read.
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* <p>
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* This method first reads chars from the pushback buffer in order to
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* satisfy the read request. If the pushback buffer cannot provide all
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* of the chars requested, the remaining chars are read from the
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* underlying stream.
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*
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* @param buffer The array into which the chars read should be stored
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* @param offset The offset into the array to start storing chars
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* @param length The requested number of chars to read
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*
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* @return The actual number of chars read, or -1 if end of stream.
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*
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* @exception IOException If an error occurs.
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*/
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public synchronized int read(char[] buffer, int offset, int length)
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throws IOException
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{
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synchronized (lock)
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{
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if (buf == null)
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throw new IOException("stream closed");
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if (offset < 0 || length < 0 || offset + length > buffer.length)
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throw new ArrayIndexOutOfBoundsException();
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int numBytes = Math.min(buf.length - pos, length);
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if (numBytes > 0)
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{
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System.arraycopy (buf, pos, buffer, offset, numBytes);
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pos += numBytes;
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return numBytes;
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}
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return super.read(buffer, offset, length);
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}
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}
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/**
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* This method pushes a single char of data into the pushback buffer.
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* The char pushed back is the one that will be returned as the first char
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* of the next read.
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* <p>
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* If the pushback buffer is full, this method throws an exception.
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* <p>
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* The argument to this method is an <code>int</code>. Only the low eight
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* bits of this value are pushed back.
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*
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* @param b The char to be pushed back, passed as an int
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*
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* @exception IOException If the pushback buffer is full.
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*/
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public void unread(int b) throws IOException
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{
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synchronized (lock)
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{
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if (buf == null)
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throw new IOException("stream closed");
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if (pos == 0)
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throw new IOException("Pushback buffer is full");
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--pos;
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buf[pos] = (char)(b & 0xFFFF);
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}
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}
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/**
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* This method pushes all of the chars in the passed char array into
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* the pushback buffer. These chars are pushed in reverse order so that
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* the next char read from the stream after this operation will be
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* <code>buf[0]</code> followed by <code>buf[1]</code>, etc.
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* <p>
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* If the pushback buffer cannot hold all of the requested chars, an
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* exception is thrown.
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*
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* @param buf The char array to be pushed back
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*
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* @exception IOException If the pushback buffer is full
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*/
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public synchronized void unread(char[] buf) throws IOException
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{
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unread(buf, 0, buf.length);
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}
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/**
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* This method pushed back chars from the passed in array into the pushback
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* buffer. The chars from <code>buf[offset]</code> to
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* <code>buf[offset + len]</code>
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* are pushed in reverse order so that the next char read from the stream
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* after this operation will be <code>buf[offset]</code> followed by
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* <code>buf[offset + 1]</code>, etc.
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* <p>
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* If the pushback buffer cannot hold all of the requested chars, an
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* exception is thrown.
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*
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* @param buffer The char array to be pushed back
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* @param offset The index into the array where the chars to be push start
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* @param length The number of chars to be pushed.
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*
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* @exception IOException If the pushback buffer is full
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*/
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public synchronized void unread(char[] buffer, int offset, int length)
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throws IOException
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{
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synchronized (lock)
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{
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if (buf == null)
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throw new IOException("stream closed");
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if (pos < length)
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throw new IOException("Pushback buffer is full");
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// Note the order that these chars are being added is the opposite
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// of what would be done if they were added to the buffer one at a time.
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// See the Java Class Libraries book p. 1397.
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System.arraycopy(buffer, offset, buf, pos - length, length);
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// Don't put this into the arraycopy above, an exception might be thrown
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// and in that case we don't want to modify pos.
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pos -= length;
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}
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}
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}
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