source: trunk/src/gcc/libjava/java/io/PushbackReader.java@ 64

/* PushbackReader.java -- An character stream that can unread chars
   Copyright (C) 1998, 2000, 2001 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
 
GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package java.io;

/**
 * This subclass of <code>FilterReader</code> provides the ability to 
 * unread data from a stream.  It maintains an internal buffer of unread
 * data that is supplied to the next read operation.  This is conceptually
 * similar to mark/reset functionality, except that in this case the 
 * position to reset the stream to does not need to be known in advance.
 * <p>
 * The default pushback buffer size one char, but this can be overridden
 * by the creator of the stream.
 *
 * @version 0.0
 *
 * @author Aaron M. Renn ([email protected])
 * @author Warren Levy <[email protected]>
 */
public class PushbackReader extends FilterReader
{
  /**
   * This is the default buffer size
   */
  private static final int DEFAULT_BUFFER_SIZE = 1;

  /**
   * This is the buffer that is used to store the pushed back data
   */
  private char[] buf;

  /**
   * This is the position in the buffer from which the next char will be
   * read.  Bytes are stored in reverse order in the buffer, starting from
   * <code>buf[buf.length - 1]</code> to <code>buf[0]</code>.  Thus when 
   * <code>pos</code> is 0 the buffer is full and <code>buf.length</code> when 
   * it is empty
   */
  private int pos;

  /**
   * This method initializes a <code>PushbackReader</code> to read from the
   * specified subordinate <code>Reader</code> with a default pushback buffer 
   * size of 1.
   *
   * @code in The subordinate stream to read from
   */
  public PushbackReader(Reader in)
  {
    this(in, DEFAULT_BUFFER_SIZE);
  }

  /**
   * This method initializes a <code>PushbackReader</code> to read from the
   * specified subordinate <code>Reader</code> with the specified buffer
   * size
   *
   * @param in The subordinate <code>Reader</code> to read from
   * @param bufsize The pushback buffer size to use
   */
  public PushbackReader(Reader in, int bufsize)
  {
    super(in);

    if (bufsize < 0)