CharArrayReader.java

/* CharArrayReader.java -- Read an array of characters as a stream
   Copyright (C) 1998, 2001, 2005  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.

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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
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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
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terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
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this exception to your version of the library, but you are not
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package java.io;

/**
  * This class permits an array of chars to be read as an input stream.
  *
  * @author Aaron M. Renn (arenn@urbanophile.com)
  * @author Warren Levy (warrenl@cygnus.com)
  */
public class CharArrayReader extends Reader
{
  /**
   * The array that contains the data supplied during read operations
   */
  protected char[] buf;

  /**
   * The array index of the next char to be read from the buffer
   * <code>buf</code>
   */
  protected int pos;

  /**
   * The currently marked position in the stream.  This defaults to 0, so a
   * reset operation on the stream resets it to read from array index 0 in
   * the buffer - even if the stream was initially created with an offset
   * greater than 0
   */
  protected int markedPos;

  /**
   * This indicates the maximum number of chars that can be read from this
   * stream.  It is the array index of the position after the last valid
   * char in the buffer <code>buf</code>
   */
  protected int count;

  /**
   * Create a new CharArrayReader that will read chars from the passed
   * in char array.  This stream will read from the beginning to the end
   * of the array.  It is identical to calling an overloaded constructor
   * as <code>CharArrayReader(buf, 0, buf.length)</code>.
   * <p>
   * Note that this array is not copied.  If its contents are changed 
   * while this stream is being read, those changes will be reflected in the
   * chars supplied to the reader.  Please use caution in changing the 
   * contents of the buffer while this stream is open.
   *
   * @param buffer The char array buffer this stream will read from.
  */
  public CharArrayReader(char[] buffer)
  {
    this(buffer, 0, buffer.length);
  }

  /**
   * Create a new CharArrayReader that will read chars from the passed
   * in char array.  This stream will read from position
   * <code>offset</code> in the array for a length of
   * <code>length</code> chars past <code>offset</code>.  If the
   * stream is reset to a position before <code>offset</code> then
   * more than <code>length</code> chars can be read from the stream.
   * The <code>length</code> value should be viewed as the array index
   * one greater than the last position in the buffer to read.
   * <p>
   * Note that this array is not copied.  If its contents are changed 
   * while this stream is being read, those changes will be reflected in the
   * chars supplied to the reader.  Please use caution in changing the 
   * contents of the buffer while this stream is open.
   *
   * @param buffer The char array buffer this stream will read from.
   * @param offset The index into the buffer to start reading chars from
   * @param length The number of chars to read from the buffer
   */
  public CharArrayReader(char[] buffer, int offset, int length)
  {
    super();
    if (offset < 0  || length < 0 || offset > buffer.length)
      throw new IllegalArgumentException();
    
    buf = buffer;

    count = offset + length;
    if (count > buf.length)
      count = buf.length;
    
    pos = offset;
    markedPos = pos;
  }

  /**
   * This method closes the stream.
   */
  public void close()
  {
    synchronized (lock)
      {
	buf = null;
      }
  }

  /**
   * This method sets the mark position in this stream to the current
   * position.  Note that the <code>readlimit</code> parameter in this
   * method does nothing as this stream is always capable of
   * remembering all the chars int it.
   * <p>
   * Note that in this class the mark position is set by default to
   * position 0 in the stream.  This is in constrast to some other
   * stream types where there is no default mark position.
   *
   * @param readAheadLimit The number of chars this stream must
   *                       remember.  This parameter is ignored.
   *
   * @exception IOException If an error occurs
   */
  public void mark(int readAheadLimit) throws IOException
  {
    synchronized (lock)
      {
	if (buf == null)
	  throw new IOException("Stream closed");
	// readAheadLimit is ignored per Java Class Lib. book, p. 318.
	markedPos = pos;
      }
  }

  /**
   * This method overrides the <code>markSupported</code> method in
   * <code>Reader</code> in order to return <code>true</code> -
   * indicating that this stream class supports mark/reset
   * functionality.
   *
   * @return <code>true</code> to indicate that this class supports
   * mark/reset.
   */
  public boolean markSupported()
  {
    return true;
  }

  /**
   * This method reads one char from the stream.  The <code>pos</code>
   * counter is advanced to the next char to be read.  The char read
   * is returned as an int in the range of 0-65535.  If the stream
   * position is already at the end of the buffer, no char is read and
   * a -1 is returned in order to indicate the end of the stream.
   *
   * @return The char read, or -1 if end of stream
   */
  public int read() throws IOException
  {
    synchronized (lock)
      {
	if (buf == null)
	  throw new IOException("Stream closed");

	if (pos < 0)
	  throw new ArrayIndexOutOfBoundsException(pos);

	if (pos < count)
	  return ((int) buf[pos++]) & 0xFFFF;
	return -1;
      }
  }

  /**
   * This method reads chars from the stream and stores them into a
   * caller supplied buffer.  It starts storing the data at index
   * <code>offset</code> into the buffer and attempts to read
   * <code>len</code> chars.  This method can return before reading
   * the number of chars requested if the end of the stream is
   * encountered first.  The actual number of chars read is returned.
   * If no chars can be read because the stream is already at the end
   * of stream position, a -1 is returned.
   * <p>
   * This method does not block.
   *
   * @param b The array into which the chars read should be stored.
   * @param off The offset into the array to start storing chars
   * @param len The requested number of chars to read
   *
   * @return The actual number of chars read, or -1 if end of stream.
   */
  public int read(char[] b, int off, int len) throws IOException
  {
    synchronized (lock)
      {
	if (buf == null)
	  throw new IOException("Stream closed");

	/* Don't need to check pos value, arraycopy will check it. */
	if (off < 0 || len < 0 || off + len > b.length)
	  throw new IndexOutOfBoundsException();

	if (pos >= count)
	  return -1;

	int numChars = Math.min(count - pos, len);
	System.arraycopy(buf, pos, b, off, numChars);
	pos += numChars;
	return numChars;
      }
  }

  /**
   * Return true if more characters are available to be read. 
   *
   * @return <code>true</code> to indicate that this stream is ready
   * to be read.
   *
   * @specnote The JDK 1.3 API docs are wrong here. This method will
   *           return false if there are no more characters available.
   */
  public boolean ready() throws IOException
  {
    if (buf == null)
      throw new IOException("Stream closed");

    return (pos < count);
  }

  /**
   * This method sets the read position in the stream to the mark
   * point by setting the <code>pos</code> variable equal to the
   * <code>mark</code> variable.  Since a mark can be set anywhere in
   * the array, the mark/reset methods int this class can be used to
   * provide random search capabilities for this type of stream.
   */
  public void reset() throws IOException
  {
    synchronized (lock)
      {
	if (buf == null)
	  throw new IOException("Stream closed");

	pos = markedPos;
      }
  }

  /**
   * This method attempts to skip the requested number of chars in the
   * input stream.  It does this by advancing the <code>pos</code> value by the
   * specified number of chars.  It this would exceed the length of the
   * buffer, then only enough chars are skipped to position the stream at
   * the end of the buffer.  The actual number of chars skipped is returned.
   *
   * @param n The requested number of chars to skip
   *
   * @return The actual number of chars skipped.
   */
  public long skip(long n) throws IOException
  {
    synchronized (lock)
      {
	if (buf == null)
	  throw new IOException("Stream closed");

	// Even though the var numChars is a long, in reality it can never
	// be larger than an int since the result of subtracting 2 positive
	// ints will always fit in an int.  Since we have to return a long
	// anyway, numChars might as well just be a long.
	long numChars = Math.min((long) (count - pos), n < 0 ? 0L : n);
	pos += numChars;
	return numChars;
      }
  }
}