001/* CharArrayReader.java -- Read an array of characters as a stream
002   Copyright (C) 1998, 2001, 2005  Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
010
011GNU Classpath is distributed in the hope that it will be useful, but
012WITHOUT ANY WARRANTY; without even the implied warranty of
013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
015
016You should have received a copy of the GNU General Public License
017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
029modules, and to copy and distribute the resulting executable under
030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
032module.  An independent module is a module which is not derived from
033or based on this library.  If you modify this library, you may extend
034this exception to your version of the library, but you are not
035obligated to do so.  If you do not wish to do so, delete this
036exception statement from your version. */
037
038
039package java.io;
040
041/**
042  * This class permits an array of chars to be read as an input stream.
043  *
044  * @author Aaron M. Renn (arenn@urbanophile.com)
045  * @author Warren Levy (warrenl@cygnus.com)
046  */
047public class CharArrayReader extends Reader
048{
049  /**
050   * The array that contains the data supplied during read operations
051   */
052  protected char[] buf;
053
054  /**
055   * The array index of the next char to be read from the buffer
056   * <code>buf</code>
057   */
058  protected int pos;
059
060  /**
061   * The currently marked position in the stream.  This defaults to 0, so a
062   * reset operation on the stream resets it to read from array index 0 in
063   * the buffer - even if the stream was initially created with an offset
064   * greater than 0
065   */
066  protected int markedPos;
067
068  /**
069   * This indicates the maximum number of chars that can be read from this
070   * stream.  It is the array index of the position after the last valid
071   * char in the buffer <code>buf</code>
072   */
073  protected int count;
074
075  /**
076   * Create a new CharArrayReader that will read chars from the passed
077   * in char array.  This stream will read from the beginning to the end
078   * of the array.  It is identical to calling an overloaded constructor
079   * as <code>CharArrayReader(buf, 0, buf.length)</code>.
080   * <p>
081   * Note that this array is not copied.  If its contents are changed
082   * while this stream is being read, those changes will be reflected in the
083   * chars supplied to the reader.  Please use caution in changing the
084   * contents of the buffer while this stream is open.
085   *
086   * @param buffer The char array buffer this stream will read from.
087  */
088  public CharArrayReader(char[] buffer)
089  {
090    this(buffer, 0, buffer.length);
091  }
092
093  /**
094   * Create a new CharArrayReader that will read chars from the passed
095   * in char array.  This stream will read from position
096   * <code>offset</code> in the array for a length of
097   * <code>length</code> chars past <code>offset</code>.  If the
098   * stream is reset to a position before <code>offset</code> then
099   * more than <code>length</code> chars can be read from the stream.
100   * The <code>length</code> value should be viewed as the array index
101   * one greater than the last position in the buffer to read.
102   * <p>
103   * Note that this array is not copied.  If its contents are changed
104   * while this stream is being read, those changes will be reflected in the
105   * chars supplied to the reader.  Please use caution in changing the
106   * contents of the buffer while this stream is open.
107   *
108   * @param buffer The char array buffer this stream will read from.
109   * @param offset The index into the buffer to start reading chars from
110   * @param length The number of chars to read from the buffer
111   */
112  public CharArrayReader(char[] buffer, int offset, int length)
113  {
114    super();
115    if (offset < 0  || length < 0 || offset > buffer.length)
116      throw new IllegalArgumentException();
117
118    buf = buffer;
119
120    count = offset + length;
121    if (count > buf.length)
122      count = buf.length;
123
124    pos = offset;
125    markedPos = pos;
126  }
127
128  /**
129   * This method closes the stream.
130   */
131  public void close()
132  {
133    synchronized (lock)
134      {
135        buf = null;
136      }
137  }
138
139  /**
140   * This method sets the mark position in this stream to the current
141   * position.  Note that the <code>readlimit</code> parameter in this
142   * method does nothing as this stream is always capable of
143   * remembering all the chars int it.
144   * <p>
145   * Note that in this class the mark position is set by default to
146   * position 0 in the stream.  This is in constrast to some other
147   * stream types where there is no default mark position.
148   *
149   * @param readAheadLimit The number of chars this stream must
150   *                       remember.  This parameter is ignored.
151   *
152   * @exception IOException If an error occurs
153   */
154  public void mark(int readAheadLimit) throws IOException
155  {
156    synchronized (lock)
157      {
158        if (buf == null)
159          throw new IOException("Stream closed");
160        // readAheadLimit is ignored per Java Class Lib. book, p. 318.
161        markedPos = pos;
162      }
163  }
164
165  /**
166   * This method overrides the <code>markSupported</code> method in
167   * <code>Reader</code> in order to return <code>true</code> -
168   * indicating that this stream class supports mark/reset
169   * functionality.
170   *
171   * @return <code>true</code> to indicate that this class supports
172   * mark/reset.
173   */
174  public boolean markSupported()
175  {
176    return true;
177  }
178
179  /**
180   * This method reads one char from the stream.  The <code>pos</code>
181   * counter is advanced to the next char to be read.  The char read
182   * is returned as an int in the range of 0-65535.  If the stream
183   * position is already at the end of the buffer, no char is read and
184   * a -1 is returned in order to indicate the end of the stream.
185   *
186   * @return The char read, or -1 if end of stream
187   */
188  public int read() throws IOException
189  {
190    synchronized (lock)
191      {
192        if (buf == null)
193          throw new IOException("Stream closed");
194
195        if (pos < 0)
196          throw new ArrayIndexOutOfBoundsException(pos);
197
198        if (pos < count)
199          return ((int) buf[pos++]) & 0xFFFF;
200        return -1;
201      }
202  }
203
204  /**
205   * This method reads chars from the stream and stores them into a
206   * caller supplied buffer.  It starts storing the data at index
207   * <code>offset</code> into the buffer and attempts to read
208   * <code>len</code> chars.  This method can return before reading
209   * the number of chars requested if the end of the stream is
210   * encountered first.  The actual number of chars read is returned.
211   * If no chars can be read because the stream is already at the end
212   * of stream position, a -1 is returned.
213   * <p>
214   * This method does not block.
215   *
216   * @param b The array into which the chars read should be stored.
217   * @param off The offset into the array to start storing chars
218   * @param len The requested number of chars to read
219   *
220   * @return The actual number of chars read, or -1 if end of stream.
221   */
222  public int read(char[] b, int off, int len) throws IOException
223  {
224    synchronized (lock)
225      {
226        if (buf == null)
227          throw new IOException("Stream closed");
228
229        /* Don't need to check pos value, arraycopy will check it. */
230        if (off < 0 || len < 0 || off + len > b.length)
231          throw new IndexOutOfBoundsException();
232
233        if (pos >= count)
234          return -1;
235
236        int numChars = Math.min(count - pos, len);
237        System.arraycopy(buf, pos, b, off, numChars);
238        pos += numChars;
239        return numChars;
240      }
241  }
242
243  /**
244   * Return true if more characters are available to be read.
245   *
246   * @return <code>true</code> to indicate that this stream is ready
247   * to be read.
248   *
249   * @specnote The JDK 1.3 API docs are wrong here. This method will
250   *           return false if there are no more characters available.
251   */
252  public boolean ready() throws IOException
253  {
254    if (buf == null)
255      throw new IOException("Stream closed");
256
257    return (pos < count);
258  }
259
260  /**
261   * This method sets the read position in the stream to the mark
262   * point by setting the <code>pos</code> variable equal to the
263   * <code>mark</code> variable.  Since a mark can be set anywhere in
264   * the array, the mark/reset methods int this class can be used to
265   * provide random search capabilities for this type of stream.
266   */
267  public void reset() throws IOException
268  {
269    synchronized (lock)
270      {
271        if (buf == null)
272          throw new IOException("Stream closed");
273
274        pos = markedPos;
275      }
276  }
277
278  /**
279   * This method attempts to skip the requested number of chars in the
280   * input stream.  It does this by advancing the <code>pos</code> value by the
281   * specified number of chars.  It this would exceed the length of the
282   * buffer, then only enough chars are skipped to position the stream at
283   * the end of the buffer.  The actual number of chars skipped is returned.
284   *
285   * @param n The requested number of chars to skip
286   *
287   * @return The actual number of chars skipped.
288   */
289  public long skip(long n) throws IOException
290  {
291    synchronized (lock)
292      {
293        if (buf == null)
294          throw new IOException("Stream closed");
295
296        // Even though the var numChars is a long, in reality it can never
297        // be larger than an int since the result of subtracting 2 positive
298        // ints will always fit in an int.  Since we have to return a long
299        // anyway, numChars might as well just be a long.
300        long numChars = Math.min((long) (count - pos), n < 0 ? 0L : n);
301        pos += numChars;
302        return numChars;
303      }
304  }
305}