libjava/java/io/StringReader.java

   1 /* StringReader.java -- permits a String to be read as a character input stream
   2    Copyright (C) 1998, 1999, 2000, 2003  Free Software Foundation
   3
   4 This file is part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; see the file COPYING.  If not, write to the
  18 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19 02111-1307 USA.
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version. */
  37
  38 package java.io;
  39
  40 /* Written using "Java Class Libraries", 2nd edition, ISBN 0-201-31002-3
  41  * "The Java Language Specification", ISBN 0-201-63451-1
  42  * plus online API docs for JDK 1.2 beta from http://www.javasoft.com.
  43  * Status:  Believed complete and correct
  44  */
  45
  46 /**
  47  * This class permits a <code>String</code> to be read as a character
  48  * input stream.
  49  * <p>
  50  * The mark/reset functionality in this class behaves differently than
  51  * normal.  If no mark has been set, then calling the <code>reset()</code>
  52  * method rewinds the read pointer to the beginning of the <code>String</code>.
  53  *
  54  * @author Aaron M. Renn (arenn@urbanophile.com)
  55  * @author Warren Levy (warrenl@cygnus.com)
  56  * @date October 19, 1998.
  57  */
  58 public class StringReader extends Reader
  59 {
  60   /* A String provided by the creator of the stream. */
  61   private String buf;
  62
  63   /* Position of the next char in buf to be read. */
  64   private int pos;
  65
  66   /* The currently marked position in the stream. */
  67   private int markedPos;
  68
  69   /* The index in buf one greater than the last valid character. */
  70   private int count;
  71
  72   /**
  73    * Create a new <code>StringReader</code> that will read chars from the
  74    * passed in <code>String</code>.  This stream will read from the beginning
  75    * to the end of the <code>String</code>.
  76    *
  77    * @param buffer The <code>String</code> this stream will read from.
  78    */
  79   public StringReader(String buffer)
  80   {
  81     super();
  82     buf = buffer;
  83
  84     count = buffer.length();
  85     markedPos = pos = 0;
  86   }
  87
  88   public void close()
  89   {
  90     synchronized (lock)
  91     {
  92       buf = null;
  93     }
  94   }
  95
  96   public void mark(int readAheadLimit) throws IOException
  97   {
  98     synchronized (lock)
  99     {
 100       if (buf == null)
 101         throw new IOException("Stream closed");
 102
 103       // readAheadLimit is ignored per Java Class Lib. book, p. 1692.
 104       markedPos = pos;
 105     }
 106   }
 107
 108   public boolean markSupported()
 109   {
 110     return true;
 111   }
 112
 113   public int read() throws IOException
 114   {
 115     synchronized (lock)
 116     {
 117       if (buf == null)
 118         throw new IOException("Stream closed");
 119
 120       if (pos < count)
 121         return ((int) buf.charAt(pos++)) & 0xFFFF;
 122       return -1;
 123     }
 124   }
 125
 126   public int read(char[] b, int off, int len) throws IOException
 127   {
 128     synchronized (lock)
 129     {
 130       if (buf == null)
 131         throw new IOException("Stream closed");
 132
 133       /* Don't need to check pos value, arraycopy will check it. */
 134       if (off < 0 || len < 0 || off + len > b.length)
 135         throw new ArrayIndexOutOfBoundsException();
 136
 137       if (pos >= count)
 138         return -1;
 139
 140       int lastChar = Math.min(count, pos + len);
 141       buf.getChars(pos, lastChar, b, off);
 142       int numChars = lastChar - pos;
 143       pos = lastChar;
 144       return numChars;
 145     }
 146   }
 147
 148   /**
 149    * This method determines if the stream is ready to be read.  This class
 150    * is always ready to read and so always returns <code>true</code>, unless
 151    * close() has previously been called in which case an IOException is
 152    * thrown.
 153    *
 154    * @return <code>true</code> to indicate that this object is ready to be read.
 155    * @exception IOException If the stream is closed.
 156    */
 157   public boolean ready() throws IOException
 158   {
 159     if (buf == null)
 160       throw new IOException("Stream closed");
 161
 162     return true;
 163   }
 164
 165   /**
 166    * Sets the read position in the stream to the previously
 167    * marked position or to 0 (i.e., the beginning of the stream) if the mark
 168    * has not already been set.
 169    */
 170   public void reset() throws IOException
 171   {
 172     synchronized (lock)
 173     {
 174       if (buf == null)
 175         throw new IOException("Stream closed");
 176
 177       pos = markedPos;
 178     }
 179   }
 180
 181   /**
 182     * This method attempts to skip the requested number of chars in the
 183     * input stream.  It does this by advancing the <code>pos</code> value by
 184     * the specified number of chars.  It this would exceed the length of the
 185     * buffer, then only enough chars are skipped to position the stream at
 186     * the end of the buffer.  The actual number of chars skipped is returned.
 187     *
 188     * @param n The requested number of chars to skip
 189     *
 190     * @return The actual number of chars skipped.
 191     */
 192   public long skip(long n) throws IOException
 193   {
 194     synchronized (lock)
 195     {
 196       if (buf == null)
 197         throw new IOException("Stream closed");
 198
 199       // Even though the var numChars is a long, in reality it can never
 200       // be larger than an int since the result of subtracting 2 positive
 201       // ints will always fit in an int.  Since we have to return a long
 202       // anyway, numChars might as well just be a long.
 203       long numChars = Math.min((long) (count - pos), n < 0 ? 0L : n);
 204       pos += numChars;
 205       return numChars;
 206     }
 207   }
 208 }
 209