Reader


1   /*
2    * @(#)Reader.java  1.27 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.io;
9   
10  
11  /**
12   * Abstract class for reading character streams.  The only methods that a
13   * subclass must implement are read(char[], int, int) and close().  Most
14   * subclasses, however, will override some of the methods defined here in order
15   * to provide higher efficiency, additional functionality, or both.
16   *
17   * 
18   * @see BufferedReader
19   * @see   LineNumberReader
20   * @see CharArrayReader
21   * @see InputStreamReader
22   * @see   FileReader
23   * @see FilterReader
24   * @see   PushbackReader
25   * @see PipedReader
26   * @see StringReader
27   * @see Writer
28   *
29   * @version     1.27, 03/12/19
30   * @author  Mark Reinhold
31   * @since   JDK1.1
32   */
33  
34  public abstract class Reader implements Readable  , Closeable   {
35  
36      /**
37       * The object used to synchronize operations on this stream.  For
38       * efficiency, a character-stream object may use an object other than
39       * itself to protect critical sections.  A subclass should therefore use
40       * the object in this field rather than <tt>this</tt> or a synchronized
41       * method.
42       */
43      protected Object   lock;
44  
45      /**
46       * Create a new character-stream reader whose critical sections will
47       * synchronize on the reader itself.
48       */
49      protected Reader() {
50      this.lock = this;
51      }
52  
53      /**
54       * Create a new character-stream reader whose critical sections will
55       * synchronize on the given object.
56       *
57       * @param lock  The Object to synchronize on.
58       */
59      protected Reader(Object   lock) {
60      if (lock == null) {
61          throw new NullPointerException  ();
62      }
63      this.lock = lock;
64      }
65  
66      /**
67       * Attempts to read characters into the specified character buffer.
68       * The buffer is used as a repository of characters as-is: the only
69       * changes made are the results of a put operation. No flipping or
70       * rewinding of the buffer is performed.
71       *
72       * @param target the buffer to read characters into
73       * @return The number of characters added to the buffer, or 
74       *         -1 if this source of characters is at its end
75       * @throws IOException if an I/O error occurs
76       * @throws NullPointerException if target is null
77       * @throws ReadOnlyBufferException if target is a read only buffer
78       */
79      public int read(java.nio.CharBuffer   target) throws IOException   {
80          int len = target.remaining();
81          char[] cbuf = new char[len];
82          int n = read(cbuf, 0, len);
83          if (n > 0)
84              target.put(cbuf, 0, n);
85          return n;
86      }
87  
88      /**
89       * Read a single character.  This method will block until a character is
90       * available, an I/O error occurs, or the end of the stream is reached.
91       *
92       * <p> Subclasses that intend to support efficient single-character input
93       * should override this method.
94       *
95       * @return     The character read, as an integer in the range 0 to 65535
96       *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
97       *             been reached
98       *
99       * @exception  IOException  If an I/O error occurs
100      */
101     public int read() throws IOException   {
102     char cb[] = new char[1];
103     if (read(cb, 0, 1) == -1)
104         return -1;
105     else
106         return cb[0];
107     }
108 
109     /**
110      * Read characters into an array.  This method will block until some input
111      * is available, an I/O error occurs, or the end of the stream is reached.
112      *
113      * @param       cbuf  Destination buffer
114      *
115      * @return      The number of characters read, or -1 
116      *              if the end of the stream
117      *              has been reached
118      *
119      * @exception   IOException  If an I/O error occurs
120      */
121     public int read(char cbuf[]) throws IOException   {
122     return read(cbuf, 0, cbuf.length);
123     }
124 
125     /**
126      * Read characters into a portion of an array.  This method will block
127      * until some input is available, an I/O error occurs, or the end of the
128      * stream is reached.
129      *
130      * @param      cbuf  Destination buffer
131      * @param      off   Offset at which to start storing characters
132      * @param      len   Maximum number of characters to read
133      *
134      * @return     The number of characters read, or -1 if the end of the
135      *             stream has been reached
136      *
137      * @exception  IOException  If an I/O error occurs
138      */
139     abstract public int read(char cbuf[], int off, int len) throws IOException  ;
140 
141     /** Maximum skip-buffer size */
142     private static final int maxSkipBufferSize = 8192;
143 
144     /** Skip buffer, null until allocated */
145     private char skipBuffer[] = null;
146 
147     /**
148      * Skip characters.  This method will block until some characters are
149      * available, an I/O error occurs, or the end of the stream is reached.
150      *
151      * @param  n  The number of characters to skip
152      *
153      * @return    The number of characters actually skipped
154      *
155      * @exception  IllegalArgumentException  If <code>n</code> is negative.
156      * @exception  IOException  If an I/O error occurs
157      */
158     public long skip(long n) throws IOException   {
159     if (n < 0L) 
160         throw new IllegalArgumentException  ("skip value is negative");
161     int nn = (int) Math.min(n, maxSkipBufferSize);
162     synchronized (lock) {
163         if ((skipBuffer == null) || (skipBuffer.length < nn))
164         skipBuffer = new char[nn];
165         long r = n;
166         while (r > 0) {
167         int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
168         if (nc == -1)
169             break;
170         r -= nc;
171         }
172         return n - r;
173     }
174     }
175 
176     /**
177      * Tell whether this stream is ready to be read.
178      *
179      * @return True if the next read() is guaranteed not to block for input,
180      * false otherwise.  Note that returning false does not guarantee that the
181      * next read will block.
182      *
183      * @exception  IOException  If an I/O error occurs
184      */
185     public boolean ready() throws IOException   {
186     return false;
187     }
188 
189     /**
190      * Tell whether this stream supports the mark() operation. The default
191      * implementation always returns false. Subclasses should override this
192      * method.
193      *
194      * @return true if and only if this stream supports the mark operation.
195      */
196     public boolean markSupported() {
197     return false;
198     }
199 
200     /**
201      * Mark the present position in the stream.  Subsequent calls to reset()
202      * will attempt to reposition the stream to this point.  Not all
203      * character-input streams support the mark() operation.
204      *
205      * @param  readAheadLimit  Limit on the number of characters that may be
206      *                         read while still preserving the mark.  After
207      *                         reading this many characters, attempting to
208      *                         reset the stream may fail.
209      *
210      * @exception  IOException  If the stream does not support mark(),
211      *                          or if some other I/O error occurs
212      */
213     public void mark(int readAheadLimit) throws IOException   {
214     throw new IOException  ("mark() not supported");
215     }
216 
217     /**
218      * Reset the stream.  If the stream has been marked, then attempt to
219      * reposition it at the mark.  If the stream has not been marked, then
220      * attempt to reset it in some way appropriate to the particular stream,
221      * for example by repositioning it to its starting point.  Not all
222      * character-input streams support the reset() operation, and some support
223      * reset() without supporting mark().
224      *
225      * @exception  IOException  If the stream has not been marked,
226      *                          or if the mark has been invalidated,
227      *                          or if the stream does not support reset(),
228      *                          or if some other I/O error occurs
229      */
230     public void reset() throws IOException   {
231     throw new IOException  ("reset() not supported");
232     }
233 
234     /**
235      * Close the stream.  Once a stream has been closed, further read(),
236      * ready(), mark(), or reset() invocations will throw an IOException.
237      * Closing a previously-closed stream, however, has no effect.
238      *
239      * @exception  IOException  If an I/O error occurs
240      */
241      abstract public void close() throws IOException  ;
242 
243 }
244
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