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1   /*
2    * Copyright (c) 1996, 2012, Oracle and/or its affiliates. All rights reserved.
3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4    *
5    * This code is free software; you can redistribute it and/or modify it
6    * under the terms of the GNU General Public License version 2 only, as
7    * published by the Free Software Foundation.  Oracle designates this
8    * particular file as subject to the "Classpath" exception as provided
9    * by Oracle in the LICENSE file that accompanied this code.
10   *
11   * This code is distributed in the hope that it will be useful, but WITHOUT
12   * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13   * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14   * version 2 for more details (a copy is included in the LICENSE file that
15   * accompanied this code).
16   *
17   * You should have received a copy of the GNU General Public License version
18   * 2 along with this work; if not, write to the Free Software Foundation,
19   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20   *
21   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22   * or visit www.oracle.com if you need additional information or have any
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24   */
25  
26  package java.io;
27  
28  
29  /**
30   * Abstract class for reading character streams.  The only methods that a
31   * subclass must implement are read(char[], int, int) and close().  Most
32   * subclasses, however, will override some of the methods defined here in order
33   * to provide higher efficiency, additional functionality, or both.
34   *
35   *
36   * @see BufferedReader
37   * @see   LineNumberReader
38   * @see CharArrayReader
39   * @see InputStreamReader
40   * @see   FileReader
41   * @see FilterReader
42   * @see   PushbackReader
43   * @see PipedReader
44   * @see StringReader
45   * @see Writer
46   *
47   * @author      Mark Reinhold
48   * @since       JDK1.1
49   */
50  
51  public abstract class Reader implements Readable, Closeable {
52  
53      /**
54       * The object used to synchronize operations on this stream.  For
55       * efficiency, a character-stream object may use an object other than
56       * itself to protect critical sections.  A subclass should therefore use
57       * the object in this field rather than <tt>this</tt> or a synchronized
58       * method.
59       */
60      protected Object lock;
61  
62      /**
63       * Creates a new character-stream reader whose critical sections will
64       * synchronize on the reader itself.
65       */
66      protected Reader() {
67          this.lock = this;
68      }
69  
70      /**
71       * Creates a new character-stream reader whose critical sections will
72       * synchronize on the given object.
73       *
74       * @param lock  The Object to synchronize on.
75       */
76      protected Reader(Object lock) {
77          if (lock == null) {
78              throw new NullPointerException();
79          }
80          this.lock = lock;
81      }
82  
83      /**
84       * Attempts to read characters into the specified character buffer.
85       * The buffer is used as a repository of characters as-is: the only
86       * changes made are the results of a put operation. No flipping or
87       * rewinding of the buffer is performed.
88       *
89       * @param target the buffer to read characters into
90       * @return The number of characters added to the buffer, or
91       *         -1 if this source of characters is at its end
92       * @throws IOException if an I/O error occurs
93       * @throws NullPointerException if target is null
94       * @throws java.nio.ReadOnlyBufferException if target is a read only buffer
95       * @since 1.5
96       */
97      public int read(java.nio.CharBuffer target) throws IOException {
98          int len = target.remaining();
99          char[] cbuf = new char[len];
100         int n = read(cbuf, 0, len);
101         if (n > 0)
102             target.put(cbuf, 0, n);
103         return n;
104     }
105 
106     /**
107      * Reads a single character.  This method will block until a character is
108      * available, an I/O error occurs, or the end of the stream is reached.
109      *
110      * <p> Subclasses that intend to support efficient single-character input
111      * should override this method.
112      *
113      * @return     The character read, as an integer in the range 0 to 65535
114      *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
115      *             been reached
116      *
117      * @exception  IOException  If an I/O error occurs
118      */
119     public int read() throws IOException {
120         char cb[] = new char[1];
121         if (read(cb, 0, 1) == -1)
122             return -1;
123         else
124             return cb[0];
125     }
126 
127     /**
128      * Reads characters into an array.  This method will block until some input
129      * is available, an I/O error occurs, or the end of the stream is reached.
130      *
131      * @param       cbuf  Destination buffer
132      *
133      * @return      The number of characters read, or -1
134      *              if the end of the stream
135      *              has been reached
136      *
137      * @exception   IOException  If an I/O error occurs
138      */
139     public int read(char cbuf[]) throws IOException {
140         return read(cbuf, 0, cbuf.length);
141     }
142 
143     /**
144      * Reads characters into a portion of an array.  This method will block
145      * until some input is available, an I/O error occurs, or the end of the
146      * stream is reached.
147      *
148      * @param      cbuf  Destination buffer
149      * @param      off   Offset at which to start storing characters
150      * @param      len   Maximum number of characters to read
151      *
152      * @return     The number of characters read, or -1 if the end of the
153      *             stream has been reached
154      *
155      * @exception  IOException  If an I/O error occurs
156      */
157     abstract public int read(char cbuf[], int off, int len) throws IOException;
158 
159     /** Maximum skip-buffer size */
160     private static final int maxSkipBufferSize = 8192;
161 
162     /** Skip buffer, null until allocated */
163     private char skipBuffer[] = null;
164 
165     /**
166      * Skips characters.  This method will block until some characters are
167      * available, an I/O error occurs, or the end of the stream is reached.
168      *
169      * @param  n  The number of characters to skip
170      *
171      * @return    The number of characters actually skipped
172      *
173      * @exception  IllegalArgumentException  If <code>n</code> is negative.
174      * @exception  IOException  If an I/O error occurs
175      */
176     public long skip(long n) throws IOException {
177         if (n < 0L)
178             throw new IllegalArgumentException("skip value is negative");
179         int nn = (int) Math.min(n, maxSkipBufferSize);
180         synchronized (lock) {
181             if ((skipBuffer == null) || (skipBuffer.length < nn))
182                 skipBuffer = new char[nn];
183             long r = n;
184             while (r > 0) {
185                 int nc = read(skipBuffer, 0, (int)Math.min(r, nn));
186                 if (nc == -1)
187                     break;
188                 r -= nc;
189             }
190             return n - r;
191         }
192     }
193 
194     /**
195      * Tells whether this stream is ready to be read.
196      *
197      * @return True if the next read() is guaranteed not to block for input,
198      * false otherwise.  Note that returning false does not guarantee that the
199      * next read will block.
200      *
201      * @exception  IOException  If an I/O error occurs
202      */
203     public boolean ready() throws IOException {
204         return false;
205     }
206 
207     /**
208      * Tells whether this stream supports the mark() operation. The default
209      * implementation always returns false. Subclasses should override this
210      * method.
211      *
212      * @return true if and only if this stream supports the mark operation.
213      */
214     public boolean markSupported() {
215         return false;
216     }
217 
218     /**
219      * Marks the present position in the stream.  Subsequent calls to reset()
220      * will attempt to reposition the stream to this point.  Not all
221      * character-input streams support the mark() operation.
222      *
223      * @param  readAheadLimit  Limit on the number of characters that may be
224      *                         read while still preserving the mark.  After
225      *                         reading this many characters, attempting to
226      *                         reset the stream may fail.
227      *
228      * @exception  IOException  If the stream does not support mark(),
229      *                          or if some other I/O error occurs
230      */
231     public void mark(int readAheadLimit) throws IOException {
232         throw new IOException("mark() not supported");
233     }
234 
235     /**
236      * Resets the stream.  If the stream has been marked, then attempt to
237      * reposition it at the mark.  If the stream has not been marked, then
238      * attempt to reset it in some way appropriate to the particular stream,
239      * for example by repositioning it to its starting point.  Not all
240      * character-input streams support the reset() operation, and some support
241      * reset() without supporting mark().
242      *
243      * @exception  IOException  If the stream has not been marked,
244      *                          or if the mark has been invalidated,
245      *                          or if the stream does not support reset(),
246      *                          or if some other I/O error occurs
247      */
248     public void reset() throws IOException {
249         throw new IOException("reset() not supported");
250     }
251 
252     /**
253      * Closes the stream and releases any system resources associated with
254      * it.  Once the stream has been closed, further read(), ready(),
255      * mark(), reset(), or skip() invocations will throw an IOException.
256      * Closing a previously closed stream has no effect.
257      *
258      * @exception  IOException  If an I/O error occurs
259      */
260      abstract public void close() throws IOException;
261 
262 }