1/*
2 * Copyright (c) 1996, 2006, 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
23 * questions.
24 */
25
26package 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
51public 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 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}
263