1/*
2 * Copyright (c) 1996, 2015, 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 * A character-stream reader that allows characters to be pushed back into the
31 * stream.
32 *
33 * @author      Mark Reinhold
34 * @since       1.1
35 */
36
37public class PushbackReader extends FilterReader {
38
39    /** Pushback buffer */
40    private char[] buf;
41
42    /** Current position in buffer */
43    private int pos;
44
45    /**
46     * Creates a new pushback reader with a pushback buffer of the given size.
47     *
48     * @param   in   The reader from which characters will be read
49     * @param   size The size of the pushback buffer
50     * @exception IllegalArgumentException if {@code size <= 0}
51     */
52    public PushbackReader(Reader in, int size) {
53        super(in);
54        if (size <= 0) {
55            throw new IllegalArgumentException("size <= 0");
56        }
57        this.buf = new char[size];
58        this.pos = size;
59    }
60
61    /**
62     * Creates a new pushback reader with a one-character pushback buffer.
63     *
64     * @param   in  The reader from which characters will be read
65     */
66    public PushbackReader(Reader in) {
67        this(in, 1);
68    }
69
70    /** Checks to make sure that the stream has not been closed. */
71    private void ensureOpen() throws IOException {
72        if (buf == null)
73            throw new IOException("Stream closed");
74    }
75
76    /**
77     * Reads a single character.
78     *
79     * @return     The character read, or -1 if the end of the stream has been
80     *             reached
81     *
82     * @exception  IOException  If an I/O error occurs
83     */
84    public int read() throws IOException {
85        synchronized (lock) {
86            ensureOpen();
87            if (pos < buf.length)
88                return buf[pos++];
89            else
90                return super.read();
91        }
92    }
93
94    /**
95     * Reads characters into a portion of an array.
96     *
97     * @param      cbuf  Destination buffer
98     * @param      off   Offset at which to start writing characters
99     * @param      len   Maximum number of characters to read
100     *
101     * @return     The number of characters read, or -1 if the end of the
102     *             stream has been reached
103     *
104     * @exception  IOException  If an I/O error occurs
105     * @exception  IndexOutOfBoundsException {@inheritDoc}
106     */
107    public int read(char cbuf[], int off, int len) throws IOException {
108        synchronized (lock) {
109            ensureOpen();
110            try {
111                if (len <= 0) {
112                    if (len < 0) {
113                        throw new IndexOutOfBoundsException();
114                    } else if ((off < 0) || (off > cbuf.length)) {
115                        throw new IndexOutOfBoundsException();
116                    }
117                    return 0;
118                }
119                int avail = buf.length - pos;
120                if (avail > 0) {
121                    if (len < avail)
122                        avail = len;
123                    System.arraycopy(buf, pos, cbuf, off, avail);
124                    pos += avail;
125                    off += avail;
126                    len -= avail;
127                }
128                if (len > 0) {
129                    len = super.read(cbuf, off, len);
130                    if (len == -1) {
131                        return (avail == 0) ? -1 : avail;
132                    }
133                    return avail + len;
134                }
135                return avail;
136            } catch (ArrayIndexOutOfBoundsException e) {
137                throw new IndexOutOfBoundsException();
138            }
139        }
140    }
141
142    /**
143     * Pushes back a single character by copying it to the front of the
144     * pushback buffer. After this method returns, the next character to be read
145     * will have the value <code>(char)c</code>.
146     *
147     * @param  c  The int value representing a character to be pushed back
148     *
149     * @exception  IOException  If the pushback buffer is full,
150     *                          or if some other I/O error occurs
151     */
152    public void unread(int c) throws IOException {
153        synchronized (lock) {
154            ensureOpen();
155            if (pos == 0)
156                throw new IOException("Pushback buffer overflow");
157            buf[--pos] = (char) c;
158        }
159    }
160
161    /**
162     * Pushes back a portion of an array of characters by copying it to the
163     * front of the pushback buffer.  After this method returns, the next
164     * character to be read will have the value <code>cbuf[off]</code>, the
165     * character after that will have the value <code>cbuf[off+1]</code>, and
166     * so forth.
167     *
168     * @param  cbuf  Character array
169     * @param  off   Offset of first character to push back
170     * @param  len   Number of characters to push back
171     *
172     * @exception  IOException  If there is insufficient room in the pushback
173     *                          buffer, or if some other I/O error occurs
174     */
175    public void unread(char cbuf[], int off, int len) throws IOException {
176        synchronized (lock) {
177            ensureOpen();
178            if (len > pos)
179                throw new IOException("Pushback buffer overflow");
180            pos -= len;
181            System.arraycopy(cbuf, off, buf, pos, len);
182        }
183    }
184
185    /**
186     * Pushes back an array of characters by copying it to the front of the
187     * pushback buffer.  After this method returns, the next character to be
188     * read will have the value <code>cbuf[0]</code>, the character after that
189     * will have the value <code>cbuf[1]</code>, and so forth.
190     *
191     * @param  cbuf  Character array to push back
192     *
193     * @exception  IOException  If there is insufficient room in the pushback
194     *                          buffer, or if some other I/O error occurs
195     */
196    public void unread(char cbuf[]) throws IOException {
197        unread(cbuf, 0, cbuf.length);
198    }
199
200    /**
201     * Tells whether this stream is ready to be read.
202     *
203     * @exception  IOException  If an I/O error occurs
204     */
205    public boolean ready() throws IOException {
206        synchronized (lock) {
207            ensureOpen();
208            return (pos < buf.length) || super.ready();
209        }
210    }
211
212    /**
213     * Marks the present position in the stream. The <code>mark</code>
214     * for class <code>PushbackReader</code> always throws an exception.
215     *
216     * @exception  IOException  Always, since mark is not supported
217     */
218    public void mark(int readAheadLimit) throws IOException {
219        throw new IOException("mark/reset not supported");
220    }
221
222    /**
223     * Resets the stream. The <code>reset</code> method of
224     * <code>PushbackReader</code> always throws an exception.
225     *
226     * @exception  IOException  Always, since reset is not supported
227     */
228    public void reset() throws IOException {
229        throw new IOException("mark/reset not supported");
230    }
231
232    /**
233     * Tells whether this stream supports the mark() operation, which it does
234     * not.
235     */
236    public boolean markSupported() {
237        return false;
238    }
239
240    /**
241     * Closes the stream and releases any system resources associated with
242     * it. Once the stream has been closed, further read(),
243     * unread(), ready(), or skip() invocations will throw an IOException.
244     * Closing a previously closed stream has no effect. This method will block
245     * while there is another thread blocking on the reader.
246     *
247     * @exception  IOException  If an I/O error occurs
248     */
249    public void close() throws IOException {
250        synchronized (lock) {
251            super.close();
252            buf = null;
253        }
254    }
255
256    /**
257     * Skips characters.  This method will block until some characters are
258     * available, an I/O error occurs, or the end of the stream is reached.
259     *
260     * @param  n  The number of characters to skip
261     *
262     * @return    The number of characters actually skipped
263     *
264     * @exception  IllegalArgumentException  If <code>n</code> is negative.
265     * @exception  IOException  If an I/O error occurs
266     */
267    public long skip(long n) throws IOException {
268        if (n < 0L)
269            throw new IllegalArgumentException("skip value is negative");
270        synchronized (lock) {
271            ensureOpen();
272            int avail = buf.length - pos;
273            if (avail > 0) {
274                if (n <= avail) {
275                    pos += n;
276                    return n;
277                } else {
278                    pos = buf.length;
279                    n -= avail;
280                }
281            }
282            return avail + super.skip(n);
283        }
284    }
285}
286