001 /*
002 * Copyright 1996-2006 Sun Microsystems, Inc. All Rights Reserved.
003 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
004 *
005 * This code is free software; you can redistribute it and/or modify it
006 * under the terms of the GNU General Public License version 2 only, as
007 * published by the Free Software Foundation. Sun designates this
008 * particular file as subject to the "Classpath" exception as provided
009 * by Sun in the LICENSE file that accompanied this code.
010 *
011 * This code is distributed in the hope that it will be useful, but WITHOUT
012 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
013 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
014 * version 2 for more details (a copy is included in the LICENSE file that
015 * accompanied this code).
016 *
017 * You should have received a copy of the GNU General Public License version
018 * 2 along with this work; if not, write to the Free Software Foundation,
019 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
020 *
021 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
022 * CA 95054 USA or visit www.sun.com if you need additional information or
023 * have any questions.
024 */
025
026 package java.io;
027
028 /**
029 * A character-stream reader that allows characters to be pushed back into the
030 * stream.
031 *
032 * @version 1.27, 07/05/05
033 * @author Mark Reinhold
034 * @since JDK1.1
035 */
036
037 public class PushbackReader extends FilterReader {
038
039 /** Pushback buffer */
040 private char[] buf;
041
042 /** Current position in buffer */
043 private int pos;
044
045 /**
046 * Creates a new pushback reader with a pushback buffer of the given size.
047 *
048 * @param in The reader from which characters will be read
049 * @param size The size of the pushback buffer
050 * @exception IllegalArgumentException if size is <= 0
051 */
052 public PushbackReader(Reader in, int size) {
053 super (in);
054 if (size <= 0) {
055 throw new IllegalArgumentException("size <= 0");
056 }
057 this .buf = new char[size];
058 this .pos = size;
059 }
060
061 /**
062 * Creates a new pushback reader with a one-character pushback buffer.
063 *
064 * @param in The reader from which characters will be read
065 */
066 public PushbackReader(Reader in) {
067 this (in, 1);
068 }
069
070 /** Checks to make sure that the stream has not been closed. */
071 private void ensureOpen() throws IOException {
072 if (buf == null)
073 throw new IOException("Stream closed");
074 }
075
076 /**
077 * Reads a single character.
078 *
079 * @return The character read, or -1 if the end of the stream has been
080 * reached
081 *
082 * @exception IOException If an I/O error occurs
083 */
084 public int read() throws IOException {
085 synchronized (lock) {
086 ensureOpen();
087 if (pos < buf.length)
088 return buf[pos++];
089 else
090 return super .read();
091 }
092 }
093
094 /**
095 * Reads characters into a portion of an array.
096 *
097 * @param cbuf Destination buffer
098 * @param off Offset at which to start writing characters
099 * @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 */
106 public int read(char cbuf[], int off, int len) throws IOException {
107 synchronized (lock) {
108 ensureOpen();
109 try {
110 if (len <= 0) {
111 if (len < 0) {
112 throw new IndexOutOfBoundsException();
113 } else if ((off < 0) || (off > cbuf.length)) {
114 throw new IndexOutOfBoundsException();
115 }
116 return 0;
117 }
118 int avail = buf.length - pos;
119 if (avail > 0) {
120 if (len < avail)
121 avail = len;
122 System.arraycopy(buf, pos, cbuf, off, avail);
123 pos += avail;
124 off += avail;
125 len -= avail;
126 }
127 if (len > 0) {
128 len = super .read(cbuf, off, len);
129 if (len == -1) {
130 return (avail == 0) ? -1 : avail;
131 }
132 return avail + len;
133 }
134 return avail;
135 } catch (ArrayIndexOutOfBoundsException e) {
136 throw new IndexOutOfBoundsException();
137 }
138 }
139 }
140
141 /**
142 * Pushes back a single character by copying it to the front of the
143 * pushback buffer. After this method returns, the next character to be read
144 * will have the value <code>(char)c</code>.
145 *
146 * @param c The int value representing a character to be pushed back
147 *
148 * @exception IOException If the pushback buffer is full,
149 * or if some other I/O error occurs
150 */
151 public void unread(int c) throws IOException {
152 synchronized (lock) {
153 ensureOpen();
154 if (pos == 0)
155 throw new IOException("Pushback buffer overflow");
156 buf[--pos] = (char) c;
157 }
158 }
159
160 /**
161 * Pushes back a portion of an array of characters by copying it to the
162 * front of the pushback buffer. After this method returns, the next
163 * character to be read will have the value <code>cbuf[off]</code>, the
164 * character after that will have the value <code>cbuf[off+1]</code>, and
165 * so forth.
166 *
167 * @param cbuf Character array
168 * @param off Offset of first character to push back
169 * @param len Number of characters to push back
170 *
171 * @exception IOException If there is insufficient room in the pushback
172 * buffer, or if some other I/O error occurs
173 */
174 public void unread(char cbuf[], int off, int len)
175 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.
245 *
246 * @exception IOException If an I/O error occurs
247 */
248 public void close() throws IOException {
249 super .close();
250 buf = null;
251 }
252
253 /**
254 * Skips characters. This method will block until some characters are
255 * available, an I/O error occurs, or the end of the stream is reached.
256 *
257 * @param n The number of characters to skip
258 *
259 * @return The number of characters actually skipped
260 *
261 * @exception IllegalArgumentException If <code>n</code> is negative.
262 * @exception IOException If an I/O error occurs
263 */
264 public long skip(long n) throws IOException {
265 if (n < 0L)
266 throw new IllegalArgumentException("skip value is negative");
267 synchronized (lock) {
268 ensureOpen();
269 int avail = buf.length - pos;
270 if (avail > 0) {
271 if (n <= avail) {
272 pos += n;
273 return n;
274 } else {
275 pos = buf.length;
276 n -= avail;
277 }
278 }
279 return avail + super.skip(n);
280 }
281 }
282 }
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