Source Code Cross Referenced for Reader.java in  » 6.0-JDK-Modules » j2me » java » io » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » 6.0 JDK Modules » j2me » java.io 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         *   
003:         *
004:         * Copyright  1990-2007 Sun Microsystems, Inc. All Rights Reserved.
005:         * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
006:         * 
007:         * This program is free software; you can redistribute it and/or
008:         * modify it under the terms of the GNU General Public License version
009:         * 2 only, as published by the Free Software Foundation.
010:         * 
011:         * This program is distributed in the hope that it will be useful, but
012:         * WITHOUT ANY WARRANTY; without even the implied warranty of
013:         * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014:         * General Public License version 2 for more details (a copy is
015:         * included at /legal/license.txt).
016:         * 
017:         * You should have received a copy of the GNU General Public License
018:         * version 2 along with this work; if not, write to the Free Software
019:         * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
020:         * 02110-1301 USA
021:         * 
022:         * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
023:         * Clara, CA 95054 or visit www.sun.com if you need additional
024:         * information or have any questions.
025:         */
026:
027:        package java.io;
028:
029:        /**
030:         * Abstract class for reading character streams.  The only methods that a
031:         * subclass must implement are read(char[], int, int) and close().  Most
032:         * subclasses, however, will override some of the methods defined here in order
033:         * to provide higher efficiency, additional functionality, or both.
034:         *
035:         * @version 12/17/01 (CLDC 1.1)
036:         * @see     java.io.InputStreamReader
037:         * @see     java.io.Writer
038:         * @since   JDK1.1, CLDC 1.0
039:         */
040:
041:        public abstract class Reader {
042:
043:            /**
044:             * The object used to synchronize operations on this stream.  For
045:             * efficiency, a character-stream object may use an object other than
046:             * itself to protect critical sections.  A subclass should therefore use
047:             * the object in this field rather than <tt>this</tt> or a synchronized
048:             * method.
049:             */
050:            protected Object lock;
051:
052:            /**
053:             * Create a new character-stream reader whose critical sections will
054:             * synchronize on the reader itself.
055:             */
056:            protected Reader() {
057:                this .lock = this ;
058:            }
059:
060:            /**
061:             * Create a new character-stream reader whose critical sections will
062:             * synchronize on the given object.
063:             *
064:             * @param lock  The Object to synchronize on.
065:             */
066:            protected Reader(Object lock) {
067:                if (lock == null) {
068:                    throw new NullPointerException();
069:                }
070:                this .lock = lock;
071:            }
072:
073:            /**
074:             * Read a single character.  This method will block until a character is
075:             * available, an I/O error occurs, or the end of the stream is reached.
076:             *
077:             * <p> Subclasses that intend to support efficient single-character input
078:             * should override this method.
079:             *
080:             * @return     The character read, as an integer in the range 0 to 65535
081:             *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
082:             *             been reached
083:             *
084:             * @exception  IOException  If an I/O error occurs
085:             */
086:            public int read() throws IOException {
087:                char cb[] = new char[1];
088:                if (read(cb, 0, 1) == -1)
089:                    return -1;
090:                else
091:                    return cb[0];
092:            }
093:
094:            /**
095:             * Read characters into an array.  This method will block until some input
096:             * is available, an I/O error occurs, or the end of the stream is reached.
097:             *
098:             * @param       cbuf  Destination buffer
099:             *
100:             * @return      The number of bytes read, or -1 if the end of the stream
101:             *              has been reached
102:             *
103:             * @exception   IOException  If an I/O error occurs
104:             */
105:            public int read(char cbuf[]) throws IOException {
106:                return read(cbuf, 0, cbuf.length);
107:            }
108:
109:            /**
110:             * Read characters into a portion of an array.  This method will block
111:             * until some input is available, an I/O error occurs, or the end of the
112:             * stream is reached.
113:             *
114:             * @param      cbuf  Destination buffer
115:             * @param      off   Offset at which to start storing characters
116:             * @param      len   Maximum number of characters to read
117:             *
118:             * @return     The number of characters read, or -1 if the end of the
119:             *             stream has been reached
120:             *
121:             * @exception  IOException  If an I/O error occurs
122:             */
123:            abstract public int read(char cbuf[], int off, int len)
124:                    throws IOException;
125:
126:            /**
127:             * Maximum skip-buffer size
128:             */
129:            private static final int maxSkipBufferSize = 8192;
130:
131:            /**
132:             * Skip buffer, null until allocated
133:             */
134:            private char skipBuffer[] = null;
135:
136:            /**
137:             * Skip characters.  This method will block until some characters are
138:             * available, an I/O error occurs, or the end of the stream is reached.
139:             *
140:             * @param  n  The number of characters to skip
141:             *
142:             * @return    The number of characters actually skipped
143:             *
144:             * @exception  IllegalArgumentException  If <code>n</code> is negative.
145:             * @exception  IOException  If an I/O error occurs
146:             */
147:            public long skip(long n) throws IOException {
148:                if (n < 0L)
149:                    throw new IllegalArgumentException(
150:                    /* #ifdef VERBOSE_EXCEPTIONS */
151:                    /// skipped                       "skip value is negative"
152:                    /* #endif */
153:                    );
154:                int nn = (int) Math.min(n, maxSkipBufferSize);
155:                synchronized (lock) {
156:                    if ((skipBuffer == null) || (skipBuffer.length < nn))
157:                        skipBuffer = new char[nn];
158:                    long r = n;
159:                    while (r > 0) {
160:                        int nc = read(skipBuffer, 0, (int) Math.min(r, nn));
161:                        if (nc == -1)
162:                            break;
163:                        r -= nc;
164:                    }
165:                    return n - r;
166:                }
167:            }
168:
169:            /**
170:             * Tell whether this stream is ready to be read.
171:             *
172:             * @return True if the next read() is guaranteed not to block for input,
173:             * false otherwise.  Note that returning false does not guarantee that the
174:             * next read will block.
175:             *
176:             * @exception  IOException  If an I/O error occurs
177:             */
178:            public boolean ready() throws IOException {
179:                return false;
180:            }
181:
182:            /**
183:             * Tell whether this stream supports the mark() operation. The default
184:             * implementation always returns false. Subclasses should override this
185:             * method.
186:             *
187:             * @return true if and only if this stream supports the mark operation.
188:             */
189:            public boolean markSupported() {
190:                return false;
191:            }
192:
193:            /**
194:             * Mark the present position in the stream.  Subsequent calls to reset()
195:             * will attempt to reposition the stream to this point.  Not all
196:             * character-input streams support the mark() operation.
197:             *
198:             * @param  readAheadLimit  Limit on the number of characters that may be
199:             *                         read while still preserving the mark.  After
200:             *                         reading this many characters, attempting to
201:             *                         reset the stream may fail.
202:             *
203:             * @exception  IOException  If the stream does not support mark(),
204:             *                          or if some other I/O error occurs
205:             */
206:            public void mark(int readAheadLimit) throws IOException {
207:                throw new IOException(
208:                /* #ifdef VERBOSE_EXCEPTIONS */
209:                /// skipped                   "mark() not supported"
210:                /* #endif */
211:                );
212:            }
213:
214:            /**
215:             * Reset the stream.  If the stream has been marked, then attempt to
216:             * reposition it at the mark.  If the stream has not been marked, then
217:             * attempt to reset it in some way appropriate to the particular stream,
218:             * for example by repositioning it to its starting point.  Not all
219:             * character-input streams support the reset() operation, and some support
220:             * reset() without supporting mark().
221:             *
222:             * @exception  IOException  If the stream has not been marked,
223:             *                          or if the mark has been invalidated,
224:             *                          or if the stream does not support reset(),
225:             *                          or if some other I/O error occurs
226:             */
227:            public void reset() throws IOException {
228:                throw new IOException(
229:                /* #ifdef VERBOSE_EXCEPTIONS */
230:                /// skipped                   "reset() not supported"
231:                /* #endif */
232:                );
233:            }
234:
235:            /**
236:             * Close the stream.  Once a stream has been closed, further read(),
237:             * ready(), mark(), or reset() invocations will throw an IOException.
238:             * Closing a previously-closed stream, however, has no effect.
239:             *
240:             * @exception  IOException  If an I/O error occurs
241:             */
242:            abstract public void close() throws IOException;
243:
244:        }
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