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1   /*
2    * Copyright (c) 1996, 2005, 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  
26  package java.io;
27  
28  /**
29   * This class implements a character buffer that can be used as a
30   * character-input stream.
31   *
32   * @author      Herb Jellinek
33   * @since       JDK1.1
34   */
35  public class CharArrayReader extends Reader {
36      /** The character buffer. */
37      protected char buf[];
38  
39      /** The current buffer position. */
40      protected int pos;
41  
42      /** The position of mark in buffer. */
43      protected int markedPos = 0;
44  
45      /**
46       *  The index of the end of this buffer.  There is not valid
47       *  data at or beyond this index.
48       */
49      protected int count;
50  
51      /**
52       * Creates a CharArrayReader from the specified array of chars.
53       * @param buf       Input buffer (not copied)
54       */
55      public CharArrayReader(char buf[]) {
56          this.buf = buf;
57          this.pos = 0;
58          this.count = buf.length;
59      }
60  
61      /**
62       * Creates a CharArrayReader from the specified array of chars.
63       *
64       * <p> The resulting reader will start reading at the given
65       * <tt>offset</tt>.  The total number of <tt>char</tt> values that can be
66       * read from this reader will be either <tt>length</tt> or
67       * <tt>buf.length-offset</tt>, whichever is smaller.
68       *
69       * @throws IllegalArgumentException
70       *         If <tt>offset</tt> is negative or greater than
71       *         <tt>buf.length</tt>, or if <tt>length</tt> is negative, or if
72       *         the sum of these two values is negative.
73       *
74       * @param buf       Input buffer (not copied)
75       * @param offset    Offset of the first char to read
76       * @param length    Number of chars to read
77       */
78      public CharArrayReader(char buf[], int offset, int length) {
79          if ((offset < 0) || (offset > buf.length) || (length < 0) ||
80              ((offset + length) < 0)) {
81              throw new IllegalArgumentException();
82          }
83          this.buf = buf;
84          this.pos = offset;
85          this.count = Math.min(offset + length, buf.length);
86          this.markedPos = offset;
87      }
88  
89      /** Checks to make sure that the stream has not been closed */
90      private void ensureOpen() throws IOException {
91          if (buf == null)
92              throw new IOException("Stream closed");
93      }
94  
95      /**
96       * Reads a single character.
97       *
98       * @exception   IOException  If an I/O error occurs
99       */
100     public int read() throws IOException {
101         synchronized (lock) {
102             ensureOpen();
103             if (pos >= count)
104                 return -1;
105             else
106                 return buf[pos++];
107         }
108     }
109 
110     /**
111      * Reads characters into a portion of an array.
112      * @param b  Destination buffer
113      * @param off  Offset at which to start storing characters
114      * @param len   Maximum number of characters to read
115      * @return  The actual number of characters read, or -1 if
116      *          the end of the stream has been reached
117      *
118      * @exception   IOException  If an I/O error occurs
119      */
120     public int read(char b[], int off, int len) throws IOException {
121         synchronized (lock) {
122             ensureOpen();
123             if ((off < 0) || (off > b.length) || (len < 0) ||
124                 ((off + len) > b.length) || ((off + len) < 0)) {
125                 throw new IndexOutOfBoundsException();
126             } else if (len == 0) {
127                 return 0;
128             }
129 
130             if (pos >= count) {
131                 return -1;
132             }
133             if (pos + len > count) {
134                 len = count - pos;
135             }
136             if (len <= 0) {
137                 return 0;
138             }
139             System.arraycopy(buf, pos, b, off, len);
140             pos += len;
141             return len;
142         }
143     }
144 
145     /**
146      * Skips characters.  Returns the number of characters that were skipped.
147      *
148      * <p>The <code>n</code> parameter may be negative, even though the
149      * <code>skip</code> method of the {@link Reader} superclass throws
150      * an exception in this case. If <code>n</code> is negative, then
151      * this method does nothing and returns <code>0</code>.
152      *
153      * @param n The number of characters to skip
154      * @return       The number of characters actually skipped
155      * @exception  IOException If the stream is closed, or an I/O error occurs
156      */
157     public long skip(long n) throws IOException {
158         synchronized (lock) {
159             ensureOpen();
160             if (pos + n > count) {
161                 n = count - pos;
162             }
163             if (n < 0) {
164                 return 0;
165             }
166             pos += n;
167             return n;
168         }
169     }
170 
171     /**
172      * Tells whether this stream is ready to be read.  Character-array readers
173      * are always ready to be read.
174      *
175      * @exception  IOException  If an I/O error occurs
176      */
177     public boolean ready() throws IOException {
178         synchronized (lock) {
179             ensureOpen();
180             return (count - pos) > 0;
181         }
182     }
183 
184     /**
185      * Tells whether this stream supports the mark() operation, which it does.
186      */
187     public boolean markSupported() {
188         return true;
189     }
190 
191     /**
192      * Marks the present position in the stream.  Subsequent calls to reset()
193      * will reposition the stream to this point.
194      *
195      * @param  readAheadLimit  Limit on the number of characters that may be
196      *                         read while still preserving the mark.  Because
197      *                         the stream's input comes from a character array,
198      *                         there is no actual limit; hence this argument is
199      *                         ignored.
200      *
201      * @exception  IOException  If an I/O error occurs
202      */
203     public void mark(int readAheadLimit) throws IOException {
204         synchronized (lock) {
205             ensureOpen();
206             markedPos = pos;
207         }
208     }
209 
210     /**
211      * Resets the stream to the most recent mark, or to the beginning if it has
212      * never been marked.
213      *
214      * @exception  IOException  If an I/O error occurs
215      */
216     public void reset() throws IOException {
217         synchronized (lock) {
218             ensureOpen();
219             pos = markedPos;
220         }
221     }
222 
223     /**
224      * Closes the stream and releases any system resources associated with
225      * it.  Once the stream has been closed, further read(), ready(),
226      * mark(), reset(), or skip() invocations will throw an IOException.
227      * Closing a previously closed stream has no effect.
228      */
229     public void close() {
230         buf = null;
231     }
232 }