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1   /*
2    * Copyright (c) 1996, 2013, 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  /**
30   * A character stream whose source is a string.
31   *
32   * @author      Mark Reinhold
33   * @since       JDK1.1
34   */
35  
36  public class StringReader extends Reader {
37  
38      private String str;
39      private int length;
40      private int next = 0;
41      private int mark = 0;
42  
43      /**
44       * Creates a new string reader.
45       *
46       * @param s  String providing the character stream.
47       */
48      public StringReader(String s) {
49          this.str = s;
50          this.length = s.length();
51      }
52  
53      /** Check to make sure that the stream has not been closed */
54      private void ensureOpen() throws IOException {
55          if (str == null)
56              throw new IOException("Stream closed");
57      }
58  
59      /**
60       * Reads a single character.
61       *
62       * @return     The character read, or -1 if the end of the stream has been
63       *             reached
64       *
65       * @exception  IOException  If an I/O error occurs
66       */
67      public int read() throws IOException {
68          synchronized (lock) {
69              ensureOpen();
70              if (next >= length)
71                  return -1;
72              return str.charAt(next++);
73          }
74      }
75  
76      /**
77       * Reads characters into a portion of an array.
78       *
79       * @param      cbuf  Destination buffer
80       * @param      off   Offset at which to start writing characters
81       * @param      len   Maximum number of characters to read
82       *
83       * @return     The number of characters read, or -1 if the end of the
84       *             stream has been reached
85       *
86       * @exception  IOException  If an I/O error occurs
87       */
88      public int read(char cbuf[], int off, int len) throws IOException {
89          synchronized (lock) {
90              ensureOpen();
91              if ((off < 0) || (off > cbuf.length) || (len < 0) ||
92                  ((off + len) > cbuf.length) || ((off + len) < 0)) {
93                  throw new IndexOutOfBoundsException();
94              } else if (len == 0) {
95                  return 0;
96              }
97              if (next >= length)
98                  return -1;
99              int n = Math.min(length - next, len);
100             str.getChars(next, next + n, cbuf, off);
101             next += n;
102             return n;
103         }
104     }
105 
106     /**
107      * Skips the specified number of characters in the stream. Returns
108      * the number of characters that were skipped.
109      *
110      * <p>The <code>ns</code> parameter may be negative, even though the
111      * <code>skip</code> method of the {@link Reader} superclass throws
112      * an exception in this case. Negative values of <code>ns</code> cause the
113      * stream to skip backwards. Negative return values indicate a skip
114      * backwards. It is not possible to skip backwards past the beginning of
115      * the string.
116      *
117      * <p>If the entire string has been read or skipped, then this method has
118      * no effect and always returns 0.
119      *
120      * @exception  IOException  If an I/O error occurs
121      */
122     public long skip(long ns) throws IOException {
123         synchronized (lock) {
124             ensureOpen();
125             if (next >= length)
126                 return 0;
127             // Bound skip by beginning and end of the source
128             long n = Math.min(length - next, ns);
129             n = Math.max(-next, n);
130             next += n;
131             return n;
132         }
133     }
134 
135     /**
136      * Tells whether this stream is ready to be read.
137      *
138      * @return True if the next read() is guaranteed not to block for input
139      *
140      * @exception  IOException  If the stream is closed
141      */
142     public boolean ready() throws IOException {
143         synchronized (lock) {
144         ensureOpen();
145         return true;
146         }
147     }
148 
149     /**
150      * Tells whether this stream supports the mark() operation, which it does.
151      */
152     public boolean markSupported() {
153         return true;
154     }
155 
156     /**
157      * Marks the present position in the stream.  Subsequent calls to reset()
158      * will reposition the stream to this point.
159      *
160      * @param  readAheadLimit  Limit on the number of characters that may be
161      *                         read while still preserving the mark.  Because
162      *                         the stream's input comes from a string, there
163      *                         is no actual limit, so this argument must not
164      *                         be negative, but is otherwise ignored.
165      *
166      * @exception  IllegalArgumentException  If {@code readAheadLimit < 0}
167      * @exception  IOException  If an I/O error occurs
168      */
169     public void mark(int readAheadLimit) throws IOException {
170         if (readAheadLimit < 0){
171             throw new IllegalArgumentException("Read-ahead limit < 0");
172         }
173         synchronized (lock) {
174             ensureOpen();
175             mark = next;
176         }
177     }
178 
179     /**
180      * Resets the stream to the most recent mark, or to the beginning of the
181      * string if it has never been marked.
182      *
183      * @exception  IOException  If an I/O error occurs
184      */
185     public void reset() throws IOException {
186         synchronized (lock) {
187             ensureOpen();
188             next = mark;
189         }
190     }
191 
192     /**
193      * Closes the stream and releases any system resources associated with
194      * it. Once the stream has been closed, further read(),
195      * ready(), mark(), or reset() invocations will throw an IOException.
196      * Closing a previously closed stream has no effect.
197      */
198     public void close() {
199         str = null;
200     }
201 }