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
26package 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
36public 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 readAheadLimit is < 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}
202