1/*
2 * Copyright (c) 1996, 2015, 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       1.1
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     * @exception  IndexOutOfBoundsException {@inheritDoc}
88     */
89    public int read(char cbuf[], int off, int len) throws IOException {
90        synchronized (lock) {
91            ensureOpen();
92            if ((off < 0) || (off > cbuf.length) || (len < 0) ||
93                ((off + len) > cbuf.length) || ((off + len) < 0)) {
94                throw new IndexOutOfBoundsException();
95            } else if (len == 0) {
96                return 0;
97            }
98            if (next >= length)
99                return -1;
100            int n = Math.min(length - next, len);
101            str.getChars(next, next + n, cbuf, off);
102            next += n;
103            return n;
104        }
105    }
106
107    /**
108     * Skips the specified number of characters in the stream. Returns
109     * the number of characters that were skipped.
110     *
111     * <p>The <code>ns</code> parameter may be negative, even though the
112     * <code>skip</code> method of the {@link Reader} superclass throws
113     * an exception in this case. Negative values of <code>ns</code> cause the
114     * stream to skip backwards. Negative return values indicate a skip
115     * backwards. It is not possible to skip backwards past the beginning of
116     * the string.
117     *
118     * <p>If the entire string has been read or skipped, then this method has
119     * no effect and always returns 0.
120     *
121     * @exception  IOException  If an I/O error occurs
122     */
123    public long skip(long ns) throws IOException {
124        synchronized (lock) {
125            ensureOpen();
126            if (next >= length)
127                return 0;
128            // Bound skip by beginning and end of the source
129            long n = Math.min(length - next, ns);
130            n = Math.max(-next, n);
131            next += n;
132            return n;
133        }
134    }
135
136    /**
137     * Tells whether this stream is ready to be read.
138     *
139     * @return True if the next read() is guaranteed not to block for input
140     *
141     * @exception  IOException  If the stream is closed
142     */
143    public boolean ready() throws IOException {
144        synchronized (lock) {
145            ensureOpen();
146            return true;
147        }
148    }
149
150    /**
151     * Tells whether this stream supports the mark() operation, which it does.
152     */
153    public boolean markSupported() {
154        return true;
155    }
156
157    /**
158     * Marks the present position in the stream.  Subsequent calls to reset()
159     * will reposition the stream to this point.
160     *
161     * @param  readAheadLimit  Limit on the number of characters that may be
162     *                         read while still preserving the mark.  Because
163     *                         the stream's input comes from a string, there
164     *                         is no actual limit, so this argument must not
165     *                         be negative, but is otherwise ignored.
166     *
167     * @exception  IllegalArgumentException  If {@code readAheadLimit < 0}
168     * @exception  IOException  If an I/O error occurs
169     */
170    public void mark(int readAheadLimit) throws IOException {
171        if (readAheadLimit < 0){
172            throw new IllegalArgumentException("Read-ahead limit < 0");
173        }
174        synchronized (lock) {
175            ensureOpen();
176            mark = next;
177        }
178    }
179
180    /**
181     * Resets the stream to the most recent mark, or to the beginning of the
182     * string if it has never been marked.
183     *
184     * @exception  IOException  If an I/O error occurs
185     */
186    public void reset() throws IOException {
187        synchronized (lock) {
188            ensureOpen();
189            next = mark;
190        }
191    }
192
193    /**
194     * Closes the stream and releases any system resources associated with
195     * it. Once the stream has been closed, further read(),
196     * ready(), mark(), or reset() invocations will throw an IOException.
197     * Closing a previously closed stream has no effect. This method will block
198     * while there is another thread blocking on the reader.
199     */
200    public void close() {
201        synchronized (lock) {
202            str = null;
203        }
204    }
205}
206