1/*
2 *  Licensed to the Apache Software Foundation (ASF) under one or more
3 *  contributor license agreements.  See the NOTICE file distributed with
4 *  this work for additional information regarding copyright ownership.
5 *  The ASF licenses this file to You under the Apache License, Version 2.0
6 *  (the "License"); you may not use this file except in compliance with
7 *  the License.  You may obtain a copy of the License at
8 *
9 *     http://www.apache.org/licenses/LICENSE-2.0
10 *
11 *  Unless required by applicable law or agreed to in writing, software
12 *  distributed under the License is distributed on an "AS IS" BASIS,
13 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 *  See the License for the specific language governing permissions and
15 *  limitations under the License.
16 */
17
18package java.io;
19
20/**
21 * The base class for all writers. A writer is a means of writing data to a
22 * target in a character-wise manner. Most output streams expect the
23 * {@link #flush()} method to be called before closing the stream, to ensure all
24 * data is actually written out.
25 * <p>
26 * This abstract class does not provide a fully working implementation, so it
27 * needs to be subclassed, and at least the {@link #write(char[], int, int)},
28 * {@link #close()} and {@link #flush()} methods needs to be overridden.
29 * Overriding some of the non-abstract methods is also often advised, since it
30 * might result in higher efficiency.
31 * <p>
32 * Many specialized readers for purposes like reading from a file already exist
33 * in this package.
34 *
35 * @see Reader
36 */
37public abstract class Writer implements Appendable, Closeable, Flushable {
38    /**
39     * The object used to synchronize access to the writer.
40     */
41    protected Object lock;
42
43    /**
44     * Constructs a new {@code Writer} with {@code this} as the object used to
45     * synchronize critical sections.
46     */
47    protected Writer() {
48        lock = this;
49    }
50
51    /**
52     * Constructs a new {@code Writer} with {@code lock} used to synchronize
53     * critical sections.
54     *
55     * @param lock
56     *            the {@code Object} used to synchronize critical sections.
57     * @throws NullPointerException
58     *             if {@code lock} is {@code null}.
59     */
60    protected Writer(Object lock) {
61        if (lock == null) {
62            throw new NullPointerException();
63        }
64        this.lock = lock;
65    }
66
67    /**
68     * Closes this writer. Implementations of this method should free any
69     * resources associated with the writer.
70     *
71     * @throws IOException
72     *             if an error occurs while closing this writer.
73     */
74    public abstract void close() throws IOException;
75
76    /**
77     * Flushes this writer. Implementations of this method should ensure that
78     * all buffered characters are written to the target.
79     *
80     * @throws IOException
81     *             if an error occurs while flushing this writer.
82     */
83    public abstract void flush() throws IOException;
84
85    /**
86     * Writes the entire character buffer {@code buf} to the target.
87     *
88     * @param buf
89     *            the non-null array containing characters to write.
90     * @throws IOException
91     *             if this writer is closed or another I/O error occurs.
92     */
93    public void write(char[] buf) throws IOException {
94        write(buf, 0, buf.length);
95    }
96
97    /**
98     * Writes {@code count} characters starting at {@code offset} in {@code buf}
99     * to the target.
100     *
101     * @param buf
102     *            the non-null character array to write.
103     * @param offset
104     *            the index of the first character in {@code buf} to write.
105     * @param count
106     *            the maximum number of characters to write.
107     * @throws IndexOutOfBoundsException
108     *             if {@code offset < 0} or {@code count < 0}, or if {@code
109     *             offset + count} is greater than the size of {@code buf}.
110     * @throws IOException
111     *             if this writer is closed or another I/O error occurs.
112     */
113    public abstract void write(char[] buf, int offset, int count) throws IOException;
114
115    /**
116     * Writes one character to the target. Only the two least significant bytes
117     * of the integer {@code oneChar} are written.
118     *
119     * @param oneChar
120     *            the character to write to the target.
121     * @throws IOException
122     *             if this writer is closed or another I/O error occurs.
123     */
124    public void write(int oneChar) throws IOException {
125        synchronized (lock) {
126            char[] oneCharArray = new char[1];
127            oneCharArray[0] = (char) oneChar;
128            write(oneCharArray);
129        }
130    }
131
132    /**
133     * Writes the characters from the specified string to the target.
134     *
135     * @param str
136     *            the non-null string containing the characters to write.
137     * @throws IOException
138     *             if this writer is closed or another I/O error occurs.
139     */
140    public void write(String str) throws IOException {
141        write(str, 0, str.length());
142    }
143
144    /**
145     * Writes {@code count} characters from {@code str} starting at {@code
146     * offset} to the target.
147     *
148     * @param str
149     *            the non-null string containing the characters to write.
150     * @param offset
151     *            the index of the first character in {@code str} to write.
152     * @param count
153     *            the number of characters from {@code str} to write.
154     * @throws IOException
155     *             if this writer is closed or another I/O error occurs.
156     * @throws IndexOutOfBoundsException
157     *             if {@code offset < 0} or {@code count < 0}, or if {@code
158     *             offset + count} is greater than the length of {@code str}.
159     */
160    public void write(String str, int offset, int count) throws IOException {
161        if ((offset | count) < 0 || offset > str.length() - count) {
162            throw new StringIndexOutOfBoundsException(str, offset, count);
163        }
164        char[] buf = new char[count];
165        str.getChars(offset, offset + count, buf, 0);
166        synchronized (lock) {
167            write(buf, 0, buf.length);
168        }
169    }
170
171    /**
172     * Appends the character {@code c} to the target. This method works the same
173     * way as {@link #write(int)}.
174     *
175     * @param c
176     *            the character to append to the target stream.
177     * @return this writer.
178     * @throws IOException
179     *             if this writer is closed or another I/O error occurs.
180     */
181    public Writer append(char c) throws IOException {
182        write(c);
183        return this;
184    }
185
186    /**
187     * Appends the character sequence {@code csq} to the target. This method
188     * works the same way as {@code Writer.write(csq.toString())}. If {@code
189     * csq} is {@code null}, then the string "null" is written to the target
190     * stream.
191     *
192     * @param csq
193     *            the character sequence appended to the target.
194     * @return this writer.
195     * @throws IOException
196     *             if this writer is closed or another I/O error occurs.
197     */
198    public Writer append(CharSequence csq) throws IOException {
199        if (csq == null) {
200            csq = "null";
201        }
202        write(csq.toString());
203        return this;
204    }
205
206    /**
207     * Appends a subsequence of the character sequence {@code csq} to the
208     * target. This method works the same way as {@code
209     * Writer.writer(csq.subsequence(start, end).toString())}. If {@code
210     * csq} is {@code null}, then the specified subsequence of the string "null"
211     * will be written to the target.
212     *
213     * @param csq
214     *            the character sequence appended to the target.
215     * @param start
216     *            the index of the first char in the character sequence appended
217     *            to the target.
218     * @param end
219     *            the index of the character following the last character of the
220     *            subsequence appended to the target.
221     * @return this writer.
222     * @throws IOException
223     *             if this writer is closed or another I/O error occurs.
224     * @throws IndexOutOfBoundsException
225     *             if {@code start > end}, {@code start < 0}, {@code end < 0} or
226     *             either {@code start} or {@code end} are greater or equal than
227     *             the length of {@code csq}.
228     */
229    public Writer append(CharSequence csq, int start, int end) throws IOException {
230        if (csq == null) {
231            csq = "null";
232        }
233        write(csq.subSequence(start, end).toString());
234        return this;
235    }
236
237    /**
238     * Returns true if this writer has encountered and suppressed an error. Used
239     * by PrintWriters as an alternative to checked exceptions.
240     */
241    boolean checkError() {
242        return false;
243    }
244}
245