xref: /libcore/luni/src/main/java/java/io/Writer.java

/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package java.io;

/**
 * The base class for all writers. A writer is a means of writing data to a
 * target in a character-wise manner. Most output streams expect the
 * {@link #flush()} method to be called before closing the stream, to ensure all
 * data is actually written out.
 * <p>
 * This abstract class does not provide a fully working implementation, so it
 * needs to be subclassed, and at least the {@link #write(char[], int, int)},
 * {@link #close()} and {@link #flush()} methods needs to be overridden.
 * Overriding some of the non-abstract methods is also often advised, since it
 * might result in higher efficiency.
 * <p>
 * Many specialized readers for purposes like reading from a file already exist
 * in this package.
 *
 * @see Reader
 */
public abstract class Writer implements Appendable, Closeable, Flushable {
    /**
     * The object used to synchronize access to the writer.
     */
    protected Object lock;

    /**
     * Constructs a new {@code Writer} with {@code this} as the object used to
     * synchronize critical sections.
     */
    protected Writer() {
        lock = this;
    }

    /**
     * Constructs a new {@code Writer} with {@code lock} used to synchronize
     * critical sections.
     *
     * @param lock
     *            the {@code Object} used to synchronize critical sections.
     * @throws NullPointerException
     *             if {@code lock} is {@code null}.
     */
    protected Writer(Object lock) {
        if (lock == null) {
            throw new NullPointerException("lock == null");
        }
        this.lock = lock;
    }

    /**
     * Closes this writer. Implementations of this method should free any
     * resources associated with the writer.
     *
     * @throws IOException
     *             if an error occurs while closing this writer.
     */
    public abstract void close() throws IOException;

    /**
     * Flushes this writer. Implementations of this method should ensure that
     * all buffered characters are written to the target.
     *
     * @throws IOException
     *             if an error occurs while flushing this writer.
     */
    public abstract void flush() throws IOException;

    /**
     * Writes the entire character buffer {@code buf} to the target.
     *
     * @param buf
     *            the non-null array containing characters to write.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     */
    public void write(char[] buf) throws IOException {
        write(buf, 0, buf.length);
    }

    /**
     * Writes {@code count} characters starting at {@code offset} in {@code buf}
     * to the target.
     *
     * @param buf
     *            the non-null character array to write.
     * @param offset
     *            the index of the first character in {@code buf} to write.
     * @param count
     *            the maximum number of characters to write.
     * @throws IndexOutOfBoundsException
     *             if {@code offset < 0} or {@code count < 0}, or if {@code
     *             offset + count} is greater than the size of {@code buf}.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     */
    public abstract void write(char[] buf, int offset, int count) throws IOException;

    /**
     * Writes one character to the target. Only the two least significant bytes
     * of the integer {@code oneChar} are written.
     *
     * @param oneChar
     *            the character to write to the target.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     */
    public void write(int oneChar) throws IOException {
        synchronized (lock) {
            char[] oneCharArray = new char[1];
            oneCharArray[0] = (char) oneChar;
            write(oneCharArray);
        }
    }

    /**
     * Writes the characters from the specified string to the target.
     *
     * @param str
     *            the non-null string containing the characters to write.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     */
    public void write(String str) throws IOException {
        write(str, 0, str.length());
    }

    /**
     * Writes {@code count} characters from {@code str} starting at {@code
     * offset} to the target.
     *
     * @param str
     *            the non-null string containing the characters to write.
     * @param offset
     *            the index of the first character in {@code str} to write.
     * @param count
     *            the number of characters from {@code str} to write.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     * @throws IndexOutOfBoundsException
     *             if {@code offset < 0} or {@code count < 0}, or if {@code
     *             offset + count} is greater than the length of {@code str}.
     */
    public void write(String str, int offset, int count) throws IOException {
        if ((offset | count) < 0 || offset > str.length() - count) {
            throw new StringIndexOutOfBoundsException(str, offset, count);
        }
        char[] buf = new char[count];
        str.getChars(offset, offset + count, buf, 0);
        synchronized (lock) {
            write(buf, 0, buf.length);
        }
    }

    /**
     * Appends the character {@code c} to the target. This method works the same
     * way as {@link #write(int)}.
     *
     * @param c
     *            the character to append to the target stream.
     * @return this writer.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     */
    public Writer append(char c) throws IOException {
        write(c);
        return this;
    }

    /**
     * Appends the character sequence {@code csq} to the target. This method
     * works the same way as {@code Writer.write(csq.toString())}. If {@code
     * csq} is {@code null}, then the string "null" is written to the target
     * stream.
     *
     * @param csq
     *            the character sequence appended to the target.
     * @return this writer.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     */
    public Writer append(CharSequence csq) throws IOException {
        if (csq == null) {
            csq = "null";
        }
        write(csq.toString());
        return this;
    }

    /**
     * Appends a subsequence of the character sequence {@code csq} to the
     * target. This method works the same way as {@code
     * Writer.writer(csq.subsequence(start, end).toString())}. If {@code
     * csq} is {@code null}, then the specified subsequence of the string "null"
     * will be written to the target.
     *
     * @param csq
     *            the character sequence appended to the target.
     * @param start
     *            the index of the first char in the character sequence appended
     *            to the target.
     * @param end
     *            the index of the character following the last character of the
     *            subsequence appended to the target.
     * @return this writer.
     * @throws IOException
     *             if this writer is closed or another I/O error occurs.
     * @throws IndexOutOfBoundsException
     *             if {@code start > end}, {@code start < 0}, {@code end < 0} or
     *             either {@code start} or {@code end} are greater or equal than
     *             the length of {@code csq}.
     */
    public Writer append(CharSequence csq, int start, int end) throws IOException {
        if (csq == null) {
            csq = "null";
        }
        write(csq.subSequence(start, end).toString());
        return this;
    }

    /**
     * Returns true if this writer has encountered and suppressed an error. Used
     * by PrintWriters as an alternative to checked exceptions.
     */
    boolean checkError() {
        return false;
    }
}