writer.java

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/*
 * @(#)Writer.java	1.27 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.io;


/**
 * Abstract class for writing to character streams.  The only methods that a
 * subclass must implement are write(char[], int, int), flush(), and close().
 * Most subclasses, however, will override some of the methods defined here in
 * order to provide higher efficiency, additional functionality, or both.
 *
 * @see Writer
 * @see   BufferedWriter
 * @see   CharArrayWriter
 * @see   FilterWriter
 * @see   OutputStreamWriter
 * @see     FileWriter
 * @see   PipedWriter
 * @see   PrintWriter
 * @see Reader
 *
 * @version 	1.20, 00/05/03
 * @author	Mark Reinhold
 * @since	JDK1.1
 */

public abstract class Writer {

    /**
     * Temporary buffer used to hold writes of strings and single characters
     */
    private char[] writeBuffer;

    /**
     * Size of writeBuffer, must be >= 1
     */
    private final int writeBufferSize = 1024;

    /**
     * The object used to synchronize operations on this stream.  For
     * efficiency, a character-stream object may use an object other than
     * itself to protect critical sections.  A subclass should therefore use
     * the object in this field rather than <tt>this</tt> or a synchronized
     * method.
     */
    protected Object lock;

    /**
     * Create a new character-stream writer whose critical sections will
     * synchronize on the writer itself.
     */
    protected Writer() {
	this.lock = this;
    }

    /**
     * Create a new character-stream writer whose critical sections will
     * synchronize on the given object.
     *
     * @param lock  Object to synchronize on.
     */
    protected Writer(Object lock) {
	if (lock == null) {
	    throw new NullPointerException();
	}
	this.lock = lock;
    }

    /**
     * Write a single character.  The character to be written is contained in
     * the 16 low-order bits of the given integer value; the 16 high-order bits
     * are ignored.
     *
     * <p> Subclasses that intend to support efficient single-character output
     * should override this method.
     *
     * @param c  int specifying a character to be written.
     * @exception  IOException  If an I/O error occurs
     */
    public void write(int c) throws IOException {
	synchronized (lock) {
	    if (writeBuffer == null){
		writeBuffer = new char[writeBufferSize];
	    }
	    writeBuffer[0] = (char) c;
	    write(writeBuffer, 0, 1);
	}
    }

    /**
     * Write an array of characters.
     *
     * @param  cbuf  Array of characters to be written
     * 
     * @exception  IOException  If an I/O error occurs
     */
    public void write(char cbuf[]) throws IOException {
	write(cbuf, 0, cbuf.length);
    }

    /**
     * Write a portion of an array of characters.
     *
     * @param  cbuf  Array of characters
     * @param  off   Offset from which to start writing characters
     * @param  len   Number of characters to write
     *
     * @exception  IOException  If an I/O error occurs
     */
    abstract public void write(char cbuf[], int off, int len) throws IOException;

    /**
     * Write a string.
     *
     * @param  str  String to be written
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void write(String str) throws IOException {
	write(str, 0, str.length());
    }

    /**
     * Write a portion of a string.
     *
     * @param  str  A String
     * @param  off  Offset from which to start writing characters
     * @param  len  Number of characters to write
     *
     * @exception  IOException  If an I/O error occurs
     */
    public void write(String str, int off, int len) throws IOException {
	synchronized (lock) {
	    char cbuf[];
	    if (len <= writeBufferSize) {
		if (writeBuffer == null) {
		    writeBuffer = new char[writeBufferSize];
		}
		cbuf = writeBuffer;
	    } else {	// Don't permanently allocate very large buffers.
		cbuf = new char[len];
	    }
	    str.getChars(off, (off + len), cbuf, 0);
	    write(cbuf, 0, len);
	}
    }

    /**
     * Flush the stream.  If the stream has saved any characters from the
     * various write() methods in a buffer, write them immediately to their
     * intended destination.  Then, if that destination is another character or
     * byte stream, flush it.  Thus one flush() invocation will flush all the
     * buffers in a chain of Writers and OutputStreams.
     *
     * @exception  IOException  If an I/O error occurs
     */
    abstract public void flush() throws IOException;

    /**
     * Close the stream, flushing it first.  Once a stream has been closed,
     * further write() or flush() invocations will cause an IOException to be
     * thrown.  Closing a previously-closed stream, however, has no effect.
     *
     * @exception  IOException  If an I/O error occurs
     */
    abstract public void close() throws IOException;

}