writer.java

已经移植好的java虚拟机

/*
 * Copyright 1996-2002 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */

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   OutputStreamWriter
 * @see Reader
 *
 * @version     1.18, 99/12/04 (CLDC 1.0, Spring 2000)
 * @author      Mark Reinhold
 * @since       JDK1.1, CLDC 1.0
 */

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;

}