Writer

public abstract class Writer implements Appendable, Closeable, Flushable {

	//临时的缓冲，用于存储单个字符或字符串
	private char[] writeBuffer;

	private final int writeBufferSize = 1024;

	//用于同步操作
	protected Object lock;

	protected Writer() {
		this.lock = this;
	}

	protected Writer(Object lock) {
		if (lock == null) {
			throw new NullPointerException();
		}
		this.lock = lock;
	}

	//写一个字符，int是32位的，把低的16位写进去，高的16位被忽略
	public void write(int c) throws IOException {
		synchronized (lock) {
			if (writeBuffer == null) {
				writeBuffer = new char[writeBufferSize];
			}
			writeBuffer[0] = (char) c;
			write(writeBuffer, 0, 1);
		}
	}
	
	//抽象方法
	abstract public void write(char cbuf[], int off, int len)
			throws IOException;

	public void write(char cbuf[]) throws IOException {
		write(cbuf, 0, cbuf.length);
	}

	public void write(String str) throws IOException {
		write(str, 0, str.length());
	}

	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);
		}
	}

	public Writer append(CharSequence csq) throws IOException {
		if (csq == null)
			write("null");
		else
			write(csq.toString());
		return this;
	}
	
	public Writer append(CharSequence csq, int start, int end)
			throws IOException {
		CharSequence cs = (csq == null ? "null" : csq);
		write(cs.subSequence(start, end).toString());
		return this;
	}

	public Writer append(char c) throws IOException {
		write(c);
		return this;
	}

	abstract public void flush() throws IOException;

	abstract public void close() throws IOException;

}