public final class ReadWriteLock {
    private int readingReaders = 0; // (A)...实际正在读取的执行绪数量
    private int waitingWriters = 0; // (B)...正在等待写入的执行绪数量
    private int writingWriters = 0; // (C)...实际正在写入的执行绪数量
    private boolean preferWriter = true; // 写入优先的话，值为true

    public synchronized void readLock() throws InterruptedException {
        while (writingWriters > 0 || (preferWriter && waitingWriters > 0)) {
            wait();
        }
        readingReaders++;                       //  (A)实际正在读取的线程数量加1
    }

    public synchronized void readUnlock() {
        readingReaders--;                       //  (A)实际正在读取的线程数量减1
        preferWriter = true;
        notifyAll();
    }

    public synchronized void writeLock() throws InterruptedException {
        waitingWriters++;                       // (B)正在等待写入的线程数量加1
        try {
            while (readingReaders > 0 || writingWriters > 0) {
                wait();
            }
        } finally {1
          waitingWriters--;                   // (B)正在等待写入的线程数量减1
        }
        writingWriters++;                       //  (C)实际正在写入的线程数量加1
    }

    public synchronized void writeUnlock() {
        writingWriters--;                       // (C)实际正在写入的线程数量减
        preferWriter = false;
        notifyAll();
    }
}
// 数据类
public class Data {
    private final char[] buffer;
    private final ReadWriteLock lock = new ReadWriteLock();
    public Data(int size) {
        this.buffer = new char[size];
        for (int i = 0; i < buffer.length; i++) {
            buffer[i] = '*';
        }
    }
    public char[] read() throws InterruptedException {
        lock.readLock();
        try {
            return doRead();
        } finally {
            lock.readUnlock();
        }
    }
    public void write(char c) throws InterruptedException {
        lock.writeLock();
        try {
            doWrite(c);
        } finally {
            lock.writeUnlock();
        }
    }
    private char[] doRead() {
        char[] newbuf = new char[buffer.length];
        for (int i = 0; i < buffer.length; i++) {
            newbuf[i] = buffer[i];
        }
        slowly();
        return newbuf;
    }
    private void doWrite(char c) {
        for (int i = 0; i < buffer.length; i++) {
            buffer[i] = c;
            slowly();
        }
    }
    private void slowly() {
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
        }
    }
}