一个读写锁的例子
用的比较少, 做一个参考. 原文在这里

public class Calculator {    private int calculatedValue;    private int value;    private ReadWriteLock lock = new ReentrantReadWriteLock();     public void calculate(int value) {        lock.writeLock().lock();        try {            this.value = value;            this.calculatedValue = doMySlowCalculation(value);        } finally {            lock.writeLock().unlock();        }    }     public int getCalculatedValue() {        lock.readLock().lock();        try {            return calculatedValue;        } finally {            lock.readLock().unlock();        }    }     public int getValue() {        lock.readLock().lock();        try {            return value;        } finally {            lock.readLock().unlock();        }    }}