ReentrantReadWriteLock

创建ReentrantReadWriteLock对象
private ReentrantReadWriteLock rrw= new ReentrantReadWriteLock();

创建读锁和写锁：
private Lock readLock = rrw.readlock();
private Lock writeLock = rrw.writelock();

对写程序加锁：
public double set()
{
    writeLock.lock();
    try{  doSomething(); }
    finally{  writeLock.unlock();  }
}

对读程序加锁
public double set()
{
    readLock.lock();
    try{  doSomething();  }
    finally{ readLock.unlock();  }
}