ReentrantReadWriteLock 允许多个读操作同时进行，但是只允许一个写操作同时进行，在某些情况下，可以实现更高的并发性。

举个栗子：

public class ReadAndWriteLockTest {
    static {
        System.out.println("static "+Thread.currentThread().isDaemon());
    }

    public static void main(String[] args) {
        //或者等所有的非守护线程结束后JVM终止运行
        System.out.println(Thread.currentThread().isDaemon());

        final Queue3 q3 = new Queue3();
        for (int i=0; i<3; i++) {
            new Thread(()->{
                while(true){
                    q3.get();
                }
            }).start();
        }

        for (int i=0;i<3;i++) {
            new Thread(()->{
                while(true){
                    q3.put(new Random().nextInt(10000));
                }
            }).start();
        }
    }
}

class Queue3 {
    /**共享数据，只能有一个线程能写该数据，但可以有多个线程同时读该数据*/
    private Object data = null;
    private ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
    public void get(){
        //上读锁，其他线程只能读不能写
        rwl.readLock().lock();
        System.out.println(Thread.currentThread().getName() + " be ready to read data!");
        try {
            Thread.sleep((long)(Math.random()*1000));
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            //释放读锁
            rwl.readLock().unlock();
        }
        System.out.println(Thread.currentThread().getName() + "have read data :" + data);
    }

    public void put(Object data){
        //上写锁，不允许其他线程读也不允许写
        rwl.writeLock().lock();
        System.out.println(Thread.currentThread().getName() + " be ready to write data!");
        try {
            Thread.sleep((long)(Math.random()*1000));
            this.data = data;
            System.out.println(Thread.currentThread().getName() + " have write data: " + data);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            //释放写锁
            rwl.writeLock().unlock();
        }
    }
}