leetcode1114.按序打印

题目

示例

方法一：synchronize+wait/notifyAll

具体代码

class Foo {
    private int flag = 1;
    private Object lock = new Object();
    public Foo() {
        
    }

    public void first(Runnable printFirst) throws InterruptedException {
        synchronized(lock){
            while(flag != 1){
                lock.wait();
            }
        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run();
        flag = 2;
        lock.notifyAll();
        }
    }

    public void second(Runnable printSecond) throws InterruptedException {
        synchronized(lock){
            while(flag != 2){
                lock.wait();
            }
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        flag = 3;
        lock.notifyAll();
        }
    }

    public void third(Runnable printThird) throws InterruptedException {
        synchronized(lock){
            while(flag != 3){
                lock.wait();
            }
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
        flag = 1;
        lock.notifyAll();
    }
    }
}

方法二：CountDownLatch

class Foo {
    final CountDownLatch latch1 = new CountDownLatch(1);
    final CountDownLatch latch2 = new CountDownLatch(1);
    public Foo() {
        
    }

    public void first(Runnable printFirst) throws InterruptedException {
        
        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run();
        latch1.countDown();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        latch1.await();
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        latch2.countDown();
    }

    public void third(Runnable printThird) throws InterruptedException {
        
        latch2.await();
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
    }
}

方法三：Semaphore

class Foo {
    Semaphore semaphore1 = new Semaphore(0);
    Semaphore semaphore2 = new Semaphore(0);
    public Foo() {
        
    }

    public void first(Runnable printFirst) throws InterruptedException {
        
        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run();
        semaphore1.release();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        semaphore1.acquire();
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        semaphore2.release();
    }

    public void third(Runnable printThird) throws InterruptedException {
        semaphore2.acquire();
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
    }
}