LeetCode12-多线程之按序打印

题目如图：

第一种解法(信号量)

import java.util.concurrent.Semaphore;
class Foo {
    public Semaphore Semaphore_one=new Semaphore(0);
    public Semaphore Semaphore_two=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();
        Semaphore_one.release();
    }

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

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

countdownlatch

class Foo {
    private CountDownLatch c2;
    private CountDownLatch c3;
    public Foo() {
         c2 = new CountDownLatch(1);
         c3 = new CountDownLatch(1);
    }
    
    public void first(Runnable printFirst) throws InterruptedException {
        
        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run();
        c2.countDown();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        c2.await();
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        c3.countDown();
    }

    public void third(Runnable printThird) throws InterruptedException {
        c3.await();
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
    }
}