简单的实现---->让多线程按照顺序执行

需求是这样的

两个线程执行任务，但是有要求，必须是A执行完毕 再执行B 交叉执行!

先上代码:

(改造前)

public class Fangzh {
    private int n;
    public Fangzh(int n) {
        this.n = n;
    }
    public void eat(){
    for (int i = 0; i < n; i++) {
        System.out.println("吃饭");
     }
    }
    public void sleep()  {
        for (int i = 0; i < n; i++) {
        System.out.println("睡觉");
      }
    }
 }

 public static void main(String[] args) {
    Fangzh fooBar = new Fangzh(5);
    new Thread(()->{fooBar.eat();}).start();
    new Thread(()->{fooBar.sleep();}).start();
}

输出结果：

这有问题啊！

改造后

public class Fangzh {
    Semaphore eat = new Semaphore(1, true);
    Semaphore sleep = new Semaphore(0, true);
    int n =0;
    public Fangzh(int n) {
        this.n = n;
    }

    public void eat(){
    for (int i = 0; i < n; i++) {

        try {
            eat.acquire();
            System.out.println("吃饭");
            sleep.release();
        }catch (Exception e){
            e.printStackTrace();
        }
     }

    }
    public void sleep()  {
        for (int i = 0; i < n; i++) {
            try {
                sleep.acquire();
                System.out.println("睡觉");
                eat.release();
            }catch (Exception e){
                e.printStackTrace();
            }
        }
      }

    public static void main(String[] args) {
        Fangzh fooBar = new Fangzh(5);
        new Thread(()->{
            fooBar.eat();
        }).start();

        new Thread(()->{
            fooBar.sleep();
        }).start();

    }

##知识点 Semaphore