【Java多线程】等待通知机制（一）为什么要使用等待通知机制

迈不过友情╰ 2022-03-16 05:16 255阅读 0赞

先看以下代码：

## MyList.class ##

public class MyList {
        private List list = new ArrayList();
        public void add(){
            list.add("俞育峰");
        }
        public int size(){
            return list.size();
        }
    }

## ThreadA.class ##

public class ThreadA extends Thread{
        private MyList list;
    
        public ThreadA(MyList list) {
            this.list = list;
        }
    
        @Override
        public void run() {
            super.run();
            try {
                for (int i = 0; i < 10; i++) {
                    list.add();
                    System.out.println("添加了"+(i+1)+"个元素");
                    Thread.sleep(1000);
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

## ThreadB.class ##

public class ThreadB extends Thread {
        private MyList list;
    
        public ThreadB(MyList list) {
            this.list = list;
        }
    
        @Override
        public void run() {
            super.run();
            try {
                while (true) {
                    if (list.size() == 5) {
                        System.out.println("list==5,线程B要退出了");
                        throw new InterruptedException();
                    }
                    Thread.sleep(100);
    //                System.out.println(list.size());
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

## AppTest.class ##

public class AppTest {
        public static void main(String[] args) {
            MyList service = new MyList();
            ThreadA a = new ThreadA(service);
            a.setName("A");
            a.start();
            ThreadB b = new ThreadB(service);
            b.setName("B");
            b.start();
        }
    }

从以上代码中我们可以看到ThreadA与ThreadB之间实现了通信，但是ThreadB一直在不断的监听，而且如果间隔的时间太短，很浪费CPU性能，如果间隔时间太长，数据又会读取不准确。所以我们需要线程的等待通知机制。