java多執行緒間的通訊

wait/notify
1.wait 方法是釋放鎖，notify 方法是不釋放鎖的
2.notify 每次喚醒 wait 等待狀態的執行緒都是隨機的，且每次只喚醒一個。

public class MyList {

    private static List list = new ArrayList();

    public static void add() {
        list.add("我是元素");
    }

    public static int size() {
        return list.size();
    }
}

public class ThreadA extends Thread {

    private Object lock;

    public ThreadA(Object lock) {
        super();
        this.lock = lock;
    }

    @Override
    public void run() {
        try {
            synchronized (lock) {
                if (MyList.size() != 5) {
                    System.out.println("wait begin " + System.currentTimeMillis());
                    lock.wait();
                    System.out.println("wait end  " + System.currentTimeMillis());
                }
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class ThreadB extends Thread {

    private Object lock;

    public ThreadB(Object lock) {
        super();
        this.lock = lock;
    }

    @Override
    public void run() {
        try {
            synchronized (lock) {
                for (int i = 0; i < 10; i++) {
                    MyList.add();
                    if (MyList.size() == 5) {
                        lock.notify();
                        System.out.println("已發出通知！");
                    }
                    System.out.println("新增了" + (i + 1) + "個元素!");
                    Thread.sleep(1000);
                }
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

public class Run {

    public static void main(String[] args) {
        try {
            Object lock = new Object();
            ThreadA a = new ThreadA(lock);
            a.start();
            Thread.sleep(50);
            ThreadB b = new ThreadB(lock);
            b.start();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

wait begin 1545373376331
新增了1個元素!
新增了2個元素!
新增了3個元素!
新增了4個元素!
已發出通知！
新增了5個元素!
新增了6個元素!
新增了7個元素!
新增了8個元素!
新增了9個元素!
新增了10個元素!
wait end  1545373386385