3.1.1多线程通讯（等待通知机制）

wait()方法：使当前执行代码的线程等待，当前线程释放锁，在wait处停止执行代码，直到接到通知或被中断。在使用wait前面，线程必须获得太对象的对象锁。

notify方法：唤醒某个处于wait状态线程，使用之前，必须先获得该对象的对象锁，直到执行完同步块代码之后，wait状态的线程才会获得锁。

package test;/** * Created by sunyifeng on 17/10/15. */public class MyThread1 extends Thread {    private Object lock;    public MyThread1(Object lock) {        super();        this.lock = lock;    }    @Override    public void run(){        try {            synchronized (lock) {                System.out.println("开始等待时间：" + System.currentTimeMillis());                lock.wait();                System.out.println("结束等待时间：" + System.currentTimeMillis());            }        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

package test;/** * Created by sunyifeng on 17/10/15. */public class MyThread2 extends Thread {    private Object lock;    public MyThread2(Object lock) {        super();        this.lock = lock;    }    @Override    public void run() {        synchronized (lock) {            System.out.println("开始唤醒时间：" + System.currentTimeMillis());            lock.notify();            System.out.println("结束唤醒时间：" + System.currentTimeMillis());        }    }}

package test;/** * Created by sunyifeng on 17/10/15. */public class Run {    public static void main(String[] args) {        try {            // 锁            Object lock = new Object();            // 线程1            MyThread1 myThread1 = new MyThread1(lock);            myThread1.start();            //            Thread.sleep(3000);            // 线程2            MyThread2 myThread2 = new MyThread2(lock);            myThread2.start();        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

运行结果：

开始等待时间：1508077481913
开始唤醒时间：1508077484918
结束唤醒时间：1508077484919
结束等待时间：1508077484919

总结：wait使线程停止运行，notify使停止的线程继续运行。

再举一个栗子。

package demo;import java.util.List;import java.util.ArrayList;/** * Created by sunyifeng on 17/10/15. */public class MyList {    private static List<String> list = new ArrayList<String>();    public static void add() {        list.add("sunyf");    }    public static int size() {        return list.size();    }}

package demo;/** * Created by sunyifeng on 17/10/15. */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("等待开始，时间：" + System.currentTimeMillis());                    lock.wait();                    System.out.println("等待结束，时间：" + System.currentTimeMillis());                }            }        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

package demo;/** * Created by sunyifeng on 17/10/15. */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("已经发出通知");                    }                    System.out.println("添加了" + (i + 1) + "个元素");                    Thread.sleep(1000);                }            }        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

package demo;/** * Created by sunyifeng on 17/10/15. */public class Run {    public static void main(String[] args) {        try {            Object lock = new Object();            //            ThreadA threadA = new ThreadA(lock);            threadA.setName("A");            threadA.start();            //            Thread.sleep(1000);            //            ThreadB threadB = new ThreadB(lock);            threadB.setName("B");            threadB.start();        } catch (InterruptedException e) {            e.printStackTrace();        }    }}

运行结果：

等待开始，时间：1508079281022
添加了1个元素
添加了2个元素
添加了3个元素
添加了4个元素
已经发出通知
添加了5个元素
添加了6个元素
添加了7个元素
添加了8个元素
添加了9个元素
添加了10个元素
等待结束，时间：1508079292058

程序说明：notify方法执行之后并不是立即释放锁，直到同步块的代码执行完才释放锁。