Java wait和notify结合使用

1、代码示例

public class TestSyncro2 {

    public static void main(String[] args) {
        final Customer customer = new Customer();

        Thread t1 = new Thread(new Runnable() {

            @Override
            public void run() {
                customer.withdraw(15000);
            }
        });

        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                customer.deposit(10000);
            }
        });

        t1.start();
        t2.start();
    }
}


class Customer{
    private int amount = 10000;
    public synchronized void withdraw(int amount){  
        System.out.println("withdraw start....");
        if(this.amount < amount){
            System.out.println("less for withdraw, waiting for deposit...");
            try {
                this.wait();   // 释放对象锁,并进入等待状态,直到另一个线程notify
            } catch(Exception ex){

            }
        }

        this.amount -= amount;
        System.out.println(Thread.currentThread().getName()  + " print " + this.amount);
        System.out.println("withdraw end....");
    }

    public synchronized void deposit(int amount){
        System.out.println("deposit start....");

        this.amount += amount;
        System.out.println(Thread.currentThread().getName()  + " print " + this.amount);
        this.notify(); // 随机唤醒一个等待此对象锁的线程,但是由于当前线程还没有释放锁,被唤醒的线程还不能立即获得对象锁而执行

        try {
            Thread.sleep(2000);  // 测试被唤醒线程不能立即获得对象锁
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("deposit end....");
    } 
}

2、执行结果

withdraw start....
less for withdraw, waiting for deposit...
deposit start....
Thread-1 print 20000
deposit end....
Thread-0 print 5000
withdraw end....

3、结论

（1）wait会释放对象锁,并进入等待状态,直到另一个线程notify
（2）notify一次只随机通知一个线程进行唤醒，在执行了notify方法之后，当前线程不会马上释放该对象锁，呈wait状态的线程也不能马上获得该对象锁，要等到执行notify方法的线程将程序执行完 ，也就是退出sychronized代码块后，当前线程才会释放锁，处于wait状态的线程才可以获取该对象锁