java多线程之wait、notify和notifyAll

wait、notify和notify是Object类的3个final方法，这三个方法可以实现线程间的通信。在线程中调用Object的wait方法，将阻塞当前线程等待其它线程的通知，通知使用notify或notifyAll方法。当其它线程中调用了Object的notify或notifyAll方法后，将通知调用wait方法的线程继续执行wait后的代码。

下边的例子有两个waiter和一个notifier，waiter先输出message的content，然后调用message的wait方法阻塞当前线程，然后notifer被调用，修改message的content，再调用notify或notifyAll方法，此时waiter被唤醒，输出notifer修改后的message content。

class Message {private String content;public Message(String content) {this.content = content;}public void setContent(String content) {this.content = content;}public String getContent() {return this.content;}}class Waiter implements Runnable {private Message message;public Waiter(Message message) {this.message = message;}@Overridepublic void run() {String threadName = Thread.currentThread().getName();synchronized(message) {System.out.println(threadName + "输出message.content：" + message.getContent());System.out.println(threadName + "正在运行，现在执行wait方法。");try {message.wait();} catch (InterruptedException e) {e.printStackTrace();}System.out.println(threadName + "被重新唤醒，继续执行。");System.out.println(threadName + "输出message.content：" + message.getContent());System.out.println(threadName + "执行完成！");}}}class Notifier implements Runnable {private Message message;public Notifier(Message message) {this.message = message;}@Overridepublic void run() {String threadName = Thread.currentThread().getName();System.out.println(threadName + "正在运行，等待执行notify/notifyAll方法。");synchronized(message) {message.setContent(threadName + "修改了content");System.out.println(threadName + "执行notify方法");//message.notify();//调用notify()，只有一个waiter会被唤醒然后执行完成。message.notifyAll();//所有waiter都会被唤醒并执行完成。}}}public class WaitAndNotifyDemo {public static void main(String[] args) {Message message = new Message("一个新的Message");Waiter w1 = new Waiter(message);new Thread(w1, "waiter1").start();Waiter w2 = new Waiter(message);new Thread(w2, "waiter2").start();Notifier n1 = new Notifier(message);new Thread(n1, "notifier1").start();}}