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關(guān)于notify()和notifyAll()方法的用法與區(qū)別

更新時(shí)間：2026年04月03日 08:38:48 作者：撞撞～

本文詳細(xì)解釋了Java中`notify()`和`notifyAll()`的區(qū)別,前者喚醒一個(gè)等待線程,后者喚醒所有等待線程,并提供了示例代碼,展示了`notify()`和`notifyAll()`在實(shí)際使用中的效果

一、區(qū)別

notify()和notifyAll()都是用來用來喚醒調(diào)用wait(）方法進(jìn)入等待鎖資源隊(duì)列的線程，區(qū)別在于：

notify()

喚醒正在等待此對象監(jiān)視器的單個(gè)線程。
如果有多個(gè)線程在等待，則選擇其中一個(gè)隨機(jī)喚醒（由調(diào)度器決定），喚醒的線程享有公平競爭資源的權(quán)利

notifyAll()

喚醒正在等待此對象監(jiān)視器的所有線程，喚醒的所有線程公平競爭資源

二、示例

notify()

public class ThreadDemo implements Runnable{
	static Object lock = new Object();

	public static void main(String[] args) {
		Thread thread1 = new Thread(new ThreadDemo(), "Thread-a");
		Thread thread2 = new Thread(new ThreadDemo(), "Thread-b");
		thread1.start();
		thread2.start();
		try {
			TimeUnit.SECONDS.sleep(1); // 睡會(huì),讓走到子線程
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		synchronized (lock) {
			System.out.println(Thread.currentThread().getName() + " 獲得了鎖");
			System.out.println("notify前" + thread1.getName() + "狀態(tài)是" + thread1.getState());
			System.out.println("notify前" + thread2.getName() + "狀態(tài)是 " + thread2.getState());
			lock.notify(); // 喚醒一個(gè)等待lock鎖的線程
		}
		try {
			TimeUnit.MILLISECONDS.sleep(300); // 睡會(huì),讓被喚醒的子線程走完
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("notify后" + thread1.getName() + "狀態(tài)是" + thread1.getState());
		System.out.println("notify后" + thread2.getName() + "狀態(tài)是" + thread2.getState());
	}

	@Override
	public void run() {
		synchronized (lock) {
			System.out.println(Thread.currentThread().getName() + " 獲得了鎖");
			try {
				lock.wait(); // 等待被喚醒
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(Thread.currentThread().getName() + " end");
		}
	}
}

結(jié)果：

可以看到，子線程在wait()后釋放了鎖并進(jìn)入WAITTINT狀態(tài)，主線程獲得鎖后調(diào)用notify()，這時(shí)候其中一個(gè)線程(栗子中是Thread-b，也有可能是a)被喚醒并獲取到鎖繼續(xù)執(zhí)行到TERMINATED，而另一個(gè)線程a一直WAITTINT狀態(tài)

Thread-b 獲得了鎖
Thread-a 獲得了鎖
main 獲得了鎖
notify前Thread-a狀態(tài)是WAITING
notify前Thread-b狀態(tài)是 WAITING
Thread-b end
notify后Thread-a狀態(tài)是WAITING
notify后Thread-b狀態(tài)是TERMINATED

notifyAll()

上面的栗子如果使用notifyAll()，看下結(jié)果

public class ThreadDemo implements Runnable{
	static Object lock = new Object();

	public static void main(String[] args) {
		Thread thread1 = new Thread(new ThreadDemo(), "Thread-a");
		Thread thread2 = new Thread(new ThreadDemo(), "Thread-b");
		thread1.start();
		thread2.start();
		try {
			TimeUnit.SECONDS.sleep(1); // 睡會(huì),讓走到子線程
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("哈哈哈哈");
		synchronized (lock) {
			System.out.println(Thread.currentThread().getName() + " 獲得了鎖");
			System.out.println("notify前" + thread1.getName() + "狀態(tài)是" + thread1.getState());
			System.out.println("notify前" + thread2.getName() + "狀態(tài)是 " + thread2.getState());
			lock.notifyAll(); // 喚醒所有等待lock鎖的線程
		}
		try {
			TimeUnit.MILLISECONDS.sleep(300); // 睡會(huì),讓被喚醒的子線程走完
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		System.out.println("notify后" + thread1.getName() + "狀態(tài)是" + thread1.getState());
		System.out.println("notify后" + thread2.getName() + "狀態(tài)是" + thread2.getState());
	}

	@Override
	public void run() {
		synchronized (lock) {
			System.out.println(Thread.currentThread().getName() + " 獲得了鎖");
			try {
				lock.wait(); // 等待被喚醒
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(Thread.currentThread().getName() + " end");
		}
	}
}

結(jié)果，可以看到所有子線程都被喚醒并再次公平競爭鎖直到線程終止

Thread-b 獲得了鎖
Thread-a 獲得了鎖
哈哈哈哈
main 獲得了鎖
notify前Thread-a狀態(tài)是WAITING
notify前Thread-b狀態(tài)是 WAITING
Thread-a end
Thread-b end
notify后Thread-a狀態(tài)是TERMINATED
notify后Thread-b狀態(tài)是TERMINATED