sleep和wait的应用

在面试中经常性的遇到wait和sleep的区别？

1.sleep不会释放锁 ，而wait会释放锁 

private static final String LOCK = "lock"; public static void main(String[] args) { new Thread(() -> { System.out.println(Thread.currentThread().getName() + "====start"); test(); System.out.println(Thread.currentThread().getName() + "====end"); }).start(); new Thread(() -> { System.out.println(Thread.currentThread().getName() + "====start"); test(); System.out.println(Thread.currentThread().getName() + "=====end"); }).start(); } public static void test() { synchronized (LOCK) { System.out.println(Thread.currentThread().getName() + "====getLock" + System.currentTimeMillis()); try { LOCK.wait(5000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "====unLock" + +System.currentTimeMillis()); } } Thread-0====start Thread-0====getLock1603173719697 Thread-1====start Thread-1====getLock1603173719697 Thread-1====unLock1603173724698 Thread-1=====end Thread-0====unLock1603173724698 Thread-0====end private static final String LOCK = "lock"; public static void main(String[] args) { new Thread(() -> { System.out.println(Thread.currentThread().getName() + "====start"); test(); System.out.println(Thread.currentThread().getName() + "====end"); }).start(); new Thread(() -> { System.out.println(Thread.currentThread().getName() + "====start"); test(); System.out.println(Thread.currentThread().getName() + "=====end"); }).start(); } public static void test() { synchronized (LOCK) { System.out.println(Thread.currentThread().getName() + "====getLock" + System.currentTimeMillis()); try { Thread.sleep(4321L); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "====unLock" + +System.currentTimeMillis()); } } Thread-0====start Thread-1====start Thread-1====getLock1603173961122 Thread-1====unLock1603173965444 Thread-1=====end Thread-0====getLock1603173965444 Thread-0====unLock1603173969765 Thread-0====end

2.由上面的代码 我们发现sleep方法是通过Thead的静态方法 而wait是Object对象的方法

 

3.我们将同步块去掉 会发现sleep方法会正常使用，而wait方法会出错（wait必须依赖同步块）

public static void test() { System.out.println(Thread.currentThread().getName() + "====getLock" + System.currentTimeMillis()); try { LOCK.wait(1000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println(Thread.currentThread().getName() + "====unLock" + +System.currentTimeMillis()); } Thread-0====start Thread-1====start Thread-1====getLock1603174303023 Thread-0====getLock1603174303023 Exception in thread "Thread-1" Exception in thread "Thread-0" java.lang.IllegalMonitorStateException at java.lang.Object.wait(Native Method) at com.zexiang.java.sync.reentrantsync.T.test(T.java:31) at com.zexiang.java.sync.reentrantsync.T.lambda$main$0(T.java:17) at java.lang.Thread.run(Thread.java:745) java.lang.IllegalMonitorStateException at java.lang.Object.wait(Native Method) at com.zexiang.java.sync.reentrantsync.T.test(T.java:31) at com.zexiang.java.sync.reentrantsync.T.lambda$main$1(T.java:22) at java.lang.Thread.run(Thread.java:745)

4.sleep必须设置时间 而wait则可以都可以 。如果不给时间参数必须要唤醒LOCK.notify();

Thread.sleep(1000); LOCK.wait(1000); LOCK.wait();