Detailed explanation of the difference between sleep() and wait() in Java

This article mainly introduces the relevant information that explains the difference between sleep() and wait() in Java. I hope this article can help everyone. Friends in need can refer to the detailed explanation

The difference between sleep() and wait() in Java

For the sleep() method, we must first know that this method belongs to the Thread class. The wait() method belongs to the Object class.

The sleep() method causes the program to suspend execution for the specified time and give up the CPU to other threads, but its monitoring status is still maintained. When the specified time is up, it will automatically resume running status.

During the process of calling the sleep() method, the thread will not release the object lock.

When the wait() method is called, the thread will give up the object lock and enter the waiting lock pool waiting for this object. Only after the notify() method is called for this object, the thread will enter the object lock pool preparation

Get the object lock and enter the running state.

What does that mean?

Give an example:

/**
 * 
 */
package com.b510.test;

/**
 * java中的sleep()和wait()的区别
 * @author Hongten Java学习交流QQ群：589809992 我们一起学Java！
 * @date 2013-12-10
 */
public class TestD {

  public static void main(String[] args) {
    new Thread(new Thread1()).start();
    try {
      Thread.sleep(5000);
    } catch (Exception e) {
      e.printStackTrace();
    }
    new Thread(new Thread2()).start();
  }

  private static class Thread1 implements Runnable{
    @Override
    public void run(){
      synchronized (TestD.class) {
      System.out.println("enter thread1...");  
      System.out.println("thread1 is waiting...");
      try {
        //调用wait()方法，线程会放弃对象锁，进入等待此对象的等待锁定池
        TestD.class.wait();
      } catch (Exception e) {
        e.printStackTrace();
      }
      System.out.println("thread1 is going on ....");
      System.out.println("thread1 is over!!!");
      }
    }
  }

  private static class Thread2 implements Runnable{
    @Override
    public void run(){
      synchronized (TestD.class) {
        System.out.println("enter thread2....");
        System.out.println("thread2 is sleep....");
        //只有针对此对象调用notify()方法后本线程才进入对象锁定池准备获取对象锁进入运行状态。
        TestD.class.notify();
        //==================
        //区别
        //如果我们把代码：TestD.class.notify();给注释掉，即TestD.class调用了wait()方法，但是没有调用notify()
        //方法，则线程永远处于挂起状态。
        try {
          //sleep()方法导致了程序暂停执行指定的时间，让出cpu该其他线程，
          //但是他的监控状态依然保持者，当指定的时间到了又会自动恢复运行状态。
          //在调用sleep()方法的过程中，线程不会释放对象锁。
          Thread.sleep(5000);
        } catch (Exception e) {
          e.printStackTrace();
        }
        System.out.println("thread2 is going on....");
        System.out.println("thread2 is over!!!");
      }
    }
  }
}

Running effect:

enter thread1...
thread1 is waiting...
enter thread2....
thread2 is sleep....
thread2 is going on....
thread2 is over!!!
thread1 is going on ....
thread1 is over!!!

If you comment out the code :

1 TestD.class.notify();

Running effect:

enter thread1...
thread1 is waiting...
enter thread2....
thread2 is sleep....
thread2 is going on....
thread2 is over!!!

and the program is always in a suspended state.

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