java 线程 sleep 与 wait 的区别

java 线程 Thread 类的sleep 静态方法可以让当前线程睡眠（如果该线程持有某一对象的锁，sleep 时不会释放该锁。如果该线程没有拥有对象锁，则sleep 也不会锁定某一对象）。

而wait 方法也能够阻塞线程，让其睡眠一段时间或等待其它线程唤醒，不过，在调用wait 方法进入睡眠的时候，如果该线程拥有某一个对象锁，则在该线程进入睡眠时会释放该线程拥有的对象锁。


参考示例：

/**
 * 测试sleep 方法与 wait 方法的区别
 */
class Task implements Runnable{
	private int time = 0;
	public void run(){
		fun1();
	}
	
	public synchronized void fun1(){
		System.out.println(Thread.currentThread().getName()+ " start running time "+ time);	
	}
	
	public synchronized void fun2(){
		try{
				System.out.println(Thread.currentThread().getName()+ " start running time "+ time);
		//		Thread.sleep(3000);
				wait(3000);
				time += 3;
			  System.out.println(Thread.currentThread().getName()+ " end running time "+ time);
				}catch(Exception e){
					e.printStackTrace();
				}
	}
}

public class ThreadTest{
	public static void main(String[] args){
		Task task = new Task();
		Thread thread = new Thread(task);
		thread.start();
		task.fun2();
	}
}

运行结果：
main start running time 0
Thread-0 start running time 0
main end running time 3

改换成Thread.sleep

/**
 * 测试sleep 方法与 wait 方法的区别
 */
class Task implements Runnable{
	private int time = 0;
	public void run(){
		fun1();
	}
	
	public synchronized void fun1(){
		System.out.println(Thread.currentThread().getName()+ " start running time "+ time);	
	}
	
	public synchronized void fun2(){
		try{
				System.out.println(Thread.currentThread().getName()+ " start running time "+ time);
		//		Thread.sleep(3000);
				wait(3000);
				time += 3;
			  System.out.println(Thread.currentThread().getName()+ " end running time "+ time);
				}catch(Exception e){
					e.printStackTrace();
				}
	}
}

public class ThreadTest{
	public static void main(String[] args){
		Task task = new Task();
		Thread thread = new Thread(task);
		thread.start();
		task.fun2();
	}
}

运行结果：

main start running time 0
main end running time 3
Thread-0 start running time 3

但是如果把fun1 换成 静态方法，

/**
 * 测试sleep 方法与 wait 方法的区别
 */
class Task implements Runnable{
	private static int time = 0;
	public void run(){
		fun1();
	}
	
	public static synchronized void fun1(){
		System.out.println(Thread.currentThread().getName()+ " start running time "+ time);	
	}
	
	public synchronized void fun2(){
		try{
				System.out.println(Thread.currentThread().getName()+ " start running time "+ time);
				Thread.sleep(3000);
		//		wait(3000);
				time += 3;
			  System.out.println(Thread.currentThread().getName()+ " end running time "+ time);
				}catch(Exception e){
					e.printStackTrace();
				}
	}
}

public class ThreadTest{
	public static void main(String[] args){
		Task task = new Task();
		Thread thread = new Thread(task);
		thread.start();
		task.fun2();
	}
}

运行结果为：
main start running time 0
Thread-0 start running time 0
main end running time 3

这是因为当方法为静态时，线程锁定的是Task类对应的Class类的对象的锁，而Thread.sleep 锁定的是Task类的对象,是两个不同的对象锁，所以有以上结果。