Java多线程wait,notify实例

package com.lj.thread2;

public class Sample  
{
	private int number;

	// 实现number加1
	public synchronized void increase()
	{
		while (0 != number)
		{
			try
			{
				wait();
			}
			catch (InterruptedException e)
			{
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
		number++;
		
		System.out.println("number increased by "+Thread.currentThread().getName()+", number= "+ number);;
		notify();

	}
	
	
	public synchronized void decrease(){
		while(0==number){
			try
			{
				wait();
			}
			catch (InterruptedException e)
			{
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
		number--;
		System.out.println("number decreased by "+Thread.currentThread().getName()+", number= "+ number);;
		
		notify();
	}
	
	
	
}

这里定义了对象类， 实现数字在1和0之间进行不停的转换。

package com.lj.thread2;

public class IncreaseThread extends Thread
{
	private Sample sample;
	
	public IncreaseThread(Sample sample){
		this.sample=sample;
	}
	
	
	
	@Override
	public void run()
	{
		for(int i=0;i<20;i++){
			try
			{
				Thread.sleep(1000);
			}
			catch (InterruptedException e)
			{
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
			sample.increase();
		}
		
	}
}

对数字加1的线程.

package com.lj.thread2;

public class DecreaseThread extends Thread
{
private Sample sample;
	
	public DecreaseThread(Sample sample){
		this.sample=sample;
	}
	
	
	
	@Override
	public void run()
	{
		for(int i=0;i<20;i++){
			try
			{
				Thread.sleep(1000);
			}
			catch (InterruptedException e)
			{
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			
			sample.decrease();
		}
		
	}
}

减1的线程

package com.lj.thread2;

public class Test
{
	public static void main(String[] args)
	{	
		Sample s=new Sample();
		Thread increase=new IncreaseThread(s);
		Thread decrease=new DecreaseThread(s);
		
		Thread i2=new IncreaseThread(s);
		Thread d2=new DecreaseThread(s);
		increase.start();
		i2.start();
		decrease.start();
		
		
		d2.start();
	}
}

这里的重点就是while循环那里不能写if。因为一个线程如果处于wait阶段，当它wait结束的时候， 要运行的时候必须再验证一下condition是否符合。
使用if的话不会去进行验证， 会直接执行number++或者number--, 导致错误。