java线程通信

一说到线程通信我们就会想到生产者和消费者，哲学家就餐问题，下面例子是以生产者与消费者来实现线程之间的通信

package com.lamp.test;

public class Cake {
	private int number = 0;
	
	public synchronized void increase(){
		while(0 != number){		//如果只有一个生产者进程和一个消费者进程，我们还可以用if来判断，但是涉及到2个以上进程就需用while来判断了这也是实践中用的最多的
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		number++;				//假定资源的数量只能为0或者1，为0时加1并唤醒消费者进程，消费者进程相反
		System.out.println(number);
		this.notify();
	}
	
	public synchronized void decrease(){
		while(0 == number){
			try {
				this.wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		number--;
		System.out.println(number);
		this.notify();
	}
}

生产者进程类

package com.lamp.test;

public class Producer extends Thread {

	private Cake cake;

	public Producer(Cake cake) {
		this.cake = cake;
	}

	@Override
	public void run() {
		for (int i = 0; i < 10; i++) {
			try {
				Thread.sleep((long) (Math.random() * 1000));
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			this.cake.increase();
		}

	}
}

消费者进程类

package com.lamp.test;

public class Consumer extends Thread{
	private Cake cake = null;

	public Consumer(Cake cake) {
		this.cake = cake;
	}
	
	@Override
	public void run(){
		for(int i=0; i<10; i++){
			try {
				Thread.sleep((long) (Math.random() * 1000));
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			this.cake.decrease();
		}
		
	}

}

写个测试类

package com.lamp.test;

public class CakeTest {

	public static void main(String[] args) {
		Cake cake = new Cake();
		
		Thread t1 = new Producer(cake);
		Thread t2 = new Consumer(cake);		//确保访问的是同一资源
		
		Thread t3 = new Producer(cake);
		Thread t4 = new Consumer(cake);
		
		t1.start();
		t2.start();
		t3.start();
		t4.start();
	}

}

wait与notify方法都是定义在Object方法中，而且是final的，因此会被所有的java类继承但是不能重写，这两个方法的调用必须在synchronized方法或者synchronized块中，而且当前线程要已经拿到了对象锁，当线程执行wait方法时，它会释放对象锁