生产者/消费者 模式

目的：保证商品不多于20个，不少于0个，且当商品为20个时暂停生产并且通知消费者消费，为0个时则通知消费者无货。

注意点：注意 if 语句的选择（if 放什么、else 放什么）

public class TestProduct {
	public static void main(String[] args) {
		Clerk clerk = new Clerk();
		Consumer con = new Consumer(clerk);
		Producer pro = new Producer(clerk);
		Thread t1 = new Thread(con);
		Thread t2 = new Thread(con);
		Thread t3 = new Thread(pro);
		Thread t4 = new Thread(pro);
		t1.setName("1");
		t2.setName("2");
		t3.setName("1");
		t4.setName("2");
		t1.start();
		t2.start();
		t3.start();
		t4.start();
	}
}

class Clerk {
	int numOfProduction;// 共享資源

	public synchronized void produce() {// 定义生产共享资源的方法
		if (numOfProduction == 20) {// 达到20个则暂停生产，否则继续生产并且唤醒消费
			try {
				wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		} else {
			try {
				Thread.currentThread().sleep(100);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			numOfProduction++;
			System.out.println(Thread.currentThread().getName() + "号生产者生产了货架上第" + numOfProduction + "号产品");
			notifyAll();
		}
	}

	public synchronized void consume() {// 定义消费共享资源的方法
		if (numOfProduction == 0) {// 达到0个则暂停消费，否则继续消费并且唤醒生产
			try {
				wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		} else {
			try {
				Thread.currentThread().sleep(100);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println(Thread.currentThread().getName() + "号消费者消费了货架上第" + numOfProduction + "号产品");
			numOfProduction--;
			notifyAll();// 已消费，唤醒生产者生产
		}
	}
}

class Producer implements Runnable {
	Clerk clerk;

	public Producer(Clerk clerk) {
		super();
		this.clerk = clerk;
	}

	@Override
	public void run() {
		while (true) {
			clerk.produce();
		}
	}

}

class Consumer implements Runnable {
	Clerk clerk;

	public Consumer(Clerk clerk) {
		super();
		this.clerk = clerk;
	}

	@Override
	public void run() {
		while (true) {
			clerk.consume();
		}
	}
}