java多線程數字加減

/* 設計四個線程對象，其中兩個線程執行減操作，另外兩個執行加操作.*/

class Resource{
	private int num = 0;
	private boolean flag = true;
	public synchronized void add() throws Exception {
		if(this.flag == false) {
			super.wait();
		}
		Thread.sleep(100);
		this.num++;
		System.out.println("【加法操作 - "+ Thread.currentThread().getName()+"】num="+ num);
		this.flag = false;
		super.notifyAll();
	}
	public synchronized void sub() throws Exception{
		if(this.flag == true) {
			super.wait();
		}
		Thread.sleep(200);
		this.num--;
		System.out.println("【減法操作- " + Thread.currentThread().getName() + "】num=" + num);
		this.flag = true;
		super.notifyAll();
	}
}

class AddThread implements Runnable{
	private Resource resource;
	public AddThread(Resource resource) {
		this.resource = resource;
	}
	@Override
	public void run() {
		for(int x=0;x<50;x++) {
			try {
				this.resource.add();
			}catch(Exception e) {
				e.printStackTrace();
			}
		}
	}
}

class SubThread implements Runnable{
	private Resource resource;
	public SubThread(Resource resource) {
		this.resource = resource;
	}
	@Override
	public void run() {
		for(int x=0;x<50;x++) {
			try {
				this.resource.sub();
			}catch(Exception e) {
				e.printStackTrace();
			}
		}
	}
}

public class homework_01 {
	public static void main(String[] args) {
		Resource resource = new Resource();
		SubThread st = new SubThread(resource);
		AddThread at = new AddThread(resource);
		new Thread(at, "加法線程-A").start();
		new Thread(at, "加法線程-B").start();
		new Thread(st, "加法線程-C").start();
		new Thread(st, "加法線程-D").start();
	}
}