package demo;

public class AddSubDemo {

    public static void main(String[] args) {
        Resource resource = new Resource();
        new Thread(new AddRunnable(resource)).start();
        new Thread(new SubRunnable(resource)).start();
    }

}

class AddRunnable implements Runnable {

    private Resource resource;

    public AddRunnable(Resource resource) {
        this.resource = resource;
    }

    @Override
    public void run() {
        while (true) {
            try {
                resource.add();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }

}

class SubRunnable implements Runnable {

    private Resource resource;

    public SubRunnable(Resource resource) {
        this.resource = resource;
    }

    @Override
    public void run() {
        while (true) {
            try {
                resource.sub();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }

}

class Resource {
    private int num = 0;
    private boolean flag = true; // true：执行ADD；false：执行SUB

    public synchronized void add() throws InterruptedException {
        if (this.flag = false) {
            super.wait();
        }
        Thread.sleep(1000);
        this.num++;
        flag = false;
        System.out.println(Thread.currentThread().getName()+"：" + this.num);
        super.notifyAll();
    }

    public synchronized void sub() throws InterruptedException {
        if (this.flag == true) {
            super.wait();
        }
        Thread.sleep(2000);    
        this.num--;
        flag = true;
        System.out.println(Thread.currentThread().getName()+"：" + this.num);
        super.notifyAll();
    }
}

Thread-0：1
Thread-0：2
Thread-0：3
Thread-0：4
Thread-0：5
Thread-0：6
Thread-0：7