多线程计算j的值

package thread;

public class Calculate_value_j {
	public static void main(String[] args) {
		OperateNum opnum=new OperateNum();
		for(int i=0;i<2;i++) {
			new AddThread(opnum).start();
			new Thread(new SubThread(opnum)).start();
		}
	}
	
}

class OperateNum{
	int j=0;
	public void add() {
		synchronized (OperateNum.class) {
			j++;
			System.out.println(Thread.currentThread().getName()+"add j="+j);
		}
	}
	public void sub() {
		synchronized (OperateNum.class) {
			j--;
			System.out.println(Thread.currentThread().getName()+"sub j="+j);
		}
	}
}

class AddThread extends Thread {
	OperateNum opnum=null;
	public AddThread(OperateNum opnum) {
		this.opnum=opnum;
	}
	@Override
	public void run() {
		for(int i=0;i<10;i++) {
			opnum.add();
		}
	}
}

class SubThread implements Runnable{
	OperateNum opnum=null;
	public SubThread(OperateNum opnum){
		this.opnum=opnum;
	}
	@Override
	public void run() {
		for(int i=0;i<10;i++) {
			opnum.sub();
		}
	}
	
}