JAVA JUC 线程按顺序执行

class demo{
    private ReentrantLock lock =new ReentrantLock();
    private Condition cb = lock.newCondition();
    private Condition cc = lock.newCondition();
    private Condition ca = lock.newCondition();
    private int num = 1;
    public void loopA(int epoch){
        lock.lock();

        try {
            if(num!=1){

                ca.await();

            }
            for(int i=0;i<5;i++){
                System.out.println(Thread.currentThread().getName()+"  "+i+"\t"+epoch);
            }
            num=2;
            cb.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }
    public void loopB(int epoch){
        lock.lock();

        try {
            if(num!=2){
                cb.await();
            }
            for(int i=0;i<5;i++){
                System.out.println(Thread.currentThread().getName()+"  "+i+"\t"+epoch);
            }
            num=3;
            cc.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }
    public void loopC(int epoch){
        lock.lock();

        try {
            if(num!=3){
               cc.await();
            }
            for(int i=0;i<5;i++){
                System.out.println(Thread.currentThread().getName()+"  "+i+"\t"+epoch);
            }
            num=1;
            ca.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }

    }
}
public class alterDemo {
    public static void main(String[] args) {
        demo d = new demo();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i=0;i<20;i++)
                {
                    d.loopA(i);
                }

            }
        },"A").start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i=0;i<20;i++)
                {
                    d.loopB(i);
                }

            }
        },"B").start();
        new Thread(new Runnable() {
            @Override
            public void run() {
                for(int i=0;i<20;i++)
                {
                    d.loopC(i);
                }

            }
        },"C").start();
    }
}