多线程顺序打印，理解while if

class TestThreadOrderPrint {

    // 创建三个线程顺序打印ABC五次
    public static void main(String[] args) {
        final int[] flag = {1};
        Object a = new Object();
        Thread A = new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (a) {
                    for (int i = 0; i < 5; i++) {
                        try {
                            while(flag[0] !=1){//用while 不用if  否则状态不会重新判断，出现想不到的结果
                                a.wait();
                            }
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.print("A");
                        flag[0] =2;
                        a.notifyAll();
                    }
                }
            }
        });
        Thread B = new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (a) {
                    for (int i = 0; i < 5; i++) {
                        try {
                            while(flag[0] !=2){
                                a.wait();
                            }
                            Thread.sleep(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.print("B");
                        flag[0] =3;
                        a.notifyAll();
                    }

                }
            }
        });
        Thread C = new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (a) {
                    for (int i = 0; i < 5; i++) {
                        try {
                            while(flag[0] !=3){
                                a.wait();
                            }
                            Thread.sleep(1000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        System.out.println("C");
                        flag[0] =1;
                        a.notifyAll();
                    }
                }
            }
        });
        A.start();
        B.start();
        C.start();
    }


}