java 多线程 实现多个线程的顺序执行

场景

编写一个程序，启动三个线程，三个线程的name分别是A，B，C；，每个线程将自己的ID值在屏幕上打印5遍，打印顺序是ABCABC...

使用 synchronized 实现 

public class MyService
{
    private int flag = 1;
    
    public synchronized void printA(){
        
        while (flag != 1)
        {
            try
            {
                this.wait();
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
        System.out.print(Thread.currentThread().getName());
        flag = 2;
        this.notifyAll();
    }
    public synchronized void printB(){
        while (flag != 2)
        {
            try
            {
                this.wait();
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
        System.out.print(Thread.currentThread().getName());
        flag = 3;
        this.notifyAll();
    }
    public synchronized void printC(){
        while (flag != 3)
        {
            try
            {
                this.wait();
            }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }
        }
        System.out.print(Thread.currentThread().getName());
        flag = 1;
        this.notifyAll();
    }
}

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