线程礼让 Thread.yield(); 礼让不一定成功

package com.Java;

//线程礼让 礼让不一定成功
public class TestYield {
    public static void main(String[] args) {
        MyYield yield = new MyYield();
        new Thread(yield, "a").start();
        new Thread(yield, "b").start();
    }
}

class MyYield implements Runnable {
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName() + "开始执行");
        Thread.yield();//礼让
        System.out.println(Thread.currentThread().getName() + "停止执行");
    }
}