售票（原子性）

package DUOXIAN;

import java.util.concurrent.TimeUnit;

public class Sync {
    public static void main(String[] args) {
        MySync ms =new MySync();
        new Thread(()->{
            while (true){
                if (ms.getNum()>0){
                    ms.add();
                }else {
                    break;
                }
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"t1").start();


        new Thread(()->{
            while (true){
                if (ms.getNum()>0){
                    ms.add();
                }else {
                    break;
                }
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"t2").start();

        new Thread(()->{
            while (true){
                if (ms.getNum()>0){
                ms.add();
                }else {
                    break;
                }
                try {
                    TimeUnit.SECONDS.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"t3").start();
    }
}

class MySync{
    private int num=100;

    public int getNum() {
        return num;
    }

    public void setNum(int num) {
        this.num = num;
    }

    public synchronized void add(){//不加锁可能会出现脏读

        //2%线程名，$1数量
        System.out.printf("%2$s:add..%1$d%n",num--,Thread.currentThread().getName());
    }
}