并发

解决办法：队列 + 锁
线程不安全示例(操作同一个对象)
public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
//        BuyTicket buyTicket1 = new BuyTicket();
//        BuyTicket buyTicket2 = new BuyTicket();
        new Thread(buyTicket,"张三").start();
        new Thread(buyTicket,"李四").start();
        new Thread(buyTicket,"王五").start();
    }
	/* 买票 */
    static class BuyTicket implements Runnable{
        int ticket = 20;
        boolean flag = false;
        @Override
        public void run() {
            while(!flag){
                try {
                    Thread.sleep(200);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                buy();
            }

        }
        private void buy(){
            System.out.println(Thread.currentThread().getName()+"买到了:"+ticket--);
            if(ticket <= 0){
                flag = true;
            }
        }
    }

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