併發

解決辦法：佇列 + 鎖

執行緒不安全示例(操作同一個物件)

public static void main(String[] args) {
        BuyTicket buyTicket = new BuyTicket();
//        BuyTicket buyTicket1 = new BuyTicket();
//        BuyTicket buyTicket2 = new BuyTicket();
        new Thread(buyTicket,"張三").start();
        new Thread(buyTicket,"李四").start();
        new Thread(buyTicket,"王五").start();
    }
	/* 買票 */
    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()+"買到了:"+ticket--);
            if(ticket <= 0){
                flag = true;
            }
        }
    }