线程不安全

1.下面这一例子会造成线程不安全 
 会取出负数，会同时一起抢     要是剩最后一张票的时候
会同时取出一，这样就造成线程不安全

//不安全买票
public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station,"苦逼的我").start();
        new Thread(station,"牛逼的你").start();
        new Thread(station,"可恶的黄牛党").start();
    }

}
class BuyTicket implements Runnable{
    //票
    private int ticketNnums = 10;
    boolean flag = true;//外部停止
    public void run(){
        //买票
        while(flag){
            try {
                buy();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    private void buy() throws InterruptedException {
        //判断是否有票
        if (ticketNnums<=0){
            flag = false;
            return;
        }
        //模拟延时
        Thread.sleep(1000);
        //买票
        System.out.println(Thread.currentThread().getName()+"拿到"+ticketNnums--);
    }
}


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2.
在buys()方法前面加synchronized它是同步方法锁的是(this)当前这个方法
synchronized 作用是使当前的线程能有序地进出

public class UnsafeBuyTicket {
    public static void main(String[] args) {
        BuyTicket station = new BuyTicket();

        new Thread(station,"苦逼的我").start();
        new Thread(station,"牛逼的你").start();
        new Thread(station,"可恶的黄牛党").start();
    }

}
class BuyTicket implements Runnable{
    //票
    private int ticketNnums = 10;
    boolean flag = true;//外部停止
    public void run(){
        //买票
        while(flag){
            try {
                buy();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    private synchronized void  buy() throws InterruptedException {
        //判断是否有票
        if (ticketNnums<=0){
            flag = false;
            return;
        }
        //模拟延时
        Thread.sleep(1000);
        //买票
        System.out.println(Thread.currentThread().getName()+"拿到"+ticketNnums--);
    }
}