java多线程经典案列（卖票）

public class Ticket implements Runnable {


    private int ticket = 100;


    @Override
    public void run() {
        while (true) {
            if (ticket > 0) {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + "卖了一张票，剩下:" + ticket--);
            }
        }
    }


    public static void main(String[] args) {
        Ticket ticket = new Ticket();

        Thread t1 = new Thread(ticket, "窗口1");
        Thread t2 = new Thread(ticket, "窗口2");
        Thread t3 = new Thread(ticket, "窗口3");

        t1.start();
        t2.start();
        t3.start();

    }
}

此时会出现线程安全问题，可以加锁解决此问题

public class Ticket implements Runnable {

    private int ticket = 100;
   
    @Override
    public void run() {
        while (true) {
            synchronized (this) {
                if (ticket > 0) {
                    try {
                        Thread.sleep(100);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + "卖了一张票，剩下:" + ticket--);
                }
            }
        }
    }

    public static void main(String[] args) {
        Ticket ticket = new Ticket();
        Ticket ticket1 = new Ticket();
        Ticket ticket2 = new Ticket();

        Thread t1 = new Thread(ticket, "窗口1");
        Thread t2 = new Thread(ticket1, "窗口2");
        Thread t3 = new Thread(ticket2, "窗口3");

        t1.start();
        t2.start();
        t3.start();

    }
}

 咦？还是出现了线程安全问题，这是为什么呢？

有细心的同学想必发现了我第二个代码new了两个类，分别是

Ticket ticket1 = new Ticket();
Ticket ticket2 = new Ticket();

我们知道在java中每实例化一次就会在计算机内存中开辟一块新的内存空间，而我们的锁只锁住了

Ticket ticket = new Ticket();

，而后两者没有锁住所以可以访问到内存空间进行

ticket--操作导致数据被重复消费。我们需要做两步操作才能彻底保证数据安全性。第一：在

synchronized括号里加入类名.class例如

synchronized (Ticket.class)。第二：在变量前加上

static