线程并发及线程并发问题的解决

火车站多个窗口同时售票，假设总共500张票，四个窗口同时卖。

1.创建一个继承Thread类的子类 

package com.commons.commons.taskthread;

/**
 * @Author zhaomengxia
 * @create 2019/10/12 16:56
 */
public class SaleTicketThread extends Thread {

    static int number = 500;

    private String name;

    public SaleTicketThread(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        while (true) {
            if (number > 0) {
                System.out.println(name + "卖出" + (number--) + "号");
            } else {
                break;
            }

            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(name + "票卖完了！");
    }
}

测试 类

package com.commons.commons.taskthread;

/**
 * @Author zhaomengxia
 * @create 2019/10/12 17:02
 */
public class SaleTicketThreadTest {

    public static void main(String[] args) {

        SaleTicketThread saleTicketThread=new SaleTicketThread("窗口1");

        SaleTicketThread saleTicketThread1=new SaleTicketThread("窗口2");

        SaleTicketThread saleTicketThread2=new SaleTicketThread("窗口3");

        SaleTicketThread saleTicketThread3=new SaleTicketThread("窗口4");
        saleTicketThread.start();
        saleTicketThread1.start();
        saleTicketThread2.start();
        saleTicketThread3.start();

    }
}

从运行结果中我们可以看到有出现不同窗口卖同一张票的现象

接下来就引出

 

修改后的代码如下，就解决了上诉出现的并发问题，不会出现不同窗口卖出同一张票的情况。

package com.commons.commons.taskthread;

/**
 * @Author zhaomengxia
 * @create 2019/10/12 16:56
 */
public class SaleTicketThread extends Thread {

    static int number = 500;

    private String name;
    
    //创建一个锁对象，这个对象是多个线程对象共享的数据
    static Object object=new Object();

    public SaleTicketThread(String name) {
        this.name = name;
    }

    @Override
    public void run() {
        while (true) {
            synchronized (object){
                if (number > 0) {
                    System.out.println(name + "卖出" + (number--) + "号");
                } else {
                    break;
                }
            }
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println(name + "票卖完了！");
    }
}