java多线程中同步的问题？

一、通过模拟网络延迟，解决同步的问题、

package com.zxf.demo;

public class G01 implements Runnable{

    private int num=10;
    private int count=0;
    @Override
    public void run() {
        // TODO Auto-generated method stub
        while (true) {

            count++;
            num--;
            System.out.println(Thread.currentThread().getName()+"买到了第"+count+"条裤子，还剩"+num+"条裤子");

            //模拟网络延迟  让进程睡眠一会 1秒
            try {
                Thread.sleep(300);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            if (num<=0) {
                break;
            }

        }

    }
    public static void main(String[] args) {
        G01 g1 = new G01();

        Thread t1 = new Thread(g1,"卢本伟");
        Thread t2 = new Thread(g1,"马飞飞");
        Thread t3 = new Thread(g1,"大司马");
        Thread t4 = new Thread(g1,"骚男");

        t1.start();
        t2.start();
        t3.start();
        t4.start();

    }

}

这样写是有问题的  多个进程轮番执行，不能保证每个人买到的东西的唯一性

解决方式？

1.把可能产生的数据安全问题的代码 锁起来， 被锁定的代码就变成单线程的！

package com.zxf.demo;

public class G01 implements Runnable{

    private int num=10;
    private int count=0;
    @Override
    public void run() {
        // TODO Auto-generated method stub
        while (true) {

            // 通过synchronized (this){}  将会出问题的部分 锁在这里  ，这里就变了单线程模式 就不会出错！
            synchronized (this) {
                if (num<=0) {
                    break;
                }
                count++;
                num--;
                System.out.println(Thread.currentThread().getName()+"买到了第"+count+"条裤子，还剩"+num+"条裤子");
            }

            //模拟网络延迟  让进程睡眠一会 1秒
            try {
                Thread.sleep(300);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

    }
    public static void main(String[] args) {
        G01 g1 = new G01();

        Thread t1 = new Thread(g1,"卢本伟");
        Thread t2 = new Thread(g1,"马飞飞");
        Thread t3 = new Thread(g1,"大司马");
        Thread t4 = new Thread(g1,"骚男");

        t1.start();
        t2.start();
        t3.start();
        t4.start();

    }

}

2.同步方法  就是在方法的返回值类型前边加上 synchronize将该方法内部的代码  全部锁起来

package com.zxf.demo;

public class G01 implements Runnable{

    private int num=10;
    private int count=0;
    @Override
    public void run() {
        // TODO Auto-generated method stub
        while (true) {

            if (!buy()) {  // 调用buy的方法    不满足结果  结束循环
                break;
            }

            //模拟网络延迟  让进程睡眠一会 1秒
            try {
                Thread.sleep(300);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        }

    }
    //同步方法 定义一个方法  需要在方法的返回值类型 前边加上 synchronized 关键字。
    public synchronized boolean buy() {

        if (num<=0) {
            return false;
        }
        num--;
        count++;
        System.out.println(Thread.currentThread().getName()+"买到了第"+count+"条裤子，还剩"+num+"条裤子");

        return true;

    }

    public static void main(String[] args) {
        G01 g1 = new G01();

        Thread t1 = new Thread(g1,"卢本伟");
        Thread t2 = new Thread(g1,"马飞飞");
        Thread t3 = new Thread(g1,"大司马");
        Thread t4 = new Thread(g1,"骚男");

        t1.start();
        t2.start();
        t3.start();
        t4.start();

    }

}