要代码和思路，使用JAVA完成

. [问题描述]创建三个线程并启动，每个线程运行中每隔1秒钟更新一个共享变量var，让其加1，并打印出来。

[基本要求]

观察打印出来的顺序是不是按1递增的。如果不是，修改程序，使得打印的顺序是按1递增的。

[测试数据] 自定义。

这里有个卖票的例子可以符合这个要求， 加上线程锁就同步了！

//并发：两个或多个线程 同时访问一个共享资源的现象
public class Tickets implements Runnable {
	int count = 100;// 总票数
 
	public void run() {
		while (true) {
			// 1、给程序段加上互斥锁
			synchronized (this) {
				if (count < 1) {
					System.out.println("票已售罄");
					break;
				}
				count--;// 余票减1
				System.out.println(Thread.currentThread().getName()
						+ " 卖出了一张票，还剩" + count);
				try {
					Thread.sleep(50);
				} catch (InterruptedException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		}
	}
	
	
 
	public static void main(String[] args) {
		Tickets t = new Tickets();
 
		Thread a = new Thread(t, "赣州站");
		Thread b = new Thread(t, "广州站");
		Thread c = new Thread(t, "上海站");
 
		a.start();
		b.start();
		c.start();
	}
 
}

定义线程类，实现Runnable接口。

import java.util.concurrent.atomic.AtomicInteger;

public class IntegerAutoAdd {

    static AtomicInteger num = new AtomicInteger(0);

    static class ThreadA implements Runnable {

        @Override
        public void run() {
            int i = 0;
            while (i < 5) {
                num.incrementAndGet();
                System.err.println("线程A第" + i + "次操作，num值为：" + num);
                i++;
                try {
                    Thread.currentThread();
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    static class ThreadB implements Runnable {

        @Override
        public void run() {
            int i = 0;
            while (i < 5) {
                num.incrementAndGet();
                System.err.println("线程B第" + i + "次操作，num值为：" + num);
                i++;
                try {
                    Thread.currentThread();
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    public static void main(String[] args) {
        Thread a = new Thread(new ThreadA());
        Thread b = new Thread(new ThreadB());
        a.start();
        b.start();
    }

}

直接给这个共享变量加上volatile就好了

错误的代码

package com.xm.officialaccounts.utils;

import com.baomidou.mybatisplus.extension.api.R;

/**
 * @author 
 * @date created in 10:00 2021/6/10
 */
public class testThread extends Thread {
    static int var = 0;
    @Override
    public void run() {
        while (true){
            var++;
            System.out.println(var);
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        testThread a = new testThread();
        testThread b = new testThread();
        testThread c = new testThread();
        a.start();
        b.start();
        c.start();
    }
}
//        1
//        2
//        3
//        4
//        6
//        5
//        7
//        8
//        8
//        9
//        10
//        10
//        11
//        11
//        11
//        12
//        14
//        13
//        15
//        15
//        15

安全的

package com.xm.officialaccounts.utils;


/**
 * @author 
 * @date created in 10:00 2021/6/10
 */
public class testThread extends Thread {
    static volatile int var = 0;

    public static synchronized void add(){
        var++;
        System.out.println("ThreadName:"+Thread.currentThread().getName()+"  var:"+var);
    }
    @Override
    public void run() {
        while (true){
            add();
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }

        }
    }

    public static void main(String[] args) {
        testThread a = new testThread();
        testThread b = new testThread();
        testThread c = new testThread();
        a.start();
        b.start();
        c.start();
/*        ThreadName:Thread-0  var:1
        ThreadName:Thread-1  var:2
        ThreadName:Thread-2  var:3
        ThreadName:Thread-0  var:4
        ThreadName:Thread-1  var:5
        ThreadName:Thread-2  var:6
        ThreadName:Thread-2  var:7
        ThreadName:Thread-1  var:8
        ThreadName:Thread-0  var:9
        ThreadName:Thread-2  var:10
        ThreadName:Thread-1  var:11
        ThreadName:Thread-0  var:12
        ThreadName:Thread-2  var:13
        ThreadName:Thread-0  var:14
        ThreadName:Thread-1  var:15
        ThreadName:Thread-2  var:16
        ThreadName:Thread-1  var:17
        ThreadName:Thread-0  var:18
        ThreadName:Thread-2  var:19
        ThreadName:Thread-1  var:20
        ThreadName:Thread-0  var:21*/
    }
}