多线程

线程的三种创建方式

Thread class：继承Thread类

自定义线程类继承Threadlei类
重写run()方法，编写线程执行体

创建线程对象，调用start()启动线程

package com.thread;


//创建线程方式1：继承Thread类，重写run方法,调用start方法开启线程
public class ThreadTest01 extends Thread {
    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            System.out.println("i am watch code:" + i);
        }
    }


    public static void main(String[] args) {
        //main线程

        //创建一个线程对象
        ThreadTest01 threadTest01 = new ThreadTest01();

        //调用start()方法开启线程
        //start()方法是主线程和子线程一起执行
        //run()方法是先执行run()方法的子线程，再执行主线程
        //注意：线程开启不一定立即执行，需要等CPU的调度处理
        threadTest01.start();

        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程：" + i);
        }
    }
}

代码实现多线程下载图片

package com.thread;


import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URL;

//利用thread实现多线程同步下载图片
public class ThreadTest02 extends Thread {

    private String url;
    private String name;

    public ThreadTest02(String url, String name) {
        this.url = url;
        this.name = name;
    }


    //下载图片线程的执行体
    @Override
    public void run() {
        webDownloader webDownloader = new webDownloader();
        webDownloader.downloader(url, name);
        System.out.println("下载了文件名为：" + name);
    }

    public static void main(String[] args) {
        ThreadTest02 test01 = new ThreadTest02("https://gimg2.baidu.com/image_search/src=http%3A%2F%2F5b0988e595225.cdn.sohucs.com%2Fimages%2F20190513%2F7cb9afc55171450eaa17604c5e4fc765.jpeg&refer=http%3A%2F%2F5b0988e595225.cdn.sohucs.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=030319dc87f0a7ce129ba69ab5bda5e5", "1.jpg");
        ThreadTest02 test02 = new ThreadTest02("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.youxi369.com%2Farticle%2Fcontents%2F2021%2F01%2F07%2F2021010740735362.jpg&refer=http%3A%2F%2Fimg.youxi369.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=97f6180af2ab121b58f15c7f300a0ebb", "2.jpg");
        ThreadTest02 test03 = new ThreadTest02("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201802%2F12%2F20180212094815_MWrv5.jpeg&refer=http%3A%2F%2Fb-ssl.duitang.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=316c717e8b3e03682f56422dfa92fba0", "3.jpg");

        test01.start();
        test02.start();
        test03.start();
    }
}


//下载器
class webDownloader {
    public void downloader(String url, String name) {

        try {
            FileUtils.copyURLToFile(new URL(url), new File(name));

        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("IO异常，downloader方法出现异常");
        }
    }
}

结果：

  下载成功，注意：要先导入commons-IO包

  验证可得：start（）方法没有按程序顺序执行，先后顺序看CPU调度的执行情况

Runnable接口：实现Runnable接口

package com.thread;


//创建线程方式2：实现Runnable接口，重写run()方法，执行线程需要丢入Runnable接口实现类，调用start()方法
public class ThreadTest03 implements Runnable{
    @Override
    public void run() {
        for (int i = 0; i < 20; i++) {
            System.out.println("i am watch code:" + i);
        }
    }

    public static void main(String[] args) {
        //创建Runnable接口实现类对象
        ThreadTest03 threadTest03 = new ThreadTest03();

        //创建线程对象，通过线程对象来开启我们的线程 代理
        new Thread(threadTest03).start();


        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程：" + i);
        }
    }
}

Callable接口：实现Callable接口

package com.thread;


import org.apache.commons.io.FileUtils;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.concurrent.*;

//创建线程方式3：实现callable接口

/**
 * callable的好处：
 * 1、可以定义返回值
 * 2、可以抛出异常
 */
public class CallableTest01 implements Callable<Boolean> {
    private String url;
    private String name;

    public CallableTest01(String url, String name) {
        this.url = url;
        this.name = name;
    }


    //下载图片线程的执行体
    @Override
    public Boolean call() {
        webDownloader01 webDownloader01 = new webDownloader01();
        webDownloader01.downloader(url, name);
        System.out.println("下载了文件名为：" + name);
        return true;
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        CallableTest01 t1 = new CallableTest01("https://gimg2.baidu.com/image_search/src=http%3A%2F%2F5b0988e595225.cdn.sohucs.com%2Fimages%2F20190513%2F7cb9afc55171450eaa17604c5e4fc765.jpeg&refer=http%3A%2F%2F5b0988e595225.cdn.sohucs.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=030319dc87f0a7ce129ba69ab5bda5e5", "1.jpg");
        CallableTest01 t2 = new CallableTest01("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.youxi369.com%2Farticle%2Fcontents%2F2021%2F01%2F07%2F2021010740735362.jpg&refer=http%3A%2F%2Fimg.youxi369.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=97f6180af2ab121b58f15c7f300a0ebb", "2.jpg");
        CallableTest01 t3 = new CallableTest01("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201802%2F12%2F20180212094815_MWrv5.jpeg&refer=http%3A%2F%2Fb-ssl.duitang.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=316c717e8b3e03682f56422dfa92fba0", "3.jpg");

        //创建执行服务
        ExecutorService ser = Executors.newFixedThreadPool(3);

        //提交执行
        Future<Boolean> r1 = ser.submit(t1);
        Future<Boolean> r2 = ser.submit(t2);
        Future<Boolean> r3 = ser.submit(t3);

        //获取结果
        boolean rs1 = r1.get();
        boolean rs2 = r2.get();
        boolean rs3 = r3.get();

        //关闭服务
        ser.shutdownNow();

    }
}


//下载器
class webDownloader01 {
    public void downloader(String url, String name) {

        try {
            FileUtils.copyURLToFile(new URL(url), new File(name));

        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("IO异常，downloader方法出现异常");
        }
    }
}

并发问题

买火车票模拟代码：

package com.thread;

import java.nio.channels.NonReadableChannelException;

//多个线程操作同一个对象
//买火车票的例子
public class TreadTest04 implements Runnable {


    //火车票
    private int ticketNum = 10;


    @Override
    public void run() {
        while (true) {
            if (ticketNum <= 0) {
                break;
            }

            //模拟延时
            try {
                Thread.sleep(200);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "-->拿到了第 " + ticketNum-- + " 张票");
        }
    }

    public static void main(String[] args) {
        TreadTest04 treadTest04 = new TreadTest04();

        new Thread(treadTest04, "小明").start();
        new Thread(treadTest04, "老师").start();
        new Thread(treadTest04, "黄牛").start();
    }
}

运行结果：

问题：多个线程操作同一个资源的情况下，线程不安全，数据紊乱

案例：龟兔赛跑

首先来个赛道距离，然后要离终点越来越近
判断比赛是否结束
打印出胜利者
龟兔赛跑开始
要保证乌龟胜利，兔子需要睡觉，用sleep来模拟兔子睡觉

乌龟赢得比赛

package com.thread;

public class Race implements Runnable {

    //胜利者
    private static String winner;

    @Override
    public void run() {
        for (int i = 1; i <= 100; i++) {

            //模拟兔子睡觉
            if (Thread.currentThread().getName().equals("兔子") && i % 10 == 0) {
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }


            //判断比赛是否结束
            boolean flag = gameOver(i);
            if (flag) {
                break;
            }

            System.out.println(Thread.currentThread().getName() + "--> 跑了 " + i + " 步");
        }
    }

    //判断比赛是否结束
    public boolean gameOver(int steps) {
        //判断是否存在胜利者
        if (winner != null) {//胜利者已经存在
            return true;
        }
        {
            if (steps == 100) {
                winner = Thread.currentThread().getName();
                System.out.println("winner is " + winner);
                return true;
            }
        }
        return false;
    }


    public static void main(String[] args) {
        Race race = new Race();

        new Thread(race, "兔子").start();
        new Thread(race, "乌龟").start();
    }
}

posted @ 2022-08-03 19:04 每年桃花开的时候阅读(33) 评论(0) 收藏举报

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xiaojian1995

多线程

多线程

线程的三种创建方式

并发问题

案例：龟兔赛跑

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