线程的创建方式:1.继承Thread类

Thread

自定义线程类继承Thread类
重写run()方法，编写线程执行体
创建线程对象，调用start()方法启动线程

线程不一定立即执行，由CPU调度！

package test;

//创建线程方式一：继承Thread类 ，重写run方法 ，调用start开启线程
public class ThreadDemo1 extends Thread {
    @Override
    public void run() {
        //run方法线程体
        for (int i = 0; i < 20; i++) {
            System.out.println("测试run方法" + i);
        }
    }


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

        //创建一个线程对象
        ThreadDemo1 threadDemo1 = new ThreadDemo1();

        //调用start()方法开启线程
        threadDemo1.start();

        for (int i = 0; i < 200; i++) {
            System.out.println("主线程执行。。。" + i);
        }
    }


}

在这里插入图片描述

网图下载案例：

导入jar包

<!-- https://mvnrepository.com/artifact/commons-io/commons-io -->
<dependency>
    <groupId>commons-io</groupId>
    <artifactId>commons-io</artifactId>
    <version>2.6</version>
</dependency>

代码案例

package test;

import org.apache.commons.io.FileUtils;

import java.io.*;
import java.net.URL;
import java.net.URLConnection;

//练习Thread,实现多线程同步下载图片
public class ThreadTest1 extends Thread {

    /**
     * 网络图片地址
     */
    private String url;

    /**
     * 保存的文件名
     */
    private String name;

    public ThreadTest1(String name, String url) {
        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("下载了文件名叫：" + name);
    }

    public static void main(String[] args) {

        ThreadTest1 t1 = new ThreadTest1("1.jpg", "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1589025689098&di=7d4d3d91156334b61b7bb0ad7eb417f0&imgtype=0&src=http%3A%2F%2Fimg0.pconline.com.cn%2Fpconline%2F1303%2F12%2F3208685_java-01.jpg");
        ThreadTest1 t2 = new ThreadTest1("2.jpg", "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1589025689098&di=7d4d3d91156334b61b7bb0ad7eb417f0&imgtype=0&src=http%3A%2F%2Fimg0.pconline.com.cn%2Fpconline%2F1303%2F12%2F3208685_java-01.jpg");
        ThreadTest1 t3 = new ThreadTest1("3.jpg", "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1589025689098&di=7d4d3d91156334b61b7bb0ad7eb417f0&imgtype=0&src=http%3A%2F%2Fimg0.pconline.com.cn%2Fpconline%2F1303%2F12%2F3208685_java-01.jpg");

        //可以看到是同时执行，并不是按照顺序执行
        t1.start();
        t2.start();
        t3.start();
    }
}

//下载器
class WebDownloader {
    //下载方法
    public void downloader(String url, String name) {
        try {


          /*  URL url = new URL(link);
            url.openConnection().setRequestProperty("User-Agent", "Mozilla/4.0 (compatible; MSIE 5.0; Windows NT; DigExt)");
*/
            FileUtils.copyURLToFile(new URL(url), new File(name));
        } catch (IOException e) {
            e.printStackTrace();
            System.out.println("IO异常,downloader方法出现问题");
        }
    }
}