[Java知识库]Java多线程简介和创建（1）----狂神说JAVA

一.多线程简介

• 多任务：同时干很多件事，但是是分时进行，不同时间交替较快。
• 多线程：多条路线执行同一个任务。
  多线程：主线程先调用start方法，然后子线程执行run（）方法
  
  程序，进程，线程：
  在操作系统中运行的是进程，例如qq，播放器，游戏等，而一个进程可以有多个线程：例如，视频中同时听声音，看图像，看弹幕等
  程序是静态的，进程是程序的执行（动态的），而一个进程至少含有一个线程（main线程等），线程是cpu调度和执行的单位
  
  

二.多线程的创建

1. 继承Thread类

• 注意：线程开启未必立即执行，由cpu调度执行，直接调用run方法，不会创建新的线程
  
  线程创建
  继承Thread类，重写run方法，调用start开启线程

package demo01;
//创建线程方式之一：继承Thread类，重写run方法，调用start开启线程
public class TestThead1 extends Thread{
    @Override
    public void run() {  //run方法线程
        for (int i = 0; i < 20; i++) {
            System.out.println("我在看代码+++"+i);
        }

    }

    //main线程，主线程
    public static void main(String[] args) {
        //创建一个线程对象
        TestThead1 testThead1 = new TestThead1();
        //调用start()方法开启线程,两条线程交替执行
        testThead1.start();

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

        }
    }
}
//注意线程开启未必执行，由cpu调度执行

案例：多线程下载图片

在一个网页，下载它的三张图片
先编写下载器，然后到run（），最后再main函数中新建线程，然后启动线程

• 下载工具类及使用：
  IDEA 引入jar包 以及 commons-io-2.6.jar包的使用
  FileUtils.copyURLToFile(url, file) 的使用： Java 打开URL链接，并下载URL中的文件

代码：图片下载的顺序并不一致

package demo02;

import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;
import java.net.URL;
//实现多线程同步下载网图
public class ThreadTest02 extends Thread{
    private String url;//网络图片地址
    private String name;//保存的文件名
    @Override
    public void run() {
        WebDownLoader webDownLoader=new WebDownLoader();
        webDownLoader.downloader(url,name);
        System.out.println("下载了文件名为"+name);

    }
   //构造函数
    public ThreadTest02(String url,String name) {
        this.name=name;
        this.url= url;
    }

    public static void main(String[] args) {
        ThreadTest02 t1= new ThreadTest02("https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&hs=2&pn=2&spn=0&di=68640&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&ie=utf-8&oe=utf-8&cl=2&lm=-1&cs=3788223672%2C2933772794&os=3469738239%2C2819470525&simid=0%2C0&adpicid=0&lpn=0&ln=30&fr=ala&fm=&sme=&cg=&bdtype=0&oriquery=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%3A%2F%2Fimage.biaobaiju.com%2Fuploads%2F20191105%2F15%2F1572937434-vjDJNuBAxl.jpg%26refer%3Dhttp%3A%2F%2Fimage.biaobaiju.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1613979841%26t%3D6b74022d98f53152b4e7143934ed2714&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bktw5kwt37_z%26e3Bv54AzdH3Fi5g2geiwtztAzdH3Fl08nc_z%26e3Bip4s&gsm=3&islist=&querylist=","dog.jpeg");
        ThreadTest02 t2=new ThreadTest02("https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&hs=2&pn=5&spn=0&di=26840&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&ie=utf-8&oe=utf-8&cl=2&lm=-1&cs=2057173425%2C3288346039&os=3534193242%2C1744020036&simid=4255926711%2C726475710&adpicid=0&lpn=0&ln=30&fr=ala&fm=&sme=&cg=&bdtype=0&oriquery=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%3A%2F%2Fimg.wohaoyun.com%2Fimg_600%2FM00%2F07%2FB8%2FwKjg2lvW-dGAERdjAAEeYGzmpUA906.jpg%26refer%3Dhttp%3A%2F%2Fimg.wohaoyun.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1613979935%26t%3Dbd8042b4b6488deae4c73854e0c4dd6e&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bo5iw5y7g_z%26e3Bv54AzdH3Ff3AzdH3F15g2o7ktzitAzdH3Fda8bAzdH3F88AzdH3F8988_z%26e3Bip4s&gsm=6&islist=&querylist=","dog2.jpeg");
        ThreadTest02 t3=new ThreadTest02("https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&hs=2&pn=4&spn=0&di=13750&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&ie=utf-8&oe=utf-8&cl=2&lm=-1&cs=2136279165%2C2845293579&os=1684394320%2C374773828&simid=3423840844%2C312231934&adpicid=0&lpn=0&ln=30&fr=ala&fm=&sme=&cg=&bdtype=0&oriquery=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%3A%2F%2Fwww.cpnic.com%2FUploadFiles%2Fimg_0_3308088708_3867205912_26.jpg%26refer%3Dhttp%3A%2F%2Fwww.cpnic.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1613980066%26t%3D73944a43d2a1181ed0e4aeb6cd59da1e&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bvrgtv_z%26e3Bv54AzdH3FrtvAzdH3F%25Ec%25Ba%25bF%25Ec%25lE%25bB%25E0%25bB%25l0%25Ec%25ln%25b8%25E0%25A0%25bD%25Ec%25A9%25A0%25Ec%25bc%25Ab%25Ec%25bF%25bA%25Ec%25lB%25BE%25E0%25bl%25b0%25Ec%25bF%25bA%25E9%25BB%25B0%25Em%25Aa%25BCAzdH3F&gsm=5&islist=&querylist=","dog3.jpeg");
        t1.start();
        t2.start();
        t3.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方法出现问题");
        }
    }

}

2.实现Runnable接口（推荐）

区别：

public class TestThread03 implements Runnable{
    @Override
    public void run() {  //run方法线程
        for (int i = 0; i < 20; i++) {
            System.out.println("我在看代码+++"+i);
        }

    }

    //main线程，主线程
    public static void main(String[] args) {
        // //创建Runnable接口实现类的对象
        TestThread03 testThead3 = new TestThread03();
        new Thread(testThead3).start();
        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程+++"+i);

        }
    }

}

初识并发问题

看例子：

package demo03;
//买火车票
//多个线程操作同一个对象，会出现不同的线程抢到同一张票
public class TestThread04 implements Runnable{
    @Override
    public void run() {
        while (true){
            if (ticketNums<0){
                break;
            }
            try {  //快捷键 ctrl+alt+T
                Thread.sleep(200); //模拟延时
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+"--->拿到了第"+ticketNums-- +"张票");

        }
    }

    int ticketNums= 20;

    public static void main(String[] args) {
        TestThread04 t= new TestThread04();
        new Thread(t,"小明").start();
        new Thread(t,"小红").start();
        new Thread(t,"小杠").start();



    }
}

龟兔赛跑

package demo04;

public class race implements Runnable{
    //只有一个胜利者
    private static String winner;

    public static void main(String[] args) {
        race rubbit= new race();  //这是两个不同的线程
        race tortise = new race();
        new Thread(rubbit,"兔子").start();
        new  Thread(tortise,"乌龟").start();

    }

    @Override
    public void run() {
        for (int i = 0; i <=100; i++) {
            //模拟兔子休息，每10步休息一下
            if (Thread.currentThread().getName().equals("兔子")&&i%10==0)
                try {
                    Thread.sleep(3);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            System.out.println(Thread.currentThread().getName()+"-->跑了"+i+"步");
            //判断是否比赛结束
            boolean flag = gameOver(i);
            if (flag)
            {
                break;
            }

        }

    }
    //判断是否完成比赛
    private boolean gameOver(int steps){
        if (winner!=null){
            return true;
        }
        {
            if (steps>=100){
                winner=Thread.currentThread().getName();
                System.out.println("winner is "+ winner);
                return  true;
            }
        }
        return  false;
    }
}

3.实现Callable接口(了解)

package demo02;
import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

//实现多线程同步下载网图
public class TestCallable implements Callable<Boolean> {
    private String url;//网络图片地址
    private String name;//保存的文件名
    @Override
    public Boolean call() {
        WebDownLoader webDownLoader=new WebDownLoader();
        webDownLoader.downloader(url,name);
        System.out.println("下载了文件名为"+name);
        return  true;

    }
    //构造函数
    public TestCallable(String url,String name) {
        this.name=name;
        this.url= url;
    }
    public static void main(String[] args) {
        ThreadTest02 t1 = new ThreadTest02("https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&hs=2&pn=2&spn=0&di=68640&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&ie=utf-8&oe=utf-8&cl=2&lm=-1&cs=3788223672%2C2933772794&os=3469738239%2C2819470525&simid=0%2C0&adpicid=0&lpn=0&ln=30&fr=ala&fm=&sme=&cg=&bdtype=0&oriquery=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%3A%2F%2Fimage.biaobaiju.com%2Fuploads%2F20191105%2F15%2F1572937434-vjDJNuBAxl.jpg%26refer%3Dhttp%3A%2F%2Fimage.biaobaiju.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1613979841%26t%3D6b74022d98f53152b4e7143934ed2714&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bktw5kwt37_z%26e3Bv54AzdH3Fi5g2geiwtztAzdH3Fl08nc_z%26e3Bip4s&gsm=3&islist=&querylist=", "p.jpeg");
        ThreadTest02 t2 = new ThreadTest02("https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&hs=2&pn=5&spn=0&di=26840&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&ie=utf-8&oe=utf-8&cl=2&lm=-1&cs=2057173425%2C3288346039&os=3534193242%2C1744020036&simid=4255926711%2C726475710&adpicid=0&lpn=0&ln=30&fr=ala&fm=&sme=&cg=&bdtype=0&oriquery=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%3A%2F%2Fimg.wohaoyun.com%2Fimg_600%2FM00%2F07%2FB8%2FwKjg2lvW-dGAERdjAAEeYGzmpUA906.jpg%26refer%3Dhttp%3A%2F%2Fimg.wohaoyun.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1613979935%26t%3Dbd8042b4b6488deae4c73854e0c4dd6e&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bo5iw5y7g_z%26e3Bv54AzdH3Ff3AzdH3F15g2o7ktzitAzdH3Fda8bAzdH3F88AzdH3F8988_z%26e3Bip4s&gsm=6&islist=&querylist=", "pp.jpeg");
        ThreadTest02 t3 = new ThreadTest02("https://image.baidu.com/search/detail?ct=503316480&z=0&ipn=d&word=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&hs=2&pn=4&spn=0&di=13750&pi=0&rn=1&tn=baiduimagedetail&is=0%2C0&ie=utf-8&oe=utf-8&cl=2&lm=-1&cs=2136279165%2C2845293579&os=1684394320%2C374773828&simid=3423840844%2C312231934&adpicid=0&lpn=0&ln=30&fr=ala&fm=&sme=&cg=&bdtype=0&oriquery=%E5%B0%8F%E7%8B%97%E5%9B%BE%E7%89%87&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%3A%2F%2Fwww.cpnic.com%2FUploadFiles%2Fimg_0_3308088708_3867205912_26.jpg%26refer%3Dhttp%3A%2F%2Fwww.cpnic.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Djpeg%3Fsec%3D1613980066%26t%3D73944a43d2a1181ed0e4aeb6cd59da1e&fromurl=ippr_z2C%24qAzdH3FAzdH3Fooo_z%26e3Bvrgtv_z%26e3Bv54AzdH3FrtvAzdH3F%25Ec%25Ba%25bF%25Ec%25lE%25bB%25E0%25bB%25l0%25Ec%25ln%25b8%25E0%25A0%25bD%25Ec%25A9%25A0%25Ec%25bc%25Ab%25Ec%25bF%25bA%25Ec%25lB%25BE%25E0%25bl%25b0%25Ec%25bF%25bA%25E9%25BB%25B0%25Em%25Aa%25BCAzdH3F&gsm=5&islist=&querylist=", "ppp.jpeg");

        //创建执行服务

        ExecutorService ser = Executors.newFixedThreadPool(3);//线程池，放3个线程
        //提交执行

        Future<Boolean> r1 = (Future<Boolean>) ser.submit(t1);
        Future<Boolean> r2 = (Future<Boolean>) ser.submit(t2);
        Future<Boolean> r3 = (Future<Boolean>) 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 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方法出现问题");
        }
    }

}