JAVA多线程

1.线程就是独立的执行路径
2.main()称之为主线程，为系统的入口，用于执行整个程序
3.在一个进程中，如果开辟了多个线程，线程的运行由调度器安排调度，调度器是与操作系统紧密相关的，先后顺序是不能人为的干预的
4.对同一份资源操作是，会存在资源抢夺的问题，需要加入并发控制
5.线程会带来额外的开销，如cpu调度时间，并发控制开销
6.每个线程在自己的工作内存交互，内存控制不当会造成数据不一致

线程创建

Thread.class
1、自定义线程类继承Thread类
2、重写run()方法，编写线程执行体
3、创建线程对象，调用start()方法启动线程
注：线程开启不一定立即执行，根据cpu调度安排

public class TestThread extends Thread {
    @Override
    public void run() {
        for (int i = 0; i < 2000; i++) {
            System.out.println("run线程-------------");
        }
    }

    public static void main(String[] args) {
        //main线程，主线程
        TestThread testThread = new TestThread();
        testThread.start();
        for (int i = 0; i < 2000; i++) {
            System.out.println("main线程++++++++++++++");
        }
    }
}

例子，网络图片下载

public class TestThread2 extends TestThread{

    private String name;

    private String url;

    //构造器
    TestThread2(String url,String name){
        this.name = name;
        this.url = url;
    }

    //线程执行体
    @Override
    public void run() {
        WebDownloader webDownloader = new WebDownloader();
        webDownloader.downloader(url,name);
        System.out.println(name);
    }

    public static void main(String[] args) {
        TestThread2 t1 = new TestThread2("https://image.baidu.com/search/detail?ct=503316480&z=undefined&tn=baiduimagedetail&ipn=d&word=jpg%E5%9B%BE%E7%89%87&step_word=&ie=utf-8&in=&cl=2&lm=-1&st=undefined&hd=undefined&latest=undefined©right=undefined&cs=1671943955,3320345726&os=749330975,400155190&simid=46899987,1043920955&pn=0&rn=1&di=7060663421280190465&ln=1424&fr=&fmq=1648131319030_R&fm=&ic=undefined&s=undefined&se=&sme=&tab=0&width=undefined&height=undefined&face=undefined&is=0,0&istype=0&ist=&jit=&bdtype=0&spn=0&pi=0&gsm=0&objurl=https%3A%2F%2Fss0.baidu.com%2F-Po3dSag_xI4khGko9WTAnF6hhy%2Fbaike%2Fpic%2Fitem%2F9825bc315c6034a8cda67260c11349540823768f.jpg&rpstart=0&rpnum=0&adpicid=0&nojc=undefined&dyTabStr=MCwzLDIsNiw0LDUsNyw4LDEsOQ%3D%3D","1.jpg");
        TestThread2 t2 = new TestThread2("https://image.baidu.com/search/detail?ct=503316480&z=undefined&tn=baiduimagedetail&ipn=d&word=jpg%E5%9B%BE%E7%89%87&step_word=&ie=utf-8&in=&cl=2&lm=-1&st=undefined&hd=undefined&latest=undefined©right=undefined&cs=3496781279,3725135679&os=3411366938,3533778484&simid=3264064304,3725877970&pn=7&rn=1&di=7060663421280190465&ln=1424&fr=&fmq=1648131524239_R&fm=&ic=undefined&s=undefined&se=&sme=&tab=0&width=undefined&height=undefined&face=undefined&is=0,0&istype=0&ist=&jit=&bdtype=0&spn=0&pi=0&gsm=0&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%253A%252F%252Fwww.erdangjiade.com%252Fproject%252Fimages%252Ffb9b6a26f2f2e14cb42ff2ceeb144cb2.jpg%26refer%3Dhttp%253A%252F%252Fwww.erdangjiade.com%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Dauto%3Fsec%3D1650723522%26t%3D3c48e05f71ca421943e84fd890b202f8&rpstart=0&rpnum=0&adpicid=0&nojc=undefined&dyTabStr=MCwzLDIsNiw0LDUsNyw4LDEsOQ%3D%3D","2.jpg");
        TestThread2 t3 = new TestThread2("https://image.baidu.com/search/detail?ct=503316480&z=undefined&tn=baiduimagedetail&ipn=d&word=jpg%E5%9B%BE%E7%89%87&step_word=&ie=utf-8&in=&cl=2&lm=-1&st=undefined&hd=undefined&latest=undefined©right=undefined&cs=3134447943,3951842718&os=3545318994,2194840880&simid=4269224249,590545950&pn=1&rn=1&di=7060663421280190465&ln=1424&fr=&fmq=1648131524239_R&fm=&ic=undefined&s=undefined&se=&sme=&tab=0&width=undefined&height=undefined&face=undefined&is=0,0&istype=0&ist=&jit=&bdtype=0&spn=0&pi=0&gsm=0&objurl=https%3A%2F%2Fgimg2.baidu.com%2Fimage_search%2Fsrc%3Dhttp%253A%252F%252Fdogame.com.cn%252Fbbs%252Fattachments%252Fday_150227%252F15022720201f0cf31d827b4a84.jpg%26refer%3Dhttp%253A%252F%252Fdogame.com.cn%26app%3D2002%26size%3Df9999%2C10000%26q%3Da80%26n%3D0%26g%3D0n%26fmt%3Dauto%3Fsec%3D1650723522%26t%3D42aa03881194a732fd82cf34021b6258&rpstart=0&rpnum=0&adpicid=0&nojc=undefined&dyTabStr=MCwzLDIsNiw0LDUsNyw4LDEsOQ%3D%3D","3.jpg");
        t1.start();
        t2.start();
        t3.start();
    }
}

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");
        }
    }
}

运行结果

Runnable接口
1、定义MyRunnable类实现Runnable接口
2、实现run()方法，编写线程执行体
3、创建线程对象，调用start()方法启动线程

推荐使用Runnable对象，避免单继承局限性，灵活方便，方便同一个对象被多个线程使用

public class TestThread2 implements Runnable{
    public void run() {
        for (int i = 0; i < 2000; i++) {
            System.out.println("run线程-------------");
        }
    }

    public static void main(String[] args) {

        //创建Runnable接口的实现类对象
        TestThread2 testThread2 = new TestThread2();

        //创建线程对象，通过线程对象来开启我们的线程，代理
        new Thread(testThread2).start();

        for (int i = 0; i < 2000; i++) {
            System.out.println("main线程++++++++++++++");
        }
    }
}

Callable接口