JAVA多线程

本文主要是介绍JAVA多线程，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

1. 进程，线程

一个进程有多个线程，如视频同时听声音，看图像，看弹幕等
程序与线程----

多线程----

2. 线程创建

• 继承Thread类（重点）
• 实现Runnable接口（重点）
• 实现Callable接口（了解）

2.1 继承Thread类

三个步骤：

1. 继承Thread类
2. 重写run()方法
3. 调用start()方法开启线程
   注意：线程开启不一定立即执行，由CPU调度

//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 TestThread1 extends Thread {
    public static void main(String[] args) {
        //main线程，主线程

        //创建线程对象
        TestThread1 thread1 = new TestThread1();
        thread1.start();//调用start()方法
        
        for (int i = 0; i < 200; i++) {
            System.out.println("我在看代码---" + i);
        }
    }
    @Override
    public void run() {
        //run()方法线程体
        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程---" + i);
        }
    }
}

2.1.1 练习Thread，多线程同步下载图片

//练习Thread，多线程同步下载图片
public class TestThresd2 extends Thread{

    private String url;   //保存图片地址
    private String name;  //保存的文件名

    public TestThresd2(String url, String name) {
        this.url = url;
        this.name = name;
    }

    //下载图片的执行体
    @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) {
        TestThresd2 t1 = new TestThresd2("https://www.runoob.com/wp-content/uploads/2015/03/Git-push-command.jpeg","1.jpeg");
        TestThresd2 t2 = new TestThresd2("https://www.runoob.com/wp-content/uploads/2015/03/github1.jpg","2.jpg");
        TestThresd2 t3 = new TestThresd2("https://www.runoob.com/wp-content/uploads/2015/03/79A84530-7DC0-4D25-9F83-8776433A4C32.jpg","3.jpg");

        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");
        }
    }
}

2.2 实现Runnable接口（推荐使用）

三个步骤：

• 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

//创建线程方法二
//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 TestThread3 implements Runnable{
    @Override
    public void run() {
        //run()方法线程体
        for (int i = 0; i < 20; i++) {
            System.out.println("我在学习多线程---" + i);
        }
    }

    public static void main(String[] args) {
        //创建Runnable接口实现类对象
        TestThread3 t = new TestThread3();

        //创建线程对象，通过线程对象开启线程代理
        Thread thread = new Thread(t);
        thread.start();

        for (int i = 0; i < 200; i++) {
            System.out.println("我在看代码---" + i);
        }
    }
}

两种方法对此

2.2.1 多线程买火车票的例子

发现问题：多个线程操作同一个资源的情况下，线程不安全，并发问题

public class TestThread4 implements Runnable{

    //票数
    private int ticketNums = 10;

    @Override
    public void run() {
        while (true) {
            if (ticketNums <= 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"+ticketNums--+"票");
        }
    }

    public static void main(String[] args) {
        TestThread4 ticket = new TestThread4();
        new Thread(ticket,"小明").start();
        new Thread(ticket,"老师").start();
        new Thread(ticket,"小黄").start();
    }
}

2.2.2 龟兔赛跑

public class Race implements Runnable{

    private static String winner;

    @Override
    public void run() {
        for (int i = 0; i <= 100; i++) {

            //模拟兔子休息
            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
    private boolean gameOver(int steps) {
        //判断是否有胜利者
        if (winner != null)
            return true;
        else {
            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();
    }
}

2.3 实现Callable接口

案列：多线程下载图片

public class TestCallable implements Callable<Boolean> {

    private String url;   //保存图片地址
    private String name;  //保存的文件名

    public TestCallable(String url, String name) {
        this.url = url;
        this.name = name;
    }
    //下载图片的执行体
    @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;
    }

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        TestCallable t1 = new TestCallable("https://www.runoob.com/wp-content/uploads/2015/03/Git-push-command.jpeg","1.jpeg");
        TestCallable t2 = new TestCallable("https://www.runoob.com/wp-content/uploads/2015/03/github1.jpg","2.jpg");
        TestCallable t3 = new TestCallable("https://www.runoob.com/wp-content/uploads/2015/03/79A84530-7DC0-4D25-9F83-8776433A4C32.jpg","3.jpg");

        //1. 创建执行服务
        ExecutorService ser = Executors.newFixedThreadPool(3);
        //2. 提交执行
        Future<Boolean> r1 = ser.submit(t1);
        Future<Boolean> r2 = ser.submit(t2);
        Future<Boolean> r3 = ser.submit(t3);
        //3. 获取结果
        boolean rs1 = r1.get();
        boolean rs2 = r2.get();
        boolean rs3 = r3.get();
        //4. 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");
        }
    }
}

Callable的好处：可以定义返回值；可以抛出异常

3. 静态代理

是线程的底层实现原理
静态代理模式总结

• 真实对象和代理对象都要实现同一个接口
• 代理对象要代理真实角色
  好处：
  代理对象可以做很多真实对象做不了的事情，真实对象专注做自己的事情

public class StaticProxy {
    public static void main(String[] args) {
        You you = new You();
        WeddingCompany company = new WeddingCompany(you);
        company.HappyMarry();
    }
}

//结婚接口
interface Marry{
    void HappyMarry();
}

//真实角色
class You implements Marry{
    @Override
    public void HappyMarry() {
        System.out.println("我要结婚啦");
    }
}

//代理角色,帮助你结婚
class WeddingCompany implements Marry{

    //代理谁-->真实对象
    private Marry target;

    public WeddingCompany(Marry target) {
        this.target = target;
    }

    @Override
    public void HappyMarry() {
        before();
        this.target.HappyMarry();//真实对象
        after();
    }

    private void after() {
        System.out.println("结婚之后，收尾款");
    }

    private void before() {
        System.out.println("结婚之前，布置现场");
    }
}

4. Lamda表达式(前提是函数式接口)

new Thread(()->System.out.println("i like thread")).start();

//推导lambda表达式
public class TestLambda {

    //3. 静态内部类
    static class Like2 implements ILike{
        @Override
        public void lambda() {
            System.out.println("i like lambda2");
        }
    }
    public static void main(String[] args) {
        ILike like = new Like();
        like.lambda();

        like = new Like2();
        like.lambda();

        // 4. 局部内部类
        class Like3 implements ILike{
            @Override
            public void lambda() {
                System.out.println("i like lambda3");
            }
        }
        like = new Like3();
        like.lambda();

        //5.匿名内部类，没有类的名称，必须借助接口或父类
        like = new ILike() {
            @Override
            public void lambda() {
                System.out.println("i like lambda4");
            }
        };
        like.lambda();

        //6. lambda简化
        like = ()-> { System.out.println("i like lambda5");};
        like.lambda();
    }
}


//1. 定义一个函数式接口
interface ILike{
    void lambda();
}

//2. 实现类
class Like implements ILike{
    @Override
    public void lambda() {
        System.out.println("i like lambda1");
    }
}

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