【Java-II】多线程详解 P6-8（Day14-20210713-Day2）

06 初识并发问题——以购买火车票为例

package threadLearn.demo01;

public class TestThread4 implements Runnable{
    //票数
    private int ticketNums=10;
    @Override
    public void run() {
        while (true){
            if (ticketNums<=0){
                break;
            }
            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,"黄牛").start();
        System.out.println(Thread.currentThread().getName());
    }
}

输出：
黄牛--->拿到了第10票
老师--->拿到了第10票
小明--->拿到了第9票
老师--->拿到了第8票
黄牛--->拿到了第7票
小明--->拿到了第8票
小明--->拿到了第5票
黄牛--->拿到了第4票
老师--->拿到了第6票
小明--->拿到了第2票
黄牛--->拿到了第1票
老师--->拿到了第3票

从中我们可以看到问题：多个线程操作同一个资源的时候，容易出现并发问题，同一个资源被不同的线程访问

07 龟兔赛跑

package threadLearn.demo01;

public class Race implements Runnable{
    private static String winner;

    @Override
    public void run() {
        for (int i = 0; i <= 100; i++) {
            if (Thread.currentThread().getName().equals("兔子") && i%10==0){
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            //判断比赛是否结束
            //如果比赛结束了，就停止程序
            if (gameOver(i)){
                break;
            }
            System.out.println(Thread.currentThread().getName() + "-->跑了" + i + "步");
        }
    }

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

    public Race() {
    }

    public static void main(String[] args) {
        Race race = new Race();
        new Thread(race,"兔子").start();
        new Thread(race,"乌龟").start();

    }
}

08 实现Callable接口

package threadLearn.demo02;

import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.util.concurrent.*;

public class TestCallable implements Callable<Boolean> {
    private String url;
    private String name;

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

    @Override
    public Boolean call() throws Exception {
        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) {
        TestCallable t1 = new TestCallable("https://n.sinaimg.cn/news/transform/350/w210h140/20210713/a5f2-b6ea01a4a9952832066c1bc25dfa04e7.jpg","20210713_11.jpg");
        TestCallable t2 = new TestCallable("https://n.sinaimg.cn/news/transform/350/w210h140/20210713/64a8-8bf9fb26cdea87a38a446e5c1c685c4c.jpg","20210713_22.jpg");
        TestCallable t3 = new TestCallable("https://n.sinaimg.cn/ent/transform/175/w105h70/20210713/4047-3aee4bc841cadc336b7104473218c732.jpg","20210713_33.jpg");

        //创建执行服务：
        //提交执行
        ExecutorService executorService = Executors.newFixedThreadPool(1);

        //获取结果
        Future<Boolean> r1 = executorService.submit(t1);
        Future<Boolean> r2 = executorService.submit(t2);
        Future<Boolean> r3 = executorService.submit(t3);

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

        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

        //关闭服务
        executorService.shutdownNow();
    }
}

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");
        }
    }
}