多线程

多线程

线程的三种创建方式

1. Thread class：继承Thread类

   1. 自定义线程类继承Threadlei类

   2. 重写run()方法，编写线程执行体

   3. 创建线程对象，调用start()启动线程

      package com.thread;
       
       
      //创建线程方式1：继承Thread类，重写run方法,调用start方法开启线程
      public class ThreadTest01 extends Thread {
          @Override
          public void run() {
              for (int i = 0; i < 20; i++) {
                  System.out.println("i am watch code:" + i);
              }
          }
       
       
          public static void main(String[] args) {
              //main线程
       
              //创建一个线程对象
              ThreadTest01 threadTest01 = new ThreadTest01();
       
              //调用start()方法开启线程
              //start()方法是主线程和子线程一起执行
              //run()方法是先执行run()方法的子线程，再执行主线程
              //注意：线程开启不一定立即执行，需要等CPU的调度处理
              threadTest01.start();
       
              for (int i = 0; i < 20; i++) {
                  System.out.println("我在学习多线程：" + i);
              }
          }
      }

      ---

      代码实现多线程下载图片

      package com.thread;
       
       
      import org.apache.commons.io.FileUtils;
       
      import java.io.File;
      import java.io.IOException;
      import java.net.URL;
       
      //利用thread实现多线程同步下载图片
      public class ThreadTest02 extends Thread {
       
          private String url;
          private String name;
       
          public ThreadTest02(String url, String name) {
              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("下载了文件名为：" + name);
          }
       
          public static void main(String[] args) {
              ThreadTest02 test01 = new ThreadTest02("https://gimg2.baidu.com/image_search/src=http%3A%2F%2F5b0988e595225.cdn.sohucs.com%2Fimages%2F20190513%2F7cb9afc55171450eaa17604c5e4fc765.jpeg&refer=http%3A%2F%2F5b0988e595225.cdn.sohucs.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=030319dc87f0a7ce129ba69ab5bda5e5", "1.jpg");
              ThreadTest02 test02 = new ThreadTest02("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.youxi369.com%2Farticle%2Fcontents%2F2021%2F01%2F07%2F2021010740735362.jpg&refer=http%3A%2F%2Fimg.youxi369.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=97f6180af2ab121b58f15c7f300a0ebb", "2.jpg");
              ThreadTest02 test03 = new ThreadTest02("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201802%2F12%2F20180212094815_MWrv5.jpeg&refer=http%3A%2F%2Fb-ssl.duitang.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=316c717e8b3e03682f56422dfa92fba0", "3.jpg");
       
              test01.start();
              test02.start();
              test03.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方法出现异常");
              }
          }
      }

      结果：
      

  下载成功，注意：要先导入commons-IO包
 
  验证可得：start（）方法没有按程序顺序执行，先后顺序看CPU调度的执行情况

2. Runnable接口 ：实现Runnable接口

   package com.thread;
    
    
   //创建线程方式2：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 ThreadTest03 implements Runnable{
       @Override
       public void run() {
           for (int i = 0; i < 20; i++) {
               System.out.println("i am watch code:" + i);
           }
       }
    
       public static void main(String[] args) {
           //创建Runnable接口实现类对象
           ThreadTest03 threadTest03 = new ThreadTest03();
    
           //创建线程对象，通过线程对象来开启我们的线程 代理
           new Thread(threadTest03).start();
    
    
           for (int i = 0; i < 20; i++) {
               System.out.println("我在学习多线程：" + i);
           }
       }
   }

3. Callable接口：实现Callable接口

   package com.thread;
    
    
   import org.apache.commons.io.FileUtils;
    
   import java.io.File;
   import java.io.IOException;
   import java.net.URL;
   import java.util.concurrent.*;
    
   //创建线程方式3：实现callable接口
    
   /**
    * callable的好处：
    * 1、可以定义返回值
    * 2、可以抛出异常
    */
   public class CallableTest01 implements Callable<Boolean> {
       private String url;
       private String name;
    
       public CallableTest01(String url, String name) {
           this.url = url;
           this.name = name;
       }
    
    
       //下载图片线程的执行体
       @Override
       public Boolean call() {
           webDownloader01 webDownloader01 = new webDownloader01();
           webDownloader01.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 {
           CallableTest01 t1 = new CallableTest01("https://gimg2.baidu.com/image_search/src=http%3A%2F%2F5b0988e595225.cdn.sohucs.com%2Fimages%2F20190513%2F7cb9afc55171450eaa17604c5e4fc765.jpeg&refer=http%3A%2F%2F5b0988e595225.cdn.sohucs.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=030319dc87f0a7ce129ba69ab5bda5e5", "1.jpg");
           CallableTest01 t2 = new CallableTest01("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.youxi369.com%2Farticle%2Fcontents%2F2021%2F01%2F07%2F2021010740735362.jpg&refer=http%3A%2F%2Fimg.youxi369.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=97f6180af2ab121b58f15c7f300a0ebb", "2.jpg");
           CallableTest01 t3 = new CallableTest01("https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fb-ssl.duitang.com%2Fuploads%2Fitem%2F201802%2F12%2F20180212094815_MWrv5.jpeg&refer=http%3A%2F%2Fb-ssl.duitang.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1660887492&t=316c717e8b3e03682f56422dfa92fba0", "3.jpg");
    
           //创建执行服务
           ExecutorService ser = Executors.newFixedThreadPool(3);
    
           //提交执行
           Future<Boolean> r1 = ser.submit(t1);
           Future<Boolean> r2 = ser.submit(t2);
           Future<Boolean> r3 = 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 webDownloader01 {
       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方法出现异常");
           }
       }
   }

---

并发问题

买火车票模拟代码：

package com.thread;
 
import java.nio.channels.NonReadableChannelException;
 
//多个线程操作同一个对象
//买火车票的例子
public class TreadTest04 implements Runnable {
 
 
    //火车票
    private int ticketNum = 10;
 
 
    @Override
    public void run() {
        while (true) {
            if (ticketNum <= 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 " + ticketNum-- + " 张票");
        }
    }
 
    public static void main(String[] args) {
        TreadTest04 treadTest04 = new TreadTest04();
 
        new Thread(treadTest04, "小明").start();
        new Thread(treadTest04, "老师").start();
        new Thread(treadTest04, "黄牛").start();
    }
}

运行结果：

问题：多个线程操作同一个资源的情况下，线程不安全，数据紊乱

---

案例：龟兔赛跑

1. 首先来个赛道距离，然后要离终点越来越近

2. 判断比赛是否结束

3. 打印出胜利者

4. 龟兔赛跑开始

5. 要保证乌龟胜利，兔子需要睡觉，用sleep来模拟 兔子睡觉

6. 乌龟赢得比赛

   package com.thread;
    
   public class Race implements Runnable {
    
       //胜利者
       private static String winner;
    
       @Override
       public void run() {
           for (int i = 1; i <= 100; i++) {
    
               //模拟兔子睡觉
               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
       public boolean gameOver(int steps) {
           //判断是否存在胜利者
           if (winner != null) {//胜利者已经存在
               return true;
           }
           {
               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();
       }
   }