1.2.1继承Thread类

实现多线程的方法有2种：方法一是继承Thread，方法二是实现Runnerable接口

使用继承Thread类的方法创建多线程的时候，最大的局限性就是不支持多继承，因为java语言的特点就是单继承，因此为了支持多继承，完全可以实现Runnerabe接口的方式。

package com.cky.thread;

/**
 * Created by chenkaiyang on 2017/12/2.
 */
public class MyFirstThread  extends Thread{
    @Override
    public void run() {
        super.run();
        System.out.println("myThread");
    }
}

 package com.cky.test;

 import com.cky.thread.MyFirstThread;

 /**
  * Created by chenkaiyang on 2017/12/2.
  */
 public class Test {
     public static void main(String[] args) throws InterruptedException {
         MyFirstThread th = new MyFirstThread();
         th.start();
         System.out.println("运行结束");
     }
 }

D:\it\jdk1.8\bin\java -Didea.launcher.port=7535 "-Didea.launcher.bin.path=D:\it\idea\IntelliJ IDEA 2016.3.3\bin" -Dfile.encoding=UTF-8 -classpath "D:\it\jdk1.8\jre\lib\charsets.jar;D:\it\jdk1.8\jre\lib\deploy.jar;D:\it\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\it\jdk1.8\jre\lib\ext\cldrdata.jar;D:\it\jdk1.8\jre\lib\ext\dnsns.jar;D:\it\jdk1.8\jre\lib\ext\jaccess.jar;D:\it\jdk1.8\jre\lib\ext\jfxrt.jar;D:\it\jdk1.8\jre\lib\ext\localedata.jar;D:\it\jdk1.8\jre\lib\ext\nashorn.jar;D:\it\jdk1.8\jre\lib\ext\sunec.jar;D:\it\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\it\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\it\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\it\jdk1.8\jre\lib\ext\zipfs.jar;D:\it\jdk1.8\jre\lib\javaws.jar;D:\it\jdk1.8\jre\lib\jce.jar;D:\it\jdk1.8\jre\lib\jfr.jar;D:\it\jdk1.8\jre\lib\jfxswt.jar;D:\it\jdk1.8\jre\lib\jsse.jar;D:\it\jdk1.8\jre\lib\management-agent.jar;D:\it\jdk1.8\jre\lib\plugin.jar;D:\it\jdk1.8\jre\lib\resources.jar;D:\it\jdk1.8\jre\lib\rt.jar;F:\springboot\threaddemo\out\production\threaddemo;D:\it\idea\IntelliJ IDEA 2016.3.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.cky.test.Test
运行结束
myThread

Process finished with exit code 0

从图中结果可知

MyFirstThread类中的run方法执行的比较晚，说明当开启线程的时候，cpu首先执行的是main线程，执行结束后，cpu切换到了另一个线程，这时再执行run方法中的代码

下面来通过代码来随机展示线程的随机性

先创建线程类

 package com.cky.thread;

 /**
  * Created by chenkaiyang on 2017/11/27.
  */
 public class Mythread  extends Thread{
    @Override
     public void run(){
        try {
            for (int i=0; i<10;i++) {
                int time = (int) (Math.random() * 1000);
                Thread.sleep(time);
                System.out.println("run="+ Thread.currentThread().getName());

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

再创建测试类

 package com.cky.test;

 import com.cky.thread.Mythread;

 /**
  * Created by chenkaiyang on 2017/11/27.
  */
 public class Test1 {
     public static void main(String[] args) {
         try {
             Thread thread = new Mythread();
             thread.setName("cky");
             thread.start();
             for (int i = 0; i < 10; i++) {
                 int time = (int) (Math.random() * 1000);
                 Thread.sleep(time);
                 System.out.println("main="+ Thread.currentThread().getName());

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

     }

 }

D:\it\jdk1.8\bin\java -Didea.launcher.port=7533 "-Didea.launcher.bin.path=D:\it\idea\IntelliJ IDEA 2016.3.3\bin" -Dfile.encoding=UTF-8 -classpath "D:\it\jdk1.8\jre\lib\charsets.jar;D:\it\jdk1.8\jre\lib\deploy.jar;D:\it\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\it\jdk1.8\jre\lib\ext\cldrdata.jar;D:\it\jdk1.8\jre\lib\ext\dnsns.jar;D:\it\jdk1.8\jre\lib\ext\jaccess.jar;D:\it\jdk1.8\jre\lib\ext\jfxrt.jar;D:\it\jdk1.8\jre\lib\ext\localedata.jar;D:\it\jdk1.8\jre\lib\ext\nashorn.jar;D:\it\jdk1.8\jre\lib\ext\sunec.jar;D:\it\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\it\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\it\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\it\jdk1.8\jre\lib\ext\zipfs.jar;D:\it\jdk1.8\jre\lib\javaws.jar;D:\it\jdk1.8\jre\lib\jce.jar;D:\it\jdk1.8\jre\lib\jfr.jar;D:\it\jdk1.8\jre\lib\jfxswt.jar;D:\it\jdk1.8\jre\lib\jsse.jar;D:\it\jdk1.8\jre\lib\management-agent.jar;D:\it\jdk1.8\jre\lib\plugin.jar;D:\it\jdk1.8\jre\lib\resources.jar;D:\it\jdk1.8\jre\lib\rt.jar;F:\springboot\threaddemo\out\production\threaddemo;D:\it\idea\IntelliJ IDEA 2016.3.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.cky.test.Test1
run=cky
main=main
run=cky
run=cky
run=cky
main=main
run=cky
run=cky
main=main
run=cky
run=cky
run=cky
main=main
main=main
main=main
main=main
run=cky
main=main
main=main
main=main

Process finished with exit code 0

运行结果如上图：结果分析：代码用了随机数的方式用了Thread.sleep方法。该方法的目的是为了让当前执行的线程进行等待，这样，cpu就会切换到另一个线程。

注：执行start（）方法的顺序也不能代表线程的启动顺序。

package com.cky.thread;

/**
 * Created by chenkaiyang on 2017/12/2.
 */
public class MySecondThread extends  Thread{

    private int i;
    public MySecondThread (int i) {
        super();
        this.i = i;
    }
    @Override
    public void run() {
        super.run();
        System.out.println(i);
    }
}

 package com.cky.test;

 import com.cky.thread.MySecondThread;

 /**
  * Created by chenkaiyang on 2017/12/2.
  */
 public class Test {
     public static void main(String[] args) throws InterruptedException {
         MySecondThread t1 = new MySecondThread(1);
         MySecondThread t2 = new MySecondThread(2);
         MySecondThread t3 = new MySecondThread(3);
         MySecondThread t4 = new MySecondThread(4);
         MySecondThread t5 = new MySecondThread(5);
         MySecondThread t6 = new MySecondThread(6);
         MySecondThread t7 = new MySecondThread(7);
         t1.start();
         t2.start();
         t3.start();
         t4.start();
         t5.start();
         t6.start();
         t7.start();
     }
 }

D:\it\jdk1.8\bin\java -Didea.launcher.port=7538 "-Didea.launcher.bin.path=D:\it\idea\IntelliJ IDEA 2016.3.3\bin" -Dfile.encoding=UTF-8 -classpath "D:\it\jdk1.8\jre\lib\charsets.jar;D:\it\jdk1.8\jre\lib\deploy.jar;D:\it\jdk1.8\jre\lib\ext\access-bridge-64.jar;D:\it\jdk1.8\jre\lib\ext\cldrdata.jar;D:\it\jdk1.8\jre\lib\ext\dnsns.jar;D:\it\jdk1.8\jre\lib\ext\jaccess.jar;D:\it\jdk1.8\jre\lib\ext\jfxrt.jar;D:\it\jdk1.8\jre\lib\ext\localedata.jar;D:\it\jdk1.8\jre\lib\ext\nashorn.jar;D:\it\jdk1.8\jre\lib\ext\sunec.jar;D:\it\jdk1.8\jre\lib\ext\sunjce_provider.jar;D:\it\jdk1.8\jre\lib\ext\sunmscapi.jar;D:\it\jdk1.8\jre\lib\ext\sunpkcs11.jar;D:\it\jdk1.8\jre\lib\ext\zipfs.jar;D:\it\jdk1.8\jre\lib\javaws.jar;D:\it\jdk1.8\jre\lib\jce.jar;D:\it\jdk1.8\jre\lib\jfr.jar;D:\it\jdk1.8\jre\lib\jfxswt.jar;D:\it\jdk1.8\jre\lib\jsse.jar;D:\it\jdk1.8\jre\lib\management-agent.jar;D:\it\jdk1.8\jre\lib\plugin.jar;D:\it\jdk1.8\jre\lib\resources.jar;D:\it\jdk1.8\jre\lib\rt.jar;F:\springboot\threaddemo\out\production\threaddemo;D:\it\idea\IntelliJ IDEA 2016.3.3\lib\idea_rt.jar" com.intellij.rt.execution.application.AppMain com.cky.test.Test
1
3
4
5
2
7
6

Process finished with exit code 0

结果分析：执行start方法的顺序不能代表线程的启动顺序。