Go语言视频零基础入门到精通

javalearner

java线程一直是一个比较容易困扰的地方,很多初学者都不是很清楚,在此,我用了几个小试验,来将其基本概念说明一下,首先把run(),start()区分开来,    看看为什么直接调用run()和用start()启动一个线程的差别
1.
package com.dragon; import java.lang.Thread; public class ThreadTest extends Thread {
  public void run() {
   for(int i=0;i<10;i++){
        
   System.out.println("this is a Thread test");
    }
  }                                                                                   
  
  
   public static void main(String[] args) {
   try {
    Thread t = new ThreadTest();
    t.run();
   
    System.out.println("main thread is over");
   } catch (Exception ex) {
    ex.printStackTrace();
   }
  }
}
输出结果: this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
main thread is over
  表明,run()和其他方法的调用没任何不同,main方法按顺序执行了它,并打印出最后一句, 退出程序.下面看看把调用改为start() 2. package com.dragon; import java.lang.Thread; public class ThreadTest extends Thread {
  public void run() {
   for(int i=0;i<10;i++){
        
   System.out.println("this is a Thread test");    }
  }  public static void main(String[] args) {
   try {
    Thread t = new ThreadTest();
    t.start();
   
    System.out.println("main thread is over");
   } catch (Exception ex) {
    ex.printStackTrace();
   }
  }
}
输出结果: main thread is over
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
  这表明,start()方法重新创建了一个线程,在main方法执行结束后,由于start()方法创建的 线程没有运行结束,因此主线程未能退出,直到线程 t 也执行完毕,这里要注意,默认创建的 线程是用户线程(非守护线程),再改一下代码 3. package com.dragon; import java.lang.Thread; public class ThreadTest extends Thread {
  public void run() {
   for(int i=0;i<10;i++){
        
   System.out.println("this is a Thread test");    }
  }  public static void main(String[] args) {
   try {
    Thread t = new ThreadTest();
    t.setDaemon(true);
    t.start();
   
    System.out.println("main thread is over");
   } catch (Exception ex) {
    ex.printStackTrace();
   }
  }
}
输出为: main thread is over
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test 为什么没有打印出十句呢,因为我们将 t 线程设置为了daemon(守护)线程, 程序中只有守护线程存在的时候,是可以退出的,所以只打印了七句便退出了. 再改一下代码 4. package com.dragon; import java.lang.Thread; public class ThreadTest extends Thread {
  public void run() {
   for(int i=0;i<100;i++){
        
   System.out.println("this is a Thread test");    }
  }  public static void main(String[] args) {
   try {
    Thread t = new ThreadTest();
    t.start();
    System.out.println("main thread is over");
    System.exit(0);
   } catch (Exception ex) {
    ex.printStackTrace();
   }
  }
}
main thread is over
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test
this is a Thread test 结果可见,用户线程可以被System.exit(0)强制kill掉,所以也只打印出七句.