创建一个线程的第二种方法是创建一个新的类，该类继承Thread类，然后创建一个该类的实例。

继承类必须重写run()方法，该方法是新线程的入口点。它也必须调用start()方法才能执行。

实例

// 通过继承 Thread 创建线程
class NewThread extends Thread {
   NewThread() {
      // 创建第二个新线程
      super("Demo Thread");
      System.out.println("Child thread: " + this);
      start(); // 开始线程
   }
 
   // 第二个线程入口
   public void run() {
      try {
         for(int i = 5; i > 0; i--) {
            System.out.println("Child Thread: " + i);
                            // 让线程休眠一会
            Thread.sleep(50);
         }
      } catch (InterruptedException e) {
         System.out.println("Child interrupted.");
      }
      System.out.println("Exiting child thread.");
   }
}
 
public class ExtendThread {
   public static void main(String args[]) {
      new NewThread(); // 创建一个新线程
      try {
         for(int i = 5; i > 0; i--) {
            System.out.println("Main Thread: " + i);
            Thread.sleep(100);
         }
      } catch (InterruptedException e) {
         System.out.println("Main thread interrupted.");
      }
      System.out.println("Main thread exiting.");
   }
}

编译以上程序运行结果如下：

Child thread: Thread[Demo Thread,5,main]
Main Thread: 5
Child Thread: 5
Child Thread: 4
Main Thread: 4
Child Thread: 3
Child Thread: 2
Main Thread: 3
Child Thread: 1
Exiting child thread.
Main Thread: 2
Main Thread: 1
Main thread exiting.