为什么我的`Runnable`没有`start`方法？

Question

为什么我必须Thread在内部类中扩展而不是实现Runnable 以下代码有效: -

class Outer{

 Inner innerObj;

 Outer(){
  innerObj = new Inner();
 }

 public void begin(){

  innerObj.start();
 }

 class Inner extends Thread{

  Inner(){
   System.out.println("Thread initialized!");
  }

  public void run(){

    System.out.println("Thread running!");

  }  
 }
}

class Driver{

 public static void main(String[] args){

  Outer o1 = new Outer();
  o1.begin();

 }

}

但是使用a Runnable会导致编译错误: -

class Outer{

 Inner innerObj;

 Outer(){
  innerObj = new Inner();
 }

 public void begin(){

  innerObj.start();
 }

 class Inner implements Runnable{

  Inner(){
   System.out.println("Thread initialized!");
  }

  public void run(){

    System.out.println("Thread running!");

  }  
 }
}

class Driver{

 public static void main(String[] args){

  Outer o1 = new Outer();
  o1.begin();

 }

}

Answer 1

那是因为实现Runnable不给类提供start方法.你需要创建一个Thread来运行Inner.

Inner i = new Inner();
Thread t = new Thread( i );