Button has several Click response methods

Button bt_Demo = (Button)findViewById(R.id.bt_Demo);
   bt_Demo.setOnClickListener(new OnClickListener()
   {
       @Override
       public void onClick(View v)
       {
           //响应Clicked事件
//......
       }
   });

Button bt_Demo = (Button)findViewById(R.id.bt_Demo);
   bt_Demo.setOnClickListener(listener);
   private OnClickListener listener = new OnClickListener(){ 
       @Override
       public void onClick(View arg0) {
           // TODO Auto-generated method stub        
            switch(arg0.getId()){ 
                case R.id.bt_Demo:
                   //响应Clicked事件
//......
break;
                default:
                break;
                }
       }
   }

Button bt_Demo = (Button)findViewById(R.id.bt_Demo);
   bt_Demo.setOnClickListener(new ButtonListener());
   private class ButtonListener implements OnClickListener{
       @Override
       public void onClick(View arg0) {
               //响应Clicked事件
//......
       }        
   }