Android physical key sorting and instance code

import ;
 import ;
 import ;
 import ;
 import ;
 
 public class MainActivity extends Activity {
 
   
   @Override
   protected void onCreate(Bundle savedInstanceState) {
     (savedInstanceState);
     setContentView(.activity_main);
   }
   //When we handle physical key events, the callback methods provided are onKeyUp(), onKeyDown(), and onKeyLongPress(), such as volume keys and return keys  
  @Override
  public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(keyCode == KeyEvent.KEYCODE_BACK){
       ("TAG", "This is listening to keyboard operations, press the Back key");
     }
     return (keyCode, event);
   }
   @Override
   public boolean onKeyUp(int keyCode, KeyEvent event) {
     if(keyCode == KeyEvent.KEYCODE_VOLUME_UP){
       ("TAG", "Volume key");
     }
     return (keyCode, event);
   }
   
   //In Activity, we can rewrite the onBackPressed() method to handle the return key, such as exiting with two key presses   // When pressing for the first time, record the event  //The second pressed event is minus the first pressed time and exits if the time is less than 2s, otherwise the current time will be assigned to the first event   long startTime;
   
   @Override
   public void onBackPressed() {
     ("TAG", "Supervisor Back Key");
     
     if(()-startTime<2000){
       ();//Release resources, this can also be completed() directly, but the call to the release of the parent class is more thorough     }else{
       //Record the current time       startTime = ();
       (this, "Press Back key again to exit", Toast.LENGTH_SHORT).show();
     }
   }
   
 }