Android 按兩下退出APK的實現

app開發中，經常需要按下兩次退出apk，以下是實現方式：

     private static Boolean isExit = false;
     private static Boolean hasTask = false;
     Timer tExit = new Timer();
     TimerTask task = new TimerTask() {
             @Override
     public void run() {
          isExit = false;
          hasTask = true;
       }
     };


     @Override
     public boolean onKeyDown(int keyCode, KeyEvent event) {
          if (keyCode == KeyEvent.KEYCODE_BACK) {
               if(isExit == false ) {
                   isExit = true;
                   Toast.makeText(this, "再點擊返回鍵，退出程序",          Toast.LENGTH_SHORT).show();
               if(!hasTask) {
                    tExit.schedule(task, 2000);
                  }
               } else {
                   finish();
                    System.exit(0);
               }
          }
          if (keyCode==KeyEvent.KEYCODE_MENU) {
               openOptionsMenu();    
          }
     return true;
     }