//JAVA
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
     event.startTracking();
     return true;
    }
    return super.onKeyDown(keyCode, event);
   }

   public boolean onKeyUp(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.isTracking()
      && !event.isCanceled()) {
     Toast.makeText(app.this, "ddddd", Toast.LENGTH_SHORT).show();
     ActivityManager am = (ActivityManager) getSystemService(ACTIVITY_SERVICE);
       am.killBackgroundProcesses(getPackageName());
                    //이벤트처리
     return true;
    }
    return super.onKeyUp(keyCode, event);
   } 

//메인페스트 추가
<uses-permission android:name="android.permission.KILL_BACKGROUND_PROCESSES"></uses-permission>

이렇게 해줬는데두 안되네용 ㅜㅜ
모가 문제인지 ㅜㅜ