Get handle of back  click in java class
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK) {
        // Code here
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

@Override
public void onBackPressed()
{
  your_code(){}

  super.onBackPressed();
  return;
}