code: public void onDriveButtonClicked(View arg0) {
          Log.d(TAG, "Drive button clicked.");
          if (!mSubscribedToInfiniteGas && mTank <= 0)
              alert(R.string.out_of_gas_msg);
          else {
              if (!mSubscribedToInfiniteGas) --mTank;
              saveData();
              alert(R.string.spent_gas_msg);
              updateUi();
              Log.d(TAG, "Vrooom. Tank is now " + mTank);
          }
      }
docs: Drive button clicked. Burn gas!