code: private void checkPinBoxesAvailable() {
  
          int index = -1;
          int i = currentFocus + 1;
          while (i != currentFocus) {
  
              if (i > (mNumberPinBoxes - 1)) {
                  i = 0;
              }
  
              if (pinBoxIsEmpty(i)) {
                  index = i;
                  break;
              }
              i++;
          }
          chooseNextAction(index);
      }
docs: Check for an empty PinBox {@link EditText} from the current PinBox.
  Set focus in the next empty PinBox or notify that {@link PinView} is completed.