JSpinnerの数値の合計がグループ内で一定になるよう設定する

class SpinnerNumberModelGroup {
  private final int expectedSum;
  private final Deque<SpinnerNumberModel> candidates = new ArrayDeque<>();
  private final ChangeListener changeListener = e -> {
    SpinnerNumberModel source = (SpinnerNumberModel) e.getSource();
    update(source);
  };
  private boolean updating;

  protected SpinnerNumberModelGroup(int expectedSum) {
    this.expectedSum = expectedSum;
  }

  @SuppressWarnings("PMD.UnusedAssignment")
  private void update(SpinnerNumberModel source) {
    if (updating) {
      return;
    }
    updating = true;
    if (candidates.size() - 1 > 0) {
      int delta = computeSum() - expectedSum;
      if (delta > 0) {
        distributeRemove(delta, source);
      } else {
        distributeAdd(delta, source);
      }
    }
    updating = false;
  }

  private void distributeRemove(int delta, SpinnerNumberModel source) {
    int counter = 0;
    int remaining = delta;
    while (remaining > 0) {
      SpinnerNumberModel model = candidates.removeFirst();
      counter++;
      if (Objects.equals(model, source)) {
        candidates.addLast(model);
      } else {
        Object prev = model.getPreviousValue();
        if (prev instanceof Integer) {
          model.setValue(prev);
          remaining--;
          counter = 0;
        }
        candidates.addLast(model);
        if (remaining == 0) {
          break;
        }
      }
      if (counter > candidates.size()) {
        String msg = "Can not distribute " + delta + " among " + candidates;
        throw new IllegalArgumentException(msg);
      }
    }
  }

  private void distributeAdd(int delta, SpinnerNumberModel source) {
    int counter = 0;
    int remaining = -delta;
    while (remaining > 0) {
      SpinnerNumberModel model = candidates.removeLast();
      counter++;
      if (Objects.equals(model, source)) {
        candidates.addFirst(model);
      } else {
        // if (model.getNumber().intValue() < (int) model.getMaximum()) {
        Object next = model.getNextValue();
        if (next instanceof Integer) {
          model.setValue(next);
          remaining--;
          counter = 0;
        }
        candidates.addFirst(model);
        if (remaining == 0) {
          break;
        }
      }
      if (counter > candidates.size()) {
        String msg = "Can not distribute " + delta + " among " + candidates;
        throw new IllegalArgumentException(msg);
      }
    }
  }

  private int computeSum() {
    return candidates.stream()
        .map(SpinnerNumberModel::getNumber)
        .mapToInt(Number::intValue)
        .sum();
  }

  public void add(SpinnerNumberModel spinner) {
    candidates.add(spinner);
    spinner.addChangeListener(changeListener);
  }
}