Swing/BigDecimalSpinnerModel のバックアップ(No.8)

class BigDecimalSpinnerModel extends SpinnerNumberModel {
  public BigDecimalSpinnerModel(
      double value, double minimum, double maximum, double stepSize) {
    super(value, minimum, maximum, stepSize);
  }
  @Override public Object getPreviousValue() {
    return incrValue(-1);
  }
  @Override public Object getNextValue() {
    return incrValue(+1);
  }
  private Number incrValue(int dir) {
    Number v = getNumber();
    BigDecimal value    = new BigDecimal(v.toString());
    BigDecimal stepSize = new BigDecimal(getStepSize().toString());

    BigDecimal newValue = dir > 0 ? value.add(stepSize) : value.subtract(stepSize);

    BigDecimal maximum  = new BigDecimal(getMaximum().toString());
    if (maximum.compareTo(newValue) < 0) {
      return null;
    }

    BigDecimal minimum  = new BigDecimal(getMinimum().toString());
    if (minimum.compareTo(newValue) > 0) {
      return null;
    }
    return newValue;
  }
}