I’m trying to create a Spinner in JavaFX that accepts only multiples of 0.25 and has positive and negative masks, such as -1,50 and +1,50. In both cases, I need the mask to show (-) and (+). The TextField field must be editable and follow the same rule.

I managed to create a customizable TextField like this but i dont know how to do in a Spinner:

public class TestPane extends BorderPane {
  public TestPane() {

    TextField textField = new TextField();
    BigDecimalConverter converter = new BigDecimalConverter();
    TextFormatter<BigDecimal> textFormatter = new TextFormatter<>(converter, BigDecimal.ZERO, c -> {
      if (!c.getControl().isFocused()) return null;

      String newText = c.getControlNewText().replace(".", ",");

      if (c.getControlNewText().isEmpty()) {
        return c;
      }
      if (c.getControlNewText().equals("-") && c.getAnchor() == 1) {
        return c;
      }
      if (c.getControlNewText().equals("+") && c.getAnchor() == 1) {
        return c;
      }
      if (c.getControlNewText().startsWith("-") && c.getControlCaretPosition() == 0) {
        return c;
      }
      if (c.getControlNewText().startsWith("+") && c.getControlCaretPosition() == 0) {
        c.setText(c.getText() + " ");
        return c;
      }

      BigDecimal newValue = converter.fromString(c.getControlNewText());
      if (newValue != null) {
        return c;
      } else {
        return null;
      }
    });
    textFormatter.valueProperty().bindBidirectional(valueProperty);
    textField.setTextFormatter(textFormatter);
    setCenter(new VBox(10, new HBox(6, new Text("TextField 1"), textField)));
  }
}

public static class BigDecimalConverter extends BigDecimalStringConverter {

  @Override
  public String toString(BigDecimal value) {
    if (value == null) return "0";
    return super.toString(value);
  }

  @Override
  public BigDecimal fromString(String value) {
    if (value == null || value.isEmpty()) return BigDecimal.ZERO;
    return super.fromString(value);
  }
}