How to bind a StringProperty to a BigDecimal?

Question

I have a ChangeListener that when triggered, a findGPA() method is called.

private void findGPA(){
    GPA = gradeCre/sum;
    decGPA = new BigDecimal(GPA);
    decGPA = decGPA.setScale(2, RoundingMode.CEILING);
    System.out.println("Your average GPA is: " + decGPA);
}

The BigDecimal is initialized as follows:

private BigDecimal decGPA = BigDecimal.ZERO;

In the initialize() method:

SubmitStageBorderPane.setBottom(AddStackCircle());

which calls:

private StackPane AddStackCircle(){

    StackPane stackCircle = new StackPane();
    StringProperty gpa = new SimpleStringProperty("");
    gpa.bind(new SimpleStringProperty(decGPA.toString()));

    Text avgGPA = createText("Your semester GPA is: " + gpa);
    Circle resultCircle = createCircle(avgGPA);

    stackCircle.getStyleClass().add("stackCircle");
    stackCircle.getChildren().addAll(resultCircle, avgGPA);

    return stackCircle;
}

private Circle createCircle(Text avgGPA){

    Circle resultCircle = new Circle();
    resultCircle.setFill(Color.GREEN);
    resultCircle.setStroke(Color.GREY);
    resultCircle.setStrokeWidth(3);
    resultCircle.setRadius(getWidth(avgGPA) / 2 + 10);

    return resultCircle;
}

private Text createText(String text){

    Text avgGPA = new Text(text);
    avgGPA.setBoundsType(TextBoundsType.VISUAL);
    avgGPA.getStyleClass().add("avgGPA");

    return avgGPA;
}

However, when i run it, it produces the following label text Your semester GPA is: StringProperty[bound, invalid] , and it doesn't change even when the value of decGPA changes.

Answer 1

For the text to update, you'd need to bind the text of the Text node instead of simply setting the text. Furthermore you should bind it to a property that is actually updated, not just a property that will never be modidfied (like new SimpleStringProperty(decGPA.toString()) ).

Assuming the findGPA method is properly called, it should be implemented like this:

private final ObjectProperty<BigDecimal> decGPA = new SimpleObjectProperty(BigDecimal.ZERO);

private void findGPA(){
    GPA = gradeCre/sum;
    decGPA.set(BigDecimal.valueOf(GPA).setScale(2, RoundingMode.CEILING));
    System.out.println("Your average GPA is: " + decGPA.get());
}

private Text createText(ObservableValue<String> textExpression){

    Text avgGPA = new Text();
    avgGPA.textProperty().bind(textExpression);
    avgGPA.setBoundsType(TextBoundsType.VISUAL);
    avgGPA.getStyleClass().add("avgGPA");

    return avgGPA;
}

Text avgGPA = createText(decGPA.asString("Your semester GPA is: %s"));