In javaFx, why do we need to call "getChildren ()" when we add an item to the window?

Question

For example, when we add a new button to the panel, we need to write the following code:

 StackPane pane = new StackPane();
 pane.getChildren().add(new Button("OK"));

Why do we need to call "getChildren ()?" what is he doing Why can't we say:

 StackPane pane = new StackPane();
 pane.add(new Button("OK"));

We add a button to the panel. We don’t add it to our children,

Answer 1

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public class StackPane {

    private final List<Node> children = new ArrayList<>(); // or some other list implementation...

    public void add(Node node) {
        children.add(node);
    }

    public boolean remove(Node node) {
        return children.remove(node);
    }

    public void add(int index, Node node) {
        children.add(index, node);
    }

    public boolean remove(int index) {
        return children.remove(index);
    }

    public void addAll(Collection<Node> nodes) {
        children.addAll(nodes);
    }

    // lots more methods like this...

    // lots of layout code omitted...
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public class StackPane {
    private final List<Node> children = new ArrayList<>();

    public List<Node> getChildren() {
        return children ;
    }

    // layout code omitted...
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StackPane pane = new StackPane();

Button button = new Button("OK");

pane.getChildren()
    // oooh, a List, I know how those work
    .add(button);

List<Label> lotsOfLabels = Arrays.asList(new Label("One"), new Label("Two"), new Label("Three"));

pane.getChildren()
    // still a list, I know more things I can do here:
    .addAll(lotsOfLabels);

pane.getChildren().remove(button);

pane.getChildren().clear();

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Answer 2

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Answer 3

The panel tracks an array of its children. The reason you cannot just call pane.add(new Button("OK"));is because the StackPane class simply does not provide this method. You must add the element directly to the panel's child array.