JavaFX center stage on screen [duplicate]

Answer 1

The default implementation of centerOnScreen() is as follows :

Rectangle2D bounds = getWindowScreen().getVisualBounds();
double centerX = bounds.getMinX() + (bounds.getWidth() - getWidth())
                                           * CENTER_ON_SCREEN_X_FRACTION;
double centerY = bounds.getMinY() + (bounds.getHeight() - getHeight())
                                           * CENTER_ON_SCREEN_Y_FRACTION;
x.set(centerX);
y.set(centerY);

where

CENTER_ON_SCREEN_X_FRACTION = 1.0f / 2;
CENTER_ON_SCREEN_Y_FRACTION = 1.0f / 3;

centerY will always set the stage a little higher than the center.

To position the stage at exact center, you can use your set your custom X and Y value.

public class Main extends Application {

    @Override
    public void start(Stage primaryStage) {

        Button btn = new Button();
        btn.setText("Say 'Hello World'");
        btn.setOnAction((ActionEvent event) -> {
                System.out.println("Hello World!");
        });
        StackPane root = new StackPane();
        root.getChildren().add(btn);
        Scene scene = new Scene(root, 300, 250);
        primaryStage.setTitle("Hello World!");
        primaryStage.setScene(scene);
        primaryStage.show();
        Rectangle2D primScreenBounds = Screen.getPrimary().getVisualBounds();
        primaryStage.setX((primScreenBounds.getWidth() - primaryStage.getWidth()) / 2);
        primaryStage.setY((primScreenBounds.getHeight() - primaryStage.getHeight()) / 2);
    }

    public static void main(String[] args) {
        launch(args);
    }
}