why is my circle filled Black even though i haven't set it to be filled

Question

I am currently working on an assignment where i must print a circle in the center of the primary stage and 4 buttons on the bottom center area of the primary stage which move the circle, up, down, left, and right when clicked. when i run my code, my circle is filled in with the color black. I have set the stroke of the circle to be black but i have not set the circle to be filled black. I know i can just set my circle to be filled white and somewhat solve the problem, but i am wondering if anyone knows why this is happening. Also, i cannot get the Circle and the buttons to print into the same window. I can get either the circle to print by setting the primaryStage to the scene or print the buttons by setting the scene to hBox and then setting the primaryStage to the scene. How should i best change my code so that the buttons and the circle are both displayed?

 import javafx.application.Application;
 import javafx.geometry.Insets;
 import javafx.scene.Scene;
 import javafx.scene.layout.BorderPane;
 import javafx.scene.layout.StackPane;
 import javafx.stage.Stage;
 import javafx.scene.paint.Color;
 import javafx.scene.shape.Circle;
 import javafx.scene.control.Button; 
 import javafx.scene.layout.HBox;
 import javafx.geometry.Pos;
 import javafx.event.EventHandler;
 import javafx.event.ActionEvent;


public class Btest extends Application {
@Override // Override the start method in the Application class
public void start(Stage primaryStage) {

// Create a border pane 
BorderPane pane = new BorderPane();
// create Hbox, set to bottom center
HBox hBox = new HBox();
hBox.setSpacing(10);
hBox.setAlignment(Pos.BOTTOM_CENTER);

Button btLeft = new Button("Left");
Button btDown = new Button("Down");
Button btUp = new Button("Up");
Button btRight = new Button("Right");
hBox.getChildren().addAll(btLeft, btDown, btUp, btRight);

 // Lambda's
btLeft.setOnAction((e) -> {
System.out.println("Process Left");
});
btDown.setOnAction((e) -> {
System.out.println("Process Down");
});
btUp.setOnAction(e -> {
System.out.println("Process Up");
});
btRight.setOnAction((e) -> {
System.out.println("Process Right");   
});

pane.setCenter(new CenteredCircle("Center"));
// Create a scene and place it in the stage
Scene scene = new Scene(pane, 300, 300);

//set stage and display
primaryStage.setTitle("ShowBorderPane"); // Set the stage title
primaryStage.setScene(scene); // Place the scene in the stage
primaryStage.show(); // Display the stage
 }

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

 // create custom class for circle
class CenteredCircle extends StackPane {
public CenteredCircle(String title) {

setPadding(new Insets(11.5, 12.5, 13.5, 14.5));
Circle circle = new Circle();
circle.setStroke(Color.BLACK);
circle.setCenterX(50);
circle.setCenterY(50);
circle.setRadius(50);
getChildren().add(circle); 
 }
}

Answer 1

"Why is my circle filled Black even though i haven't set it to be filled?"

Because the default color is black. See the doc of Shape.setFill() method:

Defines parameters to fill the interior of an Shape using the settings of the Paint context. The default value is Color.BLACK for all shapes except Line, Polyline, and Path. The default value is null for those shapes.

"... Also, i cannot get the Circle and the buttons to print into the same window."

Put the Hbox to the parent BorderPane, for instance into the bottom:

pane.setBottom( hBox );