I am trying to create an application where a user inputs a number of sides, and upon clicking a button, removes any current shape from the Scene and generates a shape with the specified number of sides.

Whilst the logic to generate the shape is working, implementation root.getChildren().remove(shape); does not appear to be working?

public class genShape extends Application 
{
    @Override    
    public void start(Stage stage) 
    {       
        // configure text fields for input         
        TextField shapeNoSidesField = new TextField();         
        shapeNoSidesField.setMaxWidth(23);         
        
        // configure label fields        
        Label shapeNoSidesLabel = new Label("Enter Desired Number Of Shape Sides:");         
        shapeNoSidesLabel.setTextFill(Color.RED);         
        shapeNoSidesLabel.setFont(Font.font("Arial", 10));   

        // configure generate shape button         
        Button generateShapeButton = new Button();         
        generateShapeButton.setText("Generate Shape");
        
        // configure an HBox input components                       
        HBox inputComponents = new HBox(40);
        inputComponents.setAlignment(Pos.CENTER);        
        inputComponents.getChildren().addAll(shapeNoSidesLabel, shapeNoSidesField);  
        
        // configure vbox
        VBox root = new VBox(50);         
        root.setAlignment(Pos.CENTER);        
        root.getChildren().addAll(inputComponents, generateShapeButton); 
        
        
        // Generate shape based on user Integral input. Perform input checks.
        generateShapeButton.setOnAction( e ->                     
        {   
            Shape shape = null;
            root.getChildren().remove(shape);
            // Perform input checks using helper variables. Assert no of sides field not null.
            boolean shapeFieldIsEmpty = shapeNoSidesField.getText().isEmpty();
            if(shapeFieldIsEmpty)        
            {                               
                System.out.println("Number of Sides Field Cannot Be Empty. Please Enter a Number Between 3 and 5 Inclusive.");
                display.setText("Number of Sides Field Cannot Be Empty. Please Enter a Number Between 3 and 5 Inclusive.");
            }
            else 
            {
                // Retrieve user required number of sides
                int numberOfSides = Integer.parseInt(shapeNoSidesField.getText());
                switch(numberOfSides) 
                {
                    // User enters shape requirement of three sides (Polygon object)
                    case 3:
                        shape = new Polygon();
                        ((Polygon) shape).getPoints().addAll(new Double[]
                                {
                                    100., 70.,
                                    100., 250.,
                                    400., 250.
                                });
                        root.getChildren().add(shape);
                        break;
                    case 4:
                        shape = new Rectangle();
                        ((Rectangle) shape).setX(150f);
                        ((Rectangle) shape).setY(75.0f); 
                        ((Rectangle) shape).setWidth(300.0f); 
                        ((Rectangle) shape).setHeight(150.0f);
                        root.getChildren().add(shape);
                        break;
                    default:
                        break;
                }
      
            }                                                                        
        }                                     
    ); 
        
        // create a new scene and add it to the stage         
        Scene scene = new Scene(root, 500, 500);         
        stage.setScene(scene);         
        stage.setTitle("Shapes");        
        stage.show();             
        }
    public static void main(String[] args) 
    {
        // TODO Auto-generated method stub
        launch(args);     
    }
}

Any help greatly appreciated, thank you!

CodePudding user response：

Just make shape an instance variable. Also note there is no need for all the ugly downcasting.

public class GenShape extends Application 
{

    private Shape shape ;

    @Override    
    public void start(Stage stage) 
    {       
        // configure text fields for input         
        TextField shapeNoSidesField = new TextField();         
        shapeNoSidesField.setMaxWidth(23);         
        
        // configure label fields        
        Label shapeNoSidesLabel = new Label("Enter Desired Number Of Shape Sides:");         
        shapeNoSidesLabel.setTextFill(Color.RED);         
        shapeNoSidesLabel.setFont(Font.font("Arial", 10));   

        // configure generate shape button         
        Button generateShapeButton = new Button();         
        generateShapeButton.setText("Generate Shape");
        
        // configure an HBox input components                       
        HBox inputComponents = new HBox(40);
        inputComponents.setAlignment(Pos.CENTER);        
        inputComponents.getChildren().addAll(shapeNoSidesLabel, shapeNoSidesField);  
        
        // configure vbox
        VBox root = new VBox(50);         
        root.setAlignment(Pos.CENTER);        
        root.getChildren().addAll(inputComponents, generateShapeButton); 
        
        
        // Generate shape based on user Integral input. Perform input checks.
        generateShapeButton.setOnAction( e ->                     
        {   
            if (shape != null) {
                root.getChildren().remove(shape);
            }

            // Perform input checks using helper variables. Assert no of sides field not null.
            boolean shapeFieldIsEmpty = shapeNoSidesField.getText().isEmpty();
            if(shapeFieldIsEmpty)        
            {                               
                System.out.println("Number of Sides Field Cannot Be Empty. Please Enter a Number Between 3 and 5 Inclusive.");
                display.setText("Number of Sides Field Cannot Be Empty. Please Enter a Number Between 3 and 5 Inclusive.");
            }
            else 
            {
                // Retrieve user required number of sides
                int numberOfSides = Integer.parseInt(shapeNoSidesField.getText());
                switch(numberOfSides) 
                {
                    // User enters shape requirement of three sides (Polygon object)
                    case 3:
                        Polygon poly = new Polygon();
                        poly.getPoints().addAll(new Double[]
                                {
                                    100., 70.,
                                    100., 250.,
                                    400., 250.
                                });
                        root.getChildren().add(poly);
                        this.shape = poly ;
                        break;
                    case 4:
                        Rectangle rect = new Rectangle();
                        rect.setX(150f);
                        rect.setY(75.0f); 
                        rect.setWidth(300.0f); 
                        rect.setHeight(150.0f);
                        root.getChildren().add(rect);
                        this.shape = rect ;
                        break;
                    default:
                        break;
                }
      
            }                                                                        
        }                                     
    ); 
        
        // create a new scene and add it to the stage         
        Scene scene = new Scene(root, 500, 500);         
        stage.setScene(scene);         
        stage.setTitle("Shapes");        
        stage.show();             
        }
    public static void main(String[] args) 
    {
        // TODO Auto-generated method stub
        launch(args);     
    }
}