Question

Create a JavaFX program in java that does the following items:

1. Display a drawing area of dimension 500 x 400, with a black background.
2. Provides a radio button group to allow the user to select one of the following three colors: red, green, and blue. Upon startup, the red radio button should be selected.
3. Each time the user clicks in the drawing area, a circle of size 10 of the color selected by the radio button group in item 2 will be drawn at where the user clicks.
4. When the use selects a color in the radio button group in item 2, all the circles drawn in the drawing area should change to the color of selection.

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. If not, PLEASE let me know before you rate, I’ll help you fix whatever issues. Thanks

//DrawingProgram.java
import javafx.application.Application;
import static javafx.application.Application.launch;
import javafx.geometry.Insets;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.RadioButton;
import javafx.scene.control.ToggleGroup;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class DrawingProgram extends Application {

    //declaring important components
    private RadioButton redBtn, blueBtn, greenBtn;
    private Pane drawingPane;
    private Color selectedColor;

    @Override
    public void start(Stage primaryStage) {

        //creating a BorderPane
        BorderPane root = new BorderPane();

        selectedColor = Color.RED; //default color

        //initializing a 500x400 drawing pane
        drawingPane = new Pane();
        drawingPane.setPrefSize(500, 400);
        //using black background
        drawingPane.setStyle("-fx-background-color: black;");

        //initializing radio buttons
        redBtn = new RadioButton("RED");
        redBtn.setSelected(true); //default selection        
        greenBtn = new RadioButton("GREEN");
        blueBtn = new RadioButton("BLUE");

        //creating a ToggleGroup so that only one button can be selected at a time
        ToggleGroup group = new ToggleGroup();
        redBtn.setToggleGroup(group);
        greenBtn.setToggleGroup(group);
        blueBtn.setToggleGroup(group);

        //adding buttons to an HBox to arrange horizontally
        HBox btns = new HBox(redBtn, greenBtn, blueBtn);
        btns.setAlignment(Pos.CENTER);
        btns.setPadding(new Insets(10));
        btns.setSpacing(10);

        //adding drawing pane to center and buttons to bottom
        root.setCenter(drawingPane);
        root.setBottom(btns);

        //adding event listeners for radio buttons, to call updateDrawing() method
        redBtn.setOnAction(e -> updateDrawing());
        greenBtn.setOnAction(e -> updateDrawing());
        blueBtn.setOnAction(e -> updateDrawing());

        //adding mouse clicked listener for drawing pane
        drawingPane.setOnMouseClicked(e -> {
            //creating a 10 radius circle at mouse point
            Circle c = new Circle(e.getX(), e.getY(), 10);
            //using selected color
            c.setFill(selectedColor);
            //adding to pane
            drawingPane.getChildren().add(c);
        });

        //setting up and displaying a scene
        Scene scene = new Scene(root);
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    //event handler method for radio btn click
    public void updateDrawing() {
        //using red as initial color
        selectedColor = Color.RED;
        //if green is selected, changing selectedColor to green
        if (greenBtn.isSelected()) {
            selectedColor = Color.GREEN;
        } //if blue is selected, changing selectedColor to blue
        else if (blueBtn.isSelected()) {
            selectedColor = Color.BLUE;
        }
        //now looping through each circle in drawingPane changing color to selectedColor
        for (Object ob : drawingPane.getChildren()) {
            Circle circle = (Circle) ob;
            circle.setFill(selectedColor);
        }
    }

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

}

/*OUTPUT*/