Bouncing Ball App

The code below creates a simple JavaFX application that simulates a bouncing ball affected by gravity. The ball’s vertical position is updated based on its velocity, which is influenced by gravity. When the ball reaches the bottom of the pane, it bounces back, losing some energy in the process.

The use of AnimationTimer allows for smooth, continuous updates to the ball’s position, creating an engaging visual effect.

Instance variables:

• Circle ball: This variable represents the graphical ball that will bounce.
• ballRadius: The radius of the ball, set to 15 pixels.
• ballX and ballY: Initial coordinates for the ball’s position. ballX is fixed at 200 pixels (horizontal), while ballY starts at 100 pixels (vertical).
• velocityY: This variable tracks the ball’s vertical speed. It starts at 0, meaning the ball is initially stationary.
• gravity: A constant that simulates gravitational acceleration, set to 0.5 pixels per frame.
• bounceFactor: A constant that determines how much energy is lost when the ball bounces. A value of 0.7 means the ball retains 70% of its vertical velocity after a bounce.

import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;

public class BouncingBallApp extends Application {

    private Circle ball;
    private double ballRadius = 15;
    private double ballX = 200;
    private double ballY = 100;
    private double velocityY = 0; // Initial vertical velocity
    private final double gravity = 0.5; // Acceleration due to gravity
    private final double bounceFactor = 0.7; // Energy loss on bounce

    @Override
    public void start(Stage primaryStage) {
        Pane pane = new Pane();
        Scene scene = new Scene(pane, 400, 400);

        ball = new Circle(ballRadius, Color.BLUE);
        ball.setCenterX(ballX);
        ball.setCenterY(ballY);
        pane.getChildren().add(ball);

        startAnimation(pane);

        primaryStage.setTitle("Bouncing Ball Simulation");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void startAnimation(Pane pane) {
        new AnimationTimer() {
            @Override
            public void handle(long now) {
                update();
            }
        }.start();
    }

    private void update() {
        // Apply gravity
        velocityY += gravity;

        // Update the ball's position
        ballY += velocityY;

        // Check for collision with the bottom
        if (ballY + ballRadius >= 400) { // Assuming pane height is 400
            ballY = 400 - ballRadius; // Reset position to the edge
            velocityY = -velocityY * bounceFactor; // Reverse and reduce velocity
        }

        // Update the ball's center
        ball.setCenterY(ballY);
    }

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