(Racing cars) Write a program that simulates four cars racing, as shown in Figure 16.47b. You can set the speed for each car, with maximum 100

import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.scene.shape.Polygon;
import javafx.scene.shape.Rectangle;
import javafx.scene.shape.Circle;
import javafx.scene.paint.Color;
import javafx.util.Duration;

public class CarPane extends Pane {
	private double x;
	private double y = 40;
	private double radius = 5;
	private Rectangle rectangle;
	private Polygon polygon;
	private Circle circle1;
	private Circle circle2;
	private Timeline animation;

	/** Construct and animate a default CarPane */
	CarPane() {
		drawCar();
		animation = new Timeline(
			new KeyFrame(Duration.millis(50), e -> moveCar()));
		animation.setCycleCount(Timeline.INDEFINITE);
	}

	/** Create a car an place it in the pane */
	private void drawCar() {
		getChildren().clear();
		rectangle = new Rectangle(x, y - 20, 50, 10);
		polygon = new Polygon(x + 10, y - 20, x + 20, y - 30, x + 30, 
			y - 30, x + 40, y - 20);
		circle1 = new Circle(x + 15, y - 5, radius);
		circle2 = new Circle(x + 35, y - 5, radius);
		getChildren().addAll(rectangle, circle1, circle2, polygon);
	}

	/** Set y to specified value */
	public void setY(double y) {
		this.y = y;
	}

	/** Set x to specified value */
	public void setX(double x) {
		this.x = x;
	}

	/** return x */
	public double getX() {
		return x;
	}

	/** return y */
	public double getY() {
		return y;
	}

	/** Pause animation */
	public void pause() {
		animation.pause();
	}

	/** Play animation */
	public void play() {
		animation.play();
	}

	/** Set the animation rate to a specified amount */
	public void setSpeed(double speed) {
		if (speed <= 100)
			animation.setRate(speed);
	}

	/** Increase rate by 1 */
	public void increaseSpeed() {
		animation.setRate(animation.getRate() + 1);
	}

	/** decrease rate by 1 */
	public void decreaseSpeed() {
		animation.setRate(animation.getRate() > 0 ? animation.getRate() - 1 : 0);
	}

	/** Redraw car with new x value */
	protected void moveCar() {
		if (x <= getWidth()) {
			x += 1;	
		} 
		else
			x = 0;
		drawCar();
	}
}

Exercise_16_25.java 

/*********************************************************************************
* (Racing cars) Write a program that simulates four cars racing, as shown in     *
* Figure 16.47b. You can set the speed for each car, with maximum 100.           *
*********************************************************************************/
import javafx.application.Application;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.scene.layout.BorderPane;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.geometry.Pos;
import javafx.collections.ObservableList;
import javafx.scene.Node;
import javafx.scene.input.KeyCode;

public class Exercise_16_25 extends Application {
	protected HBox paneForSpeed = new HBox(5);
	protected VBox paneForCars = new VBox(5);
	protected ObservableList<Node> textFields = paneForSpeed.getChildren();
	protected ObservableList<Node> cars = paneForCars.getChildren();

	@Override // Override the start method in the Application class
	public void start(Stage primaryStage) {
		final int NUMBER_OF_CARS = 4;
		final int PREF_COLUMN_COUNT = 2;

		paneForSpeed.setAlignment(Pos.CENTER);

		// Place labels and text fields in a pane
		for (int i = 0; i < NUMBER_OF_CARS; i++) {
			paneForSpeed.getChildren().addAll(
				new Label("Car " + (i + 1) + ":"), new TextField());
		}

		// Set specified properties for each text field in a list
		for (int i = 1; i < textFields.size(); i+= 2) {
			((TextField)textFields.get(i)).setPrefColumnCount(PREF_COLUMN_COUNT);
		}

		// Place nodes in a pane for cars
		for (int i = 0; i < NUMBER_OF_CARS; i++) {
			paneForCars.getChildren().add(new CarPane());
		}

		// Set specified properties for each element in a list
		for (Node car: cars) {
			((CarPane)car).setStyle("-fx-border-color: black");
			((CarPane)car).setY(40);
		}

		// Create and register handlers
		for (int i = 1; i < textFields.size(); i += 2) {
			((TextField)textFields.get(i)).setOnKeyPressed(e -> {
				if (e.getCode() == KeyCode.ENTER) {
					setSpeed();
				}
			});

		}
		
		// Create a border pane
		BorderPane pane = new BorderPane();
		pane.setTop(paneForSpeed);
		pane.setCenter(paneForCars);

		// Create a scene and place it in the stage
		Scene scene = new Scene(pane, 400, 200);
		primaryStage.setTitle("Exercise_16_25"); // Set the stage title
		primaryStage.setScene(scene); // Place the scene in the stage
		primaryStage.show(); // Display the stage
	}

	/** Set specified rate for a CarPane list */
	private void setSpeed() {
		for (int i = 1, j = 0; i < textFields.size(); i += 2, j++) {
			if (((TextField)textFields.get(i)).getText().length() > 0) {
				((CarPane)cars.get(j)).setSpeed(
					Double.parseDouble(((TextField)textFields.get(i)).getText()));
				((CarPane)cars.get(j)).play();
			}
			else {
				((CarPane)cars.get(j)).pause();
			}
		}
	}
}