Java, Java, Java: Object-Oriented Problem Solving, 2022E

class Paddle {
    public static final int HEIGHT = 50; // Paddle size
    public static final int WIDTH = 10;
    private static final int DELTA = HEIGHT / 2; // Move size
    private static final int BORDER = 20;
    private int gameAreaHeight;
    private int locationX, locationY;
    private PongFrame frame;

    public Paddle(PongFrame f) {
        frame = f;
        gameAreaHeight = f.getHeight() - BORDER;
        locationX = f.getWidth() - WIDTH;
        locationY = gameAreaHeight / 2;
    } // Paddle()

    public void resetLocation() {
        gameAreaHeight = frame.getHeight() - BORDER;
        locationX = frame.getWidth() - WIDTH;
    }

    public int getX() { return locationX; }

    public int getY() {  return locationY; }

    public void moveUp() {
        if (locationY > BORDER)
            locationY -= DELTA;
    } // moveUp()

    public void moveDown() {
        if (locationY + HEIGHT < gameAreaHeight + BORDER)
            locationY += DELTA;
    } // moveDown()
} // Paddle

import javax.swing.*;
import java.awt.Toolkit;

class Ball extends Thread {
    public static final int SIZE = 10; // Diameter of the ball
    private PongFrame frame; // Reference to the frame
    private int topWall, bottomWall, leftWall, rightWall; // Boundaries
    private int locationX, locationY; // Current location of the ball
    private int directionX = 1, directionY = 1; // x- and y-direction (1 or -1)
    private Toolkit kit = Toolkit.getDefaultToolkit(); // For beep() method

    public Ball(PongFrame f) {
        frame = f;
        locationX = 50; // Set initial location
        locationY = 50;
    } // Ball()

    public int getX() { return locationX; } // getX()

    public int getY() { return locationY; } // getY()

    public void move() {
        rightWall = frame.getWidth() - SIZE; // Define bouncing region
        leftWall = 0;
        topWall = 20; // And location of walls
        bottomWall = frame.getHeight() - SIZE;
        locationX = locationX + directionX; // Calculate a new location
        locationY = locationY + directionY;
        if (frame.ballHitsPaddle()) {
            directionX = -1; // move toward left wall
            kit.beep();
        } // if ball hits paddle
        if (locationX <= leftWall) {
            directionX = +1; // move toward right wall
            kit.beep();
        } // if ball hits left wall
        if (locationY + SIZE >= bottomWall || locationY <= topWall) {
            directionY = -directionY; // reverse direction
            kit.beep();
        } // if ball hits top or bottom walls
        if (locationX >= rightWall + SIZE) {
            locationX = leftWall + 1; // jump back to left wall
        } // if ball goes through right wall
    } // move()

    public void run() {
        while (true) {
            move(); // Move
            frame.repaint();
            try {
                sleep(15);
            } catch (InterruptedException e) {
            }
        } // while
    } // run()
} // Ball

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class PongFrame extends JFrame implements KeyListener {
    private Ball ball;
    private Paddle pad;

    public PongFrame() {
        setTitle("Pong");
        setBackground(Color.white);
        addKeyListener(this);
        pad = new Paddle(this); // Create the paddle
        ball = new Ball(this); // Create the ball
        ball.start();
    } // PongFrame()

    public void paint(Graphics g) {
        g.setColor(getBackground()); // Erase the drawing area
        g.fillRect(0, 0, getWidth(), getHeight());
        g.setColor(Color.blue); // Paint the ball
        g.fillOval(ball.getX(), ball.getY(), ball.SIZE, ball.SIZE);
        pad.resetLocation(); // Paint the paddle
        g.setColor(Color.red);
        g.fillRect(pad.getX(), pad.getY(), Paddle.WIDTH, Paddle.HEIGHT);
    } // paint()

    public boolean ballHitsPaddle() {
        return ball.getX() + Ball.SIZE >= pad.getX()
                && ball.getY() >= pad.getY()
                && ball.getY() <= pad.getY() + Paddle.HEIGHT;
    } // ballHitsPaddle()

    public void keyPressed(KeyEvent e) { // Check for arrow keys
        int keyCode = e.getKeyCode();
        if (keyCode == e.VK_UP) // Up arrow
            pad.moveUp();
        else if (keyCode == e.VK_DOWN) // Down arrow
            pad.moveDown();
    } // keyReleased()

    public void keyTyped(KeyEvent e) {
    } // Unused

    public void keyReleased(KeyEvent e) {
    } // Unused

    public static void main(String[] args) {
        PongFrame f = new PongFrame();
        f.setSize(400, 400);
        f.setVisible(true);
    }
} // PongFrame