Computer Science 252
Problem Solving with Java

Spring 2015, The College of Saint Rose

Home     Syllabus     Schedule     Examples     Style Guide

Pong Demo

A working demo of Pong will appear below. Click inside the applet to interact with it.

Pong BlueJ Project

Click here to download a BlueJ project for Pong.

Pong Source Code

The Java source code for Pong is below. Click on a file name to download it.

Pong.java

import objectdraw.*;
import java.awt.*;

/*
 * Example Pong: a still-simple but playable "Pong" game that features
 * a paddle and a falling ball that can now bounce off the sides and
 * interact with the paddle.
 *
 * Jim Teresco, Siena College, CSIS 120, Spring 2011
 * The College of Saint Rose, Fall 2013
 * Based on similar example from CSCI 134, Williams College
 *
 * $Id: Pong.java 2322 2014-02-13 02:04:20Z terescoj $
 */

public class Pong extends WindowController {

    // position and dimensions of the court
    private static final int COURT_LEFT = 50;
    private static final int COURT_TOP = 50;
    private static final int COURT_HEIGHT = 300;
    private static final int COURT_WIDTH = 300;
    private static final int COURT_RIGHT = COURT_LEFT + COURT_WIDTH;

    // dimensions of the paddle
    private static final int PADDLE_WIDTH = 50;
    private static final int PADDLE_HEIGHT = 20;

    private static final int PADDLE_Y = COURT_TOP + COURT_HEIGHT - PADDLE_HEIGHT - 1;

    private FilledRect paddle;
    private FramedRect boundary; // the boundary of the playing area.

    public void begin() {
        // make the playing area
        boundary = new FramedRect(COURT_LEFT, COURT_TOP,
            COURT_WIDTH, COURT_HEIGHT,
            canvas);

        // make the paddle
        paddle = new FilledRect(COURT_LEFT + (COURT_WIDTH-PADDLE_WIDTH)/2,
            COURT_TOP + COURT_HEIGHT - PADDLE_HEIGHT -1,
            PADDLE_WIDTH, PADDLE_HEIGHT,
            canvas);
    }

    // create a new falling ball
    public void onMousePress(Location point) {

        // create the ball at the top of the playing area
        // at the mouse point's x coordinate
        if (boundary.contains(point)) {
            new PongBall(paddle, boundary, canvas);
        }
    }

    // move the paddle to follow the mouse's x coordinate
    public void onMouseMove(Location point) {

        if (point.getX() < COURT_LEFT) {
            // place paddle at left edge of the court
            paddle.moveTo(COURT_LEFT, PADDLE_Y);
        } else if (point.getX() + PADDLE_WIDTH > COURT_RIGHT) {
            // place paddle at right edge of the court
            paddle.moveTo(COURT_RIGHT - PADDLE_WIDTH, PADDLE_Y);
        } else {
            // keep the edge of the paddle lined up with the mouse
            paddle.moveTo(point.getX(), PADDLE_Y);
        }

    }
}

PongBall.java

import objectdraw.*;
import java.awt.*;
import java.util.Random;

/*
 * 
 * A simple active object that controls a ball that bounces around the
 * canvas and interacts with a boundary and a pong paddle
 *
 * Jim Teresco, Siena College, CSIS 120, Spring 2011
 *  The College of Saint Rose, Fall 2013
 *  
 * $Id: PongBall.java 2218 2013-10-18 14:06:39Z terescoj $
 */

public class PongBall extends ActiveObject {

    // size and speed of falling balls
    private static final int BALLSIZE = 30;
    private static final double MIN_SPEED = 3;
    private static final double MAX_SPEED = 10;
    private static final int DELAY_TIME = 33;

    // the ball controlled by this instance
    private FilledOval ball;

    // the paddle with which we will interact
    private FilledRect paddle;

    // how far to fall before stopping and disappearing?
    private double yMax;
    // how far up to go before bouncing off the ceiling?
    private double yMin;
    // and what about the walls?
    private double xMin, xMax;

    // Draw a ball and start it falling.
    public PongBall(FilledRect paddle, FramedRect boundary,
    DrawingCanvas aCanvas) {

        // compute/remember our boundaries (of the upper left corner of a ball)
        yMax = boundary.getY()+boundary.getHeight();
        yMin = boundary.getY();
        xMin = boundary.getX();
        xMax = boundary.getX() + boundary.getWidth() - BALLSIZE;

        // random generator for the x-coordinate
        Random posGen = new Random();

        // draw the ball at its initial position, which is at the 
        // top of the playing area, at a randomly-selected position
        ball = new FilledOval(posGen.nextDouble() * (xMax - xMin) + xMin, 
            yMin+1, BALLSIZE, BALLSIZE, aCanvas);

        // remember the paddle
        this.paddle = paddle;

        // activate!
        start();
    }

    // move the ball repeatedly until it falls off screen, bouncing
    // off the paddle and walls along the way
    public void run() {
        double xSpeed, ySpeed;

        // start by moving downward and some amount to the right
        Random speedGen = new Random();

        xSpeed = speedGen.nextDouble() * (MAX_SPEED - MIN_SPEED) + MIN_SPEED;
        double initYSpeed = speedGen.nextDouble() * (MAX_SPEED - MIN_SPEED) + MIN_SPEED;
        ySpeed = initYSpeed;

        // keep moving as long as we haven't fallen off the bottom of
        // the screen
        while (ball.getY() <= yMax) {
            // if we are above the top line, start moving down
            if (ball.getY() < yMin) {
                ySpeed = initYSpeed;
            }

            // if we are in contact with the paddle, start moving up
            if (ball.overlaps(paddle)) {
                ySpeed = -initYSpeed;
            }

            // bounce off side walls
            if (ball.getX() < xMin || ball.getX() > xMax) {
                xSpeed = -xSpeed;
            }

            // move a little in the appropriate direction
            ball.move(xSpeed, ySpeed);
            pause(DELAY_TIME);
        }

        ball.removeFromCanvas();
    }
}