This is a Pong game applet that I made in Java. It's player vs. computer, and the computer never loses. You just move the mouse up and down to control your paddle. I'd like to figure out how to change the speeds of the ball's x and y based on where it hits on the paddle, so it's not "predicted" where the ball will go.

You can play it right here! (As long as you've installed the java plugin, obviously...)

Screen:
/**
* Pong Applet
* Coded by MountainDew
*/

import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Pong extends Applet implements MouseMotionListener, KeyListener {

int my,bx,by,px,py,compx,compy,width,height,speedx,speedy,bwidth,bheight,pwidth,pheight,score;
boolean started;
private Timer timer1;

public void init() {
setSize(800,500);
width = getSize().width;
height = getSize().height;
setBackground(Color.black);
pheight = 120;
pwidth = 15;
bheight = 30;
bwidth = 30;
addKeyListener(this);
addMouseMotionListener(this);
px = 35;
compx = width - 35 - pwidth;
newgame();
timer1 = new Timer(10,new ActionListener() {
public void actionPerformed(ActionEvent e) {
height = getSize().height;
width = getSize().width;
bx += speedx;
by += speedy;
if (by <= 0 || by + bheight >= height) {
speedy = -speedy;
}
if (bx <= px + pwidth && by + bheight >= py && by <= py + pheight && bx > px) {
speedx = -speedx;
++score;
}
if (bx + bwidth >= compx && by + bheight >= compy && by <= compy + pheight && bx < compx + pwidth) {
speedx = -speedx;
}
if (speedx < 0) {
if (compy + pheight / 2 != height / 2) {
if (compy + pheight / 2 > height / 2) {
compy -= -speedx;
}
else {
compy += -speedx;
}
}
}
else {
if (by + bheight / 2 <= compy + pheight / 2) {
compy -= speedx;
}
else {
compy += speedx;
}
}
if (compy < 0) {
compy = 0;
}
if (compy + pheight > height) {
compy = height - pheight;
}
if (bx + bwidth < 0) {
py = height / 2 - pheight / 2;
timer1.stop();
started = false;
}
repaint();
}
});
}

public void mouseMoved(MouseEvent e) {
if (started) {
my = e.getY();
if (my + pheight / 2 > height) {
my = height - pheight / 2;
}
if (my < pheight / 2) {
my = pheight / 2;
}
py = my - pheight / 2;
repaint();
}
}

public void mouseDragged(MouseEvent e) { }

public void paint(Graphics g) {
Font font1 = new Font("Arial", Font.BOLD, 18);
Font font2 = new Font("Arial", Font.BOLD,40);
g.setColor(Color.white);
g.drawRect(0,0,width - 1,height - 1);
g.fillRect(px,py,pwidth,pheight);
g.fillRect(compx,compy,pwidth,pheight);
g.setFont(font1);
g.drawString("Score: " + score,20,20);
if (started) {
g.fillArc(bx,by,bwidth,bheight,0,360);
}
else {
g.setFont(font2);
g.setColor(Color.green);
g.drawString("Pong",width / 2 - 46,height / 2 - 16);
g.setFont(font1);
g.drawString("Press 's' to start",width / 2 - 69,height / 2 + 30);
}
}

public void newgame() {
py = height / 2 - pheight / 2;
compy = py;
bx = width / 2 - bwidth / 2;
by = height / 2 - bheight / 2;
speedx = 10;
speedy = 10;
score = 0;
}

public void keyPressed(KeyEvent e) {
if (e.getKeyChar() == 's') {
started = true;
newgame();
timer1.start();
}
}

public void keyTyped(KeyEvent e) { }

public void keyReleased(KeyEvent e) { }

}