Code:
package engine;
import java.awt.event.MouseMotionListener;
import java.awt.event.MouseEvent;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import screens.GameConstants;
import screens.PingPongGreenTable;
/**
* This class is a mouse and keyboard listener.
* It calculates ball and racket movements,
* changes their coordinates.
*/
public class PingPongGameEngine implements Runnable,
MouseMotionListener, KeyListener, GameConstants{
private PingPongGreenTable table;//reference to table
private int kidRacket_Y = KID_RACKET_Y_START;
private int computerRacket_Y=COMPUTER_RACKET_Y_START;
private int kidScore;
private int computerScore;
private int ballX; // ball's X position
private int ballY; // ball's Y position
private boolean movingLeft = true;
private boolean ballServed = false;
//Value in pixels of the vertical ball movement
private int verticalSlide;
// Constructor. Stores a reference to the table
public PingPongGameEngine(
PingPongGreenTable greenTable){
table = greenTable;
Thread worker = new Thread(this);
worker.start();
}
// Methods required by MouseMotionListener
// interface (some of them are empty, but must be
//included in the class anyway)
public void mouseDragged(MouseEvent e) {
}
public void mouseMoved(MouseEvent e) {
int mouse_Y = e.getY();
// If a mouse is above the kid's racket and the racket did not go over the
// table top move it up, otherwise move it down
if (mouse_Y<kidRacket_Y && kidRacket_Y>TABLE_TOP){
kidRacket_Y -= RACKET_INCREMENT;
}else if (kidRacket_Y < TABLE_BOTTOM) {
kidRacket_Y += RACKET_INCREMENT;
}
// Set the new position of the racket on the table
table.setKidRacket_Y(kidRacket_Y);
}
// Methods required by KeyListener interface
public void keyPressed(KeyEvent e){
char key = e.getKeyChar();
if ('n' == key || 'N' == key){
startNewGame();
} else if ('q' == key || 'Q' == key){
endGame();
} else if ('s' == key || 'S' == key){
kidServe();
}
}
public void keyReleased(KeyEvent e){}
public void keyTyped(KeyEvent e){}
// Start a new Game
public void startNewGame(){
computerScore=0;
kidScore=0;
table.setMessageText("Score Computer: 0 Kid: 0");
kidServe();
}
// End the game
public void endGame(){
System.exit(0);
}
//Method run() is required by Runnable interface
public void run(){
boolean canBounce=false;
while (true) {
if(ballServed){ // if ball is moving
//Step 1. Is ball moving o the left?
if ( movingLeft && ballX > BALL_MIN_X){
canBounce = (ballY >= computerRacket_Y &&
ballY < (computerRacket_Y + RACKET_LENGTH)?
true: false);
ballX-=BALL_INCREMENT;
// Add up or down slide to any left/right ball
// movement
ballY-=verticalSlide;
table.setBallPosition(ballX,ballY);
// Can bounce?
if (ballX <= COMPUTER_RACKET_X && canBounce){
movingLeft=false;
}
}
// Step 2. Is ball moving to the right?
if ( !movingLeft && ballX <= BALL_MAX_X){
canBounce = (ballY >= kidRacket_Y && ballY <
(kidRacket_Y + RACKET_LENGTH)?true:false);
ballX+=BALL_INCREMENT;
table.setBallPosition(ballX,ballY);
// Can bounce?
if (ballX >= KID_RACKET_X_START && canBounce){ movingLeft=true;
}
}
// Step 3. Move computer's racket up or down
// to block the ball
if (computerRacket_Y < ballY
&& computerRacket_Y < TABLE_BOTTOM){
computerRacket_Y +=RACKET_INCREMENT;
}else if (computerRacket_Y > TABLE_TOP){
computerRacket_Y -=RACKET_INCREMENT;
}
table.setComputerRacket_Y(computerRacket_Y);
// Step 4. Sleep a little
try {
Thread.sleep(SLEEP_TIME);
} catch (InterruptedException e) {
e.printStackTrace();
}
// Step 5. Update the score if the ball is in the
// green area but is not moving
if (isBallOnTheTable()){
if (ballX > BALL_MAX_X ){
computerScore++;
displayScore();
}else if (ballX < BALL_MIN_X){
kidScore++;
displayScore();
}
}
} // End if ballServed
} // End while
}// End run()
// Serve from the current position of the kid's racket
private void kidServe(){
ballServed = true;
ballX = KID_RACKET_X_START-1;
ballY=kidRacket_Y;
if (ballY > TABLE_HEIGHT/2){
verticalSlide=-1;
}else{
verticalSlide=1;
}
table.setBallPosition(ballX,ballY);
table.setKidRacket_Y(kidRacket_Y);
}
private void displayScore(){
ballServed = false;
if (computerScore ==WINNING_SCORE){
table.setMessageText("Computer won! " +
computerScore + ":" + kidScore);
}else if (kidScore ==WINNING_SCORE){
table.setMessageText("You won! "+ kidScore +
":" + computerScore);
}else{
table.setMessageText("Computer: "+ computerScore
+ " Kid: " + kidScore);
}
}
// check if ball did not cross the top or bottom
// borders of the table
private boolean isBallOnTheTable(){
if (ballY >= BALL_MIN_Y && ballY <= BALL_MAX_Y){
return true;
}else {
return false;
}
}
}