I barely learn Threads and animation in Java. I was trying to make a simple game. This is the code:
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
class Pong extends JFrame implements Runnable {
int pilkax, pilkay, palx, paly;
Thread runner, paletka;
Image pilkaImg;
Graphics pilkaG;
int czyMinus, koniecpal;
long losowa;
boolean czyPilka, czyPaletka;
public Pong(){
czyMinus = 0;
setSize(340, 260);
setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
setVisible(true);
pilkaImg = createImage(this.size().width, this.size().height);
pilkaG = pilkaImg.getGraphics();
addMouseListener(new MouseListener(){
public void mousePressed(MouseEvent e) {
}
public void mouseReleased(MouseEvent e) {
}
public void mouseEntered(MouseEvent e) {
}
public void mouseExited(MouseEvent e) {
}
public void mouseClicked(MouseEvent e) {
start();
}
}
);
addKeyListener(new KeyListener(){
public void keyPressed(KeyEvent e){
if(e.getKeyChar()=='a'){
startpal();
}
}
public void keyTyped(KeyEvent e){}
public void keyReleased(KeyEvent e){}
});
poczatek();
}
public void startpal(){
czyPaletka = true;
if (paletka == null) {
paletka = new Thread(this);
paletka.start();
}
}
public void stoppal() {
if (paletka != null) {
paletka.stop();
paletka = null;
}
}
public void start() {
czyPilka = true;
if (runner == null) {
runner = new Thread(this);
runner.start();
}
}
public void stop() {
if (runner != null) {
runner.stop();
runner = null;
}
}
public void poczatek(){
palx=170;
paly=230;
pilkax=180;
pilkay=paly-20;
czyMinus=3;
czyPilka = false;
czyPaletka = false;
}
public void run() {
if(czyPaletka){
czyPaletka = false;
for(int i = 0; i < 4; i++){
palx--;
try { Thread.sleep( 10 );}
catch (InterruptedException ex) {}
repaint();
}
/*while(true){
for(; palx >= 20; palx--) {
try { Thread.sleep( 10 );}
catch (InterruptedException ex) {}
repaint();
}
for(; palx <= 170; palx++) {
try { Thread.sleep( 10 );}
catch (InterruptedException ex) {}
repaint();
}
}*/
}
if(czyPilka){
czyPilka = false;
while(true){
for(; pilkay >= 40; pilkay--) {
switch(czyMinus){
case 0 :
pilkax++;
break;
case 1 :
pilkax--;
break;
}
if(pilkay==40&&pilkax>=20&&pilkax<=320){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
}
if(pilkax==300&&pilkay>=40&&pilkay<=240){
czyMinus = 1;
}
if(pilkay==240&&pilkax>=20&&pilkax<=320){
czyMinus = 1;
}
koniecpal = palx + 60;
if(pilkay>=paly&&pilkax>=palx&&pilkax<=koniecpal){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
break;
}
if(pilkax==20&&pilkay>=20&&pilkay<=240){
czyMinus = 0;
}
try { Thread.sleep( 10 /*10*/ );}
catch (InterruptedException ex) {}
repaint();
}
// powrot pilki
for(; pilkay <= 220; pilkay++) {
switch(czyMinus){
case 0 :
pilkax++;
break;
case 1 :
pilkax--;
break;
}
if(pilkay==40&&pilkax>=20&&pilkax<=320){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
}
if(pilkax==300&&pilkay>=40&&pilkay<=240){
czyMinus = 1;
}
if(pilkay==240&&pilkax>=20&&pilkax<=320){
czyMinus = 1;
}
koniecpal = palx + 60;
if(pilkay>=paly&&pilkax>=palx&&pilkax<=koniecpal){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
break;
}
if(pilkax==20&&pilkay>=20&&pilkay<=240){
czyMinus = 0;
}
try { Thread.sleep( 10 );}
catch (InterruptedException ex) {}
repaint();
}
}
}
}
public void SprawdzKrawedzie(){
switch(czyMinus){
case 0 :
pilkax++;
break;
case 1 :
pilkax--;
break;
}
if(pilkay==40&&pilkax>=20&&pilkax<=320){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
}
if(pilkax==320&&pilkay>=40&&pilkay<=240){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
}
if(pilkay==240&&pilkax>=20&&pilkax<=320){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
}
if(pilkax==20&&pilkay>=20&&pilkay<=240){
losowa = Math.round(1*Math.random());
czyMinus = (int) losowa;
}
}
public void update(Graphics gDC) {
paint(gDC);
}
public void paint(Graphics gDC){
pilkaG.clearRect(0, 0, getSize().width, getSize().height);
pilkaG.setColor(Color.RED);
koniecpal = palx + 40;
pilkaG.setColor(Color.BLACK);
pilkaG.drawRect(20, 40, 300, 200);
pilkaG.fillRect(palx, paly, 40 /*40*/, 10);
pilkaG.setColor(Color.BLUE);
pilkaG.fillOval(pilkax, pilkay, 20, 20);
gDC.drawImage(pilkaImg, 0, 0, this);
}
public void destroy() {
pilkaG.dispose();
}
public static void main(String[] args){
new Pong();
}
}
Variables' names are in Polish. pilka (actually piłka) - ball, pal (actually paletka) - palette.
I don't know:
-Why the ball doesn't bounce from the palette.
-How to move the palette after press eg. 'a'
-Why sometimes the application shows Null Pointer Exception.
Please, explain me it.
