I tested myself on a little "project". It's basically a survival game. You move by using W,A,S,D and you shoot in different directions by using the arrow keys. Your goal is to survive for as long as possible. The enemies follow you and they freeze on hit. They start moving again after 3 seconds.
The code is the following (execute the "window" class)
Window-class
package TestGame;
import java.awt.Graphics;
public class Window extends GameIntern{
public void init(){
setSize(windowX,windowY);
Thread th = new Thread(this);
th.start();
offscreen = createImage(windowX,windowY);
d = offscreen.getGraphics();
addKeyListener(this);
}
public void paint(Graphics g){
d.clearRect(0,0,windowX,windowY);//clear window
d.drawString(numberEnemies.toString(), 10, 10);//"Score" number of enemies displayed
d.drawRect(x, y, playerWidth, playerHeight);//draw player
for(Enemy e : enemies){//draw all enemies
d.drawRect(e.getx(), e.gety(), playerWidth, playerHeight);
}
for(Bullet b : bullets){//draw all bullets
d.drawOval(b.getx(), b.gety(), bulletSize, bulletSize);
}
g.drawImage(offscreen,0,0,this);
}
public void update(Graphics g){
paint(g);
}
}
GameIntern-class
package TestGame;
import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.Random;
public class GameIntern extends Applet implements Runnable , KeyListener {
public int windowX = 854;//size of the window in x direction
public int windowY = 460;//size of the window in y direction
public static int x;//x-coordinate of player
public static int y;//y-coordinate of player
public int playerpositionX = x;
public int playerpositionY = y;
public int playerHeight = 20;//player height
public int playerWidth = 20;//player width
public int playerSpeed = 3;//pixel per frame
public int bulletSize = 5;//diameter of bullets
public int spawnTime = 4;//time for new enemies to spawn in seconds
public int enemySleepTime = 180;//Time an enemy does nothing in Frames per second (180 in 60fps = 3sec)
public boolean alive = true;
public Image offscreen;
public Graphics d;
public boolean up,down,left,right;
private int delay;
private Random random= new Random();
public Integer numberEnemies = new Integer(enemies.size());
protected static List<Enemy> enemies = Collections.synchronizedList(new ArrayList<Enemy>()); //List of all enemies
protected static List<Bullet> bullets = Collections.synchronizedList(new ArrayList<Bullet>());//List of all bullets
protected static List<PowerUps> powerups = Collections.synchronizedList(new ArrayList<PowerUps>());//List of all powerups
public void run() {
this.x = 400;//startingposition x
this.y = 240;//startingposition y
double ns = 1000000000.0 / 60.0; //60 "frames"
double delta = 0;
long lastTime = System.nanoTime();
while (alive) {
long now = System.nanoTime();
delta += (now - lastTime) / ns;
lastTime = now;
while (delta >= 1) {
repaint();
tick(); //Line 53
collisionEnemy();
// collisionPowerUp();
delta--;
}
}
}
/**
* Method to calculate all objects and their positions per frame
*/
private void tick() {
if(left == true){
if(x>=0 + playerSpeed){
x-=playerSpeed;
}else{ x=0;}//Farthest left x-coordinate
repaint();
}
if(right == true){
if(x<=windowX - playerWidth - playerSpeed){
x+=playerSpeed;
}else{ x=windowX - playerWidth;}//Farthest right x-coordinate
repaint();
}
if(up == true){
if(y>=0 + playerSpeed){
y-=playerSpeed;
}else{ y=0;}//Highest y-coordinate
repaint();
}
if(down == true){
if(y<=windowY - playerHeight - playerSpeed){
y+=playerSpeed;
}else{y=windowY - playerHeight;}//Lowest y-coordinate
repaint();
}
for (Enemy e : enemies) { //Tick every enemy
e.tick();
}
for (Bullet b : bullets){ //Tick every bullet (LINE 92 !)
b.tick();
}
if(delay % (60 * spawnTime) == 0){ //Spawn enemy
enemies.add(new Enemy(random.nextInt(windowX), random.nextInt(windowY)));
numberEnemies++;
}
delay++;
//Remove bullets, in contact with enemy
LinkedList<Bullet> bulletsToRemove = new LinkedList<>();
for(Enemy e : enemies){ //collision : enemy & bullet
for(Bullet b : bullets){
if(b.getx()+bulletSize >= e.getx() && b.getx() <= e.getx()+20){
if(b.gety()+bulletSize >= e.gety() && b.gety() <= e.gety()+20){
e.setHit();
bulletsToRemove.add(b);
}
}
}
}
for(Bullet b : bulletsToRemove){ //Remove bullets from ArrayList
bullets.remove(b);
}
}
public void keyPressed(KeyEvent e) {
if(e.getKeyCode() == 65){//W
left=true;
}
if(e.getKeyCode() == 87){//A
up=true;
}
if(e.getKeyCode() == 68){//S
right=true;
}
if(e.getKeyCode() == 83){//D
down=true;
}
}
public void keyReleased(KeyEvent e) {
if(e.getKeyCode() == 65){//Arrowkey left
left=false;
}
if(e.getKeyCode() == 87){//Arrowkey up
up=false;
}
if(e.getKeyCode() == 68){//Arrowkey right
right=false;
}
if(e.getKeyCode() == 83){//Arrowkey dowm
down=false;
}
if(e.getKeyCode() == 37){//Arrowkey left
bullets.add(new Bullet(x,y,false,false,true,false)); //Direction the bullet has to go
}
if(e.getKeyCode() == 38){//Arrowkey up
bullets.add(new Bullet(x,y,true,false,false,false));//Direction the bullet has to go
}
if(e.getKeyCode() == 39){//Arrowkey right
bullets.add(new Bullet(x,y,false,false,false,true));//Direction the bullet has to go
}
if(e.getKeyCode() == 40){//Arrowkey down
bullets.add(new Bullet(x,y,false,true,false,false));//Direction the bullet has to go
}
}
public void keyTyped(KeyEvent e){}
/**
* Method to see if the player collided with an enemy
*/
public void collisionEnemy(){
for(Enemy e : enemies){
for(int i = 0;i <= playerWidth; i++){
if(GameIntern.x+i >= e.getx() && GameIntern.x+i <= e.getx()+playerWidth){
if(GameIntern.y+i >= e.gety() && GameIntern.y+i <= e.gety()+playerHeight){
alive = false;
}
}
}
}
}
// public void addEnemy(){
// enemies.add(new Enemy(random.nextInt(windowX), random.nextInt(windowY)));
//
// //Spawn enemies inside the filed, not outside the boarder
// if (playerpositionX < playerWidth * 2 || playerpositionX * 2 > windowX - 2*playerWidth || playerpositionY * 2 > windowY - 2*playerHeight || playerpositionY < playerHeight * 2){
// enemies.add(new Enemy(random.nextInt(windowX - 3*playerWidth), random.nextInt(windowY - 3*playerHeight)+3*playerHeight));
// }else {
// int temp1 = random.nextInt(windowX-3*playerWidth);
// if (temp < playerpositionX){
//
// }
// enemies.add(new Enemy(random.nextInt(windowX), random.nextInt(windowY)));
// }
//
// }
}
Bullet-class
package TestGame;
public class Bullet extends GameIntern{
public int x,y;
public boolean up,down,left,right;
public boolean remove;
public Bullet(int x, int y,boolean up,boolean down, boolean left, boolean right){
this.x = x + 8;
this.y = y + 8;
this.up = up;
this.down = down;
this.left = left;
this.right = right;
}
public int getx(){
return this.x;
}
public int gety(){
return this.y;
}
public void setRemove(){
remove=true;
}
public void tick() {
if (up == true) y-=2;
if (down == true) y+=2;
if (left == true) x-=2;
if (right == true) x+=2;
if(x < 0){
remove = true;
}
if(x > 840){
remove = true;
}
if(y < 0){
remove = true;
}
if(y > 470){
remove = true;
}
}
}
Enemy-class
package TestGame;
public class Enemy extends GameIntern {
public int x,y;
public boolean hit = false;
public int counter = 0;
public Enemy(int x, int y) {
this.x = x;
this.y = y;
}
public int getx(){
return this.x;
}
public int gety(){
return this.y;
}
public void setHit(){
hit = true;
counter = enemySleepTime;
}
public void tick() {
if(counter == 0){
if(hit == true){
hit=false;
}
if (x < GameIntern.x) x++;
if (x > GameIntern.x) x--;
if (y < GameIntern.y) y++;
if (y > GameIntern.y) y--;
}else {counter--;}
}
}
After playing for a while i get
I don't understand this exception. Can someone explain to me what am I doing wrong?
How can I solve this problem?
