Thread: Game problem: java.lang.IndexOutOfBoundsException

So i am recreating space invaders to teach myself some game programming.
For the first time i have started to use ArrayLists.
But every time i run it i get an java.lang.IndexOutOfBoundsException when the last bullet that you have shot hits a target.

Thanks for your intrest and help.

Here a full error message :
Exception in thread "Thread-2" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
at java.util.ArrayList.rangeCheck(Unknown Source)
at java.util.ArrayList.get(Unknown Source)
at com.spaceinvader.Main.colision(Main.java:172)
at com.spaceinvader.Main.update(Main.java:165)
at com.spaceinvader.Main.run(Main.java:108)
at java.lang.Thread.run(Unknown Source)

My source Code :

Main.java

package com.spaceinvader;
 
import com.spaceinvader.render.Render;
import com.spaceinvader.entity.*;
 
import javax.swing.JFrame;
 
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferStrategy;
import java.util.ArrayList;
 
public class Main extends Canvas implements Runnable, KeyListener {
	private static final long serialVersionUID = 1L;
 
	static Main main;
	static Render render;
 
	static public JFrame frame;
	Thread thread;
 
	private final static int WIDTH = 400;
	private final static int HEIGHT = 600;
	boolean running = false;
	static String Titel = "Space Invader";
 
	private boolean[] keys = new boolean[65536];
	public boolean left, right, use, back;
 
	public static EntityPlayer player;
	public static EntityBullet bullet;
 
	public static ArrayList<EntityBullet> bullets;
	public static ArrayList<EntityAlien> aliens;
 
	public int timer = 0;
	public int timed = 30;
 
	public static void main(String[] args) {
		frame = new JFrame();
		main = new Main();
		render = new Render();
		frame.setResizable(false);
		frame.setTitle(Titel);
		frame.add(main);
		frame.pack();
		frame.setLocationRelativeTo(null);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
		main.start();
	}
 
	public Main() {
		Dimension size = new Dimension(WIDTH, HEIGHT);
		setPreferredSize(size);
		setMinimumSize(size);
		setMaximumSize(size);
		addKeyListener(this);
 
		player = new EntityPlayer();
		player.setAlive(true);
		player.setWidth(40);
		player.setHeight(20);
		player.setX(WIDTH / 2 - player.getWidth() / 2);
		player.setY(HEIGHT - 50);
		player.setVelX(5);
 
		bullets = new ArrayList<EntityBullet>();
		aliens = new ArrayList<EntityAlien>();
	}
 
	public void start() {
		if (running)
			return;
		thread = new Thread(this);
		thread.start();
		running = true;
	}
 
	public void stop() {
		if (!running)
			return;
		running = false;
		try {
			thread.join();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}
 
	public void run() {
		int frames;
		long lastTime = System.nanoTime();
		long lastTimer = System.currentTimeMillis();
		double ns = 1000000000.0 / 60.0;
		double delta = 0;
		frames = 0;
		int updates = 0;
		requestFocus();
		while (running) {
			long now = System.nanoTime();
			delta += (now - lastTime) / ns;
			lastTime = now;
			if (delta >= 1) {
				update();
				updates++;
				delta--;
				timer++;
			}
			render();
			frames++;
			while (System.currentTimeMillis() - lastTimer > 1000) {
				lastTimer += 1000;
				frame.setTitle("Space Invader " + updates + " ups, " + frames + " fps");
				frames = 0;
				updates = 0;
			}
		}
	}
 
	private void render() {
		BufferStrategy bs = getBufferStrategy();
		if (bs == null) {
			createBufferStrategy(3);
			return;
		}
		Graphics g = bs.getDrawGraphics();
 
		render.render(g);
 
		g.dispose();
		bs.show();
	}
 
	public void updateKey() {
		left = keys[KeyEvent.VK_LEFT];
		right = keys[KeyEvent.VK_RIGHT];
		use = keys[KeyEvent.VK_SPACE] || keys[KeyEvent.VK_ENTER];
		back = keys[KeyEvent.VK_ESCAPE];
	}
 
	public void keyPressed(KeyEvent e) {
		keys[e.getKeyCode()] = true;
	}
 
	public void keyReleased(KeyEvent e) {
		keys[e.getKeyCode()] = false;
	}
 
	public void keyTyped(KeyEvent e) {
	}
 
	public void releaseAll() {
		left = right = use = back = false;
	}
 
	private void update() {
		updateKey();
		MovementPlayer();
		Shooting();
		SpawnAliens();
		colision();
	}
 
	private void colision() {
		if (aliens.size() > 0 && bullets.size() > 0) {
			for (int i = 0; i < bullets.size(); i++) {
				for (int i2 = 0; i2 < aliens.size(); i2++) {
					if (bullets.get(i).getBounds().intersects(aliens.get(i2).getBounds())) {
						System.out.println("collision");
						bullets.remove(i);
						aliens.remove(i2);
					}
				}
			}
		}
	}
 
	private void SpawnAliens() {
		int ALIENSWIDTH = 8;
		int ALIENSHEIGHT = 4;
		if (timer >= timed) {
			if (back) {
				timer = 0;
				for (int i = 0; i < ALIENSWIDTH; i++) {
					for (int i2 = 0; i2 < ALIENSHEIGHT; i2++) {
						aliens.add(new EntityAlien());
						aliens.get(aliens.size() - 1).setHeight(10);
						aliens.get(aliens.size() - 1).setWidth(10);
						aliens.get(aliens.size() - 1).setX(i * 30 + 100);
						aliens.get(aliens.size() - 1).setY(i2 * 30 + 100);
					}
				}
			}
		}
	}
 
	private void Shooting() {
		if (timer >= timed) {
			if (use) {
				timer = 0;
				bullets.add(new EntityBullet());
				bullets.get(bullets.size() - 1).setHeight(10);
				bullets.get(bullets.size() - 1).setWidth(10);
				bullets.get(bullets.size() - 1).setX(player.getX() + player.getHeight() / 2 + bullets.get(bullets.size() - 1).getWidth() / 2);
				bullets.get(bullets.size() - 1).setY(player.getY() - bullets.get(bullets.size() - 1).getHeight());
				bullets.get(bullets.size() - 1).setVelY(3.0);
			}
		}
		if (bullets.size() > 0) {
			for (int i = 0; i < bullets.size(); i++) {
				bullets.get(i).incY(-bullets.get(i).getVelY());
			}
			for (int i = 0; i < bullets.size(); i++) {
				if (bullets.get(i).getY() < 0 - bullets.get(bullets.size() - 1).getHeight()) {
					bullets.remove(i);
				}
			}
		}
	}
 
	private void MovementPlayer() {
		if (left && player.getX() > 0) {
			player.incX(-player.getVelX());
		}
		if (right && player.getX() + player.getWidth() < WIDTH) {
			player.incX(player.getVelX());
		}
	}
}

Render.java

package com.spaceinvader.render;
 
import com.spaceinvader.Main;
 
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
 
public class Render {
 
	Main main;
 
	Font font = new Font("Verdana", Font.BOLD, 22);
 
	public Render() {
		main = new Main();
	}
 
	public void render(Graphics g) {
		g.setColor(Color.black);
		g.fillRect(0, 0, Main.frame.getWidth(), Main.frame.getHeight());
 
		g.setColor(Color.red);
		g.fillRect((int)Main.player.getX(), (int)Main.player.getY(), (int)Main.player.getWidth(), (int)Main.player.getHeight());
 
		if (Main.bullets.size() > 0) {
			for (int i = 0; i < Main.bullets.size(); i++) {
				g.setColor(Color.blue);
				g.fillRect((int)Main.bullets.get(i).getX(), (int)Main.bullets.get(i).getY(),(int) Main.bullets.get(i).getWidth(), (int)Main.bullets.get(i).getHeight());
			}
		}
 
		if (Main.aliens.size() > 0) {
			for (int i = 0; i < Main.aliens.size(); i++) {
				g.setColor(Color.green);
				g.fillRect((int)Main.aliens.get(i).getX(), (int)Main.aliens.get(i).getY(),(int) Main.aliens.get(i).getWidth(), (int)Main.aliens.get(i).getHeight());
			}
		}
	}
}

BaseEntity.java

package com.spaceinvader.entity;
 
public class BaseEntity {
 
	private double x, y;
	private double height, width;
	private double velX, velY;
	private boolean alive;
 
	//accessor
	public boolean getAlive(){return alive;}
	public double getX(){ return x;}
	public double getY(){ return y;}
	public double getHeight(){return height;}
	public double getWidth(){return width;}
	public double getVelX(){return velX;}
	public double getVelY(){return velY;}
 
	//mutators
	public void setAlive(boolean alive){this.alive = alive;}
	public void setX(double x){this.x = x;}
	public void setY(double y){this.y = y;}
	public void incX(double i){this.x += i;}
	public void incY(double d){this.y += d;}
	public void setHeight(double height){this.height = height;}
	public void setWidth(double width){this.width = width;}
	public void incHeight(double i){this.height += i;}
	public void incWidth(double i){this.width += i;}
	public void setVelX(double velX){this.velX = velX;}
	public void setVelY(double velY){this.velY = velY;}
 
	BaseEntity(){
		setAlive(false);
		setX(0);
		setY(0);
		setWidth(0);
		setHeight(0);
	}
}

EntityAlien.java

package com.spaceinvader.entity;
 
import java.awt.Rectangle;
 
public class EntityAlien extends BaseEntity {
 
	public Rectangle getBounds() {
		Rectangle r;
		r = new Rectangle((int) getX(), (int) getY(), (int) getWidth(), (int) getHeight());
		return r;
	}
 
	public EntityAlien() {
		setAlive(true);
	}
}

EntityBullet.java

package com.spaceinvader.entity;
 
import java.awt.Rectangle;
 
public class EntityBullet extends BaseEntity {
 
	public Rectangle getBounds() {
		Rectangle r;
		r = new Rectangle((int) getX(), (int) getY(), (int) getWidth(), (int) getHeight());
		return r;
	}
 
	public EntityBullet() {
		setAlive(false);
	}
}

EntityPlayer.java

package com.spaceinvader.entity;
 
import java.awt.Rectangle;
 
public class EntityPlayer extends BaseEntity {
 
	public Rectangle getBounds() {
		Rectangle r;
		r = new Rectangle((int) getX(), (int) getY(), (int) getWidth(), (int) getHeight());
		return r;
	}
 
	public EntityPlayer() {
		setAlive(true);
	}
}

What line does the compiler say there is an error?

as said in the top its
at com.spaceinvader.Main.colision(Main.java:172)

line 172 thus
if (bullets.get(i).getBounds().intersects(aliens.get( i2).getBounds())) {

in the colision methode

it isnt a syntax error but an out of bounds

Sorry about that totally spaced out when I read that. Have you tried just adding a few bullets into the list first to see if that was the problem? Same thing with aliens?

i havent tried that yet but i dont think it will make a diffrence
but ill do that now

--- Update ---

well i initilasid the bullits earlier but what happens is that the were shot and afther that when the last bullet hits something it crhases agian at the same spot. it has to do something with these for loops i think(i and i2) but i dont know what

bullets = new ArrayList<EntityBullet>();
bullets is now initialized as an empty array list designed to hold bullets. (ie an empty clip)
There are no bullets in it to check for collisions. Which is why the error message says:
ava.lang.IndexOutOfBoundsException: Index: 0, Size: 0
Index 0 is not valid because the size is 0 not 1. When there is a bullet in the list, the size will be 1 and the index number of that bullet will be 0

Same thing applies to aliens

So i switched the for loops arround and that was it and now it works.
Here is the code if anyone wants it.

	private void colision() {
		if (aliens.size() >= 1 && bullets.size() >= 1) {
			for (int i = 0; i < aliens.size(); i++) {
				for (int i2 = 0; i2 < bullets.size(); i2++) {
					if (bullets.get(i2).getBounds().intersects(aliens.get(i).getBounds())) {
						System.out.println("collision");
						System.out.println(aliens.size() + " " + i);
						aliens.remove(i);
						bullets.remove(i2); 
					}
				}
			}
		}
	}