Thread: Game problem: java.lang.IndexOutOfBoundsException with array list

When a bullit bullit hits a alien it creates this error :

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:291)
at com.spaceinvader.Main.update(Main.java:190)
at com.spaceinvader.Main.run(Main.java:126)
at java.lang.Thread.run(Unknown Source)

This only happens when not the first bullet on the screen hits but when the others hit a alien.
I used an exeption to let it work but it isnt a sollid fix for errors should not occor regarly.
Its about this code :

private void colision() {
		if (aliens.size() >= 1 && bulletsPlayer.size() >= 1) {
			for (int i = 0; i < aliens.size(); i++) {
				for (int i2 = 0; i2 < bulletsPlayer.size(); i2++) {
					try {
						if (aliens.get(i).getBounds().intersects(bulletsPlayer.get(i2).getBounds())) {
							bulletsPlayer.remove(i2);
							aliens.remove(i);
							player.incScore(100 * niveau);
							shotsHit++;
							aliensKilled++;
						}
					} catch (Exception e) {
						e.printStackTrace();
					}
				}
			}
		}
		if (bulletsAlien.size() >= 1) {
			for (int i = 0; i < bulletsAlien.size(); i++) {
				if (player.getBounds().intersects(bulletsAlien.get(i).getBounds())) {
					gameOverMenu = true;
				}
			}
		}
	}

Furter source Code

Main.java

package com.spaceinvader;
 
import com.spaceinvader.render.*;
import com.spaceinvader.entity.*;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
 
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;
import java.util.Random;
 
public class Main extends Canvas implements Runnable, KeyListener {
	private static final long serialVersionUID = 1L;
 
	static Main main;
	static Render render;
 
	public static JFrame frame;
	public static JPanel panel;
	public static Random random;
	Thread thread;
 
	public final static int WIDTH = 400;
	public 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 boolean pauzeMenu = true;
	public static boolean gameOverMenu = false;
	public static boolean waveMenu = false;
 
	public static EntityPlayer player;
	public static ArrayList<EntityBullet> bulletsPlayer;
	public static ArrayList<EntityBullet> bulletsAlien;
	public static ArrayList<EntityAlien> aliens;
 
	public int bulletTimerPlayer = 0, bulletTimedPlayer = 25;
	public int bulletTimerAlien = 0, bulletTimedAlien = 20;
	public int TimerPauze = 0, TimedPauze = 30;
 
	public static int niveau = 0;
	public static int shotsFired = 0;
	public static int shotsHit = 0;
	public static int aliensKilled = 0;
 
	public static void main(String[] args) {
		frame = new JFrame();
		main = new Main();
		panel = new JPanel();
		render = new Render();
		random = new Random();
 
		frame.add(panel);
		frame.setResizable(false);
		frame.setTitle(Titel);
		panel.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);
 
		bulletsPlayer = new ArrayList<EntityBullet>();
		bulletsAlien = new ArrayList<EntityBullet>();
		aliens = new ArrayList<EntityAlien>();
	}
 
	public synchronized void start() {
		if (running)
			return;
		thread = new Thread(this);
		thread.start();
		running = true;
	}
 
	public synchronized 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--;
				bulletTimerPlayer++;
				bulletTimerAlien++;
				TimerPauze++;
			}
			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() {
		if (gameOverMenu) {
			ResetAll();
		}
		updateKey();
		setPauze();
		if (!pauzeMenu && !gameOverMenu) {
			MovementPlayer();
			ShootingPlayer();
			SpawnAliens();
			MovementAliens();
			ShootingAliens();
			colision();
		}
	}
 
	private void ResetAll() {
		if (TimerPauze >= TimedPauze && back) {
			aliens.clear();
			bulletsAlien.clear();
			bulletsPlayer.clear();
			player.setX(WIDTH / 2 - player.getWidth() / 2);
			player.setY(HEIGHT - 50);
			player.setScore(0);
			niveau = 0;
			niveau = 0;
			shotsFired = 0;
			shotsHit = 0;
			aliensKilled = 0;
			pauzeMenu = true;
			gameOverMenu = false;
			TimerPauze = 0;
		}
	}
 
	private void ResetField(){
		aliens.clear();
		bulletsAlien.clear();
		bulletsPlayer.clear();
	}
 
	private void setPauze() {
		if (TimerPauze >= TimedPauze && pauzeMenu && back && !gameOverMenu) {
			pauzeMenu = false;
			TimerPauze = 0;
		} else if (TimerPauze >= TimedPauze && !pauzeMenu && back && !gameOverMenu) {
			pauzeMenu = true;
			TimerPauze = 0;
		}
 
	}
 
	private void ShootingAliens() {
		if (bulletTimerAlien >= bulletTimedAlien) {
			for (int i = 0; i < aliens.size(); i++) {
				if (random.nextInt(1000 - 20 * niveau) == 0) {
					bulletsAlien.add(new EntityBullet());
					bulletsAlien.get(bulletsAlien.size() - 1).setHeight(10);
					bulletsAlien.get(bulletsAlien.size() - 1).setWidth(10);
					bulletsAlien.get(bulletsAlien.size() - 1).setX(aliens.get(i).getX() + aliens.get(i).getHeight() / 2 + bulletsAlien.get(bulletsAlien.size() - 1).getWidth() / 2);
					bulletsAlien.get(bulletsAlien.size() - 1).setY(aliens.get(i).getY() + bulletsAlien.get(bulletsAlien.size() - 1).getHeight());
					bulletsAlien.get(bulletsAlien.size() - 1).setVelY(1.8 + 0.2 * niveau);
					bulletTimerAlien = 0;
				}
			}
		}
		if (bulletsAlien.size() >= 1) {
			for (int i = 0; i < bulletsAlien.size(); i++) {
				bulletsAlien.get(i).incY(bulletsAlien.get(i).getVelY());
				if (bulletsAlien.get(i).getY() > HEIGHT) {
					bulletsAlien.remove(i);
				}
			}
		}
	}
 
	private void MovementAliens() {
		if (aliens.size() >= 1) {
			for (int i = 0; i < aliens.size(); i++) {
				if (aliens.get(i).getDown() == false && aliens.get(i).getUp() == false && aliens.get(i).getRight() == false && aliens.get(i).getLeft() == false) {
					aliens.get(i).setRight(true);
				}
				if (aliens.get(i).getUp()) {
					aliens.get(i).incY(-aliens.get(i).getVelY());
				}
				if (aliens.get(i).getDown()) {
					aliens.get(i).incY(aliens.get(i).getVelY());
				}
				if (aliens.get(i).getRight()) {
					aliens.get(i).incX(aliens.get(i).getVelX());
				}
				if (aliens.get(i).getLeft()) {
					aliens.get(i).incX(-aliens.get(i).getVelX());
				}
				if (aliens.get(i).getX() <= 0) {
					aliens.get(i).setRight(true);
					aliens.get(i).setLeft(false);
					aliens.get(i).incY(aliens.get(i).getHeight() * 1.5);
				}
				if (aliens.get(i).getX() >= WIDTH - aliens.get(i).getWidth()) {
					aliens.get(i).setRight(false);
					aliens.get(i).setLeft(true);
					aliens.get(i).incY(aliens.get(i).getHeight() * 1.5);
				}
			}
		}
	}
 
	private void colision() {
		if (aliens.size() >= 1 && bulletsPlayer.size() >= 1) {
			for (int i = 0; i < aliens.size(); i++) {
				for (int i2 = 0; i2 < bulletsPlayer.size(); i2++) {
					try {
						if (aliens.get(i).getBounds().intersects(bulletsPlayer.get(i2).getBounds())) {
							bulletsPlayer.remove(i2);
							aliens.remove(i);
							player.incScore(100 * niveau);
							shotsHit++;
							aliensKilled++;
						}
					} catch (Exception e) {
						e.printStackTrace();
					}
				}
			}
		}
		if (bulletsAlien.size() >= 1) {
			for (int i = 0; i < bulletsAlien.size(); i++) {
				if (player.getBounds().intersects(bulletsAlien.get(i).getBounds())) {
					gameOverMenu = true;
				}
			}
		}
	}
 
	private void SpawnAliens() {
		int ALIENSWIDTH = 7;
		int ALIENSHEIGHT = 4;
		if (aliens.size() == 0 && !waveMenu) {
			waveMenu = true;
			niveau++;
		}
		if (waveMenu && use) {
			ResetField();
			waveMenu = false;
			bulletTimerPlayer = 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(15);
					aliens.get(aliens.size() - 1).setWidth(15);
					aliens.get(aliens.size() - 1).setX(i * 50 + 50);
					aliens.get(aliens.size() - 1).setY(i2 * 45);
					aliens.get(aliens.size() - 1).setVelX(0.5 + 0.2 * niveau);
					aliens.get(aliens.size() - 1).setVelY(0.5 + 0.2 * niveau);
					aliens.get(aliens.size() - 1).setDown(false);
					aliens.get(aliens.size() - 1).setUp(false);
					aliens.get(aliens.size() - 1).setLeft(false);
					aliens.get(aliens.size() - 1).setRight(false);
				}
			}
		}
	}
 
	private void ShootingPlayer() {
		if (bulletTimerPlayer >= bulletTimedPlayer) {
			if (use && !waveMenu) {
				if (!(player.getScore() == 0)) {
					player.incScore(-10);
				}
				bulletTimerPlayer = 0;
				bulletsPlayer.add(new EntityBullet());
				bulletsPlayer.get(bulletsPlayer.size() - 1).setHeight(10);
				bulletsPlayer.get(bulletsPlayer.size() - 1).setWidth(10);
				bulletsPlayer.get(bulletsPlayer.size() - 1).setX(player.getX() + player.getHeight() / 2 + bulletsPlayer.get(bulletsPlayer.size() - 1).getWidth() / 2);
				bulletsPlayer.get(bulletsPlayer.size() - 1).setY(player.getY() - bulletsPlayer.get(bulletsPlayer.size() - 1).getHeight());
				bulletsPlayer.get(bulletsPlayer.size() - 1).setVelY(6.0);
				shotsFired++;
			}
		}
		if (bulletsPlayer.size() > 0) {
			for (int i = 0; i < bulletsPlayer.size(); i++) {
				bulletsPlayer.get(i).incY(-bulletsPlayer.get(i).getVelY());
			}
			for (int i = 0; i < bulletsPlayer.size(); i++) {
				if (bulletsPlayer.get(i).getY() < 0) {
					bulletsPlayer.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());
		}
	}
}

SpaceInvaderApplet.java

package com.spaceinvader;
 
import java.applet.Applet;
import java.awt.BorderLayout;
import java.util.Random;
 
import javax.swing.JPanel;
 
import com.spaceinvader.render.Render;
 
 
public class SpaceInvaderApplet extends Applet {
	private static final long serialVersionUID = 1L;
 
	private Main main = new Main();
	private JPanel panel;
 
	public void init() {
		panel = new JPanel();
		Main.render = new Render();
		Main.random = new Random();
		setLayout(new BorderLayout());
		add(panel);
		panel.add(main);
		setSize(Main.WIDTH, Main.HEIGHT);
	}
 
	public void start() {
		main.start();
	}
 
	public void stop() {
		main.stop();
	}
 
}

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 {
 
	boolean right,left, up, down;
 
	public Rectangle getBounds() {
		Rectangle r;
		r = new Rectangle((int) getX(), (int) getY(), (int) getWidth(), (int) getHeight());
		return r;
	}
 
	public EntityAlien() {
		setAlive(true);
	}
 
	//accessor
	public boolean getRight(){return right;}
	public boolean getLeft(){return left;}
	public boolean getUp(){return up;}
	public boolean getDown(){return down;}
 
	//mutator
	public void setRight(boolean right){this.right = right;}
	public void setLeft(boolean left){this.left = left;}
	public void setUp(boolean up){this.up = up;}
	public void setDown(boolean down){this.down = down;}
}

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

package com.spaceinvader.entity;
 
import java.awt.Rectangle;
 
public class EntityPlayer extends BaseEntity {
 
	public int score;
 
	public Rectangle getBounds() {
		Rectangle r;
		r = new Rectangle((int) getX(), (int) getY(), (int) getWidth(), (int) getHeight());
		return r;
	}
 
	public EntityPlayer() {
		setAlive(true);
	}
 
	//accessor
	public int getScore(){return score;}
 
	//mutator
	public void setScore(int score){this.score = score;}
	public void incScore(int i){this.score += i;}
}

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("Arial", Font.BOLD, 10);
	Font fontPauzeBig = new Font("Arial", Font.BOLD, 30);
	Font fontPauze = new Font("Arial", Font.BOLD, 15);
 
	public Render() {
		main = new Main();
	}
 
	public void render(Graphics g) {
		g.setColor(Color.black);
		g.fillRect(0, 0, Main.WIDTH, Main.HEIGHT);
 
		if (!Main.pauzeMenu || Main.gameOverMenu) {
			if (!Main.waveMenu) {
				g.setColor(Color.red);
				g.fillRect((int) Main.player.getX(), (int) Main.player.getY(), (int) Main.player.getWidth(), (int) Main.player.getHeight());
 
				if (Main.bulletsPlayer.size() > 0) {
					for (int i = 0; i < Main.bulletsPlayer.size(); i++) {
						g.setColor(Color.blue);
						g.fillRect((int) Main.bulletsPlayer.get(i).getX(), (int) Main.bulletsPlayer.get(i).getY(), (int) Main.bulletsPlayer.get(i).getWidth(), (int) Main.bulletsPlayer.get(i).getHeight());
					}
				}
				if (Main.bulletsAlien.size() > 0) {
					for (int i = 0; i < Main.bulletsAlien.size(); i++) {
						g.setColor(Color.yellow);
						g.fillRect((int) Main.bulletsAlien.get(i).getX(), (int) Main.bulletsAlien.get(i).getY(), (int) Main.bulletsAlien.get(i).getWidth(), (int) Main.bulletsAlien.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());
					}
				}
				g.setColor(Color.green);
				g.setFont(font);
				g.drawString("Level: " + Main.niveau, 0, 10);
				g.drawString("Score: " + Main.player.getScore(), 0, 20);
				g.drawString("Shots fired: " + Main.shotsFired, 0, 30);
				g.drawString("Shots hit: " + Main.shotsHit, 0, 40);
				g.drawString("Aliens killed: " + Main.aliensKilled, 0, 50);
				if (Main.gameOverMenu) {
					g.setFont(fontPauzeBig);
					g.drawString("GAME OVER", Main.WIDTH / 2 - 100, Main.HEIGHT / 2 - 30);
					g.setFont(fontPauze);
					g.drawString("Score : " + Main.player.getScore(), Main.WIDTH / 2 - 95, Main.HEIGHT / 2);
					g.drawString("Press escape to go back", Main.WIDTH / 2 - 95, Main.HEIGHT / 2 + 30);
				}
			} else {
				g.setColor(Color.green);
				g.setFont(fontPauzeBig);
				g.drawString("Wave " + Main.niveau, Main.WIDTH / 2 - 50, Main.HEIGHT / 2);
				g.setFont(fontPauze);
				g.drawString("Press spacebar to start ", Main.WIDTH / 2 - 80, Main.HEIGHT / 2 + 30);
			}
		}
		if (Main.pauzeMenu && !Main.gameOverMenu) {
			g.setColor(Color.green);
			g.setFont(fontPauzeBig);
			g.drawString("press escape", Main.WIDTH / 2 - 100, Main.HEIGHT / 2 - 150);
			g.drawString("to start/continue", Main.WIDTH / 2 - 120, Main.HEIGHT / 2 + 40 - 150);
			g.setFont(fontPauze);
			g.drawString("Controls", Main.WIDTH / 2 - 120, Main.HEIGHT / 2 + 30);
			g.drawString("-Right/Left arrow keys to move", Main.WIDTH / 2 - 120, Main.HEIGHT / 2 + 45);
			g.drawString("-Spacebar to shoot", Main.WIDTH / 2 - 120, Main.HEIGHT / 2 + 60);
			g.drawString("-Escape to pause", Main.WIDTH / 2 - 120, Main.HEIGHT / 2 + 75);
		}
	}
}

Theory: removing a bullet and an alien in the try clause is changing the size of their respective ArrayLists so that the for loop conditions become incorrect. That allows the loop control variables, i and i2, to become larger than or outside the bounds of the modified ArrayLists.

Thanks XD
I hadnt thought of that yet thank you

Glad to help. Changing loop control variables or the collection being iterated inside the loop - especially the size/length/etc. - should always raise red flags. It's doable but requires increased vigilance to avoid the kind of errors you've encountered.

I found a fix. What i did is i made 2 more array list for the dead aliens and bullets to store the index into. Afther the loops have ended i made 2 extra loops to delete the aliens and bullets.

Code :

private void colision() {
		ArrayList<Integer> deadAliens = new ArrayList<>();
		ArrayList<Integer> deadBullets = new ArrayList<>();
		if (aliens.size() >= 1 && bulletsPlayer.size() >= 1) {
			for (int i = 0; i < aliens.size(); i++) {
				for (int i2 = 0; i2 < bulletsPlayer.size(); i2++) {
					if (aliens.get(i).getBounds().intersects(bulletsPlayer.get(i2).getBounds())) {
						deadAliens.add(i);
						deadBullets.add(i2);
						player.incScore(100 * niveau);
						shotsHit++;
						aliensKilled++;
					}
				}
			}
			for (int i = 0; i < deadAliens.size(); i++) {
				int x = deadAliens.get(i);
				System.out.println("aliens : " + deadAliens.get(i));
				aliens.remove(x);
			}
			for (int i = 0; i < deadBullets.size(); i++) {
				int x = deadBullets.get(i);
				System.out.println("bullets : " + deadBullets.get(i) + x);
				bulletsPlayer.remove(x);
			}
		}
		if (bulletsAlien.size() >= 1) {
			for (int i = 0; i < bulletsAlien.size(); i++) {
				if (player.getBounds().intersects(bulletsAlien.get(i).getBounds())) {
					gameOverMenu = true;
				}
			}
		}
	}