java.lang.NullPointerException in JApplet game - nullpointerexception

Question

new guy to stack and to java.
to start off, here's my code,
AsteroidsGame.java
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.net.*;
import java.util.*;
public class AsteroidsGame extends JApplet implements Runnable, KeyListener {
Thread thread;
Dimension dim;
Image img;
Graphics g;
long endTime, startTime, framePeriod;
Ship ship;
boolean paused;
// True if the game is paused. Enter is the pause key
Shot[] shots;
int numShots;
boolean shooting;
Asteroid[] asteroids;
int numAsteroids;
double astRadius;
double minAstVel;
double maxAstVel;
int astNumHits;
int astNumSplit;
int level;
private AudioClip audioClip;
public void init() {
resize(500, 500);
shots = new Shot[41];
numAsteroids = 0;
level = 0;
astRadius = 60;
minAstVel = .5;
maxAstVel = 5;
astNumHits = 3;
astNumSplit = 2;
endTime = 0;
startTime = 0;
framePeriod = 25;
addKeyListener(this);
setFocusable(true);
requestFocusInWindow();
dim = getSize();
img = createImage(dim.width, dim.height);
g = img.getGraphics();
thread = new Thread(this);
thread.start();
URL urlAudioClip = getClass().getResource("audio/minorcircuit.wav");
audioClip = Applet.newAudioClip(urlAudioClip);
audioClip.loop();
}
public void start() {
audioClip.loop();
}
public void stop() {
audioClip.stop();
}
public void setUpNextLevel() {
level++;
ship = new Ship(250, 250, 0, .35, .98, .1, 12);
numShots = 0;
paused = false;
shooting = false;
asteroids = new Asteroid[level * (int)Math.pow(astNumSplit, astNumHits - 1) + 1];
numAsteroids = level;
for(int i = 0; i < numAsteroids; i++) {
asteroids[i] = new Asteroid(Math.random() * dim.width, Math.random() * dim.height, astRadius, minAstVel, maxAstVel, astNumHits, astNumSplit);
}
}
public void paint(Graphics gfx) {
g.setColor(Color.black);
g.fillRect(0, 0, 500, 500);
for(int i = 0; i < numShots; i++) {
shots[i].draw(g);
}
for(int i = 0; i < numAsteroids; i++) {
asteroids[i].draw(g);
}
ship.draw(g);
//draw the ship
g.setColor(Color.cyan);
g.drawString("Level " + level, 20, 20);
gfx.drawImage(img, 0, 0, this);
}
public void update(Graphics gfx) {
paint(gfx);
}
public void run() {
for(;;) {
startTime = System.currentTimeMillis();
//start next level when all asteroids are destroyed
if(numAsteroids <= 0) {
setUpNextLevel();
}
if(!paused) {
ship.move(dim.width, dim.height);
//move the ship
for(int i = 0; i < numShots; i++) {
shots[i].move(dim.width, dim.height);
if(shots[i].getLifeLeft() <= 0) {
deleteShot(i);
i--;
}
}
updateAsteroids();
if(shooting && ship.canShoot()) {
//add a shot on to the array
shots[numShots] = ship.shoot();
numShots++;
}
}
repaint();
try {
endTime = System.currentTimeMillis();
if(framePeriod - (endTime - startTime) > 0) {
Thread.sleep(framePeriod - (endTime - startTime));
}
}
catch(InterruptedException e) {
}
}
}
private void deleteShot(int index) {
//delete shot and move all shots after it up in the array
numShots--;
for(int i = index; i < numShots; i++) {
shots[i] = shots[i + 1];
shots[numShots] = null;
}
}
private void deleteAsteroid(int index) {
//delete asteroid and shift ones after it up in the array
numAsteroids--;
for(int i = index; i < numAsteroids; i++) {
asteroids[i] = asteroids[i + 1];
asteroids[numAsteroids] = null;
}
}
private void addAsteroid(Asteroid ast) {
//adds asteroid in at end of array
asteroids[numAsteroids] = ast;
numAsteroids++;
}
private void updateAsteroids() {
for(int i = 0; i < numAsteroids; i++) {
// move each asteroid
asteroids[i].move(dim.width, dim.height);
//check for collisions with the ship
if(asteroids[i].shipCollision(ship)) {
level--;
//restart this level
numAsteroids = 1;
return;
}
//check for collisions with any of the shots
for(int j = 0; j < numShots; j++) {
if(asteroids[i].shotCollision(shots[j])) {
//if the shot hit an asteroid, delete the shot
deleteShot(j);
//split the asteroid up if needed
if(asteroids[i].getHitsLeft() > 1) {
for(int k = 0; k < asteroids[i].getNumSplit(); k++) {
addAsteroid(
asteroids[i].createSplitAsteroid(
minAstVel, maxAstVel));
}
}
//delete the original asteroid
deleteAsteroid(i);
j=numShots;
i--;
}
}
}
}
public void keyPressed(KeyEvent e) {
if(e.getKeyCode() == KeyEvent.VK_ENTER) {
if(!ship.isActive() && !paused) {
ship.setActive(true);
}
else {
paused = !paused;
//enter is the pause button
if(paused) {
//grays out the ship if paused
ship.setActive(false);
}
else {
ship.setActive(true);
}
}
}
else if(paused || !ship.isActive()) {
return;
}
else if(e.getKeyCode() == KeyEvent.VK_SPACE) {
ship.setAccelerating(true);
}
else if(e.getKeyCode() == KeyEvent.VK_LEFT) {
ship.setTurningLeft(true);
}
else if(e.getKeyCode() == KeyEvent.VK_RIGHT) {
ship.setTurningRight(true);
}
else if(e.getKeyCode() == KeyEvent.VK_CONTROL) {
shooting=true;
}
else if(e.getKeyCode() == KeyEvent.VK_M) {
audioClip.stop();
}
else if(e.getKeyCode() == KeyEvent.VK_S) {
audioClip.loop();
}
}
public void keyReleased(KeyEvent e) {
if(e.getKeyCode() == KeyEvent.VK_UP) {
ship.setAccelerating(false);
}
else if(e.getKeyCode() == KeyEvent.VK_LEFT) {
ship.setTurningLeft(false);
}
else if(e.getKeyCode() == KeyEvent.VK_RIGHT) {
ship.setTurningRight(false);
}
else if(e.getKeyCode() == KeyEvent.VK_CONTROL) {
shooting=false;
}
}
public void keyTyped(KeyEvent e) {
}
}
this is a "clone" of Asteroids. Some of you who have been around maybe a little longer than myself have probably played it in an arcade. Anyways, I wrote this for a final project in my Java course, but could never get to work completely. It starts up just fine, you can turn and shoot, but not move forward. I'm not worried about moving right now though. What happens after applet starts is music plays and an "asteroid" travels across the screen. If you shoot the asteroid or shoot 3 times in any direction, a thread exception occurs.
Exception in thread "Thread-3" java.lang.NullPointerException
at AsteroidsGame.updateAsteroids(AseroidsGame.java:161)
at AsteroidsGame.run(AsteroidsGame.java:115)
at java.lang.Thread.run(Thread.java:722)
Having looked around online has benefited me very little. Most of what I have learned was self taught and not as easy to wrap my head around. I'm not exactly sure what to do here to resolve this exception. In another thread on stack, it was mentioned to use an ArrayList because the array was not formerly declared with a size. Tinkered with that; never got it to work.
I need ideas/suggestions/criticism. I want to get this to work just so I can say I finished it.
other classes,
Asteroid.java
import java.awt.*;
public class Asteroid {
double x, y, xVelocity, yVelocity, radius;
int hitsLeft, numSplit;
public Asteroid(double x,double y,double radius,double minVelocity, double maxVelocity,int hitsLeft,int numSplit) {
this.x = x;
this.y = y;
this.radius = radius;
this.hitsLeft = hitsLeft;
this.numSplit = numSplit;
double vel = minVelocity + Math.random() * (maxVelocity - minVelocity);
double dir = 2 * Math.PI * Math.random();
xVelocity = vel * Math.cos(dir);
yVelocity = vel * Math.sin(dir);
}
public void move(int scrnWidth, int scrnHeight) {
x += xVelocity;
y += yVelocity;
if(x < 0 - radius) {
x += scrnWidth + 2 * radius;
}
else if(x > scrnWidth + radius) {
x -= scrnWidth + 2 * radius;
}
if(y < 0 - radius) {
y += scrnHeight + 2 * radius;
}
else if(y > scrnHeight + radius) {
y -= scrnHeight + 2 * radius;
}
}
public void draw(Graphics g) {
g.setColor(Color.gray);
g.fillOval((int)(x - radius + .5), (int)(y - radius + .5), (int)(2 * radius), (int)(2 * radius));
}
public Asteroid createSplitAsteroid(double minVelocity,double maxVelocity) {
return new Asteroid(x, y, radius / Math.sqrt(numSplit), minVelocity, maxVelocity, hitsLeft - 1, numSplit);
}
public boolean shipCollision(Ship ship) {
if(Math.pow(radius + ship.getRadius(), 2) > Math.pow(ship.getX() - x, 2) + Math.pow(ship.getY() - y, 2) && ship.isActive()) {
return true;
}
return false;
}
public boolean shotCollision(Shot shot) {
if(Math.pow(radius, 2) > Math.pow(shot.getX() - x, 2) + Math.pow(shot.getY() - y, 2)) {
return true;
}
return false;
}
public int getHitsLeft() {
return hitsLeft;
}
public int getNumSplit() {
return numSplit;
}
}
Ship.java
import java.awt.*;
public class Ship {
final double[] origXPts = {14,-10,-6,-10}, origYPts = {0,-8,0,8}, origFlameXPts = {-6,-23,-6}, origFlameYPts = {-3,0,3};
final int radius = 6;
double x, y, angle, xVelocity, yVelocity, acceleration, velocityDecay, rotationalSpeed;
//used for movement
boolean turningLeft, turningRight, accelerating, active;
int [] xPts, yPts, flameXPts, flameYPts;
//current location of ship
int shotDelay, shotDelayLeft;
//rate of fire
public Ship(double x, double y, double angle, double acceleration, double velocityDecay, double rotationalSpeed, int shotDelay) {
this.x = x;
this.y = y;
this.angle = angle;
this.acceleration = acceleration;
this.velocityDecay = velocityDecay;
this.rotationalSpeed = rotationalSpeed;
xVelocity = 0;
yVelocity = 0;
turningLeft = false;
turningRight = false;
accelerating = false;
active = false;
xPts = new int[4];
yPts = new int[4];
flameXPts = new int[3];
flameYPts = new int[3];
this.shotDelay = shotDelay;
shotDelayLeft = 0;
}
public void draw(Graphics g) {
if(accelerating && active) {
for(int i = 0; i < 3; i++) {
flameXPts[i] = (int)(origFlameXPts[i] * Math.cos(angle) - origFlameYPts[i] * Math.sin(angle) + x + .5);
flameYPts[i] = (int)(origFlameXPts[i] * Math.sin(angle) + origFlameYPts[i] * Math.cos(angle) + y + .5);
}
g.setColor(Color.red);
//color of flame
g.fillPolygon(flameXPts, flameYPts, 3);
}
for(int i = 0; i < 4; i++) {
xPts[i] = (int)(origXPts[i] * Math.cos(angle) - origYPts[i] * Math.sin(angle) + x + .5);
yPts[i] = (int)(origXPts[i] * Math.sin(angle) + origYPts[i] * Math.cos(angle) + y + .5);
}
if(active) {
g.setColor(Color.white);
}
else {
g.setColor(Color.darkGray);
}
g.fillPolygon(xPts, yPts, 4);
}
public void move(int scrnWidth, int scrnHeight) {
if(shotDelayLeft > 0) {
shotDelayLeft--;
}
if(turningLeft) {
angle -= rotationalSpeed;
}
if(turningRight) {
angle += rotationalSpeed;
}
if(angle > (2 * Math.PI)) {
angle -= (2 * Math.PI);
}
else if(angle < 0) {
angle += (2 * Math.PI);
}
if(accelerating) {
xVelocity += acceleration * Math.cos(angle);
yVelocity += acceleration * Math.sin(angle);
}
x += xVelocity;
y += yVelocity;
xVelocity *= velocityDecay;
yVelocity *= velocityDecay;
if(x<0) {
x += scrnWidth;
}
else if(x > scrnWidth) {
x -= scrnWidth;
}
if(y < 0) {
y += scrnHeight;
}
else if(y > scrnHeight) {
y -= scrnHeight;
}
}
public void setAccelerating(boolean accelerating) {
this.accelerating = accelerating;
//start or stop accelerating the ship
}
public void setTurningLeft(boolean turningLeft) {
this.turningLeft = turningLeft;
//start or stop turning the ship
}
public void setTurningRight(boolean turningRight) {
this.turningRight = turningRight;
}
public double getX() {
return x;
//returns the ship’s x location
}
public double getY() {
return y;
//returns the ship's y location
}
public double getRadius() {
return radius;
//returns radius of circle that approximates the ship
}
public void setActive(boolean active) {
this.active = active;
//used when the game is paused or unpaused
}
public boolean isActive() {
return active;
}
public boolean canShoot() {
if(shotDelayLeft > 0) {
return false;
}
else {
return true;
}
}
public Shot shoot() {
shotDelayLeft=shotDelay;
//set delay till next shot can be fired
//a life of 40 makes the shot travel about the width of the
//screen before disappearing
return new Shot(x, y, angle, xVelocity, yVelocity, 40);
}
}
Shot.java
import java.awt.*;
public class Shot {
final double shotSpeed = 12;
double x, y, xVelocity, yVelocity;
int lifeLeft;
public Shot(double x, double y, double angle, double shipXVel, double shipYVel, int lifeLeft) {
this.x = x;
this.y = y;
xVelocity = shotSpeed * Math.cos(angle) + shipXVel;
yVelocity = shotSpeed * Math.sin(angle) + shipYVel;
this.lifeLeft = lifeLeft;
}
public void move(int scrnWidth, int scrnHeight) {
lifeLeft--;
x += xVelocity;
y += yVelocity;
if(x < 0) {
x += scrnWidth;
}
else if(x > scrnWidth) {
x -= scrnWidth;
}
if(y < 0) {
y += scrnHeight;
}
else if(y > scrnHeight) {
y -= scrnHeight;
}
}
public void draw(Graphics g) {
g.setColor(Color.yellow);
g.fillOval((int)(x - .5), (int)(y - .5), 3, 3);
}
public double getX() {
return x;
}
public double getY() {
return y;
}
public int getLifeLeft() {
return lifeLeft;
}
}
thanks for looking.
---------------------Edit 12/9/2012------------------------
Tried debugging with NetBeans IDE 7.2.1. It improperly depicts the turning of ship and gives a completely different error:
Exception in thread "Thread-3" java.lang.NullPointerException
at AsteroidsGame.run(AsteroidsGame.java:122)
at java.lang.Thread.run(Thread.java:722)
It is directing attention to the Shot[] shots array inside the run method.
This could be expected as the array for Asteroid[] and Shot[] are set up the same.