Bullets intersection asteroids: endless array trouble

in Programming Questions • 11 months ago

Again, this seems to be a fairly common problem, but none of the previous threads really helped me.

I'm struggling to get "bullets" (generated by an array, adding a new one on keypress) to collide with "asteroids" just generated by an array.

What's the best way to share the .zip with you guys?
Dropbox link ?

https://dl.dropbox.com/u/20431116/Alien%20Escape.zip

Replies(14)

calsign

Re: Bullets intersection asteroids: endless array trouble

11 months ago

As far as I can tell, you answered it yourself at the end of this thread...

BTW: Most people don't like downloading .zip files...

captpresi..

Re: Bullets intersection asteroids: endless array trouble

11 months ago

I thought that method would work like this

for (int j = 0; j < bullets.size(); j++) {
for (int k = 0; k < asteroids.length; k++) {
if (bullets[j].intersect(asteroids[k])) {
asteroid[k].collide();
bullets.remove(bullet);
}
}
}

but I get an error message saying "The type of expression must be an array type but it resolved to an ArrayList"

There's obviously something I'm still missing about arrays.

calsign

Re: Bullets intersection asteroids: endless array trouble

11 months ago

You're messing up the syntax a lot...
This should work:

for (int j = 0; j < bullets.size(); j++) {
for (int k = 0; k < asteroids.length; k++) {
if (bullets.get(j).intersect(asteroids[k])) {
asteroids[k].collide();
bullets.remove(j);
}
}
}

captpresi..

Re: Bullets intersection asteroids: endless array trouble

11 months ago

Hang on, I still get an error. Apparently "The function intersect(game.Asteroid) does not exist" even though I define it in the Bullet class like so...

boolean intersect(Asteroid a) {
float distance = dist(xpos, ypos, a.xPos, a.yPos);
if (distance <= rb + a.ar) {
return true;
}
else {
return false;
}
}

PhiLho

Re: Bullets intersection asteroids: endless array trouble

11 months ago

Ensure that bullets was defined as an ArrayList<Bullet>, otherwise get() will return an Object without this method.

captpresi..

Re: Bullets intersection asteroids: endless array trouble

11 months ago

If I edit

bullets = new ArrayList();

in setup to

bullets = new ArrayList(Bullet);

then it complains at me that it "Cannot find anything named "Bullet"". Here's the bullet class I created. What else do I need to do?

class Bullet {
float xpos, ypos;
float speed = 30;
int rb = 4;
Bullet(float tempXpos, float tempYpos) {
xpos = tempXpos;
ypos = tempYpos;
}
void display() {
fill(255, 0, 0);
rect(xpos, ypos, rb, rb*2);
}
void fire() {
ypos = ypos - speed;
}
boolean hitTop() {
if (ypos <= 0) {
return true;
}
else {
return false;
}
}
boolean intersect(Shark s) {
float distance = dist(xpos, ypos, s.xPos, s.yPos);
if (distance <= rb + s.sr ) {
return true;
}
else {
return false;
}
}
boolean intersect(Asteroid a) {
float distance = dist(xpos, ypos, a.xPos, a.yPos);
if (distance <= rb + a.ar) {
return true;
}
else {
return false;
}
}
}

PhiLho

Re: Bullets intersection asteroids: endless array trouble

11 months ago

That's not what I wrote. I used <>, not (). Beware of syntax!
You declare the list as:
ArrayList<Bullet> bullets;
and you initialize it with:
bullets = new ArrayList<Bullet>();
The <Bullet> part defines what is the type to put in the list.

captpresi..

Re: Bullets intersection asteroids: endless array trouble

11 months ago

Even with that method I still get an IndexOutOfBoundsException: Index 1, Size: 1 :(

for (int j = 0; j < bullets.size(); j++) {
for (int k = 0; k < asteroids.length; k++) {
if (bullets.get(j).intersect(asteroids[k])) { //IndexOutOfBoundsException: Index: 1, Size: 1
asteroids[k].collide();
bullets.remove(j);
}
}
}

Chrisir

Re: Bullets intersection asteroids: endless array trouble

11 months ago

try
asteroids.length - 1

but did you define your asteroids / bullets?

Greetings!

captpresi..

Re: Bullets intersection asteroids: endless array trouble

11 months ago

No joy, still the same error.

Here's the whole thing so you can see how I defined them

https://dl.dropbox.com/u/20431116/Alien%20Escape.zip

Chrisir

Re: Bullets intersection asteroids: endless array trouble

11 months ago

for (int j = 0; j < bullets.size() -1 ; j++) {
for (int k = 0; k < asteroids.length - 1; k++) {
if (bullets.get(j).intersect(asteroids[k])) { //IndexOutOfBoundsException: Index: 1, Size: 1
asteroids[k].collide();
bullets.remove(j);
}
}
}

captpresi..

Re: Bullets intersection asteroids: endless array trouble

11 months ago

Well that stopped it crashing but the bullets just go straight through the asteroids. Woe is me. I'm in over my head.

PhiLho

Re: Bullets intersection asteroids: endless array trouble

11 months ago

The problem is (probably) that you delete items from the list while looping over it. It always has been a problem.
One way to avoid this problem is to walk the list in reverse order:
for (int j = bullets.size()-1; j >= 0; j--) {

Chrisir

Re: Bullets intersection asteroids: endless array trouble

11 months ago

yes, phi.lho is right

but there is another problem:
when you removed the bullet (in line 6 below) you keep on checking for a bullet at this pos in arraylist also it doesn't exist.
So I swapped both for loops and inserted a break;

for (int k = 0; k < asteroids.length-1; k++) {
for (int j = bullets.size()-1; j>=0 ;j--) {
Bullet currentBullet=bullets.get(j);
if (currentBullet.intersect(asteroids[k])) { //IndexOutOfBoundsException: Index: 1, Size: 1 arraylist
asteroids[k].collide();
bullets.remove(j);
break;
}
}
}

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