Problem with contains() (StackOverflow)

Programming Questions

Jesse Sco..

Problem with contains() (StackOverflow)

in Programming Questions • 1 year ago

Hi...

I'm trying to help someone troubleshoot a sketch which has a series of attractors, and I have an ArrayList of a Rectangle Class which has a contains() method.... first off, their code seemed to have the int and vector syntax mixed up, so I've tried both... (this is in the Component Class, btw...)

As my data is in PVector form, here's the method ...

boolean contains(PVector ball) {
if (a.contains(ball) ) {
return true;
} else {
return false;
}
}

... which is all called by this code:

Attractors atr1 = (Attractors) attractor.get(j);
if( atr1.contains(v1) ) {

which is in a for loop within draw...

Now, the contains method stops me with a console error saying that

The function contains(PVector) does not exist...

(and I've imported java.awt.Component btw).

If I change Line #3 from

a.contains() to this.contains() , it runs, but gives me a StackOverflow almost right away... which I kind of understand... but kind of not...

It's a little late where I am, and I'm a little confused, so if anyone has any suggestions, I'm all ears...

thanks in advance...

Replies(7)

dr.mo

Re: Problem with contains() (StackOverflow)

1 year ago

yes a bit confusing. do you understand how classes work?

in your example contains is clearly part of the Attractors class as it's call using atr1.contains() however, i get the sense from you post that you just wrote a function called contains somewhere. which would also explain why it works when you leave the atr1 off!

and in that case i wonder what a is? you haven't shown where that variable is defined but it must be a global variable as it's not defined inside you contains function. unless that function is part of class. so again i am not sure.

either way, i suspect that you get some type of recursion and hence the stack overflow.

it would probably we helpful to see all of the code

Jesse Sco..

Re: Problem with contains() (StackOverflow)

1 year ago

Hey, thanks for the reply...

I'm not an expert in Classes/OOP, but I understand the basics... not so hot on inheritance, for example...

In fact, contains() is a method inside of an Attractors Class, though I'm only guessing that I've found the right syntax for it, as there was no import of the Java Component class before, for example...

And 'a' is an Object, instantiated in the Constructor, of a Rectangle Class (which was missing from the original sketch someone gave me, and I've attempted to reconstruct it... which may be part of the problem?)

Here's the Attractors Class:

class Attractors {
Rectangle a;
PVector v2;
float thresh = 50;
Attractors(int x, int y, int w, int h){
a = new Rectangle(x,y,w,h); // ADDED RECTANGLE CLASS
v2 = new PVector(a.x, a.y);
}
void renderHotels() {
// etc...
}
void renderMonuments() {
// etc...
}
boolean contains(PVector ball) {
if (a.contains(ball) ) {
return true;
} else {
return false;
}
}
boolean proximity(PVector ball){
if (ball.dist(v2) < thresh){
return true;
} else {
return false;
}
}
}

And the Rectangle Class:

class Rectangle {
int x;
int y;
int w;
int h;
Rectangle(int rx, int ry, int rw, int rh){
rx = x;
ry = y;
rw = w;
rh = h;
}
void display() {
stroke(255);
rectMode(CENTER);
rect(x, y, w, h);
}
}

I guess I don't really understand recursion - or the pitfalls that can lead to it too well. Its actually the first time ive ever had a StackOverflow in 5+ years of using Processing !?!

dr.mo

Re: Problem with contains() (StackOverflow)

1 year ago

ok this doesn't make any sense. if "a" is a an object of type Rectangle how can you call a.contains()? as rectangle has no method of that name!! i bet you have another global variable somewhere also called "a" of type attractor and that causes a recursion or something.

i would tidy this code up, rename "a" to something sensible. also, i personally like putting underscores in front of member variables to distinguish them from local variables. it makes things much clearer and stops you from hiding global/member variables

Jesse Sco..

Re: Problem with contains() (StackOverflow)

1 year ago

Right... which explains why it doesn't work!

There is no other variable called 'a' ... I've triple-checked.

Remember, I (re-)wrote the Rectangle class, as it was missing...

I never caught that, but yeah, perhaps it is supposed to have a contains() method...

The thing I don't understand in implementing it is how the contains method() would look like in the Rectangle Class...

I've never worked with that method before...

dr.mo

Re: Problem with contains() (StackOverflow)

1 year ago

well that depends on what you are trying to do. i'd imagine that you might have a bunch of balls bouncing around in a rectangle. so why not just add a public member variable of type ArrayList<ball> to your rectangle and then you don't even need to write your own contains method

Jesse Sco..

Re: Problem with contains() (StackOverflow)

1 year ago

I'm not sure I understand, but thanks for your help...

dr.mo

Re: Problem with contains() (StackOverflow)

1 year ago

i mean do somthing like this:

void setup()
{
Rectangle myRect = new Rectangle(0,0,10,10);
Ball b1 = new Ball();
Ball b2 = new Ball();
Ball b3 = new Ball();
myRect.ballList.add(b1);
myRect.ballList.add(b2);
myRect.ballList.add(b3);
if(myRect.ballList.contains(b2))
{
println("rect has stored my ball");
}
}
class Rectangle {
int x;
int y;
int w;
int h;
Rectangle(int rx, int ry, int rw, int rh){
rx = x;
ry = y;
rw = w;
rh = h;
ballList = new ArrayList<Ball>();
}
void display() {
stroke(255);
rectMode(CENTER);
rect(x, y, w, h);
}
public ArrayList<Ball> ballList;
}
class Ball
{
}

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