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Index › Programming Questions & Help › Syntax Questions › can't invoke drawing methods within a static class

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can't invoke drawing methods within a static class (Read 394 times)

controller

can't invoke drawing methods within a static class
Apr 8^th, 2006, 4:18pm

Hi!

I made a static class, but apparently it isn't possible to invoke the drawing methods like line from a static class.

Then I tried to make a normal class that handles the drawing, but I can't construct this class in the static class.

What's the reason for this behavior?

Quote:

void setup() {
size(400, 400);
background(255,255,255);
noLoop();
}

void draw() {

}

static class Vec {

VecViewer vw; // not possible?

Vec() {
line(10,10,50,50); // why can't I invoke drawing methods within a static class?
}

}

class VecViewer {

VecViewer() {

}

}

controller

fry YaBB Moderator Offline Posts: 2623 mass, usa	Re: can't invoke drawing methods within a static c Reply #1 - Apr 8^th, 2006, 4:27pm you don't need to make the class 'static'. read up on the java spec for how static classes work, it won't have access to its parent class the way that you'd like because it doesn't deal with instances the same way.

controller

Re: can't invoke drawing methods within a static c
Reply #2 - Apr 8^th, 2006, 5:47pm

thanks for the answer. I'll check the java spec.

the reason I made the class static was because I had mixed up static and non-static methods that I deleted before posting the code here and I wanted to access the static methods in a static context.

The full class implementation looks like this:

Quote:

// vector class
static class Vec {

float x,y;

Vec() {
vw = new VectorViewer();
x = 0;
y = 0;
}

Vec(float _x, float _y) {
vw = new VectorViewer();
x = _x;
y = _y;
}

void display() {
vw.display(x,y);
}

void normalize() {
x /= length();
y /= length();
}

float length() {
return sqrt(x*x + y*y);
}

float lengthSquared() {
return x*x + y*y;
}

// ** static methods ** //
// dot product
static float dot(Vec a, Vec b) {
return a.x * b.x + a.y * b.y;
}

// multiplication
static Vec mult(float factor, Vec a) {
return new Vec(factor*a.x,factor*a.y);
}

// computes the projection of a onto b
static Vec proj(Vec a, Vec b) {
return mult(dot(a,b)/b.lengthSquared(),b);
}
}

class VectorViewer {

VectorViewer() {

}

void display(float x, float y) {
line(0,0,x,y);
}
}

JohnG

Re: can't invoke drawing methods within a static c
Reply #3 - Apr 8^th, 2006, 6:10pm

Slightly out of the thread, but I see a bug in that code

Code:

void normalize() {
    x /= length();
    y /= length();
}

That isn't going to do what you want, you need to calculate length() once, then use that value for the division. The way you have it at the moment, length() changes answer between the two calculations.

controller YaBB Newbies Offline Posts: 13	Re: can't invoke drawing methods within a static c Reply #4 - Apr 8^th, 2006, 6:35pm yeah right, thanks for the advise.

fry YaBB Moderator Offline Posts: 2623 mass, usa	Re: can't invoke drawing methods within a static c Reply #5 - Apr 10^th, 2006, 1:51pm yup, you also need to do this: Code: void normalize() { float len = length(); if (len != 0) { x /= len; y /= len; } } otherwise you'll get numbers that show up as NaN or Infinity when the length is zero.

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