Error calling redraw() from static method

Programming Questions

maberi

Error calling redraw() from static method

in Programming Questions • 3 years ago

Compiler says:

Cannot make a static reference to the non-static method redraw() from the type PApplet

Why should I care about "redraw" method definition? Since compiler is making a trick assuming all this pseudo orphaned methods and variables are defined in PApplet, why can't it also assume they are static?

Update: Let's suppose I have my application working in a "redraw on event" mode and I've designed an static class with transformation methods that modify objects with visual impact and I want to make a redraw after applying the change.

What bothers me is: there are some methods and variables without explicit context. Since compiler is giving them an implicit context (breaking somehow object orientation), why don't make them static? Or, in other way, where is the static access to that implicit context to use it to call "redraw"?

Regards,

Mario

Replies(8)

PhiLho

Re: Error calling redraw() from static method

3 years ago

We are missing some context about your problem...

Why are you calling redraw()? From where?

Static methods are pure functions, like sin(): they don't need, and don't have a context. They cannot call a non-static method because these need a context (the class fields).

maberi

Re: Re: Error calling redraw() from static method

3 years ago

I've extended my question in the original post.

PhiLho

Re: Error calling redraw() from static method

3 years ago

Still missing information. Why is your class static?
" Since compiler is giving them an implicit context (breaking somehow object orientation)"
Well, thats the reverse: static is more breaking OO than non-static.
And the context is there, that's the PApplet object. redraw() need information from this object to be able to work. So you cannot get a static access to it.
Showing some very simplified code illustrating your case might allow us to fix your issue, probably.

maberi

Re: Re: Error calling redraw() from static method

3 years ago

void setup() {
noLoop();
}
static class Container {
static ArrayList objects;
static Container() {
objects = new ArrayList(40);
}
static void addObject(Drawable d) {
objects.add(d);
redraw();
}
}
void draw() {
background(0);
for (int i = 0; i < Container.objects.size(); i++) {
((Drawable) Container.objects.get(i)).draw();
}
}

This is the example. And I appreciate your offer to fix my issue, but I know how to fix it (leaving Container as non static and creating an instance in setup()). I come back to my original question: why can't be "redraw" and similar static methods or, at least, why can't be treated in a special way by the compiler, like Processing.js do? (This sample works without errors in Processing.js)

Regards,

Mario

PhiLho

Re: Error calling redraw() from static method

3 years ago

Your Container class isn't very useful: you can get a similar result by declaring objects global (making them, actually, fields of your sketch's class) and making addObject a global function (ie. a method of this class). The encapsulation provided by Container isn't strong, you can get a similar effect by putting its code in a new tab.

And I explained why these methods cannot be static: they need data from the PApplet, like g, the main PGraphics on which we operate.
Processing.js is just an emulation of Java in JavaScript, a quite different language. If it allows this, I would call that a bug...