Whats wrong in this class definition???

Programming Questions

spazza

Whats wrong in this class definition???

in Programming Questions • 6 months ago

Hi to all!!.......I want to change the value of rgb color contained in fill instruction but the class function return me an error during the execution (NullPointerException).....I'm a newby.....

.....where is the error???

void setup()

      {
      size(320, 240);
      smooth();

noStroke();

frameRate(0.5);

      }

void draw()
      {
      background(0);
      fill (255,25,70);
      rect (20,20,30,30);
      c.colore(255,25,70);
      rect (40,40,30,30);
      }

class canali {
      int rosso;
      int verde;
      int blu;

canali(int r,int v,int b)

{

      rosso = r;
      verde = v;
      blu = b;
      }

void colore(int rrosso, int vverde, int bblu)

{

      if (rrosso > 250){
            rosso=0;
            fill(rosso,verde,blu);
            }
      }
}

Thanks!!

Replies(6)

king_lemon

Re: Whats wrong in this class definition???

6 months ago

You never defined the object c, so when you call c.colour you return a null pointer because it was never initialized.

At top top add:

canali c;

In the setup function do this:

c = new canali(255,255,255);

Chrisir

Re: Whats wrong in this class definition???

6 months ago

also you say

c.colore(255,25,70);

but these values are not used, only the first one when it's >250

you could say

rosso=rrosso;
verde=vverde;
blu=bblue;

in method colore

spazza

Re: Whats wrong in this class definition???

6 months ago

ok!....I've forget to paste the canali c; instruction in the previous message.......

.....so why I've to use the

c = new canali(255,255,255);

instruction....what does it mean?....and why I've to define

rosso = r;

verde = v;

blu = b;

if I don't use them?...there is another simple class method??

...thanks to all!!!

Chrisir

Re: Whats wrong in this class definition???

6 months ago

why I've to use the

c = new canali(255,255,255);

instruction....what does it mean?

This is basic understanding of OOP.
You might want to read http://processing.org/learning/objects/

In short when you define a class you just define a type (like String or so), So still have to invoke an object from that class.

Think of a cookie cutter. A cookie cutter makes cookies, but it is not a cookie itself. The cookie cutter is the class, the cookies are the objects.

That's why you have to say give me an object c with these values of that class....

Chrisir

Re: Whats wrong in this class definition???

6 months ago

why I've to define

rosso = r;

verde = v;

blu = b;

if I don't use them?...there is another simple class method??

at the moment your class doesn't do much. This will change when your program evolves.
Leave the 3 lines above as they are. That's the way to do it....

Better change the methode colore...

spazza

Re: Whats wrong in this class definition???

6 months ago

Thanks Chrisir!!!.....I will read the link you've post to me and I hope to clarify me about object and class....

....

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