subclass constructor problem

Programming Questions

diamadis

in Programming Questions • 10 months ago

Hey guys!

This is a bit confusing. I have a superclass which looks basically like this:

class Capsule {

PVector location;

PVector velocity;

PVector acceleration;

float r;

float wandertheta;

float maxforce;

float maxspeed;

color fillColor;

int name;

Capsule(float x, float y, color c, int nam) { //the class constructor

acceleration = new PVector(0,0);

velocity = new PVector(0,0);

location = new PVector(x,y);

r = 6;

wandertheta = 0;

maxspeed = 0.5;

maxforce = 0.05;

fillColor = c;

name = nam;

}

and some subclasses that look like this:

class MW1 extends Capsule {

MW1(float x_mw1, float y_mw1, color c_mw1, int nam_mw1) {

super(x_mw1,y_mw1,c_mw1,nam_mw1);

}

when I try to run the code I get the message that:

the constructor "file_name".MW1() is undefined

and a yellow line here:

ArrayList<Capsule> agents = new ArrayList<Capsule>();

for (int i = 0; i < 40; i++) {

if (i < 20) agents.add(new MW1());

...

Does anyone know what am I doing wrong? where exactly is the problem with the subclass constructor?

Replies(9)

quarks

Re: subclass constructor problem

10 months ago

You are attempting to use a constructor that does not exist, a constructor that has no parameters.

You need to add the constructor to the MW1 class i.e.

Copy code

MW1(){
}

Java does not put in a default (no parameter) constructor in a sub-class automatically - the programmer must.

diamadis

Re: subclass constructor problem

10 months ago

i still don 't get it. I changed the constructor:

class MW1 extends Capsule {

float x_mw1;

float y_mw1;

MW1() {

super(x_mw1,y_mw1,c_mw1,nam_mw1);

}

and all I get is:

cannot refer to an instance field x_mw1 while explicitly invoking a constructor

I m really sorry... it might be a silly question but I m not really familiar with coding language, so what should I write? the examples in processing page about inheritance are almost identical; still it does not seem to work.

Chrisir

Re: subclass constructor problem

10 months ago

when this is your constructor

Copy code

MW1(float x_mw1, float y_mw1, color c_mw1, int nam_mw1) {

you need to call MW1 with all those values it's expecting - the numbers of parameters must match :

Copy code

for (int i = 0; i < 40; i++) {
if (i < 20) agents.add(new MW1( put all parameters here ));
...

as quarks said.

(I am referring to your 1st post, not to the 2nd post)

diamadis

Re: subclass constructor problem

10 months ago

thanks a lot! that solved it! :)

Chrisir

Re: subclass constructor problem

10 months ago

That's great to hear!

quarks

Re: subclass constructor problem

10 months ago

My suggextion is to change your class to look this :

Copy code

class MW1 extends Capsule {
// A default no parameter constructor must be added in a sub-class
// because Java does not do it automatically
MW1(){
}
MW1(float x_mw1, float y_mw1, color c_mw1, int nam_mw1) {
super(x_mw1,y_mw1,c_mw1,nam_mw1);
}
// rest of class
} // end of class

If you intend to use the MW1() constructor then I would also recommend that you change the parent class to ensure that all the instance variables are initialised to usable values.

Copy code

class Capsule {
// These initialisations will always be done no matter which constructor
// is used the constructor code then overwrites these if neccessary.
PVector location = new PVector(0,0);;
PVector velocity = new PVector(0,0);;
PVector acceleration = new PVector(0,0);
float r = 6;
float wandertheta = 0;
float maxforce = 0.05;
float maxspeed = 0.5;
color fillColor;
int name;
Capsule(float x, float y, color c, int nam) { //the class constructor
location = new PVector(x,y);
r = 6;
fillColor = c;
name = nam;
}
// rest of class
} // end of class

PhiLho

Re: subclass constructor problem

10 months ago

It is annoying to answer in a thread, while you get other answers in a duplicate thread.
Don't do that, please.

diamadis

Re: subclass constructor problem

10 months ago

it 's not a dublicate thread, I just tried to reformulate the problem/question cause I have to finish with the project ASAP.

sorry for the inconvenience, I forgot to erase the previews post.

Thank you all for the great help :)

PhiLho

Re: subclass constructor problem

10 months ago

Don't erase a thread where you got answers as well! It is rude for those taking time to answer.

The best way to do that, if you feel you really need another thread, is to post a message at the end of the old thread to point to the new one. Thus, no duplicate work, and answers remain for those searching for a solution.

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