Noobie OOP Question.

Programming Questions

totaldork..

in Programming Questions • 2 years ago

I am trying to make a starting screen for a game with Object-Oriented Programming. It is pretty much my first shot at OOP so I am obviously having some problems. Processing highlights the yellow area and says "Syntax error, maybe a missing semicolon?" What's the problem? There is a semicolon there so...

PFont f;

class Button{

int X1; //Coordinates for rectangle.

int Y1;

int X2 = X1+200;

int Y2 = Y1+30;

int XB = X1+10; //Coordinates for text in rectangle

int YB = Y1+10;

String buttonText; //String for actual text of button

Button(){ //Constructor method

rect(X1,Y1,X2,Y2); //Outline of Button

textFont(f,24); //Establishing font and text

fill(0);

text(buttonText,XB,YB);

}

void setup(){

size(400,400); //Screen size

f = loadFont("Dialog-48.vlw"); //Loading font

Button startGame = new Button; //New "Start Game" Button.

X1=10;

Y1=10;

this.X2=X2;

this.Y2=Y2;

this.XB=Xb;

this.YB=YB;

buttonText = "Start Game";

//Button options = new Button;

//Button about = new Button;

}

void draw(){

}

Replies(5)

benjaminm..

Re: Noobie OOP Question.

2 years ago

You need parentheses after calling the constructor of the Button class like this: Button startGame=new Button(); as it is a function, and every function needs parentheses.

There're other problems with your sketch, but you will figure them out I think (nothing too serious, but you need to be more careful about scope of variables). If you get stuck be sure to ask again!

Good luck,
Ben

totaldork..

Re: Re: Noobie OOP Question.

2 years ago

Thank you so much! How do I change the scope of the variables? I changed them to the format of

public int X1;

Shouldn't that work? All of these variables are "Class" level, right? Class variables only work within the class, what if I want to use it outside? (Like when I make the "startGame" instance of the "Button" class within the setup function)

PhiLho

Re: Noobie OOP Question.

2 years ago

Scope of variables also depends on where they are declared: outside of a function / class, they are "global" (actually, member of the sketch's class, which is hidden). Inside a function, they are local to the function. Inside a class, if not declared private, they can be accessed with instanceOfClass.someField
The "this.X" code belongs to the constructor of the class.
The drawing code you have put in the constructor really belongs to a draw() or display() method of your class, to be called from the draw() function.

Note: you do as you want, but general convention says to use all capitals only for constants (variables whose value can't change).

totaldork..

Re: Re: Noobie OOP Question.

2 years ago

Okay, so I made some improvements... I think. I moved the ".this" to the class constructor. I called the class variables by saying "startGame.X1" (etc). I get an error saying "Cannot find anything named 'X1'". I've been looking at examples and when an instance is defined, the variables for that instance are set within the parenthesis in the format of:

ClassName myObject = new ClassName(var,var,var....);

How does it know which variables I'm setting? Is it in order of when they are defined within the class?

Ok, also, really beginner question: what is a field?

PFont f;
class Button{
int X1; //Coordinates for rectangle.
int Y1;
int X2 = X1+200;
int Y2 = Y1+30;
int XB = X1+10; //Coordinates for text in rectangle
int YB = Y1+10;
String buttonText; //String for actual text of button
Button(){ //Constructor method
this.X1=X1;
this.Y1=Y1;
this.X2=X2;
this.Y2=Y2;
this.XB=XB;
this.YB=YB;
rect(X1,Y1,X2,Y2); //Outline of Button
textFont(f,24); //Establishing font and text
fill(0);
text(buttonText,XB,YB);
}
}
void displayStartGame(){
//Here?
}
void setup(){
size(400,400); //Screen size
f = loadFont("Dialog-48.vlw"); //Loading font
Button startGame = new Button(); //New "Start Game" Button.
startGame.X1 = 10;
startGame.Y1 = 10;
startGame.X2;
startGame.Y2;
startGame.XB;
startGame.YB;
startGame.buttonText = ("Start Game");
//Button options = new Button;
//Button about = new Button;
}
void draw(){
}

PhiLho

Re: Noobie OOP Question.

2 years ago

startGame.X2; and similar after startGame creation are useless. Just remove them. Or assign them a value.
Field is just a name to designate variables defined at class level. Some call them class members, too.
There are two ways to set values to fields of a class: either after creation of the class, by assigning to each field as you do. Then remove the this.XX = XX; lines.
Or, in a more orthodox way, by passing the parameters to the class constructor. That's the missing part in your constructor: when you write this.X1 = X1; you want to assign to the X1 field the content of the local variable X1, which happens, in general, to be a parameter of the constructor.

Name your method (function defined inside a class) display(), not displayStartGame(), as I suppose you will have several buttons of different functions. And it would look redundant to call startGame.displayStartGame(), and strange to call about.displayStartGame()...

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