Is Constructor a Method?

Programming Questions

Nokjao

in Programming Questions • 1 year ago

I am just another designer getting up to speed with computing, and here is another question I need to know for the sake of advancing further.

Considering a super-simple class:

class Simple {

// param
      float x, y;
      color c;
      float d;

// ctor
      Simple(float tempX, float tempY, color tempC, float tempD) {
                  x = tempX;
            y = tempY;
         c = tempC;
         d = tempD;
            }

// methods
      void setMe() {}

      void move() {}

      void update() {}
}

Main Question:
I noticed that in many cases, I do not need a constructor at all (blank ctor), since I can "construct" an object from a method (i.e. setMe() ). Can I assume that constructors are a kind of in-built overloaded methods to "construct" any first instance of a class?

            void setMe(float tempX, float tempY, color tempC, float tempD) {
                  x = tempX;
            y = tempY;
         c = tempC;
         d = tempD;
            }

A Bonus Question:
I don't mean to sound like Neo (the Matrix) but "Is everything a method afterall?" I mean, looking at programming in a naive way of mine, everything looks more or less a class, say a so-called library is a class composed of many pre-built functions and methods, and so is the Processing IDE I am using. Can I look at it that way?

Many thanks in advance,

Replies(5)

hellochar

Re: Is Constructor a Method?

1 year ago

Yes, constructors are methods. They are special in that:

a) The only way you can call them is through "new XXX()"

b) They must be the name of your class

All classes must have at least one constructor. If you don't explicitly write one, Java will implicitly add one with no arguments, that (almost) does nothing. Does that answer your question?

Bonus question: Yes. If you look at the Processing source code, you'll in fact see that calls to line(), stroke(), etc. etc. etc. are just method calls. Yes, even the Processing IDE is a Java Class. The thing about Java is that EVERYTHING has to exist inside the context of a class.

Nokjao

Re: Re: Is Constructor a Method?

1 year ago

Yes, that does answer a lot. Thanks Hellochar!

bustup

Re: Is Constructor a Method?

1 year ago

Yes well, you can have a class without a constructor, but then all the methods and variables inside that class needs to be static. Let me give you an example.

public class Simple {
public static int DEFAULT = 0;
private int x, y;
public Simple(int x, int y) {
this.x = x;
this.y = y;
}
public void setX(int x) {
this.x = x;
}
public int getX() {
return x;
}
public void setY(int y) {
this.y = y;
}
public int getY() {
return y;
}
}

Since this class has a constructor, it can either be an object or a class, you can still access DEFAULT without creating a new instance of the class, Simple. DEFAULT will return 0. You can also initialize a new instance of the class by

Simple s = new Simple(10, 20);
s.setY(60);

But you won't be able to get the value of DEFAULT by using the s variable since it's a static variable.

If you don't have a constructor in a class on the other hand, like this

public class Simple {
public static int DEFAULT = 0;
private static int x = 50;
private static int y = 100;
public static void setX(int x) {
Simple.x = x;
}
public static int getX() {
return x;
}
public static void setY(int y) {
Simple.y = y;
}
public static int getY() {
return y;
}
}

You can access all the functions and variables using Simple.getY() and so on.

As you see we can no longer call this, since we're no longer in an object, we're in a class.

Conclusion: When using a constructor you can have how many instances of that class you'd like as objects.

When not using a constructor you don't have any instance of that class, you simply (funny) call Simple.whatEverMethodOrVariable();

Edit: Okay, seems I was wrong, but I still believe having my thinking will help you through programming.

As hellochar said, Java will automatically add a none-argument constructor if you don't have one in your class.

All classes have at least one constructor. If a class does not explicitly declare any, the Java compiler automatically provides a no-argument constructor, called the default constructor. This default constructor calls the class parent's no-argument constructor, or the Object constructor if the class has no other parent. If the parent has no constructor (Object does have one), the compiler will reject the program.

Nokjao

Re: Re: Is Constructor a Method?

1 year ago

Hi Bustup. Is your explanation still partially true?

PhiLho

Re: Is Constructor a Method?

1 year ago

Not really...
I can make a simple class like:
class Struct
{
int x;
int y;
}
and it is perfectly valid. I can create it with new Struct(), and assign values to x and y and get their values. No static stuff there, all dynamic!

It is OK if the class has limited scope and usage, but for something more generic, using getters and setters is necessary. And having a constructor allowing to create the object and assign the values in the same go is just convenient.

To answer your initial question, technically, Constructor isn't the same thing than Method. It has no return declaration (not even void), it isn't called like a method, it has its own constraints (if super() is called, must be on the first line), and so on.

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