Question

I know usually, when you want to call a method on another object, you do:

NewObject *object = [NewObject alloc]init];

[object callMethod];

But I created a class that isn’t an object itself meaning it doesn’t have properties or memory management. It has a couple methods that calculate some stuff.

From any other class, all I have to do is import the header for this class and do:

#import "MyClass.h"

[MyClass callMethod];

Why in this case do I not have to alloc init? It works just fine.

Answer 1

It sounds like you are trying to call a class method. These are methods which have been defined as:

• +(void) myStaticMethod;

instead of

• -(void) myMethod;

The plus sign indicates that the method does not use any fields, and thereby does not need to instantiate the object.

In your example, “object” is an instance of a class “NewObject” which has been allocated memory and initialized. Where-as your example, “MyClass” is only a class which because it has static members declared as above, does not need to be instantiated.

Class methods provide a nice way to combine a bunch of related functions into one place, rather than having them spread out in the regular namespace, as would usually be done in straight C. You can also have both class methods and instance methods in the same class, using the class ones when needed, and instantiating the class to use the instance ones when needed.

EDIT: Changed terminology to refer to class methods instead of static methods.