Question

I’ve seen many other questions on this same topic but they’re not very clear to me, someone new to Objective-C.

I need a plain english explanation. ‘Coder speak’ is much too difficult for me to understand at this point in my learning.

Answer 1

An instance method or variable applies to that instance. A class method (classes in Objective-C don’t have variables, though they can be simulated in various ways) applies to the whole class.

Consider the quintessential Dog class, which derives from the Mammal class (and so on up the tree of life.) A particular dog has a name and a collar and an owner–those are its properties. A particular dog may -bark or -chaseBall or -buryBoneInBackyard–those are its methods.

The Dog class, on the other hand, has different methods. The Dog class has a +globalPopulation and may instantiate itself with a +dogWithDNA: factory method. The Dog class will have an +isExtinct method indicating whether the species as a whole is extinct (it’s not, of course.)

In short: class methods affect the entire class, while instance methods affect a particular instance of a class.