Static methods have nothing to do with OOP at its core. If Java had no instances of classes, this would be an example of modular programming with classes being modules and static methods being ordinary procedures.
The here relevant difference between Java and Objective-C is that the latter has a Smalltalk-like metaobject protocol: classes themselves are normal objects. A foo object may be an instance of a FooClass which eventually is an instance (!= subclass) of NSObject. When we invoke a method on a class, we send this message to the actual object representing that class. In Java, calling a static method does not involve objects at all, it's just a procedure call (and can be fully resolved before run time – no dynamic dispatch is needed).
In Java, classes are not reified beyond reflection. So instance.staticMethod() kind of makes sense, as it couldn't mean anything else (it just happens to share the syntax for ordinary method calls, but the static method is only looked up according to the static type of the instance variable:
class Super {
public static void staticMethod() { return; }
}
class Instance extends Super {
}
Instance instance = new Instance();
instance.staticMethod(); // doesn't work
((Super) instance).staticMethod(); // works with cast
Objective-C does not have such “static methods”, but it does have:
class methods, which resemble static methods if you squint your eyes. It would be very confusing if a method call on an instance would end up being a method call on a class (another object alltogether), so there is no syntactic shortcut like [instance staticMethod], which doesn't even save that much over [[instance class] staticMethod]. Such class methods are good for constructors and other factory methods. However, they are not “static” as they are subject to inheritance.
plain old C functions. These exist outside of objects and classes, and are not subject to dynamic dispatch – which also makes them interesting from a performance standpoint. These are “static” in the actual sense of that word, but they are not “methods”.
