Simulate abstract classes and abstract methods in Objective C?

Question

Possible Duplicate:
Creating an abstract class in Objective C

In Java I like to use abstract classes to make sure that a bunch of classes has the same basic behavior, e.g.:

public abstract class A
{
// this method is seen from outside and will be called by the user
final public void doSomething()
{
// ... here do some logic which is obligatory, e.g. clean up something so that
// the inheriting classes did not have to bother with it

reallyDoIt();
}
// here the actual work is done
protected abstract void reallyDoIt();

}

Now that if class B inherits from class A, it only has to implement reallyDoIt().

How to make this in Objective C? Is it at all possible? Is it feasible in Objective C? I mean the whole paradigm seems to be different in Objective C e.g. from what I understand there is no way to forbid overriding a method (like in Java with 'final')?

Thanks!

Answer 1

There is no actual constraint on not overriding a method in objective c. You can use a protocol as Dan Lister suggested in his answer but this is only good to enforce your conforming class to implement a certain behavior declared in that protocol.

A solution for an abstract class in objective c could be :

interface MyClass {

}

- (id) init;

- (id) init {
   [NSException raise:@"Invoked abstract method" format:@"Invoked abstract method"]; 
   return nil;
}

This way you can prevent methods in your abstract class to be invoked (but only at run-time unlike languages like java which can detect this when on compile-time).