Question

My program has a class and that class has an +initialize method. I wonder who calls that method? The debugging tools are very unclear:

What triggers +initialize to be called? The beginning of application launch?

Answer 1

The runtime sends initialize to each class in a program exactly one time just before the class, or any class that inherits from it, is sent its first message from within the program.

See the documentation for + (void)initialize on NSObject.

An authoritative blog post on the question of initialize states that initialize is executed once when the class is first used, i.e. as the docs state before the class is sent its first message.