Subclass does not need to define function signature

Abstract class can be instantiated for no good reason

Minimum compile time check for function existence

No concept of interface enforcement, one needs to manually ensure functions exist to satisfy interface

You do not need to know type of object before sending it a message

Sending message to NIL is allowed, avoid NULL checking

Sending unsupported messages generate only warnings.

No overloading by parameters

Weakly type, strong support for introspection

No template for containers - all containers operate on objects

No static variable for class

No stack objects - everything allocated on the heap - Java like

No double click button - have to roll your own

Often no interface for delegate to derive

nil is a blank object, NULL is a blank pointer

Delegate does not need to implement interface

Cannot force parameter by eliminate default constructor init

No private methods

introspection

isMemberOfClass

isKindOfClass

idobject pointer

SELfunction pointer

@selector()address of function

retain = increase reference count

release = decrease reference count

MDI

NSDocumentController

NSDocument- multiple

NSWindowController- multiple

NSWindow

Key elements of application:

* main routine

int main(int, char *)

This routine instantiates UIApplicationMain which looks into -info.plist to find the nib file to load. 

* main nib file

The nib file is loaded, the nib file instantiates File's Owner which is an instance of UIApplication.  UIApplication's delegate is set to an application delegate in the nib, the class of which is provided by the code as a derived class. The UIApplicationDelegate derived class dictates much of the startup behaviors.

The UIApplicationDelegate has pointers to main UIWindow and maybe also a view controller. The main window is always a requirement because it is a host for the view.

Memory Management:

Release or autorelease objects created with alloc, new, or copy, or retain

CFRelease objects created with Create or Copy