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Objective-C

Object Oriented Programming. Objective-C. Presentation by Kevin Layer. CS 331 21 April 2008. Overview. Objective-C is an object oriented language. follows ANSI C style coding with methods from Smalltalk There is no formal written standard Relies mostly on libraries written by others

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Objective-C

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  1. Object Oriented Programming Objective-C Presentation by Kevin Layer CS 331 21 April 2008

  2. Overview • Objective-C is an object oriented language. • follows ANSI C style coding with methods from Smalltalk • There is no formal written standard • Relies mostly on libraries written by others • Flexible almost everything is done at runtime. • Dynamic Binding • Dynamic Typing • Dynamic Linking

  3. Inventors • Objective-C was invented by two men, Brad Cox and Tom Love. • Both were introduced to Smalltalk at ITT in 1981 • Cox thought something like Smalltalk would be very useful to application developers • Cox modified a C compiler and by 1983 he had a working Object-oriented extension to C called OOPC.

  4. Development • Tom Love acquired a commercial copy of Smalltalk-80 while working for Schlumberger Research • With direct access Smalltalk, Love added more to OOPC making the final product, Objective-C. • In 1986 they release Objective-C through their company “Stepstone”

  5. NeXT and NeXTSTEP • In 1988 Steve Jobs acquires Objective-C license for NeXT • Used Objective-C to build the NeXTSTEP Operating System • Objective-C made interface design for NeXTSTEP much easier • NeXTSTEP was derived from BSD Unix • In 1995 NeXT gets full rights to Objective-C from Stepstone

  6. OPENSTEP API • Developed in 1993 by NeXT and Sun • An effort to make NeXTSTEP-like Objective-C implementation available to other platforms. • In order to be OS independent • Removed dependency on Mach Kernel • Made low-level data into classes • Paved the way for Mac OS X, GNUstep

  7. Apple and Mac OS X • NeXT is taken over by Apple in 1996 and put Steve Jobs and his Objective-C libraries to work • Redesigned Mac OS to use objective-C similar to that of NeXTSTEP • Developed a collection of libraries named “Cocoa” to aid GUI development • Release Mac OS X (ten), which was radically different than OS 9, in March 2001

  8. The Cocoa API • Primarily the most frequently used frameworks nowadays. • Developed by Apple from NeXTSTEP and OPENSTEP • Has a set of predefined classes and types such as NSnumber, NSstring, Nsdate, etc. • NS stands for NeXT-sun • Includes a root class NSObject where words like alloc, retain, and release come from

  9. Dynamic Language • Almost everything is done at runtime • Uses dynamic typing, linking, and binding • This allows for greater flexibility • Minimizes RAM and CPU usage

  10. To Import or Include? • C/C++’s #include will insert head.h into the code even if its been added before. • Obj-C’s #import checks if head.h has been imported beforehand. #import head.h

  11. Messages • Almost every object manipulation is done by sending objects a message • Two words within a set of brackets, the object identifier and the message to send. • Because of dynamic binding, the message and receiver are joined at runtime [Identifier message ]

  12. Basic syntax structure C++ syntax void function(int x, int y, char z); Object.function(x, y, z); Objective-C syntax -(void) function:(int)x, (int)y, (char)z; [Object function:x, y, z];

  13. The word ‘id’ indicates an identifier for an object much like a pointer in c++ This uses dynamic typing For example, if Pen is a class… Keyword: id extern id Pen; id myPen; myPen = [Pen new ]; (Cox, 59)

  14. Memory Allocation • Objects are created dynamically through the keyword, “alloc” • Objects are dynamically deallocated using the words “release” and “autorelease” • autorelease dealocates the object once it goes out of scope. • NOTE: None of these words are built-in

  15. Ownership • Objects are initially owned by the id that created them. • Like C++ pointers, multiple IDs can use the same object. • However, like in C++ if one ID releases the object, then any remaining pointers will be referencing invalid memory. • A method like “retain” can allow the object to stay if one ID releases it.

  16. Prototyping functions • When declaring or implementing functions for a class, they must begin with a + or - • + indicates a “class method” that can only be used by the class itself. In other words, they’re for private functions. • - indicates “instance methods” to be used by the client program (public functions).

  17. Class Declaration (Interface) #import <Cocoa/Cocoa.h> @interface Node : NSObject { Node *link; int contents; } +(id)new; -(void)setContent:(int)number; -(void)setLink:(Node*)next; -(int)getContent; -(Node*)getLink; @end node.h

  18. Class Definition (Implementation) #import "node.h” @implementation Node +(id)new { return [Node alloc];} -(void)setContent:(int)number {contents = number;} -(void)setLink:(Node*)next { [link autorelease]; link = [next retain]; } -(int)getContent {return contents;} -(Node*)getLink {return link;} @end node.m

  19. Adds OOP, metaprogramming and generic programming to C Comes with a std library Has numerous uses Large and complex code for OOP Only adds OOP to C Has no standard library; is dependant on other libraries Mostly used for application building Simpler way of handling classes and objects C++ VS. Objective-C

  20. Objective-C 2.0 • In October 2007, Apple Inc. releases Objective-C 2.0 for Mac OS 10.5 (Leopard) • Adds automatic garbage collection • Instance Methods (public functions) are defined differently using @property

  21. #import "linkList.h" @implementation linkList +(id)new {return [linkList alloc];} -(void)insert:(int)value { id temp = [Node new]; [temp setContent:value]; [temp setLink:head]; head = [temp retain]; [temp release]; } -(void)append:(int)value { id last = [head getLink]; while ([last getLink] != nil) {last = [last getLink];} id temp = [Node new]; [temp setContent:value]; [last setLink:temp]; [temp release]; } -(void)remove { id temp = head; head = [head getLink]; [temp release]; } -(int)getValue { return [head getContent];} @end linkList class linkList.m

  22. #import "linkList.h” @interface Stack : linkList {} +(id)new; -(void)push:(int)value; -(int)pop; @end #import "stack.h” @implementation Stack +(id)new {return [Stack alloc];} -(void)push:(int)value {[self insert:value];} -(int)pop { int ret = [self getValue]; [self remove]; return ret; } @end Stack class stack.h stack.m

  23. #import "stack.h” int main(){ Stack *s = [Stack new]; [s push:1]; [s push:2]; printf("%d\t", [s pop]); [s push:3]; printf("%d\t", [s pop]); printf("%d\t", [s pop]); [s release]; return 0; } Example: main.c main.c $ gcc -x objective-c node.m linkList.m stack.m main.c -framework Cocoa -o stackTest $./stackTest 2 3 1

  24. References • Cox, Brad. Object Oriented Programming: an Evolutioary Approach • Sebesta, Robert. Concepts of Programming Languages • Apple Inc. Apple Developer Connection http://developer.apple.com • Stevenson, Scott. Theocacao http://theocacao.com/document.page/510 • Various Authors. Wikipedia: the Free Encyclopedia http://en.wikipedia.org

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