Refenced from : http://developer.apple.com/mac/library/documentation/Cocoa/Conceptual/ObjectiveC/Introduction/introObjectiveC.html

 

 

Introduction to The Objective-C Programming Language

The Objective-C language is a simple computer language designed to enable sophisticated object-oriented programming. Objective-C is defined as a small but powerful set of extensions to the standard ANSI C language . Its additions to C are mostly based on Smalltalk , one of the first object-oriented programming languages. Objective-C is designed to give C full object-oriented programming capabilities, and to do so in a simple and straightforward way.

Most object-oriented development environments consist of several parts:

• An object-oriented programming language

• A library of objects

• A suite of development tools

• A runtime environment

This document is about the first component of the development environment—the programming language. It fully describes the Objective-C language, and provides a foundation for learning about the second component, the Mac OS X Objective-C application frameworks—collectively known as Cocoa. You can start to learn more about Cocoa by reading <!-- a target="_top" -->Getting Started with Cocoa<!-- /a--> . The two main development tools you use are Xcode and Interface Builder, described in Xcode Workspace Guide and <!-- a target="_top" -->Interface Builder<!-- /a--> respectively. The runtime environment is described in a separate document, Objective-C Runtime Programming Guide .

Important:  This document describes the version of the Objective-C language released in Mac OS X v10.6, which introduces the associative references feature (see “Associative References” ). To learn about version 1.0 of the Objective-C language (available in in Mac OS X v10.4 and earlier), read <!-- a target="_top" -->Object Oriented Programming and the Objective-C Programming Language 1.0<!-- /a--> .

Who Should Read This Document

The document is intended for readers who might be interested in:

• Programming in Objective-C

• Finding out about the basis for the Cocoa application framework

This document both introduces the object-oriented model that Objective-C is based upon and fully documents the language. It concentrates on the Objective-C extensions to C, not on the C language itself.

Because this isn’t a document about C, it assumes some prior acquaintance with that language. However, it doesn’t have to be an extensive acquaintance. Object-oriented programming in Objective-C is sufficiently different from procedural programming in ANSI C that you won’t be hampered if you’re not an experienced C programmer.

Organization of This Document

This document is divided into several chapters and one appendix.

The following chapters cover all the features Objective-C adds to standard C.

• “Objects, Classes, and Messaging”

• “Defining a Class”

• “Allocating and Initializing Objects”

• “Protocols”

• “Declared Properties”

• “Categories and Extensions”

• “Associative References”

• “Fast Enumeration”

• “Enabling Static Behavior”

• “Selectors”

• “Exception Handling”

• “Threading”

• “Remote Messaging”

The Apple compilers are based on the compilers of the GNU Compiler Collection . Objective-C syntax is a superset of GNU C/C++ syntax, and the Objective-C compiler works for C, C++ and Objective-C source code. The compiler recognizes Objective-C source files by the filename extension .m , just as it recognizes files containing only standard C syntax by filename extension .c . Similarly, the compiler recognizes C++ files that use Objective-C by the extension .mm . Other issues when using Objective-C with C++ are covered in “Using C++ With Objective-C.”

The appendix contains reference material that might be useful for understanding the language:

• “Language Summary” lists and briefly comments on all of the Objective-C extensions to the C language.

Conventions

Where this document discusses functions, methods, and other programming elements, it makes special use of computer voice and italic fonts. Computer voice denotes words or characters that are to be taken literally (typed as they appear). Italic denotes words that represent something else or can be varied. For example, the syntax:

@interface ClassName ( CategoryName )

means that @interface and the two parentheses are required, but that you can choose the class name and category name.

Where example code is shown, ellipsis points indicates the parts, often substantial parts, that have been omitted:

- (void)encodeWithCoder:(NSCoder *)coder

{

    [super encodeWithCoder:coder];

    ...

}

The conventions used in the reference appendix are described in that appendix.

See Also

If you have never used object-oriented programming to create applications before, you should read Object-Oriented Programming with Objective-C . You should also consider reading it if you have used other object-oriented development environments such as C++ and Java, since those have many different expectations and conventions from Objective-C. Object-Oriented Programming with Objective-C is designed to help you become familiar with object-oriented development from the perspective of an Objective-C developer. It spells out some of the implications of object-oriented design and gives you a flavor of what writing an object-oriented program is really like.

Runtime

Objective-C Runtime Programming Guide describes aspects of the Objective-C runtime and how you can use it.

Objective-C Runtime Reference describes the data structures and functions of the Objective-C runtime support library. Your programs can use these interfaces to interact with the Objective-C runtime system. For example, you can add classes or methods, or obtain a list of all class definitions for loaded classes.

Objective-C Release Notes describes some of the changes in the Objective-C runtime in the latest release of Mac OS X.

Memory Management

Objective-C supports two environments for memory management: automatic garbage collection and reference counting:

• Garbage Collection Programming Guide describes the garbage collection system used by Cocoa. (Not available on iPhone—you cannot access this document through the iPhone Dev Center.)

• Memory Management Programming Guide for Cocoa describes the reference counting system used by Cocoa.