Cocoa is a complete set of classes and application programming interfaces (APIs) for building Mac OS X
applications and tools. With over 240 classes, Cocoa is divided into two essential frameworks: the
Foundation framework and the Application Kit.
The Foundation framework provides a fundamental set of tools for representing fundamental data types,
accessing operating system services, threading, messaging, and more. The Application Kit provides the
functionality to build graphical user interfaces (GUI) for Cocoa applications. It provides access to the
standard Aqua interface components ranging from menus, buttons, and text fields—the building blocks of
larger interfaces—to complete, prepackaged interfaces for print dialogs, file operation dialogs, and alert
dialogs. The Application Kit also provides higher-level functionality to implement multiple document
applications, text handling, and graphics.
Classes are not the only constituents of the Cocoa frameworks. Some programming tasks, such as
sounding a system beep, are best accomplished with a simple C function. Cocoa includes a number of
functions for accomplishing tasks such as manipulating byte orders and drawing simple graphics.
Additionally, Cocoa defines a number of custom data types and constants to provide a higher degree of
abstraction to many method parameters.