Chapter 5. Exploring Protocols and Categories

Objective-C provides two additional schemes for defining methods: protocols and categories. This chapter will describe both, explain how they differ, show how they are used, and present some design patterns that incorporate them.

Objective-C protocols are equivalent to Java interfaces. Protocols are employed just as interfaces are in Java, although less frequently. Objective-C programmers are more likely to use a relaxed form called an informal protocol.