What is Protocol?

Protocols are of two types
1.Formal protocol
A formal protocol declares a list of optional and required methods that other classes are expected to implement.

Syntax:
@protocol protocolName
   //required method declarations
   @optional
   //optional method declarations
   @required
   //other required method declarations
@end
  2.Informal Protocol
An informal protocol is a category(with out implementation) on NSObject, which implicitly makes almost all objects adopters of the protocol.Implementation of the methods in an informal protocol are optional.