more info.. http://evergreenphp.blogspot.com
Object interfaces allow you to create code which specifies which methods a class must implement,
without having to define how these methods are handled.
Interfaces are defined using the interface keyword, in the same way as a standard class, but without any
of the methods having their contents defined.
All methods declared in an interface must be public, this is the nature of an interface.
To implement an interface, theim plem ents operator is used. All methods in the interface must be
implemented within a class; failure to do so will result in a fatal error. Classes may implement more
than one interface if desired by separating each interface with a comma.
Note: A class cannot implement two interfaces that share function names, since it would
Note: Interfaces can be extended like classes using theextend operator.
Note: The class implementing the interface must use the exact same method signatures as
are defined in the interface. Not doing so will result in a fatal error.
Its possible for interfaces to have constants. Interface constants works exactly like class constants. They
cannot be overridden by a class/interface that inherits it.