nterface
In the interface, you do several things:
You name the class and its superclass.
You may also specify any protocols that your class conforms to (see Protocol).
You specify the class’s instance variables.
You specify the methods and declared properties (see Declared property) that are available for the class.
In the interface file, you first import any required frameworks. (This will often be just Cocoa/Cocoa.h.) You start the declaration of the class interface itself with the compiler directive @interface and finish it with the directive @end.