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interface
subject			fact

interface	cannot have any concrete methods or instance variables
	describes a portion of the visible behaviour of a set of objects
	has purpose to specify a set of methods that a variety of different classes can implement polymorphically
	is like a class except that it does not have any executable statements - it only contains abstract methods and class variables
	is a subtopic of 2.7 - Concepts that Define Object Orientation
	is created using superclasses containing only abstract methods in some languages
	is drawn as a small circle (like a lollipop), labelled with the name of the interface or as a class rectangle, with the expression Ğinterfaceğ at the top, and (optionally) a list of supported operations in a UML diagram
	is implemented using the implements keyword in Java
	is a kind of data abstraction
	provides many of the same benefits as multiple inheritance
	see also interface^2
	see also interface^3
	should not be confused with generalizations
	shows a can-be-seen-as relation between the implementing class and the interface
data abstraction	groups the pieces of data that describe some entity, so that programmers can manipulate that data as a unit
	helps a programmer to cope with the complexity of data
	hides the details of data

Kinds of interface :

• Java interface (2 kinds, 6 facts) - In Java, a software module containing a description of a set of operations that certain classes must implement

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