Class Relationships in Inheritance, Implementation, and Composition

• Used when the has-a relationship holds

ArrSet uses DynArr via composition

class ArrSet {
	...
	DynArr dynArr;
} 

• Inheritance is NOT appropriate- an ArrSet (set implemented using an array) is NOT a dynamic array
  • In particular, ArrSet should not support a get(int i) method (which it would inherit from DynArr via inheritance
  • On the other hand composition IS appropriate-- ArrSet uses (or has) a DynArr as part of its state (in order to maintain its elements.

  Inheritance of Interface

  • Used when additional method specifications are to be added to a set of existing specification

  Set extends (inherits from) Collection

  interface Set extends Collection {
  	...
  }
  

  • Any class implementing Set, must also implement Collection