When Inheritance?

Inheritance should be used in case of

several implementations that share the same interface,

frameworks for plug-ins, and

meaningful type hierarchies if they increase static type safety.

Inheritance should not be used

as a means to use already existing code if it is not strictly a is-a relationship (example: a stack class that extends an array to use the array implementation), or

as a hierarchical classification when objects (or their natural equivalents) may change their classification during their lifetime.

	several implementations that share the same interface,
	frameworks for plug-ins, and
	meaningful type hierarchies if they increase static type safety.

	as a means to use already existing code if it is not strictly a is-a relationship (example: a stack class that extends an array to use the array implementation), or
	as a hierarchical classification when objects (or their natural equivalents) may change their classification during their lifetime.