Compos on Aggrega on and Delega on COMP 401 Spring 2013 Lecture 13 2 21 2013 Layers of Abstrac on Simple objects Object state i e elds are basic data types As objects become more complex Encapsulated object state is complex enough to require addi onal layers of abstrac on Object state is modeled by a combina on of other objects Recall earliest examples with Triangle and Point Lecture3 ta v09 and ta v10 Composi on and Aggrega on Two design techniques for crea ng an object that encapsulates other objects Any speci c situa on is not necessarily strictly one or the other In a nutshull Composi on The individual parts that make up the whole are owned solely by the whole They don t otherwise have a reason for being Aggrega on The individual parts that make up the whole may also exist on their own outside of the whole Or even as a component or part of other objects Example of Aggrega on lec13 v1 Course Models a course at the university Encapsulates Room Professor and a list of Student objects Characteris cs of Aggrega on Encapsulated objects provided externally As parameters to constructor GeYers and seYers for these components oZen provided Encapsulated objects may be independently referenced outside of the aggrega ng object Including possibly as part of another aggrega on Example of Composi on lec13 v2 Car Two implementa ons HondaOdyssey and Porche911 Both encapsulate an implementa on of Horn and an implementa on of Engine Implementa ons of Engine wriYen with inheritance EngineImpl provides most of the implementa on Abstract class ManualEngine and Automa cEngine are subclasses Override setGear Characteris cs of Composi on Encapsulated objects created internally Usually within the constructor No seYers and oZen no geYers Encapsulated objects do not make sense outside of the abstrac on Not shared with other abstrac ons Func onality state of encapsulated objects only accessible through the abstrac on Delega on Claiming an is a rela onship with an interface but relying on another object to actually do the work Can occur with either aggrega on or composi on Although more common with composi on Composi on example revisited lec13 v3 Both Car implementa ons also now claim Horn and or AdjustableHorn interfaces as well Actual work of these interfaces delegated to internal horn Discussion So which techniques are in play with StandardDeckImpl
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