Design Principles

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A good design reads like a story and not like a puzzle

DP #1 : take what varies and encapsulate it. It will not affect the rest of our code.

DP #2 : program to an interface/super type and not an implementation the actual runtime object is not locked into the code the type of variable should be supertype/interface

Dog dog = new Dog();
Animal dog = new Dog();
List<String> str = new ArrayList<>();

what is behaviour of an object and whats is its state

DP #3 : Favor composition over inheritance. good to separate behaviour from implementation

composition : HAS-A relationship, whole-part relationship you can encapsulate stuff into its own set of classes . HINT you can CHANGE the behaviour at RUNTIME with interfaces

inheritance : IS-A relationship

aggregation :

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