UML Inheritance - Principles of Object Oriented Design

[finecutmarmalade]

yo man, your tutorials are ill son! i'mma ace my principles of OOP paper tomorrow. catch you on the flipside, homie.

[murph1329]

well done video. Great real world example. Much better than the stupid triangle, square, shape one.

[eltonpiko]

great explanation really appreciate it.

[AgileJStructureViews]

@eltonpiko Thank you for commenting - I'm glad you found this video useful

[mrjayarajj]

hai paul wells,

I have a doubt.

1. why we need inheritance here, why cant we archive using polymorphisms ?

eg: RentedFlat has HouseProperty and OwnerOccupiedHouse has HouseProperty

RentedFlat r = new RentedFlat();

r.getHouseProperty().getLocati­on();

OwnerOccupiedHouse o = new OwnerOccupiedHouse ();

o.getHouseProperty().getLocati­on();

[AgileJStructureViews]

@mrjayarajj Hi. Thanks for your comment. Inheritance does two jobs: 1. Helps with re-use through generalization (you only create/test the general parts once). 2. Lets you write frameworks against a base class or interface. (See my video on polymorphism). So in this video I'm demonstrating job 1 - re-use through generalization.

[AgileJStructureViews]

@mrjayarajj (continued) But you are correct, and this is a dilemma which OO designers often have to tackle. You can implement it with a delegate (HouseProperty) and it will work, but strictly speaking you are using a HAS-A relationship to model an IS-A relationship. Probably not a big problem in this simple case, but in a larger system with a few more layers of inheritance and a few more genuine HAS-A relationships (eg heating system) it could possibly be less clear to understand the design

[wizman009]

@mrjayarajj

By using inheritance we open the door to use polymorphism as well :).

Ie, We can have a super (base) class to have common properties and a getLocati­on() method (this is a use of inheritance), .

Then derived classes RentedFlat and RentedFlat classes and then these derived classes can re-define getLocati­on() (this is polymorphism, as getLocati­on() can be called regardless of the type)...