What is composition as it relates to object oriented design?

by

Composition refers to combining simple types to make more complex ones. In your example, composition could be: 

Animal:
    Skin animalSkin
    Organs animalOrgans


Mammal::Animal: 
    Hair/fur mammalFur
    warm-blooded-based_cirulation_system heartAndStuff

Person::Mammal: 
    string firstName
    string lastName

If you wanted to go totally composition (and get rid of all inheritance) it would look like this:

Animal:
    Skin animalSkin
    Organs animalOrgans

Mammal:
    private Animal _animalRef
    Hair/fur mammalFur
    warm-blooded-based_cirulation_system heartAndStuff

Person:
    private Mammal _mammalRef
    string firstName
    string lastName

The advantage to this approach is that the types Mammal and Person do not have to conform to the interface of their previous parent. This could be a good thing because sometimes a change to the superclass can have serious effects on the subclasses.
They still can have access to the properties and behaviours of these classes through their private instances of these classes, and if they want to expose these former-superclass behaviours, they can simply wrap them in a public method.

I found a good link with good examples here: http://www.artima.com/designtechniques/compoinh.html

More Related Contents:

  1. What’s the difference between a method and a function?
  2. Examples of GoF Design Patterns in Java’s core libraries
  3. Interface vs Base class
  4. What is the difference between association, aggregation and composition?
  5. What is Inversion of Control?
  6. What does “program to interfaces, not implementations” mean?
  7. Inheritance vs. Aggregation [closed]
  8. Prefer composition over inheritance?
  9. Does functional programming replace GoF design patterns?
  10. What is the difference between an abstract method and a virtual method?
  11. What is “loose coupling?” Please provide examples
  12. Where do I use delegates? [closed]
  13. Do write-only properties have practical applications?
  14. Simple way to understand Encapsulation and Abstraction
  15. Why use inheritance at all? [closed]
  16. Interface Segregation Principle- Program to an interface
  17. Mediator Vs Observer Object-Oriented Design Patterns
  18. Fluent Interfaces – Method Chaining
  19. Can’t seem to understand SOLID principles and design patterns [closed]
  20. Differences between Proxy and Decorator Pattern
  21. Does the Single Responsibility Principle work in OOP?
  22. adapter-Any real example of Adapter Pattern [closed]
  23. Learning/Implementing Design Patterns (For Newbies) [closed]
  24. Switch statements are bad? [closed]
  25. Difference between Encapsulation and Abstraction
  26. In SOLID, what is the distinction between SRP and ISP? (Single Responsibility Principle and Interface Segregation Principle)
  27. How do you explain OO to new programmers? [closed]
  28. Is there a use-case for singletons with database access in PHP?
  29. Is it possible to access struct fields from within a trait?
  30. If Singletons are bad then why is a Service Container good?

Leave a Comment