SOLID - Principles

Make your codebase great again

S ingle Responsibility

O pen-Closed

​L iskov-Substitution

​I nterface-Segregation

D ependency-Inversion

S ingle Responsibility

• Defined by Robert C. Martin (Uncle Bob) in his book "Agile Software Development, Principles, Patterns and Practices" in 2002

Definition:

A class should have only one reason to change.

O pen-Closed

• Introduced by Bertrand Meyer (french programmer) in his book 'Object-Oriented Software Construction' in 1988

Definition:

Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.

• First introduced by Barbara Liskov in a 1987 conference keynote
• Then published by Barbara Liskov and Jeanette Wing in 1994

Definition:

Let q(x) be a property provable about objects x of type T. Then q(y) should be provable for objects y of type S where S is a subtype of T

in simple terms:

Child classes should never break the parent class' type definitions.

​L iskov-Substitution

• First introduced by Robert C. Martin during a consulting-Job for Xerox
• Problem was, that in a printer-software every Job depended on one Single Class
• Every slight Change resulted in an extensive build-process (> 1hr)
• Solution was to segregate functionality and incapsulate them within separated Interfaces/classes

​I nterface-Segregation

• Defined by Robert C. Martin in his book  'Agile Software Development, Principles, Patterns, and Practices'
• Always depend on abstract interfaces instead of implementations
• Classes can use interfaces or implement interfaces
• Allows decoupling, so consumer can handle every implementation of the interface

D ependency-Inversion

Thanks for your time and happy Coding!

Programming - Challange

Implement a Score-System for a turned-based game (like Poker) (The game(s) can be stubbed)

• it should:
  • be able to keep track of scores for each user
  • handle a variable amount of players
  • offer an interface to games with at least:
    • addScore
    • getScore
    • reduceScore
    • getResults
  • get a Winner for different games (easy rules like highest score wins lowest score wins)
  • get a List of all Players and their scores
  • keep track of a series of games
  • export results as csv