S.O.L.I.D. STANDS FOR:

• S — Single responsibility principle
• O — Open closed principle
• L — Liskov substitution principle
• I — Interface segregation principle
• D — Dependency Inversion principle

Examples taken from:

• https://scotch.io/bar-talk/s-o-l-i-d-the-first-five-principles-of-object-oriented-design
• https://dzone.com/articles/the-solid-principles-in-real-life

Single responsibility principle

"Just because you can, doesn’t mean you should."

• A class should have one and only one reason to change, meaning that a class should have only one job.
• Avoid GOD classes
• Class should be small
• Split big classes into smaller classes

Open/Closed principle

• Classes should be open for extension but closed for moditication
  • This simply means that a class should be easily extendable without modifying the class itself
• Use private variables with getters/setters
• Use abstract base class

Liskov substitution principle

"If it looks like a duck, quacks like a duck, but needs batteries – you probably have the wrong abstraction."

• Objects in a program would be replacable with instances of their subtypes without altering correctness of program
• Violations will often fails "is a" test
  • A square is a rectangle
  • A rectangle is not a square

Interface Segregation principle

• Make fine grained interfaces that are client specific
• Many client specific interfaces are better than a general purpose interface
• Keep your components focused and minimise dependencies between them

Dependency Inversion principle

• Abstractions should not depend upon details
• Details should not depend upon abstractions
• Important that higher level and lower level objects depends on the same abstract interaction
  • They should not share the same dependency by keeping them independent but by having a clearly API between them.