SOLID Software Development

Ken Burkhardt

What is SOLID?

Single Responsibility Principle Open Closed Principle

Liskov Substitution PrincipleInterface Segregation PrincipleDependency Inversion Principle

Why SOLID?

S.O.L.I.D. is a collection of best-practice, object-oriented design

principles which can be applied to your design, allowing you to

accomplish various desirable goals such as loose-coupling, higher

maintainability

Single Responsibility Principle

THERE SHOULD NEVER BE MORE THAN ONE REASON FOR A CLASS TO

CHANGE.

Demo - Superclass

Open Closed Principle

SOFTWARE ENTITIES SHOULD BE OPEN FOR EXTENSION BUT CLOSED

FOR MODIFICATION

Demo – Add New Validator

Liskov Substitution Principle

You should be able to use any derived class in place of a parent class and have it behave in the same manner without modification. It ensures that a derived class does not affect the behavior of

the parent class, i.e. that a derived class must be substitutable for its base class.

Interface Segregation Principle

CLIENTS SHOULD NOT BE FORCED TO DEPEND UPON INTERFACES THAT

THEY DO NOT USE

Demo - Animals

Dependency Inversion Principle

A. HIGH LEVEL MODULES SHOULD NOT DEPEND UPON LOW LEVEL MODULES. BOTH SHOULD DEPEND UPON ABSTRACTIONS

B. ABSTRACTIONS SHOULD NOT DEPEND UPON DETAILS. DETAILS SHOULD DEPEND UPON ABSTRACTIONS

Bad designs and poor code is not good because it's hard to change. Bad designs are:

- Rigid (change affects too many parts of the system) - Fragile (every change breaks something unexpected) - Immobile (impossible to reuse)

Demo - Interfaces