SOLID Principles tutorial _ Object-Oriented Programming
Single responsibility principle: A class should only have a single responsibility, that is, only changes to one part of the software's specification should be able to affect the specification of the class.
Open–closed principle: "Software entities ... should be open for extension, but closed for modification."
Liskov substitution principle: "Objects in a program should be replaceable with instances of their subtypes without altering the correctness of that program." See also design by contract.
Interface segregation principle: "Many client-specific interfaces are better than one general-purpose interface."
Dependency inversion principle One should "depend upon abstractions, not concretions".
https://en.wikipedia.org/wiki/SOLID
For more information refer to the Tutorial Powerpoint.
Sample codes are included in this repository as well.