S — Single Responsibility Principle (SRP) O — Open/Closed Principle (OCP) L — Liskov Substitution Principle (LSP) I — Interface Segregation Principle (ISP) Clients should not be forced to depend on methods they do not use. //Bad Example interface Worker ...

Instance Variable A class variable without static modifier is called Instance Variable, It is unique to each object(instance) of the class and not shared between the class Class Variable Class variable can be declared any where in the class level using keyword static, ...