Inheritance(IS-A) And Composition(HAS-A)
When you make a complex program which use OOP(Object Oriented Programming) concept you will find many classes that are related with another class.We may have a question why we use many classes.The important key to use many class is we devide a large program into a small program that is related with each other to become a large program. To know the work way class that is related with another one is to understand two basic concept Inheritance and Composition is very important to understand.So take a look !