Q:
Methods are effectively functions that are defined inside classes. If they look like functions and act like functions, why aren’t they called functions?
A:
Some object-oriented programming languages do call them functions (C++ calls them member functions). Other object-oriented languages differentiate between functions inside and outside a body of a class or
object, where having separate terms is important to understanding how each works. Because the difference is relevant in other languages and because the term method is now in such common use in
object-oriented technology, Java uses the word as well.
Q:
I understand instance variables and methods, but not the idea of class variables and methods.
A:
Most everything you do in a Java program will be with objects. Some behaviors and attributes, however, make more sense if they are stored in the class itself rather than in the object. For example, to create a
new instance of a class, you need a method that is defined and available in the class itself. (Otherwise, how can you create an object? You need an object to call the method, but you don’t have an object yet.)
Class variables, on the other hand, are often used when you have an attribute whose value you want to share with all the instances of a class.