The Java Object Model Overview
Programs are composed of a set of modules called classes. Each class is a template specifying a set of behaviors on the data of the class.
Each class has class variables (sometimes called instance vars) to hold the data and methods (called functions or procedures in other languages) to define the behaviors. Each object in a program is created as an instance of a class. Each class instance has its own copy of the class variables.
Classes can be used for data encapsulation, hiding the details of the data representation from the user of the class (by marking variables as private).