You should understand two important object-oriented terms: object and class. A class is a description of an object, and an object is an instance of a class. In Java, you write classes. Because Java is purely object oriented, all of the statements in your Java programs appear inside a Java class. Notice that the Hello, World program in a public class. We will discuss public in detail later, but for now I will just say that almost every class you write in Java will be declared public. The purpose of a class is to describe an object. An object is just what the word means in English: a thing, an item, a noun. For example, a car, a house, an employee of a company, a window that opens on the computer screen, or a TCP/IP socket connection between two computers.