Classes

In programming, a class describes an individual entity or part of the program. In many cases, the class can be used to describe an actual thing, such as a person, a vehicle, or a game board, or a more abstract thing such as a set of rules for a game, or even an artificial intelligence engine for making business decisions.

In object-oriented programming, a class is the basic building block of a larger program. Typically each part of the program is contained within a class, representing either the main logic of the program or the individual entities or things that the program will use.

Representing Classes in UML

We can represent the contents of a class in a UML Class Diagram. Below is an example of a class called Person:

Throughout the next few pages, we will realize the design of this class in code.

Creating Classes in Java

To create a class in Java, we can simply use the class keyword at the beginning of our file:

public class Person{
    
}

As we’ve already learned, each class declaration in Java includes these parts:

1. public - this keyword is used to identify that the item after it should be publicly accessible to all other parts of the program. Later in this chapter, we’ll discuss other keywords that could be used here.
2. class - this keyword says that we are declaring a new class.
3. Person - this is an identifier that gives us the name of the class we are declaring.

Following the declaration, we see a set of curly braces {}, inside of which will be all of the fields and methods stored in this class.

According to the Java standards, this class must be stored in a file called Person.java.