Java Programmer Skills Programme

LESSON 9

3.1 Lesson Outcomes

After completing this lesson, learners will be able to:

Define a class in Java.
Create and declare Java classes.
Explain the purpose of classes in object-oriented programming.
Identify class attributes and methods.
Create objects from Java classes.

3.2 Overview

Classes are one of the fundamental building blocks of Java programming. Java is a class-based and object-oriented programming language, meaning that applications are developed using classes and objects.

This lesson introduces learners to Java classes and explains how classes are used to organize program data and behaviour into reusable structures. Learners will also explore how classes contain variables and methods that define the characteristics and behaviour of objects.

Classes are widely used in:

banking systems,
healthcare systems,
inventory applications,
eCommerce platforms,
and enterprise software systems.

Understanding Java classes is essential because all object-oriented Java applications rely on class structures.

KT0901 — Introduction to Java Classes

A class is a blueprint used to create objects in Java.

Classes define:

object properties (attributes),
object behaviour (methods),
and program structure.

Structure of a Java Class

public class Student {

}

Explanation

Component	Description
public	Access modifier
class	Keyword used to declare a class
Student	Class name
{}	Class body

Importance of Classes

Classes help developers:

organize code,
reuse functionality,
simplify maintenance,
and model real-world systems.

KT0902 — Class Attributes

Attributes are variables declared inside a class.

Attributes store data related to objects created from the class.

Example

public class Student {

    String name;
    int age;
}

Explanation

Attribute	Purpose
name	Stores student name
age	Stores student age

Importance of Attributes

Attributes help:

represent object state,
store object information,
and manage application data.

KT0903 — Class Methods

Methods define the behaviour of objects.

Methods perform actions and operations inside a class.

Example

public class Student {

    void study() {

        System.out.println("Student is studying");
    }
}

Explanation

Component	Description
void	No return value
study()	Method name
System.out.println()	Displays output

Importance of Methods

Methods:

improve code reuse,
organize program logic,
and simplify application functionality.

KT0904 — Creating Objects from Classes

Objects are created from classes using the new keyword.

Example

public class Main {

    public static void main(String[] args) {

        Student learner = new Student();
    }
}

Explanation

Component	Description
Student	Class name
learner	Object reference
new	Creates object
Student()	Constructor

KT0905 — Accessing Attributes and Methods

Object attributes and methods are accessed using the dot operator.

Example

public class Main {

    public static void main(String[] args) {

        Student learner = new Student();

        learner.name = "John";

        System.out.println(learner.name);

        learner.study();
    }
}

Output

John
Student is studying

Importance of the Dot Operator

The dot operator allows access to:

object variables,
methods,
and behaviour.

KT0906 — Multiple Objects from One Class

One class can create many objects.

Each object contains its own data.

Example

public class Main {

    public static void main(String[] args) {

        Student learner1 = new Student();
        Student learner2 = new Student();

        learner1.name = "John";
        learner2.name = "Sarah";

        System.out.println(learner1.name);
        System.out.println(learner2.name);
    }
}

Output

John
Sarah

Importance of Multiple Objects

Multiple objects allow applications to:

manage many entities,
store separate data,
and process information efficiently.

KT0907 — Real-World Use of Java Classes

Java classes are used in:

banking systems,
school management systems,
eCommerce platforms,
healthcare systems,
and mobile applications.

Examples:

Customer class
Product class
Employee class
Vehicle class

Classes help model real-world entities inside software applications.

3.5 Key Notes / Summary

A class is a blueprint for creating objects.
Classes contain attributes and methods.
Attributes store object data.
Methods define object behaviour.
Objects are created using the new keyword.
The dot operator accesses object members.
Multiple objects can be created from one class.