📘LESSON 7

3.1 Lesson Outcomes

After completing this lesson, learners will be able to:

• Define variables in Java.
• Perform operations using Java operators.
• Explain classes and objects in Java.
• Define fields, constructors, and methods.
• Explain interfaces in Java.
• Explain the purpose of packages in Java.

3.2 Overview

Java programming is built around core programming concepts that support software development and object-oriented programming. These concepts help developers organize code, create reusable components, and build structured applications.

This lesson introduces learners to Java core concepts and explains how variables, operations, classes, objects, interfaces, and packages are used in Java applications.

Java core concepts are widely used in:

• enterprise applications,
• banking systems,
• Android applications,
• web development,
• and software engineering.

Understanding Java core concepts is important because they form the foundation of Java programming and object-oriented software development.

KT0701 — Variables

A variable is a named memory location used to store data values in a Java program.

Variables allow programs to:

• store information,
• process data,
• and perform calculations.

Variable Declaration

int age = 25;

Components of a Variable

Types of Variables

Importance of Variables

Variables support:

• data storage,
• calculations,
• and program processing.

KT0702 — Operations

Operations are actions performed on data values using operators.

Java supports:

• arithmetic operations,
• comparison operations,
• and logical operations.

Arithmetic Operators

Example

int total = 10 + 5;

Comparison Operators

Importance of Operations

Operations support:

• calculations,
• comparisons,
• and logical processing.

KT0703 — Classes + Objects

A class is a blueprint used to create objects.

An object is an instance of a class.

Class Example

public class Student {

    String name;
    int age;
}

Object Example

Student student1 = new Student();

Fields

Fields are variables declared inside a class.

Example of Fields

String name;
int age;

Constructors

Constructors are special methods used to initialize objects.

Constructor Example

public Student() {

    System.out.println("Object Created");
}

Methods

Methods are blocks of code used to perform tasks.

Method Example

public void display() {

    System.out.println("Hello");
}

Importance of Classes and Objects

Classes and objects support:

• object-oriented programming,
• reusable code,
• and software organization.

KT0704 — Interfaces

An interface is a structure that contains method declarations without full implementation.

Interfaces define behaviors that classes must implement.

Interface Example

interface Animal {

    void sound();
}

Implementing an Interface

class Dog implements Animal {

    public void sound() {

        System.out.println("Bark");
    }
}

Importance of Interfaces

Interfaces support:

• abstraction,
• flexible design,
• and code standardization.

KT0705 — Packages

A package is a collection of related classes and interfaces.

Packages help organize Java programs.

Package Example

package school;

Benefits of Packages

Importance of Packages

Packages improve:

• software organization,
• maintainability,
• and project structure.

3.5 Key Notes / Summary

• Variables store data values in Java programs.
• Operations perform calculations and comparisons.
• Classes are blueprints for objects.
• Objects are instances of classes.
• Fields store object data.
• Constructors initialize objects.
• Methods perform tasks.
• Interfaces define behaviors.
• Packages organize Java applications.