JAVA

Variables & Data Types

Almost every Java program needs to store information. A student management system stores names, ages, and marks. An e-commerce application stores product names, prices, and stock quantities. Since these values can change while a program is running, Java provides variables to store and manage data.

However, not all information is the same. An age is a number, a name is text, and a pass/fail status is either true or false. Java needs to know what type of data is being stored so it can use memory efficiently and perform the correct operations on that data. This is the purpose of data types.

In this chapter, you will learn how Java stores data using variables, how different data types work, and how to choose the right type for different situations.

What is a Variable?

A variable is a named location in memory used to store data during program execution. Instead of remembering memory addresses, developers use meaningful names such as age, price, or studentName.

The value stored in a variable can be accessed, modified, and reused throughout the program.

Creating a Variable in Java

The general syntax for creating a variable is:

dataType variableName = value;

Example:

int age = 18;

In this statement:

• int is the data type
• age is the variable name
• 18 is the value assigned to the variable

What is a Data Type?

A data type defines the kind of value a variable can store. It helps Java understand how the value should be stored in memory and what operations can be performed on it.

Examples:

18        → Integer Number
3.14      → Decimal Number
'A'       → Character
"Rahul"   → Text
true      → Boolean Value

Because different types of data are stored differently, every variable in Java must have a data type.

Primitive Data Types

Java provides several built-in primitive data types.

When starting with Java, focus primarily on:

• int for whole numbers
• double for decimal numbers
• char for single characters
• boolean for true/false values
• String for text data

These are the data types you will use most frequently while learning the language.

First Example Program

public class Main {
    public static void main(String[] args) {

        String name = "Rahul";
        int age = 18;

        System.out.println(name);
        System.out.println(age);
    }
}

Output:

Rahul
18

In this program:

• name stores text using the String data type.
• age stores a whole number using the int data type.
• The values are displayed using System.out.println().

Understanding System.out.println()

While working with java, you will frequently use:

System.out.println();

This statement is used to display output on the console.

For example:

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

Output:

Hello World

You do not need to understand every part of this statement right now. For now, simply remember:

System.out.println() is used to print information to the screen.

Whenever you want to display a variable, a value, or a message, you will use System.out.println().

Examples:

System.out.println(age);
System.out.println(name);
System.out.println("Welcome to Java");