Understand the idea

Types define which values a variable can hold and which operations make sense. Use int for ordinary whole numbers, double for many decimal calculations, boolean for true/false decisions, and String for text. These examples are a starting point, not a replacement for considering precision and range in a real application.

Explore the details

Java Data Types

Every variable in Java must have a data type — it tells Java what kind of value the variable can hold and how much memory to reserve.

Data types are divided into two groups:

• Primitive data types — the 8 built-in types: byte, short, int, long, float, double, boolean and char
• Non-primitive data types — such as String, Arrays, and Classes (you will learn these in later chapters)

Primitive Data Types

A primitive type stores a simple value directly in memory. There are exactly 8 of them in Java. Click each one below to explore its size, range, and usage:

Declaring Primitive Variables

Here is how you declare variables for each of the common primitive types:

Primitive vs Non-Primitive

• Primitive types always have a value — they can never be null
• Non-primitive types (like String) can be null — meaning they reference no object
• Primitives store values directly; non-primitives store a reference (memory address) to an object
• Non-primitive types have built-in methods you can call (e.g. "hello".length())

Types Are Fixed

Once a variable is declared with a type, it cannot change to another type. Java is a statically typed language — the type is checked at compile time, not at runtime.

Code anatomy / கோடின் விளக்கம்

byte   small  = 127;              // -128 to 127
short  medium = 32767;            // -32,768 to 32,767
int    num    = 2_000_000;        // underscores improve readability
long   big    = 9_876_543_210L;   // append L for long
float  price  = 9.99f;            // append f for float
double pi     = 3.14159265358979; // 15-16 decimal digits
boolean flag  = true;
char   ch     = 'J';

System.out.println(Integer.MAX_VALUE);        // 2147483647
System.out.println(Double.MIN_VALUE);         // 4.9E-324
System.out.println(Character.isLetter(ch));   // true

A complete runnable example

This complete Main.java program focuses on the lesson idea. Reference fragments above may demonstrate individual statements; this example includes the imports, entry point, and supporting types it needs.

public class Main {
    public static void main(String[] args) throws Exception {
        int seats = 24;
        double temperature = 28.5;
        boolean open = true;
        char section = 'A';
        String place = "Ariyalur";
        System.out.println(seats + " | " + temperature + " | " + open);
        System.out.println(section + " | " + place);
    }
}

24 | 28.5 | true
A | Ariyalur

Change it. Run it. Understand it.

Load this lesson example into the editor. Change one value or statement, predict the result, then press RUN to execute Java.

Make it your own

Your learning checkpoint

• Explain the example without reading the output first.
• Make the change requested in the practice task.
• Describe why the result changed—or why compilation failed.

Ready to move on? Follow the next lesson in course order, or return to the curriculum to review a prerequisite.