Lesson 6: Variables and Primitive Data Types

A variable is a container that holds a value. In Java, every variable must have a defined type.

Declaring and Initializing Variables

Variables are declared by specifying the type, followed by the name, and optionally initialized with a value.

java // Declaration (Type and Name) int studentCount;

// Initialization (Assigning a value) studentCount = 25;

// Declaration and initialization in one line double price = 19.99;

Java's 8 Primitive Data Types

These types store simple values directly in memory.

Type	Category	Size (bits)	Default Value	Range Example
`byte`	Integer	8	0	-128 to 127
`short`	Integer	16	0
`int`	Integer (Most Common)	32	0	Approx. +/- 2 Billion
`long`	Integer	64	0L	Very large numbers
`float`	Floating Point	32	0.0f	Single precision
`double`	Floating Point (Most Common)	64	0.0d	Double precision
`boolean`	Logical	1	false	`true` or `false` only
`char`	Character	16	'\u0000'	Single Unicode character

Examples

java int population = 1500000; long universeTime = 31556952000L; // Note the 'L' suffix for long boolean isLoggedIn = true; char grade = 'A'; // Single quotes for char double pi = 3.14159; float smallPi = 3.14f; // Note the 'f' suffix for float

Note: When defining integer literals, Java defaults to int. When defining floating-point literals, Java defaults to double. You must use L or l for long and f or F for float if the value exceeds the default range or type.