← Back to All Lessons

Primitive Data Types

// Integer types
byte small = 127;          // -128 to 127
short medium = 32000;      // -32,768 to 32,767
int normal = 2000000000;   // Most common
long big = 9000000000L;    // Note the L suffix!

// Decimal types
float pi = 3.14f;          // Note the f suffix!
double precise = 3.14159265358979;  // More precise (default)

// Other types
boolean alive = true;      // true or false only
char letter = 'A';         // Single character (use single quotes!)

Strings (Reference Type)

String name = "Alice";   // Use double quotes!
String greeting = "Hello, " + name + "!";  // Concatenation

// String methods
name.length();           // 5
name.toUpperCase();      // "ALICE"
name.charAt(0);          // 'A'
name.equals("Alice");    // true (use this, NOT ==!)
name.contains("li");     // true

Constants & var

final int MAX = 100;      // Constant — can't change
// MAX = 200;             // Error!

// Type inference (Java 10+)
var age = 25;             // Compiler infers int
var name = "Bob";         // Compiler infers String

Type Casting

// Widening (automatic): smaller → larger
int x = 10;
double y = x;  // 10.0 (auto)

// Narrowing (manual): larger → smaller
double a = 9.8;
int b = (int) a;  // 9 (decimal truncated!)

// String to number
int num = Integer.parseInt("42");
double dbl = Double.parseDouble("3.14");

// Number to String
String s = String.valueOf(42);
String s2 = Integer.toString(42);

✅ Quick Quiz

← Previous Next: Operators →