Primitive Data Types
Java has 8 primitive data types. Each has a fixed size and stores a specific kind of value.
Example
// Integer types
byte smallNum = 127; // 8-bit (-128 to 127)
short medNum = 32000; // 16-bit
int number = 2_000_000; // 32-bit (most common)
long bigNum = 9_000_000_000L; // 64-bit (note the L)
// Floating point
float price = 9.99f; // 32-bit (note the f)
double pi = 3.14159265; // 64-bit (default)
// Other
boolean isActive = true; // true or false
char letter = 'A'; // single character (single quotes)Reference Types and Strings
Reference types include classes, arrays, and interfaces. Strings are the most commonly used reference type.
Example
// String (reference type, not primitive)
String name = "Alice";
String greeting = "Hello, " + name; // concatenation
// String methods
int len = name.length(); // 5
String upper = name.toUpperCase(); // "ALICE"
char first = name.charAt(0); // 'A'
boolean starts = name.startsWith("Al"); // true
// Type casting
int x = 10;
double y = x; // implicit (widening)
int z = (int) 3.14; // explicit (narrowing) → 3
// var keyword (Java 10+)
var count = 42; // inferred as int
var text = "hello"; // inferred as String