Careeroza

Enum Basics

A Fixed Set of Constants

An enum is a special class with a fixed list of instances. Use it whenever a value can only be one of a known set: order status, day of week, payment mode, user role.

Example

public class Main {
    enum OrderStatus { PLACED, PACKED, SHIPPED, DELIVERED, CANCELLED }

    public static void main(String[] args) {
        OrderStatus s = OrderStatus.SHIPPED;
        System.out.println("Status: " + s);
        System.out.println("name(): " + s.name() + ", ordinal(): " + s.ordinal());
        System.out.println("== works: " + (s == OrderStatus.SHIPPED));

        for (OrderStatus st : OrderStatus.values()) {
            System.out.print(st + " ");
        }
        System.out.println();

        OrderStatus parsed = OrderStatus.valueOf("DELIVERED");
        System.out.println("Parsed: " + parsed);
        System.out.println("Shipped before delivered? " + (OrderStatus.SHIPPED.compareTo(OrderStatus.DELIVERED) < 0));
    }
}

Output

Status: SHIPPED
name(): SHIPPED, ordinal(): 2
== works: true
PLACED PACKED SHIPPED DELIVERED CANCELLED 
Parsed: DELIVERED
Shipped before delivered? true

Why Not String or int Constants?

String/int constantsenum
Type safetyany string/int acceptedonly valid constants compile
Typos"SHIPED" compilesSHIPED is a compile error
Extra dataseparate mapsfields and methods on the enum
switch supportyesyes, with exhaustiveness checks in switch expressions

Note: valueOf("shipped") (wrong case) throws IllegalArgumentException. Normalise input with toUpperCase() first.