Java — Enums

Basic enum

enum Day {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY
}

public class Main {
    public static void main(String[] args) {
        Day today = Day.MONDAY;
        System.out.println(today); // MONDAY
        System.out.println(today.ordinal()); // 0
    }
}

Enum with fields

enum Color {
    RED(255, 0, 0),
    GREEN(0, 255, 0),
    BLUE(0, 0, 255);

    final int r, g, b;

    Color(int r, int g, int b) {
        this.r = r;
        this.g = g;
        this.b = b;
    }

    String toHex() {
        return String.format("#%02X%02X%02X", r, g, b);
    }
}

Enum in switch

enum Season { SPRING, SUMMER, AUTUMN, WINTER }

String describe(Season s) {
    return switch (s) {
        case SPRING -> "Flowers bloom";
        case SUMMER -> "Sun is hot";
        case AUTUMN -> "Leaves fall";
        case WINTER -> "Snow falls";
    };
}

Enum with abstract methods

enum Operation {
    ADD {
        public double apply(double a, double b) { return a + b; }
    },
    SUBTRACT {
        public double apply(double a, double b) { return a - b; }
    },
    MULTIPLY {
        public double apply(double a, double b) { return a * b; }
    };

    public abstract double apply(double a, double b);
}

EnumSet and EnumMap

import java.util.*;

EnumSet<Day> weekdays = EnumSet.range(Day.MONDAY, Day.FRIDAY);
EnumSet<Day> weekend = EnumSet.of(Day.SATURDAY, Day.SUNDAY);

EnumMap<Day, String> schedule = new EnumMap<>(Day.class);
schedule.put(Day.MONDAY, "Meeting");
schedule.put(Day.FRIDAY, "Review");

Mini Practice

Write Java code that:

1. Creates an enum with fields and constructor
2. Uses an enum in a switch expression
3. Uses EnumSet for a group of enum values

Up Next

In the next lesson, you'll learn about Exceptions — error handling in Java.