Java Tutorial · Object-Oriented Java · Lesson 23 of 37

Java Enums

Define a fixed set of constants with fields, methods and switch support.

Basic enums

An enum is a type with a fixed set of named constants:

Example 1

public class Main {
    public static void main(String[] args) {
        Level level = Level.MEDIUM;
        System.out.println(level + " " + level.ordinal());
        switch (level) {
            case LOW -> System.out.println("Relax");
            case MEDIUM -> System.out.println("Pay attention");
            case HIGH -> System.out.println("Act now");
        }
        for (Level l : Level.values()) System.out.print(l + " ");
        System.out.println();
        System.out.println(Level.valueOf("HIGH") == Level.HIGH);
    }

    enum Level { LOW, MEDIUM, HIGH }
}

Output

MEDIUM 1
Pay attention
LOW MEDIUM HIGH 
true

Run this on your computer — see “Get Started” for setup.

Enums with fields and methods

Enum constants are objects, so they can have constructors, fields and methods:

Example 2

public class Main {
    public static void main(String[] args) {
        for (Planet p : Planet.values()) {
            System.out.printf("%-7s weight of 70kg person: %.1f kg%n", p, p.weightOf(70));
        }
    }

    enum Planet {
        MERCURY(0.38), EARTH(1.0), JUPITER(2.53);

        private final double gravity;

        Planet(double gravity) {
            this.gravity = gravity;
        }

        double weightOf(double earthKg) {
            return earthKg * gravity;
        }
    }
}

Output

MERCURY weight of 70kg person: 26.6 kg
EARTH   weight of 70kg person: 70.0 kg
JUPITER weight of 70kg person: 177.1 kg

Run this on your computer — see “Get Started” for setup.

EnumMap and EnumSet are very fast collections keyed by enums.

Test yourself

Which method converts the string "HIGH" into the enum constant Level.HIGH?

Level.parse("HIGH")
Level.valueOf("HIGH")
new Level("HIGH")
Level.from("HIGH")

Show answer

Answer: Level.valueOf("HIGH")