Java With Us

The <code>enum</code> Keyword in Java

Updated on 2026-04-21 Reviewed by the Java With Us editorial team

An enum is a class with a fixed, finite set of instances. Use one whenever a value must be one of a known set — days of the week, order statuses, HTTP methods, currencies. An enum is type-safe (you can't pass "foo" where an enum is expected) and far more expressive than static final constants.

Basic

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

Day d = Day.MONDAY;
d.name();             // "MONDAY"
d.ordinal();          // 0 — don't use ordinal for business logic

With fields and methods

public enum Priority {
    LOW(1), MEDIUM(5), HIGH(10);

    private final int weight;
    Priority(int weight) { this.weight = weight; }
    public int weight() { return weight; }
}

Priority.HIGH.weight();    // 10

Per-constant behaviour

public enum Operation {
    PLUS  { public int apply(int a, int b) { return a + b; } },
    MINUS { public int apply(int a, int b) { return a - b; } };
    public abstract int apply(int a, int b);
}

Operation.PLUS.apply(3, 4);    // 7

Iteration, lookup, conversion

for (Day d : Day.values()) System.out.println(d);
Day.valueOf("MONDAY");             // by name — throws IllegalArgumentException if unknown

// Robust lookup
Optional<Day> d = Arrays.stream(Day.values())
    .filter(x -> x.name().equalsIgnoreCase("monday"))
    .findFirst();

EnumSet and EnumMap

var weekdays = EnumSet.range(Day.MONDAY, Day.FRIDAY);
var weekend  = EnumSet.of(Day.SATURDAY, Day.SUNDAY);
var all       = EnumSet.allOf(Day.class);

var schedule = new EnumMap<Day, List<Task>>(Day.class);

EnumSet is a bitmap internally — blazingly fast and memory-efficient. Use it for any "set of enum values" instead of Set<Day>.

Singleton via enum

public enum Config {
    INSTANCE;
    private final Properties props = load();
    public Properties props() { return props; }
}
Config.INSTANCE.props();

switch on enum

String kind = switch (day) {
    case SATURDAY, SUNDAY -> "Weekend";
    default                -> "Weekday";
};

Common mistakes

  • Using ordinal() in business logic — adding a constant in the middle silently renumbers others. Use an explicit field.
  • Storing ordinals in a database — same problem. Store the name().
  • Too many constants — if the "enum" is really a lookup table that grows, use a regular class backed by a Map.
  • Non-exhaustive switch — add a default or handle every case; Java's exhaustiveness check is strict in switch expressions.

Related

Pillar: Java keywords. See also switch, sealed classes.

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