How to Loop Through an Enum in Java

The Challenge

Iterate through all constants in an enumeration!

Example Enum

java

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

Solutions

Method 1: Using For-Each Loop

java

for (Day day : Day.values()) {
    System.out.println(day);
}
// Output:
// MONDAY
// TUESDAY
// WEDNESDAY
// THURSDAY
// FRIDAY
// SATURDAY
// SUNDAY

Method 2: Using Traditional For Loop

java

Day[] days = Day.values();
for (int i = 0; i < days.length; i++) {
    System.out.println(days[i]);
}

Method 3: Using Arrays.stream()

java

import java.util.Arrays;

Arrays.stream(Day.values()).forEach(System.out::println);

Method 4: Using EnumSet

java

import java.util.EnumSet;

EnumSet<Day> allDays = EnumSet.allOf(Day.class);
for (Day day : allDays) {
    System.out.println(day);
}

Advanced: Enum with Fields

java

enum Planet {
    MERCURY(3.303e+23, 2.4397e6),
    VENUS(4.869e+24, 6.0518e6),
    EARTH(5.976e+24, 6.37814e6);
    
    private final double mass;
    private final double radius;
    
    Planet(double mass, double radius) {
        this.mass = mass;
        this.radius = radius;
    }
    
    public double getMass() { return mass; }
    public double getRadius() { return radius; }
}

// Loop through and access fields
for (Planet planet : Planet.values()) {
    System.out.println(planet + " - Mass: " + planet.getMass());
}

Did You Know?

The values() method returns an array of all enum constants in the order they're declared. Each enum also has an ordinal() method that returns its position!

Pro Tip

Use EnumSet for efficient enum collections:

java

// Get weekdays only
EnumSet<Day> weekdays = EnumSet.range(Day.MONDAY, Day.FRIDAY);

Real-World Use Cases

Menus: Display all menu options
Status codes: List all possible statuses
Configuration: Iterate through settings
Validation: Check against all enum values

›Short versionOpen if you only have a minute.

EnumType.values() returns the constants in declaration order.
Each call allocates a new array. Cache it if a hot loop asks for the constants repeatedly.
valueOf expects the exact constant name. "monday" is not Day.MONDAY.
Compare enum constants with ==. Do not compare their names as strings unless you are parsing text.

Loop an enum

Visit every constant of an enum type.

Working approach

Call values() once and loop the array.
Put a label or a behavior on the constant if the loop body would otherwise switch on the name.
Parse external text with a method that explains a bad name, instead of letting valueOf throw at the edge of the program.

Walk the sample

Day declares MONDAY then TUESDAY
values() returns that array
The loop prints MONDAY, then TUESDAY

The trap

Day.valueOf("monday") throws IllegalArgumentException. The name is case-sensitive and must match the constant, not a display label.

java

for (Day day : Day.values()) {
    // declaration order, a fresh array on every values() call
}

static Day parse(String text) {
    for (Day day : Day.values()) {
        if (day.name().equals(text)) {
            return day;
        }
    }
    throw new IllegalArgumentException("unknown day: " + text);
}

What does Day.valueOf("monday") do?

It throws IllegalArgumentException. valueOf looks up the constant name MONDAY, with that spelling.

A loop over values() is the place to match a label you defined. Hard-coding the same constants in a second switch drifts the moment someone adds a constant.

Time proportional to the number of constants. values() also allocates an array of that length.

Easy to get wrong

Passing a display label or a lowercase name to valueOf.
Listing the constants by hand in a second place.