Java How to Convert String to Enum Easily

In Java, convert a string to an enum by using EnumType.valueOf("STRING_VALUE"), where EnumType is your enum name and "STRING_VALUE" matches an enum constant exactly.

Examples

InputMONDAY

OutputDay.MONDAY

InputFRIDAY

OutputDay.FRIDAY

InputSUNDAY

OutputDay.SUNDAY

How to Think About It

To convert a string to an enum, think of matching the string exactly to one of the enum's named constants. Java provides a built-in method called valueOf that takes the string and returns the matching enum constant if it exists, otherwise it throws an exception.

Algorithm

1

Get the input string representing the enum name.

2

Call the enum's <code>valueOf</code> method with the input string.

3

If the string matches an enum constant, return that enum constant.

4

If no match is found, handle the error or exception.

Code

java

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

public class Main {
    public static void main(String[] args) {
        String input = "FRIDAY";
        Day day = Day.valueOf(input);
        System.out.println(day);
    }
}

Output

FRIDAY

Dry Run

Let's trace converting the string "FRIDAY" to the enum Day.

1

Input string

input = "FRIDAY"

2

Call valueOf

Day.valueOf("FRIDAY") matches Day.FRIDAY

3

Return enum

day = Day.FRIDAY

Input String	Enum Returned
FRIDAY	Day.FRIDAY

Why This Works

Step 1: Exact Match Required

The valueOf method requires the string to exactly match an enum constant name, including case.

Step 2: Returns Enum Constant

If matched, valueOf returns the enum constant as a typed enum value.

Step 3: Throws Exception if No Match

If the string does not match, valueOf throws an IllegalArgumentException.

Alternative Approaches

Using a loop to match ignoring case

java

enum Day {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY;
    public static Day fromString(String s) {
        for (Day d : Day.values()) {
            if (d.name().equalsIgnoreCase(s)) {
                return d;
            }
        }
        throw new IllegalArgumentException("No enum constant " + s);
    }
}

public class Main {
    public static void main(String[] args) {
        String input = "friday";
        Day day = Day.fromString(input);
        System.out.println(day);
    }
}

Allows case-insensitive matching but requires extra code and looping.

Using Optional with streams (Java 8+)

java

import java.util.Arrays;
import java.util.Optional;

enum Day {
    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY;
    public static Optional<Day> fromString(String s) {
        return Arrays.stream(Day.values())
            .filter(d -> d.name().equalsIgnoreCase(s))
            .findFirst();
    }
}

public class Main {
    public static void main(String[] args) {
        String input = "friday";
        Optional<Day> day = Day.fromString(input);
        day.ifPresent(System.out::println);
    }
}

Returns Optional to handle missing values gracefully, but more complex.

Complexity: O(n) time, O(1) space

Time Complexity

The valueOf method internally searches enum constants, which is typically O(n) where n is the number of enum constants.

Space Complexity

No extra space is needed besides the input string and returned enum reference, so O(1).

Which Approach is Fastest?

Using valueOf is fastest for exact matches. Alternatives with loops or streams add overhead but allow case-insensitive or safe handling.

Approach	Time	Space	Best For
Enum.valueOf()	O(n)	O(1)	Exact match, simple use
Loop with equalsIgnoreCase	O(n)	O(1)	Case-insensitive matching
Streams with Optional	O(n)	O(1)	Safe handling with Optional