How to get an enum value from a string value in Java?

Question

Say I have an enum which is just

public enum Blah {
    A, B, C, D
}

and I would like to find the enum value of a string, for example

Answer 1

I like to use this sort of process to parse commands as strings into enumerations. I normally have one of the enumerations as "unknown" so it helps to have that returned when the others are not found (even on a case insensitive basis) rather than null (that meaning there is no value). Hence I use this approach.

static <E extends Enum<E>> Enum getEnumValue(String what, Class<E> enumClass) {
    Enum<E> unknown=null;
    for (Enum<E> enumVal: enumClass.getEnumConstants()) {  
        if (what.compareToIgnoreCase(enumVal.name()) == 0) {
            return enumVal;
        }
        if (enumVal.name().compareToIgnoreCase("unknown") == 0) {
            unknown=enumVal;
        }
    }  
    return unknown;
}

Answer 2

Use the pattern from Joshua Bloch, Effective Java:

(simplified for brevity)

enum MyEnum {
    ENUM_1("A"),
    ENUM_2("B");

    private String name;

    private static final Map<String,MyEnum> ENUM_MAP;

    MyEnum (String name) {
        this.name = name;
    }

    public String getName() {
        return this.name;
    }

    // Build an immutable map of String name to enum pairs.
    // Any Map impl can be used.

    static {
        Map<String,MyEnum> map = new ConcurrentHashMap<String, MyEnum>();
        for (MyEnum instance : MyEnum.values()) {
            map.put(instance.getName(),instance);
        }
        ENUM_MAP = Collections.unmodifiableMap(map);
    }

    public static MyEnum get (String name) {
        return ENUM_MAP.get(name);
    }
}

Also see:

Oracle Java Example using Enum and Map of instances

Execution order of of static blocks in an Enum type

How can I lookup a Java enum from its String value

Answer 3

Apache's commons-lang library has a static function org.apache.commons.lang3.EnumUtils.getEnum which will map a String to your Enum type. Same answer essentially as Geoffreys but why roll your own when it's out there in the wild already.