Check if enum exists in Java

Question

Is there anyway to check if an enum exists by comparing it to a given string? I can't seem to find any such function. I could just try to use the valueOf method and catch an exception but I'v been taught that catching runtime exceptions is not good practice. Anybody have any ideas?

Answer 1

If I need to do this, I sometimes build a Set<String> of the names, or even my own Map<String,MyEnum> - then you can just check that.

A couple of points worth noting:

• Populate any such static collection in a static initializer. Don't use a variable initializer and then rely on it having been executed when the enum constructor runs - it won't have been! (The enum constructors are the first things to be executed, before the static initializer.)
• Try to avoid using values() frequently - it has to create and populate a new array each time. To iterate over all elements, use EnumSet.allOf which is much more efficient for enums without a large number of elements.

Sample code:

import java.util.*;

enum SampleEnum {
    Foo,
    Bar;

    private static final Map<String, SampleEnum> nameToValueMap =
        new HashMap<String, SampleEnum>();

    static {
        for (SampleEnum value : EnumSet.allOf(SampleEnum.class)) {
            nameToValueMap.put(value.name(), value);
        }
    }

    public static SampleEnum forName(String name) {
        return nameToValueMap.get(name);
    }
}

public class Test {
    public static void main(String [] args)
        throws Exception { // Just for simplicity!
        System.out.println(SampleEnum.forName("Foo"));
        System.out.println(SampleEnum.forName("Bar"));
        System.out.println(SampleEnum.forName("Baz"));
    }
}

Of course, if you only have a few names this is probably overkill - an O(n) solution often wins over an O(1) solution when n is small enough. Here's another approach:

import java.util.*;

enum SampleEnum {
    Foo,
    Bar;

    // We know we'll never mutate this, so we can keep
    // a local copy.
    private static final SampleEnum[] copyOfValues = values();

    public static SampleEnum forName(String name) {
        for (SampleEnum value : copyOfValues) {
            if (value.name().equals(name)) {
                return value;
            }
        }
        return null;
    }
}

public class Test {
    public static void main(String [] args)
        throws Exception { // Just for simplicity!
        System.out.println(SampleEnum.forName("Foo"));
        System.out.println(SampleEnum.forName("Bar"));
        System.out.println(SampleEnum.forName("Baz"));
    }
}