[FIXED] Case-insensitive matching of a string to a Java enum

Issue

Java provides a valueOf() method for every Enum<T> object, so given an enum like

public enum Day {
  Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday
}

one can do a lookup like

Day day = Day.valueOf("Monday");

If the string passed to valueOf() does not match (case sensitive) an existing Day value, an IllegalArgumentException is thrown.

To do a case-insensitive matching, one can write a custom method inside the Day enum, e.g.

public static Day lookup(String day) {
  for (Day d : Day.values()) {
    if (d.name().equalsIgnoreCase(day)) {
      return type;
    }
  }
  return null;
}

Is there any generic way, without using caching of values or any other extra objects, to write a static lookup() method like the above only once (i.e., not for every enum), given that the values() method is implicitly added to the Enum<E> class at compile time?

The signature of such a "generic" lookup() method would be similar to the Enum.valueOf() method, i.e.:

public static <T extends Enum<T>> T lookup(Class<T> enumType, String name);

and it would implement exactly the functionality of the Day.lookup() method for any enum, without the need to re-write the same method for each enum.

Solution

I found getting the special blend of generics a little tricky, but this works.

public static <T extends Enum<?>> T searchEnum(Class<T> enumeration,
        String search) {
    for (T each : enumeration.getEnumConstants()) {
        if (each.name().compareToIgnoreCase(search) == 0) {
            return each;
        }
    }
    return null;
}

Example

public enum Horse {
    THREE_LEG_JOE, GLUE_FACTORY
};

public static void main(String[] args) {
    System.out.println(searchEnum(Horse.class, "Three_Leg_Joe"));
    System.out.println(searchEnum(Day.class, "ThUrSdAy"));
}

Answered By - Adam
Answer Checked By - Timothy Miller (JavaFixing Admin)