Android: "Smart" enum class

private enum Key {

  TRANSPARENCY("transparecy"); 

  private String stringValue;

  Key(String stringValue) {

   this.stringValue = stringValue;
  }

  @Override
  public String toString() {

   return this.stringValue;
  }

  public static Key getEnum(String stringValue) {

   if (stringValue == null) {
    throw new IllegalArgumentException();
   }

   for (Key key : values()) {

    if (stringValue.equalsIgnoreCase(key.toString())) {
     return key;
    }
   }

   throw new IllegalArgumentException();
  }
 }