isEnum?

Main.java

public class Main {
  public enum Days {
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY,
    SATURDAY {
      public String toString() {
        return "Samstag";
      }
    };
  }

  public static void main(String[] args) {
    System.out.println(Days.class.isEnum()); // true
    System.out.println(Days.SUNDAY.getClass().isEnum()); // true
    System.out.println(Days.SATURDAY.getClass().isEnum()); // false
  }
}

> javac Main.java; java Main
true
true
false