Iterating enum of enums

Question

I have a structure some-thing like

public class EnumTest{
     enum fauna
     {
         Animals, Birds;

         enum Animals
         {
              Tiger("tiger"),
              Lion("lion");

              String name;

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

         enum Birds
         {
              Peacock("peacock"),
              owl("Owl");

              String name;

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

Now I couldn't find a way to iterate over the enum fauna to print the names of enum animals and birds. Is there any way to do it??

Answer 1

Unfortunately, you can't group enums like this. The enum Birds is distinct from the Birds value inside the fauna enum. The usual way to do it is to add a field which is also an enum:

enum Fauna {
    enum Type { MAMMAL, BIRD }

    TIGER(Type.MAMMAL), 
    LION(Type.MAMMAL), 
    PEACOCK(Type.BIRD), 
    OWL(Type.BIRD);

    private final Type type;

    Fauna(Type type) { this.type = type; }

}

If you only want the animals of a specific type, for example all BIRDs, you will unfortunately have to write a helper method to do that, iterating over all the Fauna values and picking those of the correct type. (Unless you're running Java 8, in which case it's just Stream.of(Fauna.values()).filter(f -> f.type == BIRD).toList() or something similar).