Java enum extends workaround

Question

Is there a better \"workaround\" than this? I want to avoid the use of a PREFIX (local var) when accessing the methods on TableMap.

public class TableMap ext         


        

Answer 1

I think you may be trying to put too much intelligence into the enum.

I have found this approach very useful. It avoids many of the issues arising from the fact that you cannot extend enums (well actually you can but not in a very useful way).

Essentially, make the enum a sub-class and pass its characteristics up to your super class as an EnumSet. This way you still get all the benefits of enums including type safety.

public static class MappedEnum<E extends Enum<E>> extends TreeMap<String, String> {
  public MappedEnum(EnumSet<E> e) {
    // Whatever you like with the set.
  }

  public void method(E e) {
  }

}

public static class Foo extends MappedEnum<Foo.Tables> {
  public enum Tables {
    table1, table2, table3;
  }

  public Foo() {
    super(EnumSet.allOf(Tables.class));
  }

  @Override
  public void method(Foo.Tables e) {
  }

}

You could probably even use an EnumMap instead of your TreeMap for better efficiency.

Answer 2

In Java, enum types must extend java.lang.Enum. Since Java types can every only extend a single type, you might think that public class TableMap extends Enum might work, but no, the compiler won't allow this.

In my own code, I use enums often as mere keys because they are so hostile. I have them implement a common interface and then use a factory to look up specific implementations of "worker" instances that I can then use.

One way to get closer to the syntax that you want is to use the delegate pattern:

public enum Tables {
    ...
    public void method() {
        MAP.method();
    }
}