Can enums be subclassed to add new elements?

Question

I want to take an existing enum and add more elements to it as follows:

enum A {a,b,c}

enum B extends A {d}

/*B is {a,b,c,d}*/

Is this po

Answer 1

Based on @Tom Hawtin - tackline answer we add switch support,

interface Day {
    ...
  T valueOf();
}

public enum Weekday implements Day {
    MON, TUE, WED, THU, FRI;
   Weekday valueOf(){
     return valueOf(name());
   }
}

public enum WeekendDay implements Day {
    SAT, SUN;
   WeekendDay valueOf(){
     return valueOf(name());
   }
}

Day wds = Weekday.MON;
Day wends = WeekendDay.SUN;

switch(wds.valueOf()){
    case MON:
    case TUE:
    case WED:
    case THU:
    case FRI:
}

switch(wends.valueOf()){
    case SAT:
    case SUN:
}