Question

Lets say i have two classes A and B, which have theirs internal state represented by enum State. Class B extends A to add new functionality, but it also adds new internal state. To be precise, it adds fine-grained state support, by dividing one of the A`s state into two new states.

I also need to use PropertyChangeSupport to monitor state changes.

Currently I have all states defined in class A in enum State. I have protected methods setState() and getState(). To check on state from the outside, I wrote methods isAvaible(), isComplete(), etc. These methods are present only in appropriate class, depending on their hierarchy and state support.

I realy dont like the idea, having all states defined in parent class. How do I implement this correctly in Java? As far as I know, it`s not possible to use inheritance with enums.

Answer 1

Delegation is preferred to inheritance.

enum StateA
{
       AVAILABLE , COMPLETE ;
}

class A
{
      private StateA state ;
}

enum StateB
{
     AVAILABLE_TO_PUBLIC ( StateA . AVAILABLE ) , AVAILABLE_INTERNALLY ( StateA . AVAILABLE ) , COMPLETE ( COMPLETE ) ;

     StateB ( StateA sa )
     {
          this . sa = sa ;
     }

     private StateA sa ;
}

class B
{
      private StateB state ;
}