Question

I’m designing an enemy framework for java and working with observer. I’m wondering if it is possible | worth the effort to have one class implement both observer and subject in java?

I want to have an enemy interface which implements both subject and observer so that the enemies within a certain distance of each other can alert each other if a player or enemy is sighted.

Is there a better pattern to use here?

Answer 1

I think one of these would be slightly more appropriate to use than observer pattern, depending on actually how you want to implement your framework:

• Implicit Invocation
• Event-Driven
• Publish-Subscribe

The trouble with subject / observer is that they involve registering / deregistering when your enemies move in / out of range of each other.

I would recommend implicit invocation or event-driven as follows:

• Each time an enemy sights a player, generate an “event” that gets broadcast to all other enemies.
• This event will have a coordinate to specify from where it was broadcasted.
• For each enemy that receives the event (which is all of them), look at the coordinate and see if it’s within a certain range of itself
  • If not, ignore it (and pretend as if it never heard it)
  • If so, do something as required.