I'm implementing a Linear Planner with a stack of goals in Java. For that reason I'm using a Stack in which I need to store different objects: predicates, operators, states. To achieve this, I created an Interface called Stackable, so I have a Stack<Stackable>. This interface is empty as there's nothing that all stackable objects have in common, except that all of them have to be stacked.
public Interface Stackable {
}
public class Predicate implements Stackable {
private String name;
private List<Parameter> params;
...
}
public class Operator implements Stackable {
private String name;
private List<Parameter> params;
private List<Predicate> preconditions;
private List<Predicate> adds;
private List<Predicate> deletes;
...
}
public class State implements Stackable {
private List<Predicate> preds;
...
}
As I didn't like the idea of an empty interface, I started reading and came accross with the term Marker interface, which I think is the case of my Stackable. I also found that they can be replaced by annotations in general, but I have never used them and I don't know whether they can solve my problem.
That's why I'd like to know:
- Is there a better alternative to my design (either by using annotations or by another means)?
- In case marker interfaces are still a solution in some cases, how can I discriminate when should I use them?
