Cross-Class Implementation

[FreakyCheeseMan]

So, I have a situation where I have a set of abstract classes that have to interact with themselves and eachother, but only within a certain implementation. This results in a situation where I have something that looks like:

public interface Map
{
     public Location getNearest(Location l);
}

Which I can implement with something that looks like:

public class 2DMap implements Map
{
     public Location getNearest(Location l)
     {
           //actual code goes here
      }
}

Or something that looks like:

public class 2DMap implements Map
{
    public 2DLocation getNearest(2DLocation l){
          //actual code goes here
    }
}

In the first option, the 2DMap would be expected to handle Locations from other implementations- something from a 3D map or a hex grid, which it clearly could not do. The second option, however, does not compile, because it doesn't really fufill the method header.

This is something I could fix easily enough with casting- within each method cast the relevant types to what they need to be- but it feels like there should be a more elegant, OOP-friendly way do to so.

What would be the "correct" way to go about this? Mind, not just looking for specific answers to the example listed, but for this type of situation in general- abstract systems where the specific implementations work in the described way, but only within the implementation.

[Tolls]

Generics?
Map<T extends Location>?
(Note syntax is suspect as I rarely write these things).