Dijkstra's Algorithm - Linked List

I managed to get the Linked List version of the assignment completed. Now that all remains is the challenge of the Hash Set (if I can figure it out). I may need to look into Sets more to see if I can gain a little more understanding before attempting it.

One odd thing I encountered when testing the linked list version I have was that it seemed to clobber the results of other maps. Once I click to select anther map, the error results for the other maps pop up. This could be a serious problem when grading this assignment. Every map after the linked list map was wrong. It's as though I destroyed a resource. After a little poking around, I discovered that if I use the remove method on the destinations list, I permanently remove that coordinate from the destinations list. Apparently that list was passed by reference or something of the sort. Either way, this allows the programmer to clobber the destinations list. If a student, by accident uses the remove method, then the destination is removed from the list for the remainder of the time programmer is running the game. I'm not certain where cache for the route maps are called so I'm not certain if I can fix it. I tried using different search methods (like for SDRouteMap or Cache in the project) but I couldn't find it. Unless I can un-bury it, all I can do is leave a warning of what might happen if the destinations list is tampered with.

Note: Giving in to my mischievous side, I even tried to insert a different destination GridCoordinate into first element of the destinations list. As I predicted, it changed the destination node.