code: public static List<String> neighbours(String hash) {
          List<String> list = new ArrayList<String>();
          String left = adjacentHash(hash, Direction.LEFT);
          String right = adjacentHash(hash, Direction.RIGHT);
          list.add(left);
          list.add(right);
          list.add(adjacentHash(hash, Direction.TOP));
          list.add(adjacentHash(hash, Direction.BOTTOM));
          list.add(adjacentHash(left, Direction.TOP));
          list.add(adjacentHash(left, Direction.BOTTOM));
          list.add(adjacentHash(right, Direction.TOP));
          list.add(adjacentHash(right, Direction.BOTTOM));
          return list;
      }
docs: Returns a list of the 8 surrounding hashes for a given hash in order
  left,right,top,bottom,left-top,left-bottom,right-top,right-bottom.
  
  @param hash
  source
  @return a list of neighbour hashes