code: public static Set<Character> getNeighbors(final AdjacencyGraph adjacencyGraph, final Character key)
      {
          final Set<Character> neighbors = new HashSet<>();
  
          if (adjacencyGraph.getKeyMap().containsKey(key))
          {
              String[] tmp_neighbors = adjacencyGraph.getKeyMap().get(key);
              for (final String tmp_neighbor : tmp_neighbors)
              {
                  if (null == tmp_neighbor)
                  {
                      continue;
                  }
                  for (Character character : tmp_neighbor.toCharArray())
                  {
                      neighbors.add(character);
                  }
              }
          }
          return neighbors;
      }
docs: Returns a set of neighbors for a specific character.
  
  @param adjacencyGraph the graph you are using to get the neighbors.
  @param key            the character you are getting neighbors for.
  @return A set of characters which are neighbors to the passed in character.