code: public String[] keys () {
          String[] keys = new String[count];
          for (int i = 0; i < count; ++i) {
              keys[i] = container[i].key;
          }
          return keys;
      }
docs: Returns an array of the keys contained in the underlying container. it does not enumerate the
  container and all of its children.
  
  @return The keys in the underlying map as an array of Strings.