code: public static String joinKeys(final Map<String, ?> aMap, final char aSeparator) {
          if (aMap.isEmpty()) {
              return "";
          }
  
          final Iterator<String> iterator = aMap.keySet().iterator();
          final StringBuilder buffer = new StringBuilder();
  
          while (iterator.hasNext()) {
              buffer.append(iterator.next()).append(aSeparator);
          }
  
          final int length = buffer.length() - 1;
  
          return buffer.charAt(length) == aSeparator ? buffer.substring(0, length) : buffer.toString();
      }
docs: Turns the keys in a map into a character delimited string. The order is only consistent if the map is sorted.
  
  @param aMap The map from which to pull the keys
  @param aSeparator The character separator for the construction of the string
  @return A string constructed from the keys in the map