code: public static <T> String join(String delimiter, Collection<T> strings) {
          StringBuilder builder = new StringBuilder();
          boolean first = true;
          for (T o : strings) {
              if (first) {
                  first = false;
              } else {
                  builder.append(delimiter);
              }
              builder.append(Objects.toString(o));
          }
          return builder.toString();
      }
docs: Join collection with delimiter.
  
  @param <T> Collection item type.
  @param delimiter The delimiter.
  @param strings   The string collection to join.
  @return The joined string.