code: static String toStringImpl(final Collection<?> collection) {
      StringBuilder sb = newStringBuilderForCollection(collection.size()).append('[');
      boolean first = true;
      for (Object o : collection) {
        if (!first) {
          sb.append(", ");
        }
        first = false;
        if (o == collection) {
          sb.append("(this Collection)");
        } else {
          sb.append(o);
        }
      }
      return sb.append(']').toString();
    }
docs: An implementation of {@link Collection#toString()}.