public final String toString() {
          StringBuilder sb = new StringBuilder();
          sb.append('[');
          Iterator<E> it = iterator();
          if (it.hasNext()) {
              for (;;) {
                  Object e = it.next();
                  sb.append(e == this ? "(this Collection)" : e);
                  if (!it.hasNext())
                      break;
                  sb.append(',').append(' ');
              }
          }
          return sb.append(']').toString();
      }
public final String toString()