builder.appendCodePoint(cp);
      }
      return builder.toString();
    }
    // Use a shuffled index array to ensure constant percentage of matching
    // characters
    List<Integer> list = Lists.newArrayList();
    for (int i = 0; i < length; i++) {
      list.add(i);
    }
    Collections.shuffle(list, rand);
    if (forceSlow) {
      // Move zero index to front to force a matching character (if percent > 0)

        builder.appendCodePoint(cp);
      }
      return builder.toString();
    }
    // Use a shuffled index array to ensure constant percentage of matching
    // characters
    List<Integer> list = Lists.newArrayList();
    for (int i = 0; i < length; i++) {
      list.add(i);
    }
    Collections.shuffle(list, rand);
    if (forceSlow) {
      // Move zero index to front to force a matching character (if percent > 0)