code: private int computeCapacity(int initial) {
      if (initial < MINIMUM_CAPACITY) {
        return MINIMUM_CAPACITY;
      }
      if (initial > MAXIMUM_CAPACITY) {
        return MAXIMUM_CAPACITY;
      }
      int capacity = 1;
      while (capacity < initial) {
        capacity <<= 1;
      }
      return capacity;
    }
docs: Compute capacity given initial capacity.
  
  @return final capacity, either MIN_CAPACITY, MAX_CAPACITY, or power of 2
  closest to the requested capacity.