code: public E get(long index) {
          // @@@ can further optimize by caching last seen spineIndex,
          // which is going to be right most of the time
  
          // Casts to int are safe since the spine array index is the index minus
          // the prior element count from the current spine
          if (spineIndex == 0) {
              if (index < elementIndex)
                  return curChunk[((int) index)];
              else
                  throw new IndexOutOfBoundsException(Long.toString(index));
          }
  
          if (index >= count())
              throw new IndexOutOfBoundsException(Long.toString(index));
  
          for (int j=0; j <= spineIndex; j++)
              if (index < priorElementCount[j] + spine[j].length)
                  return spine[j][((int) (index - priorElementCount[j]))];
  
          throw new IndexOutOfBoundsException(Long.toString(index));
      }
docs: Retrieve the element at the specified index.