code: public void copyInto(E[] array, int offset) {
          long finalOffset = offset + count();
          if (finalOffset > array.length || finalOffset < offset) {
              throw new IndexOutOfBoundsException("does not fit");
          }
  
          if (spineIndex == 0)
              System.arraycopy(curChunk, 0, array, offset, elementIndex);
          else {
              // full chunks
              for (int i=0; i < spineIndex; i++) {
                  System.arraycopy(spine[i], 0, array, offset, spine[i].length);
                  offset += spine[i].length;
              }
              if (elementIndex > 0)
                  System.arraycopy(curChunk, 0, array, offset, elementIndex);
          }
      }
docs: Copy the elements, starting at the specified offset, into the specified
  array.