code: public int lastIndexOf(Object o) {
          for (int i = size - 1; i >= 0; i--) {
              if (o == elementData[i]) {
                  return i;
              }
          }
          return -1;
      }
docs: Returns the index of the last occurrence of the specified element
  in this list, or -1 if this list does not contain the element.
  More formally, returns the highest index <tt>i</tt> such that
  <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o == get(i))</tt>,
  or -1 if there is no such index.