code: protected E update (E elem)
      {
          // look up this entry's position in our set
          int eidx = ArrayUtil.binarySearch(_entries, 0, _size, elem, ENTRY_COMP);
  
          // if we found it, update it
          if (eidx >= 0) {
              E oldEntry = _entries[eidx];
              _entries[eidx] = elem;
              _modCount++;
              return oldEntry;
          } else {
              return null;
          }
      }
docs: Updates the specified entry by locating an entry whose key matches the key of the supplied
  entry and overwriting it. This should not be called directly, instead the associated
  <code>update{Set}()</code> method should be called on the distributed object that contains
  the set in question.
  
  @return the old entry that was replaced, or null if it was not found (in which case nothing
  is updated).