code: @Override
      public boolean replaceRef(Object oldRef, Object newRef)
          throws IOException
      {
          if (_isUnshared) {
              return false;
          }
  
          int value = _refs.get(oldRef);
  
          if (value >= 0) {
              addRef(newRef, value, true);
  
              _refs.remove(oldRef);
  
              return true;
          }
          else
              return false;
      }
docs: Replaces a reference from one object to another.