code: private void deallocate(HashtableEntry entry)
                      throws IOException,
                      EOFException,
                      FileManagerException,
                      ClassNotFoundException,
                      HashtableOnDiskException {
          if (entry.location == 0) {
              throw (new HashtableOnDiskException("deallocate:  space not allocated."));
          }
  
          filemgr.deallocate(entry.location);
          entry.location = 0;
      }
docs: ************************************************************************
  Common code to deallocate the space taken by header, key, and data.
  ***********************************************************************