public ProteinXref addCrossReference(ProteinXref ProteinXref) throws IllegalArgumentException {
  if (ProteinXref == null) {
    throw new IllegalArgumentException("'ProteinXref' must not be null");
  }
  crossReferences.add(ProteinXref);
  ProteinXref.setProtein(this);
  return ProteinXref;
}

public ProteinXref addCrossReference ( ProteinXref ProteinXref ) throws IllegalArgumentException { if ( ProteinXref == null ) { throw new IllegalArgumentException ( "'ProteinXref' must not be null" ) ; } crossReferences . add ( ProteinXref ) ; ProteinXref . setProtein ( this ) ; return ProteinXref ; }
adds and returns cross - reference
