String () { String removed = StreamEx.of(myRemovedRelations).map(Object::toString).append(myOldType.toString()) .without("").joining(", "); String added = StreamEx.of(myAddedRelations).map(Object::toString).append(myNewType.toString()) .without("").joining(", "); return (removed.isEmpty() ? "" : "-{" + removed + "} ") + (added.isEmpty() ? "" : "+{" + added + "}"); }