@Override
    public int hashCode() {
        return getClassId();
    }
Declares that all subclasses of Identifiable supports clone() by _not_ throwing CloneNotSupported exceptions.

@return A cloned instance of this.
@throws AssertionError Thrown if a subclass does not implement clone().
vespajlib/src/main/java/com/yahoo/vespa/objects/Identifiable.java