Java Streams - Get a “symmetric difference list” from two other lists

Question

Im trying to use Java 8 streams to combine lists. How can I get a \"symmetric difference list\" (all object that only exist in one list) from two existing lists. I know how

Answer 1

the lambda solution with groupingBy:
the map values with the true-key are in both lists
the map values with the false-key are disjoint

Map> map = Stream.concat(bigCarList.stream(),
    smallCarList.stream()).collect(
        groupingBy( b -> bigCarList.stream().anyMatch( s -> b.equals( s ) )
            && smallCarList.stream().anyMatch( s -> b.equals( s ) ) ) );
List disjoint = map.get( false );  // [Toyota Corolla, Ford Focus]

same principle but shorter w/o inline streams:

Map> map = Stream.concat(bigCarList.stream(),
    smallCarList.stream()).collect(
        groupingBy( b -> bigCarList.contains( b )
            && smallCarList.contains( b ) ) );
List disjoint = map.get( false );  // [Toyota Corolla, Ford Focus]

both are working with duplicates as well
means: duplicates in one list that are not contained in the other list
If the amount of data is not so huge that you are running into disk space issues, a simple groupingBy ‑ without filtering or additional queries to reduce the result set ‑ should be the clearest and fastest solution.