import java.util.*;
import java.util.stream.*;
public class Main {
    public static void main(String[] args) {
        List<String> strings = Arrays.asList("foo", "bar", "foo", "baz", "foo", "bar");
 
        Set<String> distinct = new HashSet<>();
        List<String> extras = new ArrayList<>();
 
        strings
          .stream()
          .filter(x -> !distinct.add(x))
          .forEach(extras::add);
        System.out.println(distinct);
        System.out.println(extras);
    }
}

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