import java.util.*;
import java.awt.Color;
import static java.awt.Color.*;

public class d2 {

    public static void main(String[] args)  {

        // populate first collection
        Collection <Color> hs1 = new HashSet<Color>();
        hs1.add( red );
        hs1.add( green );
        hs1.add( blue );
        hs1.add( magenta );

        // populate second collection
        Collection<Color> hs2 = new HashSet<Color>();
        hs2.add( red );
        hs2.add( green );
        hs2.add( yellow );

        // intersect is the things that are in hs1 AND in hs2
        Collection <Color> intersect = hs1;
        Collection <Color> hs3 = new HashSet<Color> (hs1);
        boolean ok = intersect.retainAll(hs2);

        System.out.println("intersect:  " + intersect);
        System.out.println("hs1:  " + hs1);
        System.out.println("hs3:  " + hs3);

    }
}