// Canonical example of bottom-up (implementation) inheritance.

import java.util.ArrayList;
import java.util.Set;
import java.util.HashSet;
import java.util.Random;

public class CountUniqueArrayList<T> extends ArrayList<T> {

    public int countUnique() {
        Set<T> s = new HashSet<T>();
        for (T o : this) {
            s.add(o);
        }
        return s.size();
    }
}