import java.util.*;

class Item {
    @Override
    public boolean equals(Object obj) {
        return false;   // not even equal to itself.
    }
}

public class Main {
    public static void main(String[] args) {
        Collection<Item> items = new HashSet<Item>();
        Item i = new Item();
        items.add(i);
        System.out.println(items.contains(i));   // Prints true!
    }
}