language: Java (sun-jdk-1.7.0_10)
date: 661 days 9 hours ago
link:
visibility: public 
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import java.util.*;
 
class Item {
    @Override
    public boolean equals(Object obj) {
        return false;  // not even equal to itself.
    }
}
 
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));
    }
}