My answer to Cedric Beust's coding challenge ("Light" edition) http://beust.com/weblog/2013/02/13/coding-challenge-light-edition/

SchoolTest.java

// My implementation of Cedric Beust's coding challenge:
//
// A School has either a name (“Stanford”) or a nickname (“UCSD”) or both.
//
// Your task is to write equals() and hashCode() methods for the School class
// that satisfy the following requirement: two Schools are identical if they
// either have the same name or the same nickname.
//
// http://beust.com/weblog/2013/02/13/coding-challenge-light-edition/

import nl.jqno.equalsverifier.EqualsVerifier;
import org.junit.Test;

public class SchoolTest {
    public static final class School {
        private final String name;
        private final String nickname;
        
        public School(String name, String nickname) {
            this.name = name;
            this.nickname = nickname;
        }
        
        // OK, let's give this equals method a try.
        @Override
        public boolean equals(Object obj) {
            if (!(obj instanceof School)) {
                return false;
            }
            School other = (School)obj;
            return nullSafeEqual(name, other.name) ||
                    nullSafeEqual(nickname, other.nickname);
        }
        
        private boolean nullSafeEqual(String a, String b) {
            return a == null ? b == null : a.equals(b);
        }
        
        @Override
        public int hashCode() {
            // Well, this *does* satisfy the hashCode contract, doesn't it :)?
            return 42;
        }
        
        @Override
        public String toString() {
            return "School: name=" + name + ", nickname=" + nickname;
        }
    }
    
    
    @Test
    public void testEquals() {
        // My alma mater:
        School tue = new School("Technische Universiteit Eindhoven", "TU/e");
        
        // There's a university in my home town that famously changed its name:
        School one = new School("Katholieke Universiteit Brabant", "KUB");
        School two = new School("Katholieke Universiteit Brabant", "UvT");
        School three = new School("Universiteit van Tilburg", "KUB");
        School four = new School("Universiteit van Tilburg", "UvT");
        
        
        // Using EqualsVerifier to check equality.
        // Full disclosure: it's written by me.
        // See http://code.google.com/p/equalsverifier/
        
        // It works for any pair of schools:
        EqualsVerifier.forRelaxedEqualExamples(one, two)
                .andUnequalExample(tue)
                .verify();
        
        EqualsVerifier.forRelaxedEqualExamples(three, four)
                .andUnequalExample(tue)
                .verify();
        
        EqualsVerifier.forRelaxedEqualExamples(one, three)
                .andUnequalExample(tue)
                .verify();
        
        EqualsVerifier.forRelaxedEqualExamples(two, four)
                .andUnequalExample(tue)
                .verify();
        
        // But once you add a third school, it breaks down:
        EqualsVerifier.forRelaxedEqualExamples(one, two, three)
                .andUnequalExample(tue)
                .verify();
        
        // And that makes sense, because the transitivity requirement cannot hold:
        //   * one equals two
        //   * two equals three
        //   * one does not equal three
        // Therefore, there is no way to write this equals method, and still satisfy
        // the requirements of the equals contract.
        
        // P.S. If I'm wrong, please let me know, so I can update EqualsVerifier :).
    }
}