### Question:
Tuple { @Override public int hashCode() { if ((this.first == null) && (this.second == null)) { return "".hashCode(); } return this.first == null ? this.second.hashCode() : this.first.hashCode() ^ this.second.hashCode(); } Tuple(T firstValue, U secondValue); @Override boolean equals(Object obj); T getFirst(); U getSecond(); @Override int hashCode(); @Override String toString();  }### Answer:
@Test public void testTupleHashcode() { Tuple<String, String> t1 = new Tuple<String, String>("S1", "S2"); Tuple<String, String> t2 = new Tuple<String, String>("S1", "S2"); assertEquals(t1.hashCode(), t2.hashCode()); Tuple<String, String> t3 = new Tuple<String, String>(null, null); t3.hashCode(); }