### Question:
ColumnPair implements Serializable, Hashable { public Class<T> getType() { return left.getType(); }  Class<T> getType(); @Override void hash(Hasher hasher); @Override String toString();  }### Answer:
@Test public void test() { Column<Integer> left = Column.of("a", Integer.class); Column<Integer> right = Column.of("a", Integer.class); ColumnPair<Integer> pair = new ColumnPair<>(left, right); assertThat(pair.getType()).isEqualTo(Integer.class); assertThat(pair.getType()).isEqualTo(left.getType()); assertThat(pair.getType()).isEqualTo(right.getType()); }