Sums { public static ReduceByKey.CombineFunctionWithIdentity<Long> ofLongs() { return SUMS_OF_LONG; } private  Sums(); static ReduceByKey.CombineFunctionWithIdentity<Long> ofLongs(); static ReduceByKey.CombineFunctionWithIdentity<Integer> ofInts(); static ReduceByKey.CombineFunctionWithIdentity<Float> ofFloats(); static ReduceByKey.CombineFunctionWithIdentity<Double> ofDoubles();  }
@Test public void testSumOfLongs() { assertEquals(6L, (long) apply(Stream.of(1L, 2L, 3L), Sums.ofLongs())); }