@Test
public void reduce() {
IntStream stream = IntStream.of(1, 2, 3, 4);
assertEquals(10, stream.reduce(0, (a, b) -> a + b));
Stream<Integer> stream2 = Arrays.asList(1, 2, 3, 4).stream();
stream2.reduce(0, (a, b) -> a + b);
// obviously the operations can be more complex :)
Stream<Integer> stream3 = Arrays.asList(1, 2, 3, 4).stream();
// reduce is a superset of map :D
System.err.println(
stream3.reduce(
new ArrayList<Integer>(),
(List<Integer> a, Integer b) -> {
a.add(b);
return a;
},
(a, b) -> {
List<Integer> c = new ArrayList<>(a);
c.addAll(b);
return c;
}));
}
@Test
public void _08_리덕션() {
Stream<Integer> values = Stream.of(digits);
// x 이전값, y 지금 요소 (v0 + v1 + v2.....)
Optional<Integer> sum = values.reduce((x, y) -> x + y);
assertThat(sum, is(Optional.of(366)));
}
public String getStatRow(String delimiter) {
Stream<String> pValues = stats.stream().map(s -> Double.toString(s.getPValue()));
String row = pValues.reduce((s, t) -> s + delimiter + t).get();
return this.toString() + delimiter + row;
}
@Test(expectedExceptions = MonetaryException.class)
public void shouldMaxMoneratyExceptionWhenHasDifferenctsCurrencies() {
Stream<MonetaryAmount> stream = streamCurrencyDifferent();
stream.reduce(max()).get();
}
@Test(expectedExceptions = NullPointerException.class)
public void shouldMaxWithNPEWhenAnElementIsNull() {
Stream<MonetaryAmount> stream = streamNull();
stream.reduce(max()).get();
}
@Test
public void shouldMaxCorretly() {
Stream<MonetaryAmount> stream = StreamFactory.streamNormal();
MonetaryAmount max = stream.reduce(max()).get();
Assert.assertTrue(max.getNumber().intValue() == 10);
}
@Test
public void shouldMinCorretly() {
Stream<MonetaryAmount> stream = streamNormal();
MonetaryAmount min = stream.reduce(min()).get();
Assert.assertTrue(min.getNumber().intValue() == 0);
}
@Test
public void shouldSumCorrectly() {
Stream<MonetaryAmount> stream = streamNormal();
MonetaryAmount sum = stream.reduce(sum()).get();
Assert.assertTrue(sum.getNumber().intValue() == 20);
}
public static Optional<String> longestArtistNameByReduce(Stream<String> names) {
return names.reduce((acc, x) -> x.length() > acc.length() ? x : acc);
}
public int addUp(Stream<Integer> numbers) {
return numbers.reduce((acc, element) -> acc + element).get().intValue();
}