public static void main(String... args) {

List<Integer> numbers = Arrays.asList(3, 4, 5, 1, 2);

Arrays.stream(numbers.toArray()).forEach(System.out::println);

int calories = menu.stream()

.mapToInt(Dish::getCalories)

.sum();

System.out.println("Number of calories:" + calories);

// max and OptionalInt

OptionalInt maxCalories = menu.stream()

.mapToInt(Dish::getCalories)

.max();

int max;

if (maxCalories.isPresent()) {

max = maxCalories.getAsInt();

} else {

// we can choose a default value

max = 1;

}

System.out.println(max);

// 直接使用 orElse

System.out.print("使用 orElse: ");

System.out.println(maxCalories.orElse(1));

// numeric ranges

IntStream evenNumbers = IntStream.rangeClosed(1, 100)

.filter(n -> n % 2 == 0);

System.out.println(evenNumbers.count());

// 勾股数

Stream<int[]> pythagoreanTriples =

IntStream.rangeClosed(1, 100)

.boxed()

.flatMap(a -> IntStream.rangeClosed(a, 100)

.filter(b -> isPerfectSquare(a * a + b * b))

.boxed()

.map(b -> new int[] {a, b, (int) Math.sqrt(a * a + b * b)})

);

pythagoreanTriples.forEach(t -> System.out.println(t[0] + ", " + t[1] + ", " + t[2]));

}

public static boolean isPerfectSquare(int n) {

return Math.sqrt(n) % 1 == 0;

}