Java Stream - 如何使用mapToInt映射到OptionalInt

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import java.util.Arrays;
import java.util.List;
import java.util.OptionalInt;
public class Main {
  public static void main(String[] args) throws Exception{
    List<Dish> menu =
        Arrays.asList( new Dish("pork", false, 800, Dish.Type.MEAT),
                       new Dish("beef", false, 700, Dish.Type.MEAT),
                       new Dish("chicken", false, 400, Dish.Type.MEAT),
                       new Dish("rice", true, 350, Dish.Type.OTHER),
                       new Dish("pizza", true, 550, Dish.Type.OTHER),
                       new Dish("prawns", false, 400, Dish.Type.FISH),
                       new Dish("salmon", false, 450, Dish.Type.FISH));
    List<Integer> numbers = Arrays.asList(3,4,5,1,2);
    Arrays.stream(numbers.toArray()).forEach(System.out::println);
    // max and OptionalInt
    OptionalInt maxCalories = menu.stream()                                                      
                                  .mapToInt(Dish::getCalories)
                                  .max();
    System.out.println("Number of calories:" + maxCalories);
  }
}
class Dish {
  private final String name;
  private final boolean vegetarian;
 
 
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