如何避免在Java Lambda表达式中定义单元素数组

Question

I have written code segment which fetches a single element from list matching some condition. Is there any way I could replace single element array with the object of the same type?

final PromoSlotSize[] slot = new PromoSlotSize[1];
promoSlotSizeList.stream()
    .filter(promoSlotSize -> promoSlotSize.getOfferSet().equals(Constants.HVT_RATE_OFFER_SET))
    .findFirst()
    .ifPresent(p-> slot[0] =p);

Answer 1

Your approach seems to be such overkill. Note that initializing an array with

final PromoSlotSize[] slot = new PromoSlotSize[1];

Makes the first and only element slot[0] = null bu default. Thus, you can make the Stream-API return the first found object PromoSlotSize or null again using Optional::orElse :

slot[0] = promoSlotSizeList.stream()
              .filter(i-> i.getOfferSet().equals(Constants.HVT_RATE_OFFER_SET))
              .findFirst()
              .orElse(null);

---

As @YCF_L says: Do you recognize that the Stream returns an object which might be used directly instead of creating an array of one element? If you don't need an array as input to another method/class, do the following :

PromoSlotSize slot = promoSlotSizeList.stream()
          .filter(i-> i.getOfferSet().equals(Constants.HVT_RATE_OFFER_SET))
          .findFirst()
          .orElse(null);

Answer 2

The code uses a trick, as only (effectively) final variables may be used from outside in the lambda. Hence a final array where the first element can be set. In effect it uses imperative style coding, with a loop and a result.

However the following is far better.

Optional<PromoSlotSize> slot = promoSlotSizeList.stream()
                        .filter(i -> i.getOfferSet().equals(Constants.HVT_RATE_OFFER_SET))
                        .findAny();

slot.ifPresent(sl -> System.out.println("Slot present: " + sl));

As it can be parallelized, and the two attributes: boolean found + Slot result are incorporated in one Optional.

Answer 3

One way is to create a copy from method on PromoSlotSize class. That method should take and argument of PromoSlotSize object and populate it self with given PromoSlotSize data

final PromoSlotSize slot = new PromoSlotSize();
promoSlotSizeList.stream()
            .filter(promoSlotSize -> promoSlotSize.getOfferSet().equals(Constants.HVT_RATE_OFFER_SET))
            .findFirst().ifPresent(p-> slot.copy(p));

Assuming PromoSlotSize is a class you wrote, this should allow you to get rid of single element arrays.