Question

private Set<String> extractOfferKeysForAbstractOffers(List<AbstractOfferDto> selectedOffers) {
        Set<String> offerKeys = new HashSet<String>();
        for (AbstractOfferDto offer : selectedOffers) {
            offerKeys.add(offer.getOfferKey());
        }
        return offerKeys;
    }

 private Set<String> extractOfferKeysForOffers(List<OfferDto> selectedOffers) {
        Set<String> offerKeys = new HashSet<String>();
        for (OfferDto offer : selectedOffers) {
            offerKeys.add(offer.getOfferKey());
        }
        return offerKeys;
    }

我不想使用几乎相同的方法，只是输入不同，我想使用泛型。我这样创造它。

private <T> Set<String> extractOfferKeysForOffers(List<T> offers) {
        Set<String> offerKeys = new HashSet<String>();
        for (T offer : offers) {
            offerKeys.add(offer.getOfferKey());
        }
        return offerKeys;
    }

但问题是offer.getOfferKey()无法识别。只有优惠选项为AbstractOfferDto或OfferDto。

如何在此示例中使用泛型？

Answer 1

告诉编译器有关抽象类型的信息：

private <T extends AbstractOfferDto> Set<String> extractOfferKeysForOffers(List<T> offers) {
        Set<String> offerKeys = new HashSet<String>();
        for (T offer : offers) {
            offerKeys.add(offer.getOfferKey());
        }
        return offerKeys;
    }

Answer 2

是的，你可以：

  public interface IOffer {
     String getOfferKey();
  }

  public class OfferDto implements IOffer { ... }

  public class AbstractOfferDto implements IOffer { ... }

  class X {    
    private <T extends IOffer> Set<String> extractOfferKeysForOffers(List<T> offers) {
        Set<String> offerKeys = new HashSet<String>();
        for (T offer : offers) {
            offerKeys.add(offer.getOfferKey());
        }
        return offerKeys;
    }
  }

以上是一般解决方案。如果OfferDto扩展AbstractOfferDto，则不需要额外的接口：

  class X {    
    private <T extends AbstractOfferDto> Set<String> extractOfferKeysForOffers(List<T> offers) {
        Set<String> offerKeys = new HashSet<String>();
        for (T offer : offers) {
            offerKeys.add(offer.getOfferKey());
        }
        return offerKeys;
    }
  }

如何使用不同输入的相同方法使用泛型

2 个答案: