如何使用不同輸入的相同方法的泛型

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; 
    } 

而不是使用幾乎相同的方法只是輸入是不同的我想使用泛型。我是這樣創建的。

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

但問題是offer.getOfferKey()不被識別。只有報價選項是AbstractOfferDto或OfferDto。

如何在此示例中使用泛型？

Answer 1

是，您可以：

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; 
    } 
    } 

上面是通用的解決方案。如果OfferDto延伸AbstractOfferDto，不需要額外的接口：

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; 
    } 
    } 

Answer 2

告訴抽象類型編譯：

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; 
    }