如何处理通用接口实现并避免@SuppressWarnings？

Question

我正在尝试对不同的服务实现进行通用处理，但我经常收到“由于原始类型而导致未检查的调用”错误。我尝试了几种实现，但不太明白这里的问题是什么。我有以下模型：public abstract class Fruit {  public List<String> vitamins;  public String originCountry;  // getters and setters omitted}具体实现如下：public class Kiwi extends Fruit {}public class Pineapple extends Fruit {}我有以下界面：public interface FruitCheckService<T extends Fruit> {  List<String> compareVitaminsFromDifferentCountries(T firstFruit, T secondFruit);  Class<T> getImplementation();}对于上面给出的 2 个模型的实现：@Servicepublic class KiwiCheckServiceImpl implements FruitCheckService<Kiwi> {  @Override  public List<String> compareVitaminsFromDifferentCountries(Kiwi firstFruit, Kiwi secondFruit) {    // some implementation    return new ArrayList<>();  }  @Override  public Class<Kiwi> getImplementation() {    return Kiwi.class;  }}还有菠萝：@Servicepublic class PineappleCheckServiceImpl implements FruitCheckService<Pineapple> {  @Override  public List<String> compareVitaminsFromDifferentCountries(Pineapple firstFruit, Pineapple secondFruit) {    // some implementation    return new ArrayList<>();  }  @Override  public Class<Pineapple> getImplementation() {    return Pineapple.class;  }}我有以下类正在使用不同的 bean 进行操作：@Servicepublic class FruitServices {  private Map<Class, FruitCheckService> beansMap;  @Autowired  public FruitServices(List<FruitCheckService> fruitCheckServices) {    beansMap = new HashMap<>();    fruitCheckServices      .forEach(        fruitCheckService -> {          Class implementation = fruitCheckService.getImplementation();          beansMap.put(implementation, fruitCheckService);        }      );  }  public FruitCheckService getFruitCheckService(Class clazz) {    return beansMap.get(clazz);  }}

Answer 1

问题是您Class在服务定义中使用原始类型。要解决此问题，您可以使用有界通配符类型 ?，如下所示：

class FruitServices {

  private Map<Class<? extends Fruit>, FruitCheckService<? extends Fruit>> beansMap;

  public FruitServices(List<FruitCheckService<? extends Fruit>> fruitCheckServices) {

    beansMap = new HashMap<>();

    fruitCheckServices

      .forEach(

        fruitCheckService -> {

          Class<? extends Fruit> implementation = fruitCheckService.getImplementation();

          beansMap.put(implementation, fruitCheckService);

        }

      );

  }

  public FruitCheckService<? extends Fruit> getFruitCheckService(Class<? extends Fruit> clazz) {

    return beansMap.get(clazz);

  }

}

对于课堂来说，BusinessService事情会变得更加棘手。首先，有必要制定compareVitamins一个通用方法来确保两个水果属于同一类型。但即使那样，我也不相信你可以避免 unchecked cast from the result，getFruitCheckService因为，由于FruitServices必须处理不同类型水果的服务，你不能为 的返回值提供精确的类型参数getFruitCheckService。

class BusinessService {

    private FruitServices fruitServices;

    public <T extends Fruit> void compareVitamins(T one, T two) {

        @SuppressWarnings("unchecked")

        FruitCheckService<T> fruitCheckService = 

            (FruitCheckService<T>) fruitServices.getFruitCheckService(one.getClass());

        List<String> result = fruitCheckService.compareVitaminsFromDifferentCountries(one, two);

    }

}