一个 Java 泛型套泛型的问题

This topic created in 2566 days ago, the information mentioned may be changed or developed.

有如下 mapper：

public interface PeopleMapper extends BaseMapper<People> {}

现在我只能写成这样：

List<SelectAllMapper> mappers = Util.getMappers(SelectAllMapper.class, People.class);

这个工具函数意思是：找到全部的以 People 为实体类，并实现了 SelectAllMapper 接口的 mapper：

public static <T> List<T> getMappers(Class<T> mapperClass, Class<?> entityClass){...}

但我想做到这样：

List<SelectAllMapper<? extends People>> mappers = Util.getMappers(SelectAllMapper.class, People.class);

这样就不需要我之后再强制转换类型：

(List<People>) mapper.selectAll()

但不知道该怎么声明这个函数，有木有大佬教教我

7 replies • 2019-05-06 08:47:40 +08:00

mk0114

May 5, 2019

`public static <T,R> List<T<R>> getMappers(Class<T> mapperClass, Class<R> entityClass) {...}`

这样明显是不对的

mk0114

May 5, 2019

public static <T<R>,R> List<T> getMappers(Class<T> mapperClass, Class<R> entityClass) {...}
这样也是不行

xingda920813

May 5, 2019

public static <T extends BaseMapper<R>, R> List<T> getMappers(Class<T> mapperClass) {...}

List<? extends BaseMapper<People>> mappers = getMappers(new BaseMapper<People>() {}.getClass());

mk0114

May 5, 2019 via Android

@xingda920813 BaseMapper 是 SelectAllMapper 的子接口，这样写应该是不行的。我怀疑是不是 java 不可能做到这样

HuHui

May 5, 2019

用我的理解写了你的需求，感觉没你的复杂
```
public class People {
}

public interface SelectAllMapper<T> extends BaseMapper<T> {
List<T> selectAll();
}

public interface PeopleMapper extends BaseMapper<People> {
}

public static <T> List<SelectAllMapper<T>> getMappers(Class<T> clazz) {
return null;
}

List<SelectAllMapper<People>> mappers = Util.getMappers(People.class);
List<People> list = mappers.get(0).selectAll();
```

billlee

May 5, 2019

换 scala （逃

mk0114

May 6, 2019 via Android

@HuHui 是 BaseMapper 继承了 SelectAllMapper，我放弃了，写个 suppressWarnings 得了