如何指示泛型类从一个或另一个类扩展？

Question

Hi I have the next class

public class ApiResponse<T extends ApiResponseData > 

When T is a type of the ApiResponseData , but sometimes I receive to a list instead of an object and for this case I need the T to be extended from ApiResponseData or List<ApiResponseData> how can do it this?

My attempt

public class ApiResponse<T extends ApiResponseData || T extends List<ApiResponseData>> 

Answer 1

I think you have a fundamental misunderstanding of the purpose of generic type parameters. Why do you think you need the type parameter to change to accommodate lists?

Why is something like this not sufficient?

class ApiResponse<T extends ApiResponseData>
{
    final List<T> data;

    ApiResponse(T datum)
    {
        data = Collections.singletonList(datum);
    }

    ApiResponse(List<T> data)
    {
        this.data = data;
    }
}

Answer 2

您可以等待public class ApiResponse<T extends List<ApiResponseData> >并在调用此方法时将T extends ApiResponseData情况视为一个元素的列表（在代码中较高）

Answer 3

It is not possible as because it will be ambiguous for java to decide which class to use during type erasing. You can use Generic to specify the constraint like T needs to be a subclass of multiple class like (A & B) like <T extends A & B> but your use case not possible.