Java type parameterized Class argument

Question

JPA has a method of the following signature:

<T> CriteriaQuery<T> createQuery(Class<T> resultClass);

How do I invoke this method when my resultClass type is, itself, type parameterized?

For example:

public class ResultDto<T> {
...
}

I tried the following but it didn't work:

createQuery(ResultDto<String>.class);

Answer 1

There is no Class instance for any specific instantiation of a generic type (e.g. ResultDto<String>, ResultDto<Integer>, ResultDto<MyObject>, ...).

No matter whether the class is generic or not there is always only one Class instance which represents raw version of the class. In your case, it is ResultDto.class.

Answer 2

You can use createQuery(ResultDto.class)

The reason is when you are going to create a object of ResultDto , you will always create it using a type parameter for eg ResultDTo<String> rs = new ResultDTo<String>() So this type parameter will be considered in the <T> CriteriaQuery<T> createQuery(Class<T> resultClass);