有什么方法可以实例化一个类 <C<A,B> &gt; Java中的对象？

Question

I'm trying to use Hibernate and TypedQuery in java.

The method I'm trying to call has a signature of

<T> TypedQuery<T>   createQuery(String qlString, Class<T> resultClass)

I want to call it like bellow but with null replaced by a real instance.

 Class<Tuple2<Date,String>> cls=null;
 List<Tuple2<Date,String>> books=em.createQuery("select new io.vavr.Tuple2(date,title) from Book where publicationdate > '2008-01-01'",cls).getResultList();

the above code compiles but obviously chrashes with a null pointer exception.

If my understanding of erasure is correct this would work as long as I get an instance of the Class object as all generic type information would be lost at runtime anyway.

Is there any way I can get an instance of Class that i can assign to the variable cls so that this code will work?

Answer 1

Based on @Thomas comments on the first post I came upp with the following.

While it dies not seems to be a way to instantiate such a Class object a relativly readable solution can be achived with subclassing.

In the class where the code resides add outside any function

public static class DateStringPair extends Pair<Date,String>{
      public DateStringPair(Date d,String s){super(d,s);}
}

And then the call becomes

List<DateStringPair> books=em.createQuery(
        "select new com.example.ConnectionAndQueryTest$DateStringPair(publicationDate,title) from Book where publicationDate > '2008-01-01'"
    ,DateStringPair.class).getResultList( );

this have the limitation that the Pair class must not be final.

While not as flexible as full generics support in the query readability of the query can be maintained without that much fuss.