CODEWITHSUNDEEP
javagenerics
Blake Beaupain
Blake Beaupain

Reputation: 638

Generic method without type argument

I was wondering if there's a way to, in Java, use a generic type within a generic method without requiring an argument specifying the class type. Here's the normal way of doing it:

public <T> T doSomethingGeneric(Class<T> type, int a) {
    return (T) doSomethingElse(type, a);
}

I would like this as an alternative:

public <T> T doSomethingGeneric(int a) {
    return (T) doSomethingElse(/* some magic with T here */, a);
}

Background: I'm writing utility methods with Hibernate. Here's an example of what I'm actually trying to do, and you can infer how it applies to this problem.

public static <M extends Model> M get(Class<M> type, Serializable id) {
    Session session = newSession();
    Transaction t = session.beginTransaction();
    Object model = null;
    try {
        model = session.get(type, id);
        t.commit();
    } catch (HibernateException ex) {
        t.rollback();
        throw ex;
    }
    return (M) model;
}

Is this possible? If so, how is it done? Thanks!

Upvotes: 1

Views: 452

Answers (2)

Matt Ball
Matt Ball

Reputation: 360066

You want to get a Class<T> at runtime to pass to doSomethingElse()? No, that is not possible.

If you describe why doSomethingElse needs a Class<T>, perhaps we could suggest a workaround.

Upvotes: 4

Marko Topolnik
Marko Topolnik

Reputation: 200306

This isn't possible: the code of doSomethingGeneric is only compiled once, unlike the instantiation of a template in C++. The type T is erased to Object in the process.

Notice also that (T) will be flagged as an unchecked downcast.

Upvotes: 2

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