How to avoid type safety warnings with Hibernate H

Question

For example I have such query:

Query q = sess.createQuery("from Cat cat");
List cats = q.list();

If I try to make something like this it will show warning "Type safety: The expression of type List needs unchecked conversion to conform to List":

List<Cat> cats = q.list();

Is there a way to avoid it?

Answer 1

I know this is older but 2 points to note as of today in Matt Quails Answer.

Point 1

This

List<Cat> cats = Collections.checkedList(Cat.class, q.list());

Should be this

List<Cat> cats = Collections.checkedList(q.list(), Cat.class);

Point 2

From this

List list = q.list();

to this

List<T> list = q.list();

would reduce other warnings obviously in original reply tag markers were stripped by the browser.

Answer 2

Try this:

Query q = sess.createQuery("from Cat cat");
List<?> results = q.list();
for (Object obj : results) {
    Cat cat = (Cat) obj;
}

Answer 3

In our code we annotate the calling methods with:

@SuppressWarnings("unchecked")

I know it seems like a hack, but a co-developer checked recently and found that was all we could do.

Answer 4

Joe Dean's solution looks interesting, but do you think it's worth it - create a new List and loop through all elements just to get rid of warnings?

(sorry, can't add a comment directly to his solution for some reason)

Answer 5

It is been a long time since the question was asked but I hope my answer might be helpful to someone like me.

If you take a look at javax.persistence api docs, you will see that some new methods have been added there since Java Persistence 2.0. One of them is createQuery(String, Class<T>) which returns TypedQuery<T>. You can use TypedQuery just as you did it with Query with that small difference that all operations are type safe now.

So, just change your code to smth like this:

Query q = sess.createQuery("from Cat cat", Cat.class);
List<Cat> cats = q.list();

And you are all set.

Answer 6

Try to use TypedQuery instead of Query. For example instead of this:-

Query q = sess.createQuery("from Cat cat", Cat.class);
List<Cat> cats = q.list();

Use this:-

TypedQuery<Cat> q1 = sess.createQuery("from Cat cat", Cat.class);
List<Cat> cats = q1.list();