The expression of type List needs unchecked conversion to conform to List<Student>, when using Hibernate Criteria

just_a_girl picture just_a_girl · Dec 18, 2013 · Viewed 10.8k times · Source

I have this piece of code that gives the warning mentioned in the title:

List<Student> studentList = session.createCriteria(Student.class)
    .add(Restrictions.eq("indexNumber", indexNum))
    .list();

I've read the thread How do I fix "The expression of type List needs unchecked conversion...'? and there's a great solution by @BrunoDeFraine:

public static <T> List<T> castList(Class<? extends T> clazz, Collection<?> c) {
    List<T> r = new ArrayList<T>(c.size());
    for(Object o: c)
      r.add(clazz.cast(o));
    return r;
}

then I can just do this:

List<SyndEntry> entries = castList(SyndEntry.class, sf.getEntries());

This works great, but in my case I have Criteria as argument, not class and collection. My question is, can this method be adapted to have criteria as argument, or should I simply use @SuppressWarnings("unchecked")?

Answer

Taylor picture Taylor · Dec 20, 2013

Moved from comment: You want to cast a Criteria object? That makes no sense. criteria.list() returns a List, so you could just use that.

The castList method is odd anyways, you don't gain any compile-time type-safety (it will still only fail at runtime if something is wrong), and it could slow things down, especially if the list is long. I'd just use @SuppressWarnings or live with the warning.