JPA createQuery()

When using JPA createQuery(), I found that we can use both class name and entity name to get the DB data.

This is by class name

em.createQuery("from com.model.Stuff s", Stuff.class).getResultList();

And this is from entity name

em.createQuery("from Stuff s", Stuff.class).getResultList();

This is in orm.xml

<entity class="com.model.Stuff" name="Stuff"> 

No matter which one i use, JPA can get the specific class that i am using from the orm.xml or from the annotation that i put in class.

1. So why i have to put Stuff.class in the parameter?

2. Because it can only put at most two parameters in createQuery(), What if i have to select two Class to do some join?

   i cannot do this

   em.createQuery("from Stuff s, Thing t where s.id = t.stuff_id", Stuff.class, Thing.class).getResultList();

3. Is

   em.createQuery("from Stuff s", Stuff.class).getResultList();

   equal

   em.createQuery("select s from Stuff s", Stuff.class).getResultList();

Thanks to give me some help.