java.lang.ClassCastException: sametype cannot be cast to sametype

问题

very strange exception

my code

 Query q = em.createQuery("SELECT  u FROM Chatuser u");

            List<Chatuser> list = (List<Chatuser>) q.getResultList();
            for (int i = 0; i < list.size(); i++) {
                Object aa = list.get(i);
                Chatuser chatuser = (Chatuser)aa;

exception

   ex = (java.lang.ClassCastException) java.lang.ClassCastException: Entities.service.Chatuser cannot be cast to Entities.service.Chatuser

what is the problem ?

回答1:

This post probably answers also your question
Java, getting class cast exception where both classes are exactly the same

There could be problem with conflicting Classloaders

回答2:

please try the following :

Query q = em.createQuery("SELECT  u FROM Chatuser u", Chatuser.class);

List<Chatuser> list = q.getResultList();

for (Chatuser chatuser : list) {
    ....
    chatuser.doSomething();
    ...
}

If you set the target Class on the createQuery Method already, you can avoid the downcast. If its not working, please past more infos, (Chatuser.java) JPA(Hibernate) Version, etc)

Cheers Jens

回答3:

it is because the generics

List<Chatuser> list = 

use this form

for(ChatUser u : list) {
u.doSomething();
}

来源：https://stackoverflow.com/questions/17231535/java-lang-classcastexception-sametype-cannot-be-cast-to-sametype