如何转换对象数组？

Question

I am new to java and exploring java ee application with netbeans.

I have the code :

Method in userbean:

public List userList() {

  Query q = em.createNativeQuery("select username,address from tbuser");

  Iterator i = q.getResultList.iterator;

  ArrayList<UserState> userinfo = new ArrayList<UserState>();

  while (i.hasNext()) {

    Vector result = (Vector) i.next(); // <- HERE

    UserState us = new UserState();

    us.setName((String) result.get(0));

    us.setAddress((String) result.get(1));

    userinfo.add(us);

  }

  return userinfo;

}

I use this method to construct jsf datatable and work fine with netbeans6.5 and glassfish2

however when i use the same method except i change the vector to arraylist in netbean 6.9

and glassfish 3 i got the class cast

exception at run time: object cannot be cast to java.util.list;

Does anybody know how to do it? thank you..

Answer 1

Hmm, better is to create DTO directly inside JPA query:

public List userList() {

  Query q = em.createNativeQuery("SELECT new UserState(username,address) FROM tbuser");

  return q.getResultList();

}

Something like this (this is not verified code)

Answer 2

I doubt that the code works like this, methods such as hasNext() are missing the parentheses. If you copied the code, please do so again as having us guessing your code won't improve the quality of the answers.

Your problem is that you want to access an element from the Vector. But The type of the objects inside the Vector is not Vector , but a different type of collection. You want to retrieve an element of this Vector (which is perfectly fine), but then you try to cast it to Vector , which fails.

As I cannot see which type of objects will be in the Vector at runtime, you could, for a start, use System.out.println(i.next().getClass().getCanonicalName()); before the line where your current error occurs. That prints the type of the Vector's element.