Which child class should be cast ?

prettyhandling · **Joined:** Mon Aug 02, 2004 9:33 am **Posts:** 69

Need help with Hibernate? Read this first:
http://www.hibernate.org/ForumMailingli ... AskForHelp

Hibernate version:3.1

Name and version of the database you are using:MySql 5.0

Hi guys,

I got 3 classes below:

Code:

public abstract class Animal{
   private Long id;
   private String name;
}

public class Dog extends Animal{
        private boolean bark;
        private String typeOfDogFood;
}

public class Cat extends Animal{
        private boolean miau;
        private String typeOfCatFood;
}

if I do a query like below:

Code:

public List findAnimal(Long id) {
      return getHibernateTemplate().find(
            "from Animal ani where ani.id = ?",
            new Object[] { id});
}

and return a List, how do I know which class, Dog or Cat should I cast to when iterating over the list:

Code:

    for (Iterator it=clist.iterator(); it.hasNext(); ) {
        Object element = (Dog)it.next();
        Object element = (Cat)it.next();
    }

if I cast the wrong class, system will throw severe exception ! Pls help, Thanks !

ramnath · **Posted:** Mon Jan 23, 2006 3:35 am

Hi,

Change your code like this

for (Iterator it=clist.iterator(); it.hasNext(); ) {
Animal element = (Animal)it.next();
if(element instanceof Dog){
Dog dog = (Dog)element ;
}else{
Cat cat = (Cat)element ;
}
}

prettyhandling · **Joined:** Mon Aug 02, 2004 9:33 am **Posts:** 69

Your code will work only if the return query if instance of Animal like the query below:

Code:

public Animal findAnimal(Long id) {
    Animal ani = (Animal )getHibernateTemplate().get(Animal .class, id);
    return ani;
} 

Please help on the one returning a List, Thanks !

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

No, ranmath's suggestion will work, no matter what. Dog and Cat will both cast to Animal just fine.

Code:

for (Animal ani : findAnimal(id))
{
  if (ani instanceof Dog)
  {
    Dog dog = (Dog) ani;
  }
}

This will work just fine.

prettyhandling · **Joined:** Mon Aug 02, 2004 9:33 am **Posts:** 69

Hi,

I really don't know why my case doesn't work. My query is like below:

Code:

public List findAnimal(List id) {
      String[] param = {"ani_ids"};
      return getHibernateTemplate().findByNamedQueryAndNamedParam(
            "from Animal ani where ani.id in (:ani_ids)",param,
            new Object[] { id});
} 

Code:

List aniList = new ArrayList();
aniList.add(new Long(1000));
aniList.add(new Long(2000));
aniList.add(new Long(3000));

List <Animal> list = animalManager.findAnimal(aniList)
for(Animal element : list){
   if(element instanceof Dog)
      log.info("Dog");
   else if(element instanceof Cat)
      log.info("Dog");
   else
      log.info("Animal ");   
}

and the log always print out Animal. Please help, Thanks !

regards,
Mark

tenwit · **Joined:** Thu Dec 23, 2004 9:08 pm **Posts:** 2008

If you're always getting objects of type Animal and you're expecting other types, then your mapping must be wrong. Can you post that?