ObjectSet to ArrayList

feylya

Hopefully this isn't blatantly obvious and it's possible but I'm using DB4O to store objects in a file and to read, write and update those objects. I have an existing project that I have to make work with DB4O. When I run a query on the database, it returns an ObjectSet. However, the rest of my code requires an ArrayList to be returned. Is there any reasonably handy way to convert one to the other?

aidan_walsh

Well, I'm not signing up just so I can check their documentation on ObjectSet, but is it anything like org.odbms.ObjectSet? If it is, the problem is that since it doesn't inherit anything, it isn't as easy to cast it. You'll probably have to loop through it.

ObjectSet os = ~~
ArrayList al = new ArrayList();

while(os.hasNext())
	al.add(os.next());

feylya

I wrote a function to do that:

public static ArrayList listResultToArray(ObjectSet result)
    {
    	ArrayList a = null;
        System.out.println(result.size());
        while(result.hasNext()) 
        {
        	System.out.println(result.next());
            a.add(result.next());
        }
        return a;
    }

but any time I run it:

java.lang.NullPointerException
	at cp3036proj.Util.listResultToArray(Util.java:25)
	at cp3036proj.dao.CategoryDao.getCategories(CategoryDao.java:43)
	at cp3036proj.dao.CategoryDao.main(CategoryDao.java:77)

There's something obvious there but I can't see it.

aidan_walsh

Can't add anything to an ArrayList until you create one

feylya

Gah. Spot on. Cheers mate. That'll teach me for trying to code tired!