Berkeley DB Family

I've just come to thought that I might be doing the wrong thing using initializers instead of initializing fields in the constructor. Of cause I'm speaking of DPL..
I'm used to do something like this:

@Persistent
class Compound
{
   private final Map<Integer, Integer> elements = new HashMap<Integer, Integer>();

   private Compound() {} //dummy private default constructor to be used by BDB

   //actual constructor to be used in the code
   public Compound(int initialValue)
   {
     //some specific initialization...
     //e.g.:
     elements.add(initialValue, initialValue);
   } 
}

But while thinking about what will BDB actually do when demarshaling the object instance, I came to idea that it would re-construct the elements map and forget the one I carefully create in the initializer.. So to avoid the useless object instantiation I'd have to initialize the field in constructor like this:

@Persistent
class Compound
{
   private final Map<Integer, Integer> elements;

   //dummy private default constructor to be used by BDB
   private Compound()
   {
     //now I have to assign something to elements field because it's final.. 
     // or just remove the *final* modifier???
     elements = null;
   } 

   //actual constructor to be used in the code
   public Compound(int initialValue)
   {
     elements = new HashMap<Integer, Integer>()
     //some specific initialization...
     //e.g.:
     elements.add(initialValue, initialValue);
   } 
}

So my question is: is there any actual difference between the first and second approaches? Or I just thinking the wrong way?..