Serializing classes that contain other classes

Question

Hi all,
Hoping someone can answer me a quick question, I'm familiar enough with Java + OO in general but just starting to try to put a multiplayer game framework together so running into a few areas I haven't encountered before... so sorry if this is a bit of a newbie sounding question...
I have a serializable class that contains a reference to another serializable class, very similar to:
public class ClassA implements Serializable
    private ClassB b;
    ...and some other fields...
    public ClassA ()
        super ();
    ...and a standard public getB and setB
public class ClassB implements Serializable
    int someValue;
    ...standard no arguments constructor...
    ...standard getSomeValue and setSomeValue...
}Now that all works fine, serializes fine, send it down an ObjectOutputStream down a network socket, deserializes the other end, all no problem. What I don't like is that to create a ClassA I have to do:
ClassA myClassA = new ClassA ();
myClassA.setB (new ClassB ());   <--- this line
myClassA.getB ().setSomeValue (5);because it could easily be ommitted (especially since the real situation is more complex that two simple classes like above) and I'll get a NullPointerException. Normally (in a non-serialized ClassA) I'd have put b = new ClassB (); in the constructor.
However I don't like the idea of doing that because when deserializing a ClassA, I imagine the deserialization mechanism creates its own ClassB object to set into ClassA? And so if in the ClassA constructor, I create my own ClassB, then the deserialization will then immediately go and create its own ClassB and the ClassB I created will go to the garbage collector, i.e. it was a pointless object to create?
Just wondering what suggestions anyone has on this, there must be a standard approach to deal with this?
Thanks very much,
Nigel.

Answer 1

Allthough you give a lot of information I do not quite understand what you mean, but maybe a little re-arrangement of the setB en getB methods will do it:
public ClassB getB() {
    if(b == null) {
        setB(new ClassB());
    return b;
public void setB(ClassB b) {
    this.b = b;
}