Deserialization order problem

Question

Hi,
For a game i am making i am storing the map as a Serialized Object.
The problem is when i try to paint an image (which should be loaded in the constructor) it is null and thus causing a nullpointer. This only happens after serializing and deserializing the Map. It appears to me that somehow the constructors are not called anymore.
I am using the following (simplified) objects:
public class Map implements java.io.Serializable
     //also included are some protected final static primitives
     protected MapModel model;
     //and some other protected primitives and objects     
     public Map()
          this(null);
     public Map(MapModel model)
          this.model=model;
public class MapModel implements java.io.Serializable
     protected Terrain[][] data;
     private Size size;//simple serializable class
     public MapModel()
          this(new Size());
     public MapModel(Size s)
          data=new Terrain[s.width][s.height];
          size=s;
public abstract class Terrain implements java.io.Serializable
     protected transient Image view;     
     //some more protected primitives     
     public Terrain()
          this(Allignment.SOUTHWEST);
     public Terrain(int allignment)
          System.out.println("Terrain constructor: "+getClass().getName());
          view=loadImage();
     protected abstract Image loadImage();
     //some more abstract methods
public abstract class Tile extends Terrain
     //some public final static ints     
     //some protected ints
     public Tile()
          this(Allignment.SOUTHWEST);
     public Tile(int allignment)
          super(allignment);
          System.out.println("Tile constructor");
     //loadImage() is still not implemented
public class GreyTile extends Tile
     public GreyTile()
          this(Allignment.SOUTHWEST);
     public GreyTile(int allignment)
          super(allignment);
          System.out.println("GreyTile constructor");
     protected java.awt.Image loadImage()
          System.out.println("GreyTile loadImage()");
          //load and return an image
}The above object tree is created and serialized and produces the expected output:
Terrain constructor: heroquest.terrain.tiles.GreyTile
GreyTile loadImage()
Tile constructor
GreyTile constructor
Deserialization however does not produce any output, so loadImage is never called and Terrain.view is null. Which explains the Nullpointer i am getting when trying to paint the GreyTile.
However i do not understand why my constructors are never called.
any thoughts?
Thanks,
Mr Mean

Answer 1

This image is loaded in the constructor. And the
problem is that after deserialization the constructor
is never exectued.
My Question is why.First of all, I apologize for not reading through your code thoroughly. Yes your Image object is transient.
A Ctor is called only when a new instance is created. When deserializing, we are not creating a new instance , we are only restoring a persisted object.
The deserialization process does not use the Ctor because it is not needed. The only time it needs a Ctor is when deserializing the state of the first non-serializable superclass of a serializable one (deserialization needs to reconstruct the entire object state, which includes the state of any superclasses. If the superclass is not itself serializable, then deserialization needs to instantiate that superclass from scratch ).That superclass won't be restored from the stream, but by invoking that class' no-argument constructor.
If the default behavior of this process does not suit your purposes, the solution would be to provide your own writeObject/readObject methods to do what you need to do.