Externalizable and serializable superclass

Question

hi!
i've got al lot of objects that extend jcomponent and i don't want to serialize all the fields of those. so i implemented the externalizable interface, but the superclass is also serialized, why does this happen??? here's a test-class:
class TestExtOrig implements Serializable
   public String test = "Hi";
public class TestExt extends TestExtOrig implements Externalizable
   private static final long serialVersionUID = 2494746796557083423L;
   public static void main(String[] args) throws SecurityException, IOException
      ByteArrayOutputStream bos = new ByteArrayOutputStream();
      DebugObjectOutputStream dos = new DebugObjectOutputStream(bos);
      dos.writeObject(new TestExt());
      dos.close();
   public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException
   public void writeExternal(ObjectOutput out) throws IOException
}The DebugObjectOutputStream simply extends ObjectOutputStream and prints the called method on StdOut, so that i can see what's really written. Well, here it is:
writeUTF(org.wimberger.hptoolkit.client.TestExt)
writeLong(2494746796557083423)
defaultByte(12)
writeShort(0)
writeUTF(org.wimberger.hptoolkit.client.TestExtOrig)
writeLong(7683992437612625549)
defaultByte(2)
writeShort(1)
defaultByte(76)
writeUTF(test)The problem with that is that it writes the TestExtOrig class also. How can i avoid that???
thanks in advance,
Christoph Wimberger

Answer 1

Hi Christoph,
I think the debug you are seeing is when the ObjectOutputStream write the ClassDescriptor to the OutputStream, not the object. I believe this happens the first time an instance of a particular class is written to the ObjectOutputStream.
Regards,
Scott