Yes - this is good desicion. Thanks!
But I already have searialized objects - I forgot to put the version field,
although I had seen this method already :-((
----- Original Message -----
From: "Lesden, Kim" <[EMAIL PROTECTED]>
To: "JDJList" <[EMAIL PROTECTED]>
Sent: Monday, August 26, 2002 2:45 PM
Subject: [jdjlist] AW: problem with serizlization
> Hello Zlatko,
>
> a simple way would be to store a version attribute before you store
anything else. That way you can also easily migrate old data on the fly. I
have seen this work very well in C++. However, if you have lots of data and
complex version migrations (v1->v2, v2->v3, ...) this will cost you lots of
extra cpu. (see sample below)
>
> Regards
> Kim
>
> /**
> * Version 1:
> */
> class A {
> private static final int version = 1;
> private ArrayList data = new ArrayList();
>
> private void writeObject(ObjectOutputStream ous) throws IOException {
> out.writeObject(version);
> out.writeObject(data);
> }
>
> private void readObject(ObjectInputStream ois) throws IOException,
> ClassNotFoundException {
> version = out.readObject();
> if ( 1 == version ) {
> data = out.readObject();
> }
> }
> }
>
> /**
> * Version 2:
> */
> class A {
> private static final int version = 2;
> private ArrayList data = new ArrayList();
> private String name = "name";
>
> private void writeObject(ObjectOutputStream ous) throws IOException {
> out.writeObject(version);
> out.writeObject(data);
> out.writeObject(name);
> }
>
> private void readObject(ObjectInputStream ois) throws IOException,
> ClassNotFoundException {
> version = out.readObject();
> data = out.readObject();
> if (version > 1) {
> name = out.readObject();
> }
> else {
> /* convert version 1 data to meaningful version 2 or throw
exception */
> name = "none";
> }
> }
> }
>
> /**
> * Version 3:
> */
> class A {
> private static final int version = 3;
> private ArrayList data = new ArrayList();
> private String name = "name";
> private int age = 0;
>
> private void writeObject(ObjectOutputStream ous) throws IOException {
> out.writeObject(version);
> out.writeObject(data);
> out.writeObject(name);
> out.writeObject(age);
> }
>
> private void readObject(ObjectInputStream ois) throws IOException,
> ClassNotFoundException {
> version = out.readObject();
> data = out.readObject();
> if (version > 1) {
> name = out.readObject();
> }
> else {
> /* convert version 1 data to meaningful version 2 or throw
exception */
> name = "name";
> }
> if (version > 2) {
> age = out.readObject();
> }
> else {
> /* convert version 2 data to meaningful version 3 or throw
exception */
> age = 0;
> }
> }
> }
>
>
> -----Ursprungliche Nachricht-----
> Von: Zlatko Kostadinov [mailto:[EMAIL PROTECTED]]
> Gesendet: Montag, 26. August 2002 13:14
> An: JDJList
> Betreff: [jdjlist] problem with serizlization
>
>
> Hi guys
>
> I had serizlized objects in this way:
>
> class A {
> private ArrayList data = new ArrayList();
>
> private void writeObject(ObjectOutputStream ous) throws IOException {
> out.writeObject(data);
> }
>
> private void readObject(ObjectInputStream ois) throws IOException,
> ClassNotFoundException {
> data = out.readObject();
> }
> }
>
> And my program now works with objects of this type. I want to add new
field
> in the class so the class will be
>
> class A {
> private ArrayList data = new ArrayList();
> private name = "name";
>
> private void writeObject(ObjectOutputStream ous) throws IOException {
> out.writeObject(data);
> out.writeObject(name);
> }
>
> private void readObject(ObjectInputStream ois) throws IOException,
> ClassNotFoundException {
> data = out.readObject();
> // here is the problem - how to determine is this an instance of
the
> new version or no.
> // must I read the name or not.
> }
> }
>
> Any ideas are wellcome
> Regards
> Zlatko
>
>
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