Modifying a Class that implements Serializable

I have a class LDAPUser
import java.io.*;
public class LDAPUser implements java.io.Serializable{
     private java.lang.String name;
     private java.lang.String userID;
     private java.lang.String associateNumber;
public LDAPUser() {
     super();
public boolean equals(Object o) {
     if (o == this)
     return true;
     if (!(o instanceof LDAPUser))
     return false;
     return (((LDAPUser)o).getAssociateNumber().equals(this.getAssociateNumber()));
public java.lang.String getAssociateNumber() {
     if(associateNumber == null){
          return getUserID();
     return associateNumber;
public java.lang.String getName() {
     return name;
public java.lang.String getUserID() {
     return userID;
public void setAssociateNumber(java.lang.String newAssociateNumber) {
     associateNumber = newAssociateNumber;
public void setName(java.lang.String newName) {
     name = newName;
public void setUserID(java.lang.String newUserID) {
     userID = newUserID;
It works fine.
I needed to add functionality to it. These were the modifications.
private java.lang.String distinguishedName;
private boolean validUser;
public java.lang.String getDistinguishedName() {
     return distinguishedName;
public boolean isValidUser() {
     return validUser;
public void setDistinguishedName(java.lang.String newDistinguishedName) {
     distinguishedName = newDistinguishedName;
public void setValidUser(boolean newValidUser) {
     validUser = newValidUser;
I am using visual age for java and in the Test environment the changes work fine.
When I promote the changes to our application server (websphere) the changes are not there. I get a method not found error and though trial and error have identified that the server is not actually using the class from the jar. I have removed any other occurences of the class from the server.
My question is if I change a Serializable class how do I make those changes take affect (thorough better coding) and for right now, where is this "old instance" of my class coming from and how do I get rid of it.
Thanks in Advance,
Jason Grieve

If the server is running than the class might be already loaded through the class loader, so it wont be load again.
this unless you use hot deployment, which you have to figure how it is being handled in your srver.
Doron

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Example class that implements Serializable interface

Dear,
I have a class myData that I want to implement Serializable interface. class myData has only two fields: Integer iData1, String sData2.
Could anybody shown me how my myData class should be?
Thanks a lot!

Hey, if you have yet to obtain a remote reference from the app server ...then we are into pandora's box. I lost three whole heads of hair getting up on JBoss when I first started. You want to check out the JBoss forums on the JBoss website, and the enterprise javabeans forum here. Search some posts and read the free JBoss manual.
Unfortunately, there isn't a 'here, do this' solution to getting connected with JBoss. There are quite a few gotcha's. There are descriptors, descriptor syntax ...and this changes between releases so there seems to be alot of people saying 'here, do this' ...but you try and it doesn't work (wrong release). Here are some descriptors that I threw up recently for someone ...a place to start.
http://forum.java.sun.com/thread.jsp?forum=13&thread=414432
This drove me nuts until it all worked right. I was stuck for three weeks at one point ...ready to give up, but then I got it. Perservere ...its a nice container for learning in (its free!).
I will try and watch for you.
Oh, and put something in your head ...at least then you will keep your hair !
:)

Using a class or servlet that implements Serializable

Hello everyone,
Can someone please help me. I need to make a program that uses a class or servlet that implements Serializable and then use the values of the variables in servlets.
The first is using it to validate login. then changing the color of the background, header and footer of each servlet.
the variables in the Serialized file are all Strings for color, username, password, header text and footer text.
I tried using the applet tag to run the class in the servlet but it is not working.

It's not working because you seem to be making random guesses what servlets, serialization and files are

Serializing a class that implements the Singleton pattern

Hello,
I am relatively new to Java and especially to serialization so the answer to this question might be obvious, but I could not make it work event though I have read the documentation and the article "Using XML Encoder" that was linked from the documentation.
I have a class that implements the singleton pattern. It's definition is as follows:
public class JCOption implements Serializable {
private int x = 1;
private static JCOption option = new JCOption();
private JCOption() {}
public static JCOption getOption() { return option; }
public int getX() { return x; }
public void setX(int x) { this.x = x; }
public static void main(String args[]) throws IOException {
    JCOption opt = JCOption.getOption();
    opt.setX(10);
    XMLEncoder encoder = new XMLEncoder(new BufferedOutputStream(new FileOutputStream("Test.xml")));
    encoder.setPersistenceDelegate(opt.getClass(), new JCOptionPersistenceDelegate());
    encoder.writeObject(opt);
    encoder.close();
}Since this class does not fully comply to the JavaBeans conventions by not having a public no-argument constructor, I have create a class JCOptionPersistenceDelegate that extends the PersistenceDelegate. The implementation of the instantiate method is as follows:
protected Expression instantiate(Object oldInstance, Encoder out) {
       Expression expression = new Expression(oldInstance, oldInstance.getClass(), "getOption", new Object[]{});
        return expression;
}The problem is that the resulting XML file only contains the following lines:
    <java version="1.5.0_06" class="java.beans.XMLDecoder">
        <object class="JCOption" property="option"/>
    </java> so there is no trace of the property x.
Thank you in advance for your answers.

How about this:
import java.beans.DefaultPersistenceDelegate;
import java.beans.Encoder;
import java.beans.Expression;
import java.beans.Statement;
import java.beans.XMLEncoder;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
public class JCOption {
    private int x = 1;
    private static JCOption option = new JCOption();
    private JCOption() {}
    public static JCOption getOption() { return option; }
    public int getX() { return x; }
    public void setX(int x) { this.x = x; }
    public static void main(String args[]) throws IOException {
      JCOption opt = JCOption.getOption();
      opt.setX(10);
      ByteArrayOutputStream os = new ByteArrayOutputStream();
      XMLEncoder encoder = new XMLEncoder( os );
      encoder.setPersistenceDelegate( opt.getClass(), new JCOptionPersistenceDelegate() );
      encoder.writeObject(opt);
      encoder.close();
      System.out.println( os.toString() );
class JCOptionPersistenceDelegate extends DefaultPersistenceDelegate {
    protected Expression instantiate(Object oldInstance, Encoder out) {
        return new Expression(
                oldInstance,
                oldInstance.getClass(),
                "getOption",
                new Object[]{} );
    protected void initialize( Class<?> type, Object oldInstance, Object newInstance, Encoder out ) {
        super.initialize( type, oldInstance, newInstance, out );
        JCOption q = (JCOption)oldInstance;
        out.writeStatement( new Statement( oldInstance, "setX", new Object[] { q.getX() } ) );
}   Output:
<?xml version="1.0" encoding="UTF-8"?>
<java version="1.5.0_06" class="java.beans.XMLDecoder">
<object class="JCOption" property="option">
<void property="x">
   <int>10</int>
</void>
</object>
</java>

Transform a class that implements JPanel into a bean.

I'd to create a bean, from a class that implements JPanel, that in fact is a custom component.
How can I create a bean?
I have absolutely no idea about beans.
What can make beans for me?
I know a lot about the theory of ejb, is this what I need?
I'm quite confused, please make me see the light!!!!!
Thanks.

Hi Daniel!
To answer your question short as possible:
Java -Beans are reusable code - components,
similar to VB Active -X components,
which you can use when developing your own
applications.
Beans can have a graphic user interface, so you
can use builder tools like JBuilder or Beanbox
to show them graphically in a designer.
You can modify them about their properties,
mostly shown in a special property window of a
builder tool.
It's really not very hard to create your own beans,
the only thing you have to do is to pack all the
classes which make the bean into a jar file.
Then you can import the bean with the builder
and it will be shown.
The jar manifest file needs to look like for example:
Manifest-Version: 1.0
Name: BeanClock.class
Java-Bean: True
All the properties are implemented by public property-get
and property-set methods, in order to show them in the property window.
Java is doing that by introspection.
Hope, this makes it a little bit clearer for you!

Reflect the class that implements Runnable

Hi,
I am implementing the reflection of the class that implements Runnable. In order to start a new thread I am trying to invoke "start()" method ( which is obviously not defined my class ) and I therefore I am getting "java.lang.NoSuchMethodException".
I am wondering is it possible at all to start a new thread on a reflected class?
thanks in advance.
{ Class refClass = Class.forName(className);
String methodName = "start";
Class[] types = new Class[1];
types[0] = Class.forName("java.util.HashMap");
Constructor cons = refClass.getConstructor(types);
Object[] params = new Object[5];
params[0] = new HashMap();
Method libMethod = refClass.getMethod(methodName, null);
libMethod.invoke(objType, null); }

Well, if we knew what it meant to "start a thread on a class" we could probably figure out how to "start a thread on a reflected class". If we knew what a "reflected class" was, that is.
In other words, it would help if you rephrased your question using standard terminology (and also explained why you want to do whatever it is you want to do).
But let's guess for now: If you have an object which implements Runnable then you start a thread to run that object like this:
Runnable r = // some object which implements Runnable
new Thread(r).start();Not what you wanted? Go ahead and clarify then.

HELP?! a class that implements ..... : java.util.Vector

My instructions say this:
In the constructor, create the collection object (Since java.util.List is an interface, you will need to instantiate a class that implements this interface: java.util.Vector or java.util.LinkedList or java.util.ArrayList).
I know, this IS a homework assignment - I am not sure how to go about this. I DO have code so far up to this point, can anyone help?
import dLibrary.*;
import java.awt.Color;
* @author Rob
* @version 8/18/03
public class PhrasesII extends A3ButtonHandler
        private A3ButtonWindow win;
        private ATextField stringAcceptor;
        private ALabel listOstrings;
        private ALabel inputString;
        private ALabel status;
        private java.awt.List display;
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public PhrasesII()
        win = new A3ButtonWindow(this);
        stringAcceptor= new ATextField (50,420,200,25);
        stringAcceptor.place(win);
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        inputString.setFontSize(10);
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        inputString.place(win);
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        display.setSize(200, 250);
        display.setBackground(Color.lightGray);
        win.add(display, 0);
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public void leftAction()
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I am getting a " can't resolve symbol" when I do thisYou have to either import java.util.ArrayList or specify it fully, e.g., "new java.util.ArrayList()".
Is that the line that is causing you problems? The error message should give the line number.
my instructions also say I have to use "interface
java.util.List when declaring your reference" so I am
confused about using "= new ArrayList();"What they're saying is that you want code like this:
private java.util.List frogs;    // this is the reference declaration
//... later on...
frogs = new java.util.ArrayList(); // this isn't a declarationWhat this means is that when you declare a field or variable, you should declare its type to be an interface.
But when you actually instantiate a value for that variable, then you should use a concrete class that implements that interface. (You have to; interfaces can't be instantiated.)
This is good programming style for reasons I don't have the space to explain here.

Abstract Class that implements Comparable

I am trying to understand how a comparable interface works with an abstract class. Any help is greatly appreciated.
I have a class ClassA defined as follows:
public abstract class ClassA implements Comparable I have a method, compareTo(..), within ClassA as follows:
public int compareTo(Object o) I have a sub-class ClassB defined as follows:
public class ClassB extends ClassAI am receiving a compile error:
Class must implement the inherited abstract method packagename.ClassA.compareTo(Object)
Should or can the compareTo be abstract in ClassA and executed in ClassB? Just not sure how this works.

???? if you are inheriting from an abstract class your subclass must implement methods that were declared in the parent (abstract) class but not implemented
When in doubt, refer to the Java Language Specification..

Question about methods in a class that implements Runnable

I have a class that contains methods that are called by other classes. I wanted it to run in its own thread (to free up the SWT GUI thread because it appeared to be blocking the GUI thread). So, I had it implement Runnable, made a run method that just waits for the thread to be stopped:
while (StopTheThread == false)
try
Thread.sleep(10);
catch (InterruptedException e)
//System.out.println("here");
(the thread is started in the class constructor)
I assumed that the other methods in this class would be running in the thread and would thus not block when called, but it appears the SWT GUI thread is still blocked. Is my assumption wrong?

powerdroid wrote:
Oh, excellent. Thank you for this explanation. So, if the run method calls any other method in the class, those are run in the new thread, but any time a method is called from another class, it runs on the calling class' thread. Correct?Yes.
This will work fine, in that I can have the run method do all the necessary calling of the other methods, but how can I get return values back to the original (to know the results of the process run in the new thread)?Easy: use higher-level classes than thread. Specifically those found in java.util.concurrent:
public class MyCallable implements Callable<Foo> {
public Foo call() {
return SomeClass.doExpensiveCalculation();
ExecutorService executor = Executors.newFixedThreadPool();
Future<Foo> future = executor.submit(new MyCallable());
// do some other stuff
Foo result = future.get(); // get will wait until MyCallable is finished or return the value immediately when it is already done.

Importing classes that implement jsp tags

          I was making a custom JSP tag library. The tag functionality was implemented in
          a class called, lets cay ClassA. I made the tld file and put it under the WEB-INF
          directory. The class which implemented the functionality was placed under WEB-INF/classes
          directory. I had the imported the tag library using the taglib directive. I was
          getting an error which said "cannot resolve symbol". But when I in the JSP file
          I imported the class file which implemented the taglib functionality the error
          vanished. Is it necessary to import the class files even if the taglib is imported.
          The documentation does not say so. Or is there some configuration I have to make.


I think was a side effect of the .jsp changing redeploys the web app in 6.0.
          When the web app was redeployed your directory structure was reread and thus
          it found your .tld.
          Sam
          "bbaby" <[email protected]> wrote in message
          news:3b422db7$[email protected]..
          >
          > I was making a custom JSP tag library. The tag functionality was
          implemented in
          > a class called, lets cay ClassA. I made the tld file and put it under the
          WEB-INF
          > directory. The class which implemented the functionality was placed under
          WEB-INF/classes
          > directory. I had the imported the tag library using the taglib directive.
          I was
          > getting an error which said "cannot resolve symbol". But when I in the JSP
          file
          > I imported the class file which implemented the taglib functionality the
          error
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          imported.
          > The documentation does not say so. Or is there some configuration I have
          to make.
          >
          >

Compile-time warning during javac of a Class that implements Comparable

Hello All,
I have defined a class as follows;
public class CardTiles extends JButton implements Comparable{
During normal compilation with javac, it tell me to use Xlint to compile and the warning it throws is below:
CardTiles.java:4: warning: [serial] serializable class CardTiles has no definition of serialVersionUID
public class CardTiles extends JButton implements Comparable{
^
1 warning
What does this warning mean?
Many thanks!

ejp wrote:
you can choose to to differentiate between various versions of your CardTiles classThat's back to front. Serialization will always do that unless you stop it, which you can do via a fixed serialVersionUID. This tells Serialization that different versions of your class are compatible under serialization.I suppose I see it this way because I wouldn't have a serializable object without an ID. Without having an explicit ID the process isn't as transparent to me. It's the same sort of thing as using braces for statements when they're not necessary, e.g.
          if(check)
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               System.out.println("check is on");
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               System.out.println("check is off");
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My class is serializing w/o implementing serializable

I have a class Foo that implements Serializable.
Foo has a data member that is an instance of class Bar.
Class Bar does NOT implement Serializable.
When I serialize an instance of Foo out to a file and
then deserialize it back in, I'm seeing Bar's no-arg
constructor being called.
Shouldn't I be getting IOExceptions on the write and
and read of my Foo instance when the JVM tries to
write/read the Bar member, since only classes that implement
Serializable can be serialized/deserialized?
Oh, I'm using JDK 2SDK version 1.3.1
-Steve

From the Serializable API
"To allow subtypes of non-serializable classes to be serialized, the subtype may assume responsibility for saving and restoring the state of the supertype's public, protected, and (if accessible) package fields. The subtype may assume this responsibility only if the class it extends has an accessible no-arg constructor to initialize the class's state. It is an error to declare a class Serializable in this case. The error will be detected at runtime."
There seems to be a mistake in the second to last sentence. I would think itr should say 'It is an error to declare a class Serializable if this is not the case'.

Serialize a value object that implements Comparator T

Hi.
I'm implementing a VO like this:
public class RegionVO implements Serializable, Comparable<RegionVO>My problem is that i need that the class could be serialized completely.
The VO will be transfered throught EJB's and by past experiences with EJB 2 projects (the actual project is developed with EJB 3) and running the project in clusters, the application crashes to use VO defined like that.
I think that the problem is caused by implement Comparable too, this inteface isn't serializable and even if implement of Serializable interface, at least 1 method (compareTo(RegionVO o))not would serializable.
My question is if that is true, how to solve to serialize the entire VO.
Thanks.
Edited by: terinlagos on Jul 24, 2008 2:48 PM

terinlagos wrote:
Well, the question was because if eventually could have the same problem when in the future the application run in a clusterized server. Actually in my pc has no problem.Well at least you are thinking that clustering will introduce problems you don't have currently.
I suggest you start trying to cluster you application as early as possible, you undoubtedly will have allot of lessons to learn (I have never seen a cluster solution from an it-works-on-my-pc solution not run into unexpected problems)
Note: you can run a "clustered" solution on a single PC just in multiple JVMs (which would be deployed to different machines in your final solution)
You should make looking at this your top priority. IMHO.

Problem with NotSerializableException on class implementing Serializable

Hi,
Any idea as to why I get this exception, and what I can do to avoid it ?
java.io.NotSerializableException: util.NumberStore$UserI have this, relatively simple, class
class User implements Serializable
     private static long serialVersionUID = 1L;
     private String uid;
     private String nr;
     public User(){}
     public User( String uid, String nr ) {
          this.uid = uid;
          this.nr = nr;
     public String getUid()     {
          return uid;
     public String getNr() {
          return nr;
     public void setUid(String uid){
          this.uid = uid;
     public void setNr(String nr){
          this.nr = nr;
}When loading and saving it, I use these two methods:
     private void saveLocalList()
          FileOutputStream f = null;
          try {
               f = new FileOutputStream("./users.dat");
               ObjectOutputStream out = new ObjectOutputStream(f);
               for (User u: numbers)
                    out.writeObject(u);
               f.close();
          } catch (IOException e) {
               System.err.println("User info not saved:"+e.getLocalizedMessage());
               if (f != null)
                    try {
                         f.close();
                    } catch (IOException e1) {
     private boolean loadLocalList()
          FileInputStream f = null;
          try {
               f = new FileInputStream("./users.dat");
               ObjectInputStream input = new ObjectInputStream(f);
               numbers = new ArrayList<User>();
               User u = (User) input.readObject();
               while (u != null)
                    numbers.add(u);
                    u = (User) input.readObject();
               f.close();
               return true;
          } catch (FileNotFoundException e) {
               return false;
          } catch (IOException e) {
               e.printStackTrace();
               if (f != null)
                    try {
                         f.close();
                    } catch (IOException e1) {
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               return false;
          } catch (ClassNotFoundException e) {
               if (f != null)
                    try {
                         f.close();
                    } catch (IOException e1) {
                         // ignore close errors
               return false;
     }Both the User class and the methods are found within the NumberStore class.

The User class indeed does not contain any references at all to the NumberStore classIf 'User' is nested inside 'NumberStore' and it isn't static, User does indeed have a hidden reference to the outer class NumberStore. That's how the syntax 'NumberStore.this' works.
I can say with absolute certainty that an object which was not marked as serializable was written to the users.dat file.Quite apart from the fact that the source code of ObjectOutputStream makes it utterly impossible, I don't see how you can possibly say that 'with absolute certainty'. For a start there's no information in the file to indicate what interfaces were and weren't implemented by the class of the serialized object at the time it was serialized.
I'm not absolutely positive about whether or not it bombed out on this occassion, or when trying to re-read it next time aroundNotSerializableException is only thrown when writing, not when reading, so that answers that.
Do you still have the file? I'd like to see exactly what was written. In any case a serialization file that copped any kind of IOException when being written should have been thrown away immediately, you're right about that.
BTW your reading code is wrong. You shouldn't be testing for null, unless you are deliberately writing a null as a sentinel value. You should be catching EOFException.

SerialVersionUID of a class that extends a serializable object

I have class Foo that implements Serializable. In Foo, I have manually hardcoded the serialVersionUID as: private static long serialVersionUID = -7589377069041161459L;Now I created a class SubFoo that extends Foo, but I have not overrided the serialVersionUID. However, when I run serialver command on SubFoo I get 2152116903368641813L, instead of my hardcoded serialVersionUID. Shouldn't I be getting my hardcoded value?
This is important to me because I am running into a Serialization Mismatch on about 100+ subclasses of Foo. So I was hoping to fix this by adding a hardcoded serialVersionUID into the one parent class and hoping not to manually change 100+ subclasses.

Now I created a class SubFoo that extends Foo, but I
have not overrided the serialVersionUID.When the compiler calculates the serialVersionUID, it hashes many things, including the fully qualified class name.
So, even though you may not have added any member variables, the serialVersionUID has changed because the class name has changed from Foo to SubFoo.
You need to manually specify / hardcode the serialVersionUID in all subclasses.
You can see section 12.24.4 of The Java Programming Language, 2nd Ed. for more details.
Best,
Garrett

Modifying a Class that implements Serializable

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