Serializing object of class implementing Singleton Pattern

hi ,
if i've a object of a singleton pattern based class and i seriailize that and when i'm desrializing that, i 'll get the object back, but on calling getInstance() method for my singleton class, it will agian call constructor because for the class's static object reference is null, i need to avoid this, for this i've written a setInstance method, which sets the Singleton class's static refernce to the object i desialized, which is fine, but it defeats the singleton pattern
can anybody suggest me some other way of achieving this...

If you are trying to deserialize a Singleton implement the Object readResolve() method.
http://java.sun.com/javase/6/docs/platform/serialization/spec/input.html#5903
~Ryan

Similar Messages

Implementing Singleton Pattern in ESB

How do I go about implementing a singleton pattern within the ESB. Example usage would be for a cache. Prior to making an expensive service call I want to make sure that the data does not already exist within the cache.

Have a look at metalink note 746108.1
cheers
James

GC + Singleton pattern

I have a class implementing singleton pattern, which has a private static variable meant to be used by all other classes.
public class MyClass {
private static MyClass shareVar;
private MyClass() {
// do something
public static MyClass getInstanceof() {
if( shareVar == null )
shareVar = new MyClass();
return shareVar;
// other methods ...
I have noticed that this instance is never garbage collected.
Is the static variable holding back the GC?
Any other alternatives for this?
Thanks

I have noticed that this instance is never garbage
collected.Which is exactly the way it should work. If the instance were GC'ed before MyClass is unloaded, shareVar would be a dangling pointer.
Is the static variable holding back the GC?Yes.

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>

Implementing the Singleton pattern

Has anyone implemented the singleton pattern in Forte? A singleton is simply ensuring that there is one unique instance of a class. In other OO languages I would create a class method which would use a class variable to hold onto the unique instance. Since forte doesn't have either of these (class methods or variables), I'm not sure how to do it. I thought of using named objects, but it seems like a heavy implementation. Any ideas.

An SO with its shared=TRUE and anchored=TRUE?
Venkat J Kodumudi
Price Waterhouse LLP
Internet: [email protected]
Internet2: [email protected]
-----Original Message-----
From: [email protected] [SMTP:[email protected]]
Sent: Monday, February 02, 1998 1:09 PM
To: Venkat Kodumudi
Subject: Implementing the Singleton pattern
To: [email protected] @ Internet
cc:
From: [email protected] @ Internet
Date: 02/02/98 12:36:02 PM
Subject: Implementing the Singleton pattern
Has anyone implemented the singleton pattern in Forte? A singleton is
simply
ensuring that there is one unique instance of a class. In other OO
languages I
would create a class method which would use a class variable to hold
onto the
unique instance. Since forte doesn't have either of these (class
methods or
variables), I'm not sure how to do it. I thought of using named
objects, but it
seems like a heavy implementation. Any ideas.

How to implement Strategy pattern in ABAP Objects?

Hello,
I have a problem where I need to implement different algorithms, depending on the type of input. Example: I have to calculate a Present Value, sometimes with payments in advance, sometimes payment in arrear.
From documentation and to enhance my ABAP Objects skills, I would like to implement the strategy pattern. It sounds the right solution for the problem.
Hence I need some help in implementing this pattern in OO. I have some basic OO skills, but still learning.
Has somebody already implemented this pattern in ABAP OO and can give me some input. Or is there any documentation how to implement it?
Thanks and regards,
Tapio

Keshav has already outlined required logic, so let me fulfill his answer with a snippet
An Interface
INTERFACE lif_payment.
METHODS pay CHANGING c_val TYPE p.
ENDINTERFACE.
Payment implementations
CLASS lcl_payment_1 DEFINITION.
PUBLIC SECTION.
INTERFACES lif_payment.
ALIASES pay for lif_payment~pay.
ENDCLASS.
CLASS lcl_payment_2 DEFINITION.
PUBLIC SECTION.
INTERFACES lif_payment.
ALIASES pay for lif_payment~pay.
ENDCLASS.
CLASS lcl_payment_1 IMPLEMENTATION.
METHOD pay.
    "do something with c_val i.e.
    c_val = c_val - 10.
ENDMETHOD.
ENDCLASS.
CLASS lcl_payment_2 IMPLEMENTATION.
METHOD pay.
    "do something else with c_val i.e.
    c_val = c_val + 10.
ENDMETHOD.
Main class which uses strategy pattern
CLASS lcl_main DEFINITION.
PUBLIC SECTION.
    "during main object creation you pass which payment you want to use for this object
    METHODS constructor IMPORTING ir_payment TYPE REF TO lif_payment.
    "later on you can change this dynamicaly
    METHODS set_payment IMPORTING ir_payment TYPE REF TO lif_payment.
    METHODS show_payment_val.
    METHODS pay.
PRIVATE SECTION.
    DATA payment_value TYPE p.
    "reference to your interface whcih you will be working with
    "polimorphically
    DATA mr_payment TYPE REF TO lif_payment.
ENDCLASS.
CLASS lcl_main IMPLEMENTATION.
METHOD constructor.
    IF ir_payment IS BOUND.
      me->mr_payment = ir_payment.
    ENDIF.
ENDMETHOD.
METHOD set_payment.
    IF ir_payment IS BOUND.
      me->mr_payment = ir_payment.
    ENDIF.
ENDMETHOD.
METHOD show_payment_val.
    WRITE /: 'Payment value is now ', me->payment_value.
ENDMETHOD.
"hide fact that you are using composition to access pay method
METHOD pay.
    mr_payment->pay( CHANGING c_val = payment_value ).
ENDMETHOD.                   ENDCLASS.
Client application
PARAMETERS pa_pay TYPE c. "1 - first payment, 2 - second
DATA gr_main TYPE REF TO lcl_main.
DATA gr_payment TYPE REF TO lif_payment.
START-OF-SELECTION.
"client application (which uses stategy pattern)
CASE pa_pay.
    WHEN 1.
      "create first type of payment
      CREATE OBJECT gr_payment TYPE lcl_payment_1.
    WHEN 2.
      "create second type of payment
      CREATE OBJECT gr_payment TYPE lcl_payment_2.
ENDCASE.
"pass payment type to main object
CREATE OBJECT gr_main
    EXPORTING
      ir_payment = gr_payment.
gr_main->show_payment_val( ).
"now client doesn't know which object it is working with
gr_main->pay( ).
gr_main->show_payment_val( ).
"you can also use set_payment method to set payment type dynamically
"client would see no change
if pa_pay = 1.
    "now create different payment to set it dynamically
    CREATE OBJECT gr_payment TYPE lcl_payment_2.
    gr_main->set_payment( gr_payment ).
    gr_main->pay( ).
    gr_main->show_payment_val( ).
endif.
Regads
Marcin

Singleton pattern class and static class

Hi,
what is difference between the singleton pattern class and static class ?
in singleton pattern, we declare a static member[which hold one value at a time] ,static method[ which return static member value] and a private constructor[not allow to direct instantiation]. My words are -- as a singleton pattern we implement static class .
so can we say a singleton pattern is static class it means both are same or is any difference between these two ??

malcolmmc wrote:
On several occasions I've had to convert a static (never instanceated) class to a singleton type, for example because I realise I need an instance per thread, or I decide to make a program more modular, with more than one configuration.
I've never done the opposite.
So generally I favour the singleton if there any "state" involved, because it's more flexible in unanticipated directions. It also gives extra flexibility when building tests, especially if you program to an interface.Total agreement; if anything it is dead hard to override static method logic with mock code in unit tests (I had to do it by keeping the static methods in place but making them internally use a singleton instance of itself of which the instance variable could be overwritten with a mock implementation for unit testing purposes...).
'Static classes' and/or methods are great for very simple util functions, but I wouldn't use them for anything other than that.

Does any one implemented solution for httpservlet request/response object in IWSDLInterceptor implemented class?

I am trying to handle Producer not available situation in which I am using Interceptor IWSDLInterceptor in WLP 10.3.4. I am able to retrieve exception using onWSDLException but from here if I have to forward my pageURL object I need httpservlet request and response. I tried my own filter class to have its own customize request and also tried it out all other Interceptor to see if any one can handle IOException. I did manage to throw my own Customize exception but that also did not work out as Page does not have any backing file or any supportive Controller class.
Does any one implemented solution for httpservlet request/response object in IWSDLInterceptor implemented class? or do we have any specific documentation in regards to this? As I am not able to find much martial on IWSDLInterceptor except Java API from Oracle and article defining Two way SSL handshake Producer.
Any kind of help is appreciated.
Thanks
PT

Thanks Emmanuel for your response but render behavior is not available for IWSDLRequestContext/IWDSLResponseContext object which IWSDLInterceptor uses for implementation.
Let me put my question in little simpler manner. May be my approach to the problem is not proper.
Problem : Handle Producer Not available (no application exists on server) on consumer side.
So far tried approach : Producer is not running then I am able to handle that TransportException at IInitCookieInterceptor/IHandleEventInterceptor onFault behaviour but in the case of Producer not even exists Consumer try to get WSDL fetch operation and failed with FileNotFoundException.
To handle this exception, I used IWSDLInterceptor which is available under IWSDLInterceptor.OnWSDLException (Oracle Fusion Middleware Java API for Oracle WebLogic Portal)
I am able to catch the exception but problem arise when application needs to forward at specific page/render portlet for this situation. For that it required request/response object but IWSDLInterceptor does not give any kind of instances to redirect request as there is no direct access to HTTPServlet request/response object.
I tried my custom request object to use there. I tried out custom filter object of IWSDLrequestContext. nothing works.
One approach works is to put producer WSDL file at consumer level. But in that, you need to handle different producer files for different environment. Which I don't think its a good approach.
eAny one Let me know if my approach to the problem/scenario is wrong. Or if I am missing out any other supporting interface which also required to handle this scenario. or I am using wrong interface for this scenario.
Thanks for your help in advance.
PT.

Opening files with serialized objects even if class definition has changed.

Dear all,
We are deploying an application wich saves serialized objects. But when changing something in the code and especially in the serialized classes we are not able to open files which have been saved with the old 'outfit' of the class.
I think, that this is probably a common problem and therefore I am interested whether there exists also a common or practical solution.
What is the direction I have to look in? XML, Serializable or is it something else?
Thanks for a short answer,
Axel

If you add, remove or change a classes variables, then it will be serialized differently.
Any fields which you do not need to be serialized, may be marked as transient, so you can add and remove them at will.
In the longer term, you can override the readObject() / writeObject() methods and explicitely load/save what fields you want. This will also allow you to set intelligent defaults, if for example, you added a new field, but your old serialised classes do not have this field. You can also precede all serialised data with version numbers... might help a bit.
So code ( psuedocode ) might look like this...
private void readObject(java.io.ObjectInputStream in)
     throws IOException, ClassNotFoundException;
    int ver = in.readInt();
     classfield1 = in.readLong();
    if ( ver >= 2 )
        classfield2 = in.readLong();
    if ( ver >= 3 )
         classfield3 = in.readLong();
}regards,
Owen

Is abap thread safe? Some question in Singleton pattern in ABAP

Hi Grus,
I have a very basic question but really make me headache...
Recently I am learning the design pattern in ABAP and as you know in JAVA there is a key word "Synchronized" to keep thread safe. But in ABAP, I didn't find any key words like that. So does that mean ABAP is always a single thread language? And I found that there is a way looks like "CALL FUNCTION Remotefunction STARTING NEW TASK Taskname DESTINATION dest" to make multi-thread works. As you can see it use the destination, so does that mean actually the function module is always executed in a remote system, and in every system, it is always single thread?
Could you help me on the question? Thanks a lot, grus
And here comes up to my mind another question...It's a little bit mad but I think it may works....What if I set every attribute and method as static in the singleton class...Since as you can see it is already a singleton so every attribute in it should be only one piece. So then I don't even need to implement a get_instance( ) method to return the instance. Just call "class_name=>some_method( )" directly then singleton is achieved...What do you think?
BR,
Steve

Steve,
I've the same question, few days ago I tried to use the singleton in ABAP. In Java programming is possible to use the same reference in two sessions or programs, sharing attributes, methods and all data, but I could not do in ABAP.
In my test I created a program with one global class using the singleton pattern, so I expected that when I run my program and see the reference returned after the get_instance method it should be equal to the same program run in another session, but the ABAP will create a new reference and instantiate again.
So I deduced that the only way to share it between sessions in ABAP is using the ABAP Shared Memory Objects.
I can be wrong, but I think that ABAP use a thread by user session (Each window) and we can't change it.
Best regards.

Re: Singleton Pattern

At PerSe Technologies, we have implemented the singleton pattern in our
Enterprise Component Toolkit Framework. We have what we call our "shared
data managers", which are visible to the appropriate architecture layer.
We did not implement this as a service object and do not use a Forte
"Shared" object. Instead, we use mutexes to control data locking ourselves
which allows multiple tasks to execute against the shared data manager
concurrently. This approach ensures us that we have one and only one copy
of a given object at a time. Our approach also gives another benefit in
that it caches frequently accessed data and has improved overall
performance of our applications.
Dustin Breese
[email protected]
Supervising Technical Consultant
PerSe Technologies
From: Mark Addesso <[email protected]>
Date: Mon, 2 Feb 1998 12:36:02 -0500
Subject: Implementing the Singleton pattern
Has anyone implemented the singleton pattern in Forte? A singleton is =
simply ensuring that there is one unique instance of a class. In other =
OO languages I would create a class method which would use a class =
variable to hold onto the unique instance. Since forte doesn't have =
either of these (class methods or variables), I'm not sure how to do it.=
I thought of using named objects, but it seems like a heavy =
implementation. Any ideas.

Is the danger that someone might make the Singleton
cloneable really a the most important reason to make a
Singleton non-extensible? I think not.It IS a good reason if cloning or subclassing it means
you can end up with more than one in the same JVM. If
you really implemented Singleton because "There Can
Only BE One", I'd say prohibiting subclassing and
cloning might be important.
I gotta go with the OP on this. That comment is abit queer.
I gotta go with the definition of Singleton on this
and disagree. It's not like it's that difficult.
Don't implement Cloneable or Serializable and make
the constructors private. Done. What's the
problem?
At some point it is just too much.
Are you going to implement a security manager as well? Because unless you do I can create JNI method and create a new object as well.
If they don't understand that the singleton is a singleton then are you going to assume that that is the only problem that they are having?
When I program I make assumptions about those that I work with and those that will come after me. I like to think that they have a minimal level of intelligent. They might not write the best code all the time but they do understand most of the ideas. And given that singleton the most used and probably easiest pattern to understand is it really necessary to be so protective?

StreamCorruptedException: does not contain a serialized object?

Can someone tell me why am I getting this exception:
C:\javapr>java FetchObject
Couldn't retrieve binary data: java.io.StreamCorruptedException: InputStream
does not contain a serialized object
java.io.StreamCorruptedException: InputStream does
not contain a serialized object
at java.io.ObjectInputStream.readStreamHeader
(ObjectInputStream.java:849)
at java.io.ObjectInputStream.<init>
(ObjectInputStream.java:168)
at FetchObject.main(FetchObject.java:23)
import java.sql.*;
import java.util.*;
import java.io.*;
class FetchObject implements Serializable {
    public static void main (String[] args) {
        try {
            String driver = "oracle.jdbc.driver.OracleDriver";
            Class.forName(driver);
            String url = "jdbc:oracle:thin:@mymachine:1521:homedeva";
            Connection conn = DriverManager.getConnection(url,"cnn","cnn");
            FetchObject i = new FetchObject();
                // Select related
                try
                     byte[] recdBlob = i.selectBlob( 1 , conn );
                     ByteArrayInputStream bytes = new ByteArrayInputStream(recdBlob);
                     ObjectInputStream deserialize = new ObjectInputStream( bytes );
          Employee x = (Employee)deserialize.readObject();
                catch( Exception ex )
              System.err.println("Couldn't retrieve binary data: " + ex);
              ex.printStackTrace();
     catch( Exception ex )
          ex.printStackTrace();
    public byte[] selectBlob( int id, Connection conn )
     byte[] returndata = null;
     try
          Statement stmt = conn.createStatement();
          String sql = "SELECT id, rowdata FROM blobs WHERE id = " + id;
          ResultSet rs = stmt.executeQuery(sql);
          if ( rs.next() )
                       try
                           ByteArrayOutputStream baos = new ByteArrayOutputStream(1024);
                           BufferedInputStream bis = new BufferedInputStream( rs.getBinaryStream("rowdata") );
                       byte[] bindata = new byte[4096];
                           int bytesread = 0;
                           if ( !rs.wasNull() )
                                   if ( (bytesread = bis.read(bindata,0,bindata.length)) != -1 )
                                      baos.write(bindata,0,bytesread);
                            returndata = baos.toByteArray();
                         baos.flush();
                            bis.close();
                   catch ( Exception ex )
                        System.err.println("Problem retrieving binary data: " + ex);
                    rs.close();
                     stmt.close();
           catch ( Exception ex )
                System.err.println("Couldn't retrieve binary data: " + ex);
        return returndata;
import java.io.*;
class Employee implements Serializable
     private String lastName;
     private String firstName;
     public Employee(String lastName, String firstName)
          this.lastName = lastName;
          this.firstName = firstName;
}

To clarify I have stored an Employee Object as a Blob in the Oracle database and am attempting to retreive the
Employee Object from this Blob.
Thanks

Java.io.StreamCorruptedException: InputStream does not contain a serialized object

          I have an applet which calls a JSP to write data object to the db and then the
          JSP sends back the updated data object. The writing part is ok but the response
          is giving the following error. The data object is in a separate class which implements
          Serialized.
          Here's the code in the applet calling the JSP and the response from the JSP
          URL server = null;
          String urlConnectionString = "http://localhost:7001/isLoginValid.jsp";
          try
          server = new URL(urlConnectionString);
          catch(MalformedURLException e)
          System.out.println("URL exception: " + e );
          // send request
          ObjectInputStream response = null;
          Object result = null;
          try
          URLConnection conn = server.openConnection();
          conn.setDoOutput(true);
          conn.setUseCaches(false);
          conn.setRequestProperty("Content-Type", "application/octet-stream");
          ObjectOutputStream request = new ObjectOutputStream(new
          BufferedOutputStream(conn.getOutputStream()));
          request.writeObject((Object)dvo);
          request.flush();
          request.close();
          // get the result input stream
          response = new ObjectInputStream(new BufferedInputStream
          (conn.getInputStream()));
          // read response back from the server
          result = response.readObject();
          if( result!=null && (result instanceof DataVO))
          dvo = (DataVO)result;
          String vo = dvo.printDataVO();
          System.out.println("*DataVO*\n"+vo);
          else
          System.out.println("not an instanceof DataVO");
          catch(IOException ignored)
          System.out.println("Error in DataVO response");
          ignored.printStackTrace();
          Here's the code in the JSP sending the response back to the applet. The 'dvo'
          object is the object which is serialized and has gets and sets for the diff. data
          elements. When I print the 'dvo' before writing the object to outputStream it
          prints the correct values for the data element.
          // send response
          response.setStatus(HttpServletResponse.SC_OK);
          ObjectOutputStream outputStream = new ObjectOutputStream (new BufferedOutputStream
          (response.getOutputStream()));
          outputStream.writeObject(dvo);
          outputStream.flush();
          ERROR is as follows:
          Error in DataVO response
          java.io.StreamCorruptedException: InputStream does not contain a serialized object
          at java/io/ObjectInputStream.readStreamHeader
          at java/io/ObjectInputStream.<init>
          What am I doing wrong?. Please respond soon. The applet is run on IIS and the
          JSP in on weblogic 6.1. I'm not sure if that makes any difference.


          I have an applet which calls a JSP to write data object to the db and then the
          JSP sends back the updated data object. The writing part is ok but the response
          is giving the following error. The data object is in a separate class which implements
          Serialized.
          Here's the code in the applet calling the JSP and the response from the JSP
          URL server = null;
          String urlConnectionString = "http://localhost:7001/isLoginValid.jsp";
          try
          server = new URL(urlConnectionString);
          catch(MalformedURLException e)
          System.out.println("URL exception: " + e );
          // send request
          ObjectInputStream response = null;
          Object result = null;
          try
          URLConnection conn = server.openConnection();
          conn.setDoOutput(true);
          conn.setUseCaches(false);
          conn.setRequestProperty("Content-Type", "application/octet-stream");
          ObjectOutputStream request = new ObjectOutputStream(new
          BufferedOutputStream(conn.getOutputStream()));
          request.writeObject((Object)dvo);
          request.flush();
          request.close();
          // get the result input stream
          response = new ObjectInputStream(new BufferedInputStream
          (conn.getInputStream()));
          // read response back from the server
          result = response.readObject();
          if( result!=null && (result instanceof DataVO))
          dvo = (DataVO)result;
          String vo = dvo.printDataVO();
          System.out.println("*DataVO*\n"+vo);
          else
          System.out.println("not an instanceof DataVO");
          catch(IOException ignored)
          System.out.println("Error in DataVO response");
          ignored.printStackTrace();
          Here's the code in the JSP sending the response back to the applet. The 'dvo'
          object is the object which is serialized and has gets and sets for the diff. data
          elements. When I print the 'dvo' before writing the object to outputStream it
          prints the correct values for the data element.
          // send response
          response.setStatus(HttpServletResponse.SC_OK);
          ObjectOutputStream outputStream = new ObjectOutputStream (new BufferedOutputStream
          (response.getOutputStream()));
          outputStream.writeObject(dvo);
          outputStream.flush();
          ERROR is as follows:
          Error in DataVO response
          java.io.StreamCorruptedException: InputStream does not contain a serialized object
          at java/io/ObjectInputStream.readStreamHeader
          at java/io/ObjectInputStream.<init>
          What am I doing wrong?. Please respond soon. The applet is run on IIS and the
          JSP in on weblogic 6.1. I'm not sure if that makes any difference.

How to implement Observer Pattern?

Hello guys,
I have some problems with implementing the observer pattern. So i m making an sound application and i need to put a meter changing with the volume.
I have already the meter designed and the volume is calculated.
So i have a class called Application (is the main class) and this class have the graphic designer from the application, makes the audio capture and calculate the volume.
And i have the MeterMic class and in this class i have the graphic Meter where i send this graphic meter to the application via JPanel.
In MeterMic i have the variable "value" and this variable will make the changes in the bars of the meter and i want to equal the value to the volume from the application. I try referencing by the Application object but doesnt pass the value from the volume.
So i would like to implement the Observer pattern.
I need to observ the variable volume and than the volume have changes i want to send that change to variable value in MeterMic.
My problem is: who is the observer and observ? And what i need to do to implement the pattern.
My best,
David

Kayaman wrote:
DavidHenriques wrote:
So i just need to implement the observers interfaces and than implement the method update and notify in the classes.You should probably forget the Observer/Observable classes, they're Java 1.0 stuffDo you think they are usless just because they are old?
so you don't have to or need to use them, even though the names sound appealing.I still like them because the Observable saves me from repetitively implementing (hopefully thread save) method for notifying the observers...
It's basically the same thing, you just see a lot more talk about Events/Listeners than Observers/Observables these days.The good thing on Events/Listeners is that they are type save which is an importand feature.
But I like to build them on top of Observer/Observable on the event source side.
bye
TPD

How to implement command pattern into BC4J framework?

How to implement command pattern into BC4J framework, Is BC4J just only suport AIDU(insert,update,delete,query) function? Could it support execute function like salary caculation in HR system or posting in GL(general ledger) system? May I create a java object named salaryCalc which use view objects to get the salary by employee and then write it to database?
Thanks.

BC4J makes it easy to support the command pattern, right out of the box.
You can write a custom method on your application module class, then visit the application module wizard and see the "Client Methods" tab to select which custom methods should be exposed for invocation as task-specific commands by clients.
BC4J is not only for Insert,Update,Delete style applications. It is a complete application framework that automates most of the typical things you need to do while building J2EE applications. You can have a read of my Simplifying J2EE and EJB Development Using BC4J whitepaper to read up on an overview of all the basic J2EE design patterns that the framework implements for you.
Let us know if you have more specific questions on how to put the framework into practice.

Serializing object of class implementing Singleton Pattern

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