Implementing Observeable pattern:

Hi, i am having difficulty implementing Observeable and observer pattern. Please, can anyone help? I want to have a small program (no interface required) which will let an online user login with their account number and password. After loging in, user can register for news and if they have registered, they will get a news item displayed on their next login, only if the new news item is available. Can anyone guide me towards the solution, please!!!
I can send a class diagram if required.

Have a look at metalink note 746108.1
cheers
James

Similar Messages

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

Implementing DAO Pattern in ABAP

This discussion implement DAO pattern asked the question of how to develop a DAO pattern in ABAP but i'd like to go a little deeper.
The only answer given suggested the following design pattern:
I don't have an coded example here, but isn't it sufficient for this pattern to build an interface with some get- and set-methods? This interface can be implemented by several classes with different data retrieval logic. Then a static factory-method could do the job to decide during runtime which actual class is instantiated, returning the interface.
Can anyone give an abstract description of this implementation relative to an SAP module (How would one approach this implementation in MM, PM, FICO, HR)
Can anyone see any issues in this design?
Can anyone provide an alternate design?
Are we missing any steps?
Together we can build a solid abap DAO everyone can use.

I started to read about DAO pattern some days ago and found this great blog post:
ABAP Unit Tests without database dependency - DAO concept
I am starting to implement unit test in my developments and DAO pattern seems to be a clever choice.
Regards,
Felipe

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.

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

Implement DAO pattern

In my application I have some database tables with a persistency class. Some other objects are implemented by calling the service bus, some others are implemented by function modules.
I want that the developer doesn't need to know where the object is coming from.
Therefore I want to implement the DAO pattern (Data Access Object).
I'm new on abap objects, so can somebody give me a working example or blog, or guidelines how to code this pattern?

I don't have an coded example here, but isn't it sufficient for this pattern to build an interface with some get- and set-methods? This interface can be implemented by several classes with different data retrieval logic. Then a static factory-method could do the job to decide during runtime which actual class is instantiated, returning the interface.

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

Implement command pattern in any way or anything similar or anything at all

I have a controller class that listens to button presses from my button panel, and it also listens to mouse actions from another drawing panel.
When I press a button, it indicates some kind of drawing is going to happen in the drawing area. Only one action could be "active" at the same time. (To exemplify, put out square, put out circle, or whatever).
First I thought of using something similar to the command pattern. But when I press the button (here I wanted to create the command since then I know which one) I dont know yet which coordinates that are of interest. That would mean I would have to pass that data into the command�s execute() method, or create the command first now (right before it should execute)
Any suggestions of what could be a nice approach here are very welcome.
I know I am in that phase that I want to "patternize" a bit to much, but hey, at least you learn something and eventually you learn when not/how to use it more properly.

Maybe you could have a method that would return when the command needed to be excuted.
I dont get you fully there.
or could pass something else to the command that it could use determine when it needed to be executed?
I will however try to also send a bool which indicates whether it comes from a click or not. If that succeeds, I have managed to get all the commands to know by themselves when to do or not to do their stuff.
The only things that feels bad about that, is that only one command (for the moment at least) makes use of it. But I get rid of the bad smell ;-)
Add: Turned out that after all changes, most of the commands needed this variable too. Now everything feels good again ;)
Message was edited by:
sandsater
Message was edited by:
sandsater

Best Strategy to implement Functor pattern with Filter

Hi,
We have around 1 million Objects for e.g. Master each Master have 10 associated slaves (Collocated to Master), each slave needs some operations to be performed on it, each operation on slave modifies the state of Master, when all the slaves are operated/enriched, we need the master to raise and event and its state to be written to database and Master along with slave needs to be removed from cache.
There are 10 different operations each corresponding to a slave, we want these to be run in parallel using functor pattern, we need to filter the cache on Slave type and
run a functor for each slave type for all slaves, each execution should update slave and master. Kindly provide your feedback on the best approach for the same.
Regards
Jay
Edited by: 997509 on Apr 2, 2013 5:46 AM

>direct sun of course gets "warmer" (lower color temperature - I hate that contradiction, by the way)
Higher color temp actually...if "daylight" is D55 (5500ºK) then you'll need to increase the color temp to replicate a warmer light and add Magenta tint.
Also remember that *** the sun goes down, if goes through more air and the output decreases relative to the skylight...so at sunset the sun is warmer yet the shadows are cooler and the intensity of the skylight is greater. Which is why in addition to WB adjustment I'll often add a warm sat boost to highlights and a cool sat boost to shadows in Split Tone. But that's for effect, not to replicate an LB filter.
And yes, WB temp is relative...it's relative to the starting temp of the light. The warmer the start, the less you would need to add. The cooler the start the more you would have to add. But there's really nothing one can do about that...there's no way to have the EXACT same effect of LB filters since film had a fixed white balance and a sensor merely records what's there. Even if you slapped on an 81A over a DSLR, you could still balance it out after the fact because unlike film which is fixed, the sensor is not.

How to implement DAO pattern in CMP

How do I use the DAO pattern when going for container managed persistence, because all the database access is defined by the CMP.
How to go about it ?

Hi,
The DAO pattern http://java.sun.com/blueprints/patterns/DAO.html
is used with Bean Managed Persitence(BMP). For CMP you should not write the SQL in the EJB code, but instead let the container generate the SQL and handle all the data access.
Another pattern that might help when modelling your EJBs is the Composite Entity pattern at
http://java.sun.com/blueprints/patterns/CompositeEntity.html
Also, the new J2EE BluePrints book has some tips and strategies in the EJB tier chapter at
http://java.sun.com/blueprints/guidelines/designing_enterprise_applications_2e/index.html
hope that helps,
Sean

Ways to implement factory pattern

Hi I have following implmentation to factory
Method 1:
interface Product(){
public void method();
interface Factory(){
public Product createProduct();
class ConcreteProduct1 implements Product{
public void method(){
System.out.println("Concrete Product 1");
class ConcreteFactory1 implements Factory{
public Product createProduct(){
return new ConcreteProdct1();
}similarly ConcreteFactory 2 & 3
in mainclass we create as
Factory f = new ConcreteFactory1(); Product p = f.createProduct();Method 2:
Product creation as above and factory comes below as
public class Factory{
public Product createProduct(int type){
if(type == 1)
return new ConcreteProduct1();
else
return new ConcreteProdct2();
return null;
}main class comes as
Factory f = new Factory();
Product p = f.createProduct(1); which implementation is better and how?
Thanks,..

You should absolutely use method 1 because it is more object oriented and you don't have to keep track of a type key (if you DO should it then be implemented as an enum and not as an, ughh, int!). Actually, you may also extend the first solution with more products and concrete factories without access to the source as you just need to implement the interfaces. You don't need to edit the factory class that use type keys to track which product type to instantiate.
Well, this is at least my opinion and it is built on what I have learnt so far from reading the two good books Effective Java Programming Language Guide of Joshua Bloch and Refactoring of Martin Fowler. If you want to learn more about good use of Java and good object oriented design in practise are these books you should read.

Trying to implement the Builder pattern with inheritance

This is just a bit long, but don't worry, it's very understandable.
I'm applying the Builder pattern found in Effective Java (J. Bloch). The pattern is avaiable right here :
http://books.google.fr/books?id=ka2VUBqHiWkC&lpg=PA15&ots=yXGmIjr3M2&dq=nutritionfacts%20builder%20java&pg=PA14
My issue is due to the fact that I have to implement that pattern on an abstract class and its extensions. I have declared a Builder inside the base class, and the extensions specify their own extension of the base's Builder.
The abstract base class is roughly this :
public abstract class Effect extends Trigger implements Cloneable {
    protected Ability parent_ability;
    protected Targetable target;
    protected EffectBinder binder;
    protected Effect(){
    protected Effect(EffectBuilder parBuilder){
        parent_ability = parBuilder.parent_ability;
        target = parBuilder.target;
        binder = parBuilder.binder;
    public static class EffectBuilder {
        protected Ability parent_ability;
        protected Targetable target;
        protected EffectBinder binder;
        protected EffectBuilder() {}
        public EffectBuilder(Ability parParentAbility) {
            parent_ability = parParentAbility;
        public EffectBuilder target(Targetable parTarget)
        { target = parTarget; return this; }
        public EffectBuilder binder(EffectBinder parBinder)
        { binder = parBinder ; return this; }
    // etc.
}And the following is one of its implementation :
public class GainGoldEffect extends Effect {
    private int gold_gain;
    public GainGoldEffect(GainGoldEffectBuilder parBuilder) {
        super(parBuilder);
        gold_gain = parBuilder.gold_gain;
    public class GainGoldEffectBuilder extends EffectBuilder {
        private int gold_gain;
        public GainGoldEffectBuilder(int parGoldGain, Ability parParentAbility) {
            this.gold_gain = parGoldGain;
            super.parent_ability = parParentAbility;
        public GainGoldEffectBuilder goldGain(int parGoldGain)
        { gold_gain = parGoldGain; return this; }
        public GainGoldEffect build() {
            return new GainGoldEffect(this);
    // etc.
}Effect requires 1 parameter to be correctly instantiated (parent_ability), and 2 others that are optional (target and binder). Implementing the Builder Pattern means that I won't have to rewrite specific construcors that cover all the combination of parameters of the Effect base class, plus their own parameter as an extension. I expect the gain to be quite huge, as there will be at least a hundred of Effects in this API.
But... in the case of these 2 classes, when I'm trying to create the a GoldGainEffect like this :
new GainGoldEffect.GainGoldEffectBuilder(1 , locAbility).goldGain(5);the compiler says "GainGoldEffect is not an enclosing class". Is there something wrong with the way I'm trying to extend the base Builder ?
I need your help to understand this and find a solution.
Thank you for reading.

The GainGoldEffectBuilder class must be static.
Otherwise a Builder would require a GainGoldEffect object to exist, which is backwards.

How to implement pattern matching in RFC input paramenter?

Dear Friend.......
I have a requirment for implement a pattern match for name field of vendor in one of RFC.........
For ex..........
Name field:- A* -> give all list of name starting with a.
how can we implement this?
Any way............Suggest me
Regards
Ricky

Hi,
I am not using any ABAP program for calling this RFC,I am using Webdynpro for this one.
so how it possible to implemnet same things at there.
Regards
ricky

Interface Mappings in BPM Collect Pattern

Hello
I am new to XI development and currently facing problems while implementing collect pattern of BPM.
I am trying to map IDoc structure with target legacy format.In BPM I had a block with infinite loop where I am transforming IDocs to target legacy format.Then I am trying to transform list element (Multiline Abstract container variable) to form a single message.For this I tried to have interface map with Occurences 0..unbound..but while activation of Interface Map it gives error
<b> Mapping program Message does not match the interface mapping. The number or frequencies of source or target messages for the message mapping are not identical to the number or frequencies of source or target interfaces.</b>
If I use single line in Interface map then in BPM it gives error when passed Multiline element to this Interface map.
I checked the sample program provided by SAP but I found out that every message interface was using same Message Type which has got occurence as 1 but in the message mapping program its 0..unbound.
My question is can we have data type (or Message type )with Occurence as 1 and Message Mapping program using same message type with occurences 0..unbound..I tried to find such option but could'nt find that.Otherwise how to do Interface Map for transforming Multiline parameter of BPM to a single message.
Please help..Thanks in advance..
Regards
Rajeev Patkie

Initially I tried to perform test by tree view and it worked fine.But it was one message in the source and the same was in target.Later as given by you I updated XML source message.The source message looks like
******************Source Message***********************
<ns0:Messages xmlns:ns0="http://sap.com/xi/XI/SplitAndMerge">
<ns0:Message1>
    <ns1:MATMAS_to_Stockware_MT xmlns:ns1="http://mccormick.com/ez_dev">
      <MAT_List>
        <ZPITNO>121212</ZPITNO>
        <ZPIDS>Test Message</ZPIDS>
        <ZPPOPN />
        <ZPCNQT />
        <ZPZLOC />
        <ZPZPCB />
        <ZPZCPA />
        <ZPGRWE />
        <ZPSAEL />
        <ZSPLDY />
        <ZPFRAG />
        <ZPZCRO />
        <ZPZOPT />
      </MAT_List>
    </ns1:MATMAS_to_Stockware_MT>
</ns0:Message1>
</ns0:Messages>
<ns0:Messages xmlns:ns0="http://sap.com/xi/XI/SplitAndMerge">
<ns0:Message2>
    <ns1:MATMAS_to_Stockware_MT xmlns:ns1="http://mccormick.com/ez_dev">
      <MAT_List>
        <ZPITNO>78912</ZPITNO>
        <ZPIDS>Test Message12</ZPIDS>
        <ZPPOPN />
        <ZPCNQT />
        <ZPZLOC />
        <ZPZPCB />
        <ZPZCPA />
        <ZPGRWE />
        <ZPSAEL />
        <ZSPLDY />
        <ZPFRAG />
        <ZPZCRO />
        <ZPZOPT />
      </MAT_List>
    </ns1:MATMAS_to_Stockware_MT>
</ns0:Message2>
</ns0:Messages>
************************End Source*********************
if this would be the message multiline is generating its bound to fail as I guess every XML has one topmost element and over here.So I changed my source XML to look like
******************Start message******************
<ns0:Messages xmlns:ns0="http://sap.com/xi/XI/SplitAndMerge">
<ns0:Message1>
    <ns1:MATMAS_to_Stockware_MT xmlns:ns1="http://mccormick.com/ez_dev">
      <MAT_List>
        <ZPITNO>121212</ZPITNO>
        <ZPIDS>Test Message</ZPIDS>
        <ZPPOPN />
        <ZPCNQT />
        <ZPZLOC />
        <ZPZPCB />
        <ZPZCPA />
        <ZPGRWE />
        <ZPSAEL />
        <ZSPLDY />
        <ZPFRAG />
        <ZPZCRO />
        <ZPZOPT />
      </MAT_List>
    </ns1:MATMAS_to_Stockware_MT>
</ns0:Message1>
<ns0:Message2>
    <ns1:MATMAS_to_Stockware_MT xmlns:ns1="http://mccormick.com/ez_dev">
      <MAT_List>
        <ZPITNO>78912</ZPITNO>
        <ZPIDS>Test Message12</ZPIDS>
        <ZPPOPN />
        <ZPCNQT />
        <ZPZLOC />
        <ZPZPCB />
        <ZPZCPA />
        <ZPGRWE />
        <ZPSAEL />
        <ZSPLDY />
        <ZPFRAG />
        <ZPZCRO />
        <ZPZOPT />
      </MAT_List>
    </ns1:MATMAS_to_Stockware_MT>
</ns0:Message2>
</ns0:Messages>
**********************End Message****************
but this produces only one output message
******************Start Message***********************
<?xml version="1.0" encoding="UTF-8"?>
<ns0:Messages xmlns:ns0="http://sap.com/xi/XI/SplitAndMerge">
<ns0:Message1>
    <ns1:MATMAS_to_Stockware_List xmlns:ns1="http://mccormick.com/ez_dev">
      <MAT_List>
        <ZPITNO>121212</ZPITNO>
        <ZPIDS>Test Message</ZPIDS>
        <ZPPOPN />
        <ZPCNQT />
        <ZPZLOC />
        <ZPZPCB />
        <ZPZCPA />
        <ZPGRWE />
        <ZPSAEL />
        <ZSPLDY />
        <ZPFRAG />
        <ZPZCRO />
        <ZPZOPT />
      </MAT_List>
    </ns1:MATMAS_to_Stockware_List>
</ns0:Message1>
</ns0:Messages>
**********************End Message****************
I am also pasting schema of message mappings
*****************Source Schema************************
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema targetNamespace="http://sap.com/xi/XI/SplitAndMerge" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://sap.com/xi/XI/SplitAndMerge">
<xsd:import namespace="http://mccormick.com/ez_dev" />
<xsd:element name="Messages" xmlns:p0="http://mccormick.com/ez_dev">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:element name="Message1" form="qualified">
          <xsd:complexType>
            <xsd:sequence>
              <xsd:element ref="p0:MATMAS_to_Stockware_MT" minOccurs="0" maxOccurs="unbounded" xmlns:xsd="http://www.w3.org/2001/XMLSchema" />
            </xsd:sequence>
          </xsd:complexType>
        </xsd:element>
      </xsd:sequence>
    </xsd:complexType>
</xsd:element>
</xsd:schema>
********************End Source***********************
********************Target Schema******************
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema targetNamespace="http://sap.com/xi/XI/SplitAndMerge" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://sap.com/xi/XI/SplitAndMerge">
<xsd:import namespace="http://mccormick.com/ez_dev" />
<xsd:element name="Messages" xmlns:p0="http://mccormick.com/ez_dev">
    <xsd:complexType>
      <xsd:sequence>
        <xsd:element name="Message1" form="qualified">
          <xsd:complexType>
            <xsd:sequence>
              <xsd:element ref="p0:MATMAS_to_Stockware_List" />
            </xsd:sequence>
          </xsd:complexType>
        </xsd:element>
      </xsd:sequence>
    </xsd:complexType>
</xsd:element>
</xsd:schema>
****************************End Target*************
Thanks in advance.
Regards
Rajeev

Implementing Observeable pattern:

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