Basic design patterns

I have learnt basic design patterns, such as
Singelton, Objects pool, Reflection, Delegation and
so on. I would like to build some application, using
these patterns for exercise. Can you please give me
an idea for such application ? Thanks.Here are some simple examples that I found helpful. You can ignore the AspectJ parts.
http://www.cs.ubc.ca/~jan/AODPs/
regards

Similar Messages

How to study design pattern?

I have learn java for nearly a year and want to know more about design pattern.Fundemanetal instances of basic design pattern are appriciated.Thanks for your answer.

The most famous book on patterns is :
Design Patterns: Elements of Reusable Object-Oriented Software. Gamma et. al.
You should start there if you are interested in the subject.
There are tons of books since then on the subject. There is a list at
http://hillside.net/patterns/books/

What is the best design pattern for this problem?

No code to go with the question. I am trying to settle on the best design pattern for the problem before I code. I want to use an Object Oriented approach.
I have included a basic UML diagram of what I was thinking so far.
Stated simply, I have three devices; Module, Wired Modem, and Wireless Modem.
In the Device Under Test parent class, I have put the attributes that are variable from device to device, but common to all of them.
In the child classes, I have put the attributes that are not variable to each copy of that device. The attributes are common across device types. I was planning to use controls in the class definition that have the data set to a default value, since it doesn't change for each serial number of that device. For example, a Module will always have a Device Type ID of 1. These values are used to query the database.
An example query would be [DHR].[GetDeviceActiveVersions] '39288', 1, '4/26/2012 12:18:52 PM'
The '1' is the device type ID, the 39288 is the serial number, and the return would be "A000" or "S002", for example.
So, I would be pulling the Serial Number and Device Type ID from the Device Under Test parent and child, and passing them to the Database using a SQL string stored in the control of the Active Versions child class of Database.
The overall idea is that the same data is used to send multiple queries to the database and receiving back various data that I then evaluate for pass of fail, and for date order.
What I can't settle on is the approach. Should it be a Strategy pattern, A Chain of Command pattern, a Decorator pattern or something else.
Ideas?

elrathia wrote:
Hi Ben,
I haven't much idea of how override works and when you would use it and why. I'm the newest of the new here.
Good. At least you will not be smaking with a OPPer dOOPer hammer if I make some gramatical mistake.
You may want to look at this thread in the BreakPoint where i trie to help Cory get a handle on Dynamic Dispatching with an example of two classes that inherit from a common parent and invoke Over-ride VIs to do the same thing but with wildly varying results.
The example uses a Class of "Numeric" and a sibling class "Text" and the both implement an Add method.
It is dirt simple and Cory did a decent job of explaining it.
It just be the motivation you are looking for.
have fun!
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Choice of design pattern for data acquisition system

Hello all
I have a trouble about selecting the suitable design pattern / architecture for a data acquisition system.
Here is the details of the desired system:
There is data acquisition hardware and I need to use it by observing parameters on User interface.
the data acquisiton period, channel list to scan should be chosen on User interface. Besides, there are many user interface interactions. e.g. if user selects a channel to add scanlist, then I need to enable and make visible some other parts on user interface.
When user completes the channel selection, then he will press the button to start data acquisition. Then I also need to show the scanned values on a graph in real time and log them in txt file.
I know that I cannot use producer consumer pattern here. because the data acquisition loop should wait for parameters to scan channels. and it works in a given period by user. so the user interface loop performs higher rate then consumer loop (data acquisition loop). it means queue will be bigger bigger. if I use notifier it will loss some data come from user interface.
is there any idea about that ? is there any suitable design pattern for this case ?
Thanks in advance
best regards
Veli BAYAR
Embedded Systems Software and Hardware Engineer
"You live in a graphical world. Why not program in one?"
Solved!
Go to Solution.

johnsold wrote:
Veli,
I recommend the Producer/Consumer model with some modifications.
You might need three loops. I cannot tell for sure from your brief description.
The User Interface loop responds to the user inputs for configuration and start/stop of acquisition. The parameters and commands are passed to the Data Acquisition loop via a queue. In this loop is a state machine which has Idle, Configuration, Acquisition, and Shutdown states (and perhaps others). The data is sent to the Processing loop via a different queue. The Processing loop performs any data processing, displays the data to the user, and saves it to file. A notifier can be used to send the Stop or shutdown command from the User Interface loop to the other loops. If the amount of processing is minimal and the file write times are not too long, the Processing loop functions might be able to occur in the Timeout case of the UI loop Event structure. This simplifies things somewhat but is not as flexible when changes need to be made.
I am not sure that a Design Pattern for this exact setup exists but it is basically a combination of the Producer/Consumer (Events) and Producer/Consumer (Data) Design Patterns.
Lynn
Check out this thread: http://forums.ni.com/t5/LabVIEW/Multiple-poll-case-structures-to-event-help/td-p/2551309
There are discussions there about a 3-loop architecture that may help you.
Jeff
Jeffrey Zola

Design pattern / data loading solution

Hello all!
I have been working on a few projects which involve loading data, sometimes remotely, sometimes local, sometimes JSON, sometimes XML. The problem I am having is that due to the speed of development and the changing minds of various clients I am finding my designs are too rigid and I would like them to be more flexable. I have been trying to think of a reusable solution to data loading, and would like some advice as I imagine many of you out there have had the same problem.
What I would like to do is to create a generic LoadingOperation abstract class, which has member variables of type Parser and Loader, which have parse() and loadData() methods respectivly. The Parser and Loader classed are interfaces and classes that implement these could be XMLParser and JSONParser, LocalLoader and RemoteLoader etc. With something like this i would like to have a new class which extends LoadingOperation for each thing to be loaded, weather thats a local XML file, or remote JSON, or whatever.
The problem is is that specific Parser implementation cannot return custom data types without breaking the polymorphic behavior of the LoadingOperation class. I have been messing around with generics and declaring subclasses of LoadingOperation like
class SpecificLoader extends LoadingOperation<CustomDataType>
and doing similar things with Parser classes, but this seems a bit weird.
Does anyone have any suggestions on what im doing wrong / could be doing better. I want to be able to react quickly to changing specifications (ignoring the fact that they shouldnt be changing that much!) and have a logical seperation of code etc...
thanks for any help!
psi have also asked this question here [http://stackoverflow.com/questions/4329087/design-pattern-data-loading-solution]

rackham wrote:
Hello all!
I have been working on a few projects which involve loading data, sometimes remotely, sometimes local, sometimes JSON, sometimes XML. The problem I am having is that due to the speed of development and the changing minds of various clients I am finding my designs are too rigid and I would like them to be more flexable. I have been trying to think of a reusable solution to data loading, and would like some advice as I imagine many of you out there have had the same problem.
What I would like to do is to create a generic LoadingOperation abstract class, which has member variables of type Parser and Loader, which have parse() and loadData() methods respectivly. The Parser and Loader classed are interfaces and classes that implement these could be XMLParser and JSONParser, LocalLoader and RemoteLoader etc. With something like this i would like to have a new class which extends LoadingOperation for each thing to be loaded, weather thats a local XML file, or remote JSON, or whatever.
The problem is is that specific Parser implementation cannot return custom data types without breaking the polymorphic behavior of the LoadingOperation class. I have been messing around with generics and declaring subclasses of LoadingOperation like
class SpecificLoader extends LoadingOperation<CustomDataType>
and doing similar things with Parser classes, but this seems a bit weird.
Does anyone have any suggestions on what im doing wrong / could be doing better. I want to be able to react quickly to changing specifications (ignoring the fact that they shouldnt be changing that much!) and have a logical seperation of code etc...That depends on the specifics.
The fact that it seems like processes are similar doesn't mean that they are in fact the same. My code editor and Word both seem to be basically the same but I am rather sure that generalizing between the two would be a big mistake.
And I speak from experience (parsing customer data and attempting to generalize the process.)
The problem with attempting to generalize is if you generalize functionality that is not in fact the same. And then you end up with conditional logic all over the place to deal with differences dependent on the users. Rather than saving time that actually costs time because the code becomes more fragile.
Doesn't mean it isn't possible but just rather that you should insure that it is in fact common behavior before implementing anything.

Design Pattern / Best Practice Question

Hi,
I have been using Flex for a while now, but there is a
scenario which I still have not found a solution I'm entirely happy
with. I'm wondering if anyone else out there might have suggestions
on a design pattern or best practice.
Suppose I have a view which depends on model data which
resides in some back end systems. That model data may or may not
have been loaded (e.g. via a web service or remote object call) at
the time the view is displayed.
I don't know if the user will ever visit this part of the
application so I would prefer to defer retrieval of the data until
the user actually navigates to this view. Or I want to retrieve the
data each time the view is displayed because the data is dynamic
and could change between one presentation of the view and the next.
Because the data comes from several systems, I cannot simply
make one service call and display the view when it completes and
all the data is available. I need to call several services which
could complete in any order but I only want to display my view
after I know all of them have completed and all of the model data
is available. Otherwise, I can present the user an incomplete view
(e.g. some combo boxes are empty until the corresponding service
call to get the data completes).
The solution I like best so far is to dispatch a single event
(I am using Cairngorm) handled by a single command which acts as
the caller and responder for all of the services. This command then
remembers which responses it has received and dispatches another
event to navigate to the view once all the results have returned.
If the services being called are used in different
combinations on different screens, this results in proliferation of
events and commands. An event and command for each service and
additional events and commands to bundle the services and the
handling of their responses in the right combinations for each of
the views.
Another approach is to have some helper class listen for all
of the model changes and only display the view when the model
enters some state that is acceptable. It is sometimes difficult to
determine just by looking at the model whether it is in the right
state (e.g. how can I tell that a collection is the new collection
that should just have been requested versus an old one lingering
from a previous call). The logic required can get kind of
convoluted and brittle.
Basically, all of the solutions I've come up with so far seem
less than ideal and a little hackish. I keep thinking there is some
elegant solution out there that I am just missing ... but so far,
no luck finding it. Thoughts?
Thanks.
Bill

i think a service class is right - to coordinate your calls.
i would have 1 event per call (so you could listen to individual
responses if you wanted to).
then i would use a flag. if you want to check for staleness,
you would probably want two objects to map your service flag to
lastRequested and lastCompleted. when you check, check if it's
completed, and if it's not stale and that your lastRequested is
less than lastCompleted (meaning that you're not currently waiting,
i.e. you've returned since making a request). then make the request
and update your lastRequested.
here's a snippet of what i mean.
./paul
public static const SVC1_LOADED:int = 1;
public static const SVC2_LOADED:int = 2;
public static const SVC3_LOADED:int = 4;
public static const SVCALL_LOADED:int = 7;
private var completedFlag:int = 0;
then each call would have it's own callback.
private function onSvc1Complete( evt:Event):void {
completedFlag |= SVC1_LOADED;
lastCompleted[ SVC1_LOADED ] = getTimer();
dispatchEvent( new Event("svc1complete") );
checkDone();
private function checkDone():void{
if( completedFlag == SVCALL_LOADED )
dispatchEvent(new Event( "allLoaded" ));

Best architecture and design pattern to use

I am currently designing a moderately sized LabView application and cannot decide on the best architecture/design pattern or combinations thereof to implement.
The program basically polls an instrument connected to a serial port continuously at a 2-10Hz rate. When operator clicks a button to start a run, the polled data is then filtered, has math functions performed on the data, writes collected data to files, and produces reltime graphs and calculates point-by-point statistics. At the completion of a run, some additional data files are written. I pretty much know how to accomplish all these tasks.
What is also required is main-vi front panel interaction by the operator to access a database (via a C# dll with .Net) to query for specifications to apply in order to determine pass/fail status. Setup conditions also need to be changed from time to time by the operator and applied to the data in real time (ie- a measurement offset). I have prototyped the database portion successfully thus far.
For the main vi, I started off using the Top Level Application Using Events design pattern (Event structure within a while loop). Copious use of bundled clusters and shift registers keep the database data updated. I cannot figure out how to have the top level vi concurrently poll the serial device as outlined above. The Event structure is only active when defined control values change, and use of a timeout is no help since it prevent data from being collected while the user is accessing the database. All database and setup parameters must be applied to the data as it comes in from the serial port. Error trapping/recovery is a must.
I believe what I need is two parallel processes running under my main vi (one for database and setup, the other for polling and data processing/display, but what would be the preferred choice here?
Revert back to a polled loop in lieu of Events, use notifiers, occurrences, user-defined events, Producer-consumer loops?
It�s been about 3 years since I have had an application on this level (which used a state machine architecture), and a lot has changed in LabView (using 7.1 Prof Devel). I am currently having a mental block while trying to digest a lot of features I have never used before.
Suggestions Welcome!
Thanks.
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

I suggest a (3) state machine(s) architecture. The first is the user interface. Your main VI is a good start. Another state machine handles the instrument I/O (your serial polling). The third handles all data processing. The three loops run independently. Each has a wait to allow LV's scheduler to share CPU time among the loops. I like queues or functional globals for inter-loop communications.
This allows a lot of flexibility. Each portion can be tested alone. Each can have different timing and priority.
Spend some time thinking about what needs to be done and plan the structure carefully before you do any coding (except for little test programs to try new ideas).
I also like Conway and Watts "A Software Engineering Approach to LabVIEW", published
by Prentice Hall.
Lynn

Design Pattern and ABAP Objects

Hello Friends,
I would like to know, if ABAP Objects can be used to do pattern oriented programming ?
For example GANG of four has provided almost more then 30 design pattern ( MVC, singelton, Obserable, FACADE,,,etc) can we implement patterns using ABAP ??
Many thanks
Haider Syed

Hi,
Take a look at the following site:
http://patternshare.org/
It has all the basic patterns from the GOF and a lot more. I can recommend the ones from Martin Fowler but be sure you start with the ones from the GOF.
All patterns are described by using UML so it's very easy to translate them into ABAP OO code.
Regarding your other question. For the observer pattern I used an interface which the SAP had already created if_cm_observer and created my own abstract observable class. The observable class is nearly a 100% copy of the java.util. one
regards
Thomas

Design Patterns w/o EJB

Greetings, I am attempting to build a JSF application while learning JSR 127 and a few of the J2EE design patterns. The problem that I am having is that I don't plan on using EJB/Spring with my project and many of the tutorials I have been able to find place a focus on the EJB/Spring implementation details which are both overkill for this project. That said, I want to learn the appropriate patterns to build a functional application without catching "pattern fever".
I have a general idea of some of the patterns I need to use to get from the presentation tier to the data tier, such as Business Delegate and Data Transfer Object. However, I'm not sure I understand how to use these in conjunction with the managed beans facility. Do the managed beans contain (as in composition) the Business Delegate objects? Or do I use a DTO to push the data from the managed bean to the Delegate? How much if any logic do I put in the managed beans if I'm using them in this fashion (or are they basically just fields and getter/setters)?
All comments or suggestions are sincerely appreciated,
Jon

Hi,
Have you taken a look at Java BluePrints Solutions Catalog:
https://blueprints.dev.java.net/bpcatalog/
The Solutions Catalog focuses on different topics specifically so that you can pick and choose which articles are most interesting to you.
-Larry

Design patterns for Dynamic Class Loading

Hi,
I have to develop a program for uni that dynamically loads classes based on names in a text file. All the classes subclass an abstract class with a constructor that takes one argument. This means I can't use the Class.forName(className).newInstance() method of class loading. I have researched some design patterns I could use and have come up with the following 3:
Factory pattern; "Robocode" pattern (not it's real name, but Robocode uses it); and, the "one I made up myself" pattern.
The robocode pattern instantiates a class using the default no-argument constructor then immediately sets all properties that shoud have been provided in the constructor:
Object o = Class.forName(myClass).newInstance();
o.setProperty(property);Personally I think this is ugly and a cheap fix instead of doing it properly.
My own pattern finds the constructor that takes the arguments I need then calls it to create the object:
Class c = Class.forName(myClass);
Constructor cons = c.getConstructor(new Class[]{Class.forName("java.lang.String")});
Object o = cons.newInstance(new Object[]{"hello"});What's the best to use? Are there any other patterns I should consider?

My own pattern finds the constructor that takes the
arguments I need then calls it to create the object:
Class c = Class.forName(myClass);
Constructor cons = c.getConstructor(new
Class[]{Class.forName("java.lang.String")});
Object o = cons.newInstance(new Object[]{"hello"});
I have followed this basic 'pattern' several times though I would use
Constructor cons = c.getConstructor(new Class[]{String.class});
It works great.

Which Design Pattern and how to design using OOP this scenario

I am having trouble designing a module, can anybody help me?
Because it will be hard to maintain this kind of module, I also think that this can test my skill of design pattern usage.
Requirement
This is basically an agricultural project (web application). I need to design a module where some calculation takes place.
There are different crops involved like maize, tomato, okra etc. Each of these crops has different traits.
Each trait has a measurement scale which lies in integer like 200-1000. Now let's say I have planted the crop and done measurement noted down the traits. Now I want to do some sort of measurement. Some measurements are simple and some are complex.
Example
Lets take an example of crop maize. I have recorded observations for 15 traits. (We'll use trait1-trait15 as examples, the actual name can be like plt_ht, yld, etc.)
I recorded 5 observations for each trait:
trait1 trait2 trait3 trait5 trait6..... trait15
01,02,03,04 01,02,03,04 01,02,03,04
User logs into system and selects his crops and enters data for these observations. I have to calculate either average or sum of the data entered for each trait.
Complexity / centre of the problem
So far it's simple but complexity comes when I have some different formulas for some of the traits.
Example: trait YLD has a formula based on which I have to calculate its value, which may also depend on some other traits. Each different crop can have different traits.
All this I am able to do - whenever user selects crop I will check for those specific traits and do calculations (if it's not a special trait then I either average or sum it, based on db entry), but there is a lot of hard coding.
I would like to have suggestions on a better way of handling this.
My code needs to handle both simple and complex calculations.
Simple calculations are easy, I have take average of value entered for trait.
The problem comes when I have to do complex calculations, since each crop have different traits with their own formulas, so to calculate I have to check for crop and then for complex trait. So I have to hardcode the trait name of complex traits.
Can any tell me how I can design this using Java oops [?!?] so that I can make it generic?
I have about 10 different crops. Some calculations are specific to crops, so there will be lot of code like the if below:
hasZeroValue = (HashMap<String, ArrayList<String>>) dataValues[1];
} else if(cropId.equalsIgnoreCase("MZ") && traitName.equalsIgnoreCase("Shelling")) {
    avg=HybridTestDataUtility.calculateAvg(traitName, dataPoint, dataTraits, traitValues,dataPvalues, dataPoint, type);
    avg=avg*dataPoint;
    traitAvg=getMaizeYeild(traitName, traitAvg, population, avg, hybrid, area);
} else if(cropId.equalsIgnoreCase("OK") && traitName.equalsIgnoreCase("YLDGM")) {
    avg=HybridTestDataUtility.calculateAvg(traitName, dataPoint, dataTraits, traitValues,dataPvalues, dataPoint, type);
    //avg=avg*dataPoint;
    Object[] dataValues=getOKRAYield(traitName, traitAvg, population, avg, dividend,hasZeroValue,hybrid,repl);
    traitAvg = (HashMap<String, Float>) dataValues[0];
    hasZeroValue = (HashMap<String, ArrayList<String>>) dataValues[1];
} else if(cropId.equalsIgnoreCase("HP") && traitName.equalsIgnoreCase("w1-w10")) {
    avg=HybridTestDataUtility.calculateAvg(traitName, dataPts, dataTraits, traitValues,dataPvalues, dataPoint, type);
    avg=avg*dataPoint;
    Object[] dataValues=getHotPepperYield(traitName, traitAvg, population, avg,dividend,hasZeroValue,hybrid,repl);
    traitAvg = (HashMap<String, Float>) dataValues[0];
    hasZeroValue = (HashMap<String, ArrayList<String>>) dataValues[1];
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("TLSSG_70")) {
    traitAvg=calculateTLCV(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues,50);
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("TLSSG_100")) {
    traitAvg=calculateTLCV(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues,50);
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("YVMV_60")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("YVMV_90")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("YVMV_120")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("ELCV_60")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("ELCV_90")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("TO") && traitName.equalsIgnoreCase("ELCV_120")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("OK") && traitName.equalsIgnoreCase("YVMV_60")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("OK") && traitName.equalsIgnoreCase("YVMV_90")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg,dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("OK") && traitName.equalsIgnoreCase("YVMV_120")) {
    traitAvg=tomatoYVMVCalculation(traitName, traitAvg, dataPoint, dataTraits, hybrid, repl, traitValues, dataPvalues);
} else if(cropId.equalsIgnoreCase("OK") && traitName.equalsIgnoreCase("ELCV_60")) {Can anybody think of a way to make a generic approach to this?

There are crops and each crop have traits , traits are actually a mesuremet
scale to decide growth of a seed of a particular crop.
This module is to for planters to observe growth of seeds sowed of certain
crops and take down n no of observation for each trait and upload in csv format.Once they enter
data i have to either avg out the values or sum the values or sometimes
there are more complex function that i have to apply it may differe for each
trait .This is the whole module about.Just to give an idea about how they
will enter data
Hyubrid(seed) trait1 trait2 trait3 trait5 trait6..... trait15
Hybrid1 01 02 03 04 01
HYbrid2 04 06 08 04 01
HYbrid2 04 06 08 04 01
HYbrid2 04 06 08 04 01
HYbrid2 04 06 08 04 01
Once they enter data in this format i have to give result something like
this.
Here avg colum does not necessaryly mean avg it can be sum or any formula
based resutl.Hybrid is the seed for which they record the observation.
I have shown avg column only for two tratis it is actually for all the
traits.
Hyubrid(seed) trait1 Avg trait2 avg trait3 trait5 trait6..... trait15
Hybrid1 01 01 02 04 03 04 01
HYbrid2 04 04 06 10 08 04 01
HYbrid2 04 04 06 12 08 04 01
HYbrid2 04 04 06 14 08 04 01
HYbrid2 04 04 06 12 08 04 01
Hope this clarifies atleat a but
The data are not correctly indented but there is no way i can format it.

Regarding which design pattern to use for this scenario???

hi guys
I am working on a J2EE application where I need to do translations for 3 different scenarios. It is basically a conversion from service order objects to invoices.
First from a service order object to an invoice.
Second a conversion from a transaction table.
Third a conversion from a remote system.
Finally the product is an invoice..
What design pattern can i use ....is strategy pattern a good idea??
Thanks
J

Hi,
I think your problem is in result state. You can you sequencial block but for approve or reject you need to set target for each result state. Here I am providing a link. I think you will get your solution here please go through it.
http://help.sap.com/saphelp_nw2004s/helpdata/en/44/429bbd709914bce10000000a155369/frameset.htm
if you have any query please let me know.
Thanks
Chandan

Abstract Factory Design Pattern

Could someone please explain the abstract factory design pattern in simple english. As far as I understand it is used to create a bunch of related objects based on parameter/s provided at runtime.
However, why would one use this compared to an Interface.
I actually am reading a great book on design patterns (Design Pattern by James Cooper) but having a bit of problem really understanding this one.
Cheers

As far as I
understand it is used to create a bunch of related
objects based on parameter/s provided at runtime. There may be variations but as I understand it basically an Abstract Factory defines two interfaces, one is the factory and one is the product. A good example is iterators in Java. The iterator factory is the Iterable interface and the iterator product is the Iterator interface.
ArrayList implements Iterable so it's an iterator factory. If you call the iterator() method of an ArrayList object you'll get an Iterator object. The same applies to TreeSet and many other classes.
The Iterator objects sport the same Interface but they're quite different internally of course (Iterating an array is not the same as iterating a tree) so they're a "family of related products".

Design pattern -- using the correct one...?

I'm in need of some advice regarding design patterns in general.
I have a prototype whereby Objects B, C and D observe Object A's attribute (let's call it theAttribute -- imaginative, eh? )
In my system, every time theAttribute is changed, I've implemented the Gang's Observer pattern so that the observer objects are notified (...and do something with the information that Object A has changed in some way... they basically update a theTimestamp attribute when the subject's updated... but that really is beside the point right now).
However, only ONE observer will ever be created for each observable subject.
To my dismay, I've just been reading on the IBM Research site that the memory implications of this are horrendous (that for potentially a great many subjects only having a few observers each is bad practice) -- d'oh.
I've looked at other ways I could achieve what I need to without the above practice, but the only things I can come up with are the Mediator pattern or the State pattern, neither of which I'm sure are ideal (the former because of I'm worried that it'd be total overkill, the latter because I don't really need dynamic reclassification if the truth's told, I think).
Anyone got any thoughts on this? (I've considered referencing observers with their observables using a hash table but don't really wish to go down that route unless absolutely neccesary... it seems a bit like putting electrical tape over a sparking wire :) I'd rather just do it properly).
Sarah.

However, only ONE observer will ever be created for each observable subject.If you can absolutely, positively, definitely, mathematically, logically, legally
and morally prove that fact, indeed, you're wasting some resources here,
a couple of hundred bytes mayhap ...
In the mean time, keep your Observer/Observable pattern/implementation
or have a look at the PropertyChangeSupport class ...
kind regards,
Jos

DAO Design pattern

Hi,
what is the advantages of DAO Design pattern over other design patterns?
Can anybody tel me

valooCK wrote:
NANDA wrote:
Hi,
what is the advantages of DAO Design pattern over other design patterns?
Can anybody tel methe answer is none!
DAO stands for data access object, it is a non oo pattern, oo is data centric, it makes sense for data to access data. it is something created by poor procedural minds who can never understand what oo is.
you may occasionary use it as a collection of functionalities or utilities, but thou shalt never use in as a pattern in oop!There are as-yet undiscovered tribes living in the Amazon, who knew you were going to say that
@OP: Please ignore this troll, he doesn't even understand the very basics of OO, as can be demonstrated in the following thread
http://forum.java.sun.com/thread.jspa?threadID=5273397&tstart=0
Just ignore him. He only wants attention. He hasn't got the faintest idea how to write even "Hello World", let alone actually do any OO design

Basic design patterns

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