Design Patterns and J2mE

Hey,
I do wanna know if is recommendable to use a Java Design Pattern (like Singleton, Fa�ade, etc)... in a J2ME application. I mean, a colleague of mine made a j2me application using these kind of technologies, but, when he installed in his cell phone, the application occuppied much memory. So, another guy told me that due to the limited memory space we find on these devices it's better for us to use only the MVC idea. So, is it recommendable for me to use this kind of resources???
Thanks!

Hi,
it is a good programming practice to use Design patterns. But too much of design patterns results in more classes which will be a problem in j2me sometimes.
Most of the MIDP classes uses Singleton and abstract design patterns

Similar Messages

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

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.

Data Lista Handler Design Pattern and paging queries

I'm using Toplink in an MVC (Regular Beans, JSP and Struts) application. I'm not using ADF. At least not until i make up my mind on the features-portability tradeoff.
Anyway, my application will have to use queries to show the data to the user. This can easily be accomplished by putting the search parameters on my jsp and using ReadAllQuery to compose my query.
My problem is that the result can return a large amount of records and show all this records at once on the jsp might take a time the user won't be willing to wait. That's when paging the results will come handy.
In another application of mine i use paging manipulating the rownum of the query, but in that case, i had control of the whole sql statement. As this is the first time i'm working with Toplink, i'm feeling that can't be done.
There's the Data List Handler design pattern too, but that one also manipulates the sql statement.
I'm wondering now whether paging can be accomplished using Toplink..? Will i have to use ADF...? This kind of stuff.
Thanks a lot to all.
- Eduardo

Eduardo,
What you need to do is use Cursors in TopLink.Scrollable cursors enable you to scroll through a result set from the database without reading the whole result set in a single database read. The ScrollableCursor class implements the Java ListIterator interface to allow for direct and relative access within the stream. Scrollable cursors also enable you to scroll forward and backward through the stream.
Here is an example:
ReadAllQuery query = new ReadAllQuery();
query.setReferenceClass(Employee.class);
query.useScrollableCursor();
ScrollableCursor cursor = (ScrollableCursor) session.executeQuery(query);
while (cursor.hasNext()) {
System.out.println(cursor.next().toString());
cursor.close();
I hope this answers your question.
Deepak

JavaBean Models, Command Bean and J2EE Design Pattern

Hello,
I have read the available "How To", Using EJBs in Web Dynpro Applications where the author mentions that one should use a Command Bean (according to J2EE Design Patterns) so that one can invoke business methods in a Session Bean from our Web Dynpro Application. Well, although, I have read some available articles in the internet about J2EE design patterns, I still have some questions about command beans and its usage in Web Dynpro applications.
I have developed a WD App which uses EJBs to read data from the DB.
Let's suppose I only have two tables: BOOKS and AUTHORS.
Lets also suppose I have to Entity Beans (one for each table) and a Session Bean with two methods: Book[] getAllBooks() and Author[] getAllAuthors();
I also have a Command Bean which I imported in my WD App.
My questions are:
How should I design my Command Bean?
Can I have only one Command Bean with two methods each calling one of the methods of the Session Bean?
Or instead should I design two Command Beans, one for each call?
In the last case do the methods must be named <b>execute</b> or can I name them whatever I want?
Furthermore, how should I store the data in my command bean? In instance variables?
If so, can I use array of a class representing a record in the database table (for instance, classes Book and Author) or do I have to store the data in a generic collection (such as ArrayList for instance)?
I ask this last question because if I try to store the data in an array when I am importing the Command Bean as a JavaBean model I always get an error.
One last question: Can the Command Bean execute method directly return the data or should I always store the data in an instance variable an then get it using getter methods?
I know this questions are more about J2EE Design Patterns and JavaBeans specification than they are about Web Dynpro but I also have doubts about the rules that the command bean must obey in order to accomplish a successful JavaBean model import in WD.
Some guidance or tips would be highly appreciated.
King Regards

I have the same problem.
Does anyone know the solution?
Thanks
Davide

MIDlet framework's design pattern

What design pattern does the MIDlet framework work on?

That's just as silly as asking:
"What design pattern doesn J2me work on?"
A framework doesn't work on a particular design pattern. The software you write does, and surly the api of the framework will make use of several pattern.
Why not take a look at the api yourself and find out?

Design patterns concern

i am designing a graph api. i have defined interfaces for a node, arc, and graph. there are multiple interfaces defined (using inheritance) defined for each of these three interfaces.
all my implementations of these interfaces have not considered fields relevant to display on a x-y coordinate graph. now that i have coded the implementations, i am ready to display these objects.
the problem is that i have many implementations, but they now have to extend another interface for display. i find that i have to create a new class to implement the existing one and implement the new interface for each implementation.
to illustrate, i have a Node interface. there are only two methods i.e. String getId() and void setId(String id). i have two additional interfaces that extends this Node interface i.e. SimpleNode and ComplexNode (these have their own pertinent methods, not listed). I have implemented the Node interface with NodeImpl, and implemented the other 2 interfaces with SimpleNodeImpl and ComplexNodeImpl, both of which extends NodeImpl and each implementing SimpleNode and ComplexNode interfaces, respectively. at this point, i define another node interface for the purpose of drawing i.e. DrawableNode (which extends the Node interface and has getters/setters for x and y coordinate.
my problem is, how do i get SimpleNodeImpl and ComplexNodeImpl to implement the DrawableNode interface? i have considered the following approaches:
1. have SimpleNodeImpl and ComplexNodeImpl implement DrawableNode as well as what they are already implementing (i.e. SimpleNode and ComplexNode).
2. extend SimpleNodeImpl and implement DrawableNode interface i.e. DrawableSimpleNodeImpl (and likewise with ComplexNodeImpl).
3. create an implementation of DrawableNode, DrawableNodeImpl, and use composition to place type Node as a field member.
i find option #1 problematic because that means i have to define getters/setters for x and y in SimleNodeImpl and ComplexNodeImpl. this would NOT take advantage of inheritance.
i find option #2 problematic because this would mean i would have to extends all my node implementations just to have them drawable. (i actually have more than 2 extensions of nodes that i want to draw). moreover, i would also run into the problem in option #1, where i have to define getters/setters for x and y in each of these subclasses.
i am currently leaning towards option #3, but i find the relationship clumsy and even counterintuitive to myself; i plan to use the MVC design pattern, and i have calculated that this approach will result in a web of event/listener complications.
i am sure there are more options, but these are the ones that i have thought of. the goals are to keep the inheritance simple, implementations to a bare minimum, and have something that will fit nicely in with the MVC design pattern.
the general question may be: how do i design the relationships so that they will operate in the business logic layer and then be displayable on some GUI layer? is inheritance the way? or is composition the way? or is there yet another way that i have overlooked?

really long questions dont usually get answered here.

DAO pattern and Java Persistence API

Hi
This is a question for anyone who might be familiar with the standard DAO design pattern and the Java Persistence API (JPA - part of EJB3). I'm new to this technology, so apologies for any terminology aberrations.
I am developing the overall architecture for an enterprise system. I intend to use the DAO pattern as the conceptual basis for all data access - this data will reside in a number of forms (e.g. RDBMS, flat file). In the specific case of the RDBMS, I intend to use JPA. My understanding of JPA is that it does/can support the DAO concept, but I'm struggling to get my head around how the two ideas (can be made to) relate to each other.
For example, the DAO pattern is all about how business objects, data access objects, data transfer objects, data sources, etc relate to each other; JPA is all about entities and persistence units/contexts relate to each other. Further, JPA uses ORM, which is not a DAO concept.
So, to summarise - can DAO and JPA work together and if so how?
Thanks
P.S. Please let me know if you think this topic would be more visible in another forum (e.g. EJB).

Thanks, duffymo, that makes sense. However ... having read through numerous threads in which you voice your opinion of the DAO World According to Sun, I'd be interested to know your thoughts on the following ...
Basically, I'm in the process of proposing an enterprise system architecture, which will use DAO as the primary persistence abstraction, and DAO + JPA in the particular case of persistence to a RDBMS. In doing so, I'd like to illustrate the various elements of the DAO pattern, a la the standard class diagram that relates BusinessObject / DataAccessObject / DataSource / TransferObject (http://java.sun.com/blueprints/corej2eepatterns/Patterns/DataAccessObject.html). With reference to this model, I know that you have a view on the concept of TransferObject (aka ValueObject?) - how would you depict the DAO pattern in its most generic form? Or is the concept of a generic DAO pattern compromised by the specific implementation that is used (in this case JPA)?

BPM design pattern

can any provide information on BPM design pattern and give examples scenarios.
thank you

hi vicky,
check this links
Design Patterns in Exchange Infrastructure
https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/f0ad6de0-7cd6-2910-f894-dd7fe18b6fbf
BPM with Patterns explained Part-1
regards
reddy

Producer consumer design pattern

Hello,
I am trying to build a simple program that does the following:
1. when program starts, the indicator is initialized to -999
2. when Measure button is clicked, the indicator shows random number continuously.
3. when Save button is clicked, the indicator shows 1
I use the event-based producer-consumer design pattern and it works great. However, I cannot find a way to allow the CONTINUOUSLY generating of random number when Measure is clicked. Can someone shed a light on it? Thanks a lot for the help.
Attachments:
CommandList.ctl ‏6 KB
Untitled 1.vi ‏25 KB

One simple way to do it is to use the Timeout event case. You can modify the timeout value based on what events have occurred. See attached mod.
Not saying this is the best way. Kind of depends on where the program goes from here.
Attachments:
Untitled 1-2 MOD.vi ‏27 KB

What are design patterns ?

what are design patterns ?
what is the difference between design patterns and frameword ?
any help would be really appreciated !!

A quick [url http://www.google.com/search?hl=en&q=what+are+design+patterns+%3F+&btnG=Google+Search&meta=] google will bring more answers than you know what to do with.

What is a design pattern?

Howdy,
I hear a lot of talk of deasign patterns in ABAP...
My question is what on earth is a design pattern and why/how would it be useful?
Any ideas anyone

Hi Steve.
The good point to start with design patterns is to read book "Design Patterns - Elements of Reusable Object-Oriented Software" by Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides. It gives strong, consistent understanding of patterns basis with real life examples.
Short introduction extract:
"Christopher Alexander says, "Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice". Even though Alexander was talking about patterns in buildings and towns, what he says is true about object-oriented design patterns. Our solutions are expressed in terms of objects and interfaces instead of walls and doors, but at the core of both kinds of patterns is a solution to a problem in a context.
In general, a pattern has four essential elements:
The pattern name is a handle we can use to describe a design problem, its solutions, and consequences in a word or two. Naming a pattern immediately increases our design vocabulary. It lets us design at a higher level of abstraction. Having a vocabulary for patterns lets us talk about them with our colleagues, in our documentation, and even to ourselves. It makes it easier to think about designs and to communicate them and their trade-offs to others. Finding good names has been one of the hardest parts of developing our catalog.
The problem describes when to apply the pattern. It explains the problem and its context. It might describe specific design problems such as how to represent algorithms as objects. It might describe class or object structures that are symptomatic of an inflexible design. Sometimes the problem will include a list of conditions that must be met before it makes sense to apply the pattern.
The solution describes the elements that make up the design, their relationships, responsibilities, and collaborations. The solution doesn't describe a particular concrete design or implementation, because a pattern is like a template that can be applied in many different situations. Instead, the pattern provides an abstract description of a design problem and how a general arrangement of elements (classes and objects in our case) solves it.
The consequences are the results and trade-offs of applying the pattern. Though consequences are often unvoiced when we describe design decisions, they are critical for evaluating design alternatives and for understanding the costs and benefits of applying the pattern. The consequences for software often concern space and time trade-offs. They may address language and implementation issues as well. Since reuse is often a factor in object-oriented design, the consequences of a pattern include its impact on a system's flexibility, extensibility, or portability. Listing these consequences explicitly helps you understand and evaluate them."
Regards,
Maxim.

Design Patterns: Do you have a good STRATEGY?

1. Context: Create a XML file. And since there
are many ways: DOM, WAY1, OTHERWAYS, ETC...
2. Question: As a Design Patterns application purpose,
can we use the Strategy Pattern? Is it appropriate one?
If not, what are the alternatives?
CLIENT
--CREATEXML (CONTEXT)
----CREATEXMLSTRATEGY (STRATEGY)
------CREATEXMLSTRATEGY_DOM (CONCRETE STRATEGY)
------CREATEXMLSTRATEGY_WAY1 (CONCRETE STRATEGY)
------CREATEXMLSTRATEGY_OTHERWAYS (CONCRETE STRATEGY)

Hi Paul,
I have myself recently started doing the Design Patterns and believe me after understanding the Patterns OOD have become more clear. >>1. Context: Create a XML file. And since there are many ways: DOM, >>WAY1, OTHERWAYS, ETC...
My understanding regarding the Strategy and Tempelate method Pattern has become stronger after reading the "Thinking in Patterns in Java" , the author is mentioning there these Behavioural Patterns are used for Framework development , infact there he has used example of Framework development.
Now regarding your question it seems to me that your entire applicaiotn can use the Creational Pattern , like Abstract Factory.You can use the DOM,WAY1,OTHERWAYS as the concrete Prodcuts and all will be extracted from the Factory XMLGeneratorFactory.
Strategy Pattern is changing the algorthims at the run time , the temlate can work for your applicaiton but then what you are trying to achieve.Currently this much I can say ..
Let us see for more opinions
Regards
Vicky

"State" Design Pattern Issues

I am implementing a class that requires state information. I decided to follow the design pattern, and I found a great site for reference (which provided the code below) but I need to implement substates. It would be impractical to store all of the states in the fashion below. I am trying to find a way to somehow store another substate in the class below without creating so many classes. I am thinking about creating the substates the classic way with just constants, but I cant store the current substate in the static final States. In short, either using the code below or not, how do I implement a system with states and substates following the State Design Pattern?
abstract class State {
    static State initialState;
    static final State state1 = new State1();
    static final State state2 = new State2();
    protected State() {
      if (initialState == null) initialState = this;
    abstract void stateExit(StateOwner owner);
    abstract void stateEnter(StateOwner owner);
class State1 extends State {
    void stateExit(StateOwner owner) {
    void stateEnter(StateOwner owner) {
class State2 extends State {
    void stateExit(StateOwner owner) {
    void stateEnter(StateOwner owner) {
}

This isn't exactly an implementation of the state pattern.
I suggest that you check out the GOF book for details but here are some suggestions:
1) Your abstract State should not contain State objects but should provide the interface for your State behavior.
2) Each substate that you describe is actually an individual State and should be a concrete implementation of the State class or interface.
3) There are several ways to handle state transitions but one that I like is to have the concrete States know about when to make state transitions and provide a call back mechanism to the context that has the handle to the state to allow the state to set the new state in the context when a state transition occurs.
For example
abstract class State
    abstract void stateExit(StateOwner owner);
    abstract void stateEnter(StateOwner owner);
class State1 extends State {
    void stateExit(StateOwner owner) {
        owner.setState(new State2().stateEnter(owner));
    void stateEnter(StateOwner owner) {
class State2 extends State {
   void stateExit(StateOwner owner) {
    void stateEnter(StateOwner owner) {
public class StateOwner
    State s;
    public StateOwner()
        s = new State1(this);
        s.stateEnter(this);
    public void setState(State s)
        this.s = s;
}This is how I've implemented it and in general how it is done in GOF.
Hope this helps.
Charles

Suggestions regarding corej2ee design patterns

hi all
i wanted to go through the core j2ee design pattern but i don't know which one to refer and what to
so i need suggestions that what to read in a design pattern
and which is the best book or pdf if possible send me the link too

Core J2EE patterns are not what they were. A lot of them would be considered anti-patterns, work arounds for deficiencies in the EJB 1.0 and 2.0 specs that have been addressed in EJB 3.0.
The "Core J2EE Patterns" (Amazon.com search will find it) sounds like what you want.
%

Design Patterns and J2mE

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