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• Design Patterns: What is a type

  - by contactmatt

  A very basic question, but after reading the "Design Patterns: Elements of reusable OO Software" book, I'm a little confused. The book states, "An object's type only refers to its interface-the set of request to which it can respond. An object can have many types, and objects of different classes can have the same type." Could someone please better explain what a Type is? I also don't understand how one object can have multiple types...unless the book is speaking of polymorphism....

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• Useful design patterns for working with FragmentManager on Android

  - by antman8969

  When working with fragments, I have been using a class composed of static methods that define actions on fragments. For any given project, I might have a class called FragmentActions, which contains methods similar to the following: public static void showDeviceFragment(FragmentManager man){ String tag = AllDevicesFragment.getFragmentTag(); AllDevicesFragment fragment = (AllDevicesFragment)man.findFragmentByTag(tag); if(fragment == null){ fragment = new AllDevicesFragment(); } FragmentTransaction t = man.beginTransaction(); t.add(R.id.main_frame, fragment, tag); t.commit(); } I'll usually have one method per application screen. I do something like this when I work with small local databases (usually SQLite) so I applied it to fragments, which seem to have a similar workflow; I'm not married to it though. How have you organized your applications to interface with the Fragments API, and what (if any) design patterns do you think apply do this?

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• Useful design patterns for working with FragmentManger on Android

  - by antman8969

  When working with fragments, I have been using a class composed of static methods that define actions on fragments. For any given project, I might have a class called FragmentActions, which contains methods similar to the following: public static void showDeviceFragment(FragmentManager man){ String tag = AllDevicesFragment.getFragmentTag(); AllDevicesFragment fragment = (AllDevicesFragment)man.findFragmentByTag(tag); if(fragment == null){ fragment = new AllDevicesFragment(); } FragmentTransaction t = man.beginTransaction(); t.add(R.id.main_frame, fragment, tag); t.commit(); } I'll usually have one method per application screen. I do something like this when I work with small local databases (usually SQLite) so I applied it to fragments, which seem to have a similar workflow; I'm not married to it though. How have you organized your applications to interface with the Fragments API, and what (if any) design patterns do you think apply do this?

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• Choosing the right Design Pattern

  - by Carl Sagan

  I've always recognized the importance of utilizing design patterns. I'm curious as to how other developers go about choosing the most appropriate one. Do you use a series of characteristics (like a flowchart) to help you decide? For example: If objects are related, but we do not want to specify concrete class, consider Abstract When instantiation is left to derived classes, consider Factory Need to access elements of an aggregate object sequentially, try Iterator or something similar?

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• Help me to find a better approach-Design Pattern

  - by DJay

  I am working on an ASP.Net web application in which several WCF services are being used. At client level, I am creating channel factory mechanism to invoke service operations. Right now, I have created an assembly having classes used for channel factory creation code for every service. As per my assumption this is some sort of facade pattern. Please help me to find a better approach or any design pattern, which I can use here.

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• What's the difference between these design pattern books? [on hold]

  - by BSara

  I'm currently looking for a good reference/guide for design patterns and in my search I've found the following three books highly recommended: Design Patterns: Elements of Reusable Object-Oriented Software Pattern Hatching: Design Patterns Applied Design Patterns Explained: A New Perspective on Object-Oriented Design I can't decide which book (if any) to purchase. So, my question is this: What are the fundamental differences between these books?

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• Class library modification / migration

  - by Clint

  I have 3 class libraries. A BBL, a DAL, and a DATA (about 15 datasets). Currently 4 [major] applications utilize the functionality in these DLL's. I'm rewriting one of those applications and I need to (1) Use some of the existing functionality in the libraries (2) Change some of it (3) Add new functionality (4) Add new datasets. I'm back and forth about the best way to do this, while keeping my risks at a minimum. Some thoughts.. 1) Use the existing projects and don't make any modifications, only additions 2) Make new libraries, bring over the code I can use, and make additions as needed 3) Implement partial classes in the existing projects Eventually all 4 applications will use the newest functionality, but it will be a slow migration; so the old code can't be depricated yet. Any thoughts?

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• designing solution to dynamically load class

  - by dot

  Background Information I have a web app that allows end users to connect to ssh-enabled devices and manipulate them. Right now, i only support one version of firmware. The logic is something like this: user clicks on a button to run some command on device. web application looks up the class name containing the correct ssh interface for the device, using the device's model name. (because the number of hardware models is so small, i have a list that's hardcoded in my web app) web app creates a new ssh object using the class loaded in step 2. ssh command is run and session closed. command results displayed on web page. This all works fine. Now the end user wants me to be able to support multiple versions of firmware. But the catch is, they don't want to have to document the firmware version anywhere becuase the amount of overhead this will create in maintaining the system database. In other words, I can't look up the firmware version based on the device. The good news is that it sounds like at most, I'll have to support two different versions of firmware per device. One option is to name the the classes like this: deviceX.1.php deviceX.2.php deviceY.1.php deviceY.2.php where "X" and "Y" represent the model names, and 1 and 2 represent the firmware versions. When a user runs a command, I will first try it with one of the class files, if it fails, i can try with the second. I think always try the newer version of firmware first... so let's say in the above example, I would load deviceX.2.php before deviceX.1.php. This will work, but it's not very efficient. But I can't think of another way around this. Any suggestions?

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• @Override causes issues with class hierarchy involving interface, abstract class and concrete class

  - by Nayn

  Hi, My classes are as follows public interface A { public void doSomething(); } public abstract class B implements A { public void doOneMoreThing() { // Do one more thing } } public class C extends B { @Overrides <---- Causes error public void doSomething() { // Do something } } Could somebody tell me, why this @Overrides annotation is causing error? Thanks Nayn

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• C# Design How to Elegantly wrap a DAL class

  - by guazz

  I have an application which uses MyGeneration's dOODads ORM to generate it's Data Access Layer. dOODad works by generating a persistance class for each table in the database. It works like so: // Load and Save Employees emps = new Employees(); if(emps.LoadByPrimaryKey(42)) { emps.LastName = "Just Got Married"; emps.Save(); } // Add a new record Employees emps = new Employees(); emps.AddNew(); emps.FirstName = "Mr."; emps.LastName = "dOOdad"; emps.Save(); // After save the identity column is already here for me. int i = emps.EmployeeID; // Dynamic Query - All Employees with 'A' in thier last name Employees emps = new Employees(); emps.Where.LastName.Value = "%A%"; emps.Where.LastName.Operator = WhereParameter.Operand.Like; emps.Query.Load(); For the above example(i.e. Employees DAL object) I would like to know what is the best method/technique to abstract some of the implementation details on my classes. I don't believe that an Employee class should have Employees(the DAL) specifics in its methods - or perhaps this is acceptable? Is it possible to implement some form of repository pattern? Bear in mind that this is a high volume, perfomacne critical application. Thanks, j

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• Design Pattern for building a Budget

  - by Scott

  So I've looked at the Builder Pattern, Abstract Interfaces, other design patterns, etc. - and I think I'm over thinking the simplicity behind what I'm trying to do, so I'm asking you guys for some help with either recommending a design pattern I should use, or an architecture style I'm not familiar with that fits my task. So I have one model that represents a Budget in my code. At a high level, it looks like this: public class Budget { public int Id { get; set; } public List<MonthlySummary> Months { get; set; } public float SavingsPriority { get; set; } public float DebtPriority { get; set; } public List<Savings> SavingsCollection { get; set; } public UserProjectionParameters UserProjectionParameters { get; set; } public List<Debt> DebtCollection { get; set; } public string Name { get; set; } public List<Expense> Expenses { get; set; } public List<Income> IncomeCollection { get; set; } public bool AutoSave { get; set; } public decimal AutoSaveAmount { get; set; } public FundType AutoSaveType { get; set; } public decimal TotalExcess { get; set; } public decimal AccountMinimum { get; set; } } To go into more detail about some of the properties here shouldn't be necessary, but if you have any questions about those I will fill more out for you guys. Now, I'm trying to create code that builds one of these things based on a set of BudgetBuildParameters that the user will create and supply. There are going to be multiple types of these parameters. For example, on the sites homepage, there will be an example section where you can quickly see what your numbers look like, so they would be a much simpler set of SampleBudgetBuildParameters then say after a user registers and wants to create a fully filled out Budget using much more information in the DebtBudgetBuildParameters. Now a lot of these builds are going to be using similar code for certain tasks, but might want to also check the status of a users DebtCollection when formulating a monthly spending report, where as a Budget that only focuses on savings might not want to. I'd like to reduce code duplication (obviously) as much as possible, but in my head, every way I can think to do this would require using a base BudgetBuilderFactory to return the correct builder to the caller, and then creating say a SimpleBudgetBuilder that inherits from a BudgetBuilder, and put all duplicate code in the BudgetBuilder, and let the SimpleBudgetBuilder handle it's own cases. Problem is, a lot of the unique cases are unique to 2/4 builders, so there will be duplicate code somewhere in there obviously if I did that. Can anyone think of a better way to either explain a solution to this that may or may not be similar to mine, or a completely different pattern or way of thinking here? I really appreciate it.

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• ASIHTTPRequest code design

  - by nico

  I'm using ASIHTTPRequest to communicate with the server asynchronously. It works great, but I'm doing requests in different controllers and now duplicated methods are in all those controllers. What is the best way to abstract that code (requests) in a single class, so I can easily re-use the code, so I can keep the controllers more simple. I can put it in a singleton (or in the app delegate), but I don't think that's a good approach. Or maybe make my own protocol for it with delegate callback. Any advice on a good design approach would be helpful. Thanks.

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• UI Design Help / Advice

  - by Greg Andora

  Hey everyone, I have a dillema where our client relations department has been brought in for advice on UI and I vehemently disagree with it...even though I don't consider myself a designer at all. While I have been vocal about my disagreement about it, I've been asked to point to design standards to prove that what I'm saying is correct and that the guys in Client Relations are flat out wrong. A mockup is below, I'm trying to argue that the icons of the airplane, boat, and couch (ya, I didn't choose those either) belong in the header of the page (same area as the logo) and not in the content area of the page. Can anybody please help me by pointing me to something that helps prove my point? Thanks a lot, Greg Andora

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• Database design suggestions for a configurable product eshop

  - by solomongaby

  Hello, I am biulding an e-shop that will have configurable products. The configurable parts will need to have different prices and stocks from the main product. What database design would be best in this case? I started with something like this. Features id name Features Options id id_feature value Products id name price Products Features id id_product id_feature value ( save the value from the feature-options for ease in search ) configurable (yes, no) The problem is that now I am stuck on how to save the configurable product features. I was thinking of saving their value as a json. But that will make saving price modification for a certain option difficult. How would you go about this ? Thank you.

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• Best approach to design a service oriented system

  - by Gustavo Paulillo

  Thinking about service orientation, our team are involved on new application designs. We consist in a group of 4 developers and a manager (that knows something about programming and distributed systems). Each one, having own opinion on service design. It consists in a distributed system: a user interface (web app) accessing the services in a dedicated server (inside the firewall), to obtain the business logic operations. So we got 2 main approachs that I list above : Modular services Having many modules, each one consisting of a service (WCF). Example: namespaces SystemX.DebtService, SystemX.CreditService, SystemX.SimulatorService Unique service All the business logic is centralized in a unique service. Example: SystemX.OperationService. The web app calls the same service for all operations. In your opinion, whats the best? Or having another approach is better for this scenario?

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• Java Program Design Layout Recommendations?

  - by Leebuntu

  I've learned enough to begin writing programs from scratch, but I'm running into the problem of not knowing how to design the layout and implementation of a program. To be more precise, I'm having difficulty finding a good way to come up with an action plan before I dive in to the programming part. I really want to know what classes, methods, and objects I would need beforehand instead of just adding them along the way. My intuition is leading me to using some kind of charting software that gives a hierarchal view of all the classes and methods. I've been using OmniGraffle Pro and while it does seem to work somewhat, I'm still having trouble planning out the program in its entirety. How should I approach this problem? What softwares out there are available to help with this problem? Any good reads out there on this issue? Thanks so much! Edit: Oh yeah, I'm using Eclipse and I code mainly in Java right now.

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• Windows Services -- High availability scenarios and design approach

  - by Vadi

  Let's say I have a standalone windows service running in a windows server machine. How to make sure it is highly available? 1). What are all the design level guidelines that you can propose? 2). How to make it highly available like primary/secondary, eg., the clustering solutions currently available in the market 3). How to deal with cross-cutting concerns in case any fail-over scenarios If any other you can think of please add it here .. Note: The question is only related to windows and windows services, please try to obey this rule :)

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• How to find rows between other rows w/ID then add class

  - by Ravex

  Hi guys. i'm stuck with my table. need create toggle rows function. but i no idea how to find sub rows in table. Some one can help me? I have table with many rows 500 All Rows have class="row-1,row-2.....row-600 etc" And all main rows also have class="parent" between each "parent" rows i have 6 rows So i need for toggle/collapse purposes find all (sub)rows betwen parent rows. and add class with id like in prevous parent row. For example: parent have class="row-1 parent" all sub must have - class="child-row-1" default table <table id="table"> <tr class="row-1 odd parent"> <th class="column-1">st. 3 - 5</th> <th class="column-2">Profile</th> <th class="column-3">Purpose</th> </tr> <tr class="row-2 even"> <td class="column-1">Metal Stamp</td> <td class="column-2">Width</td> <td class="column-3">Price</td> </tr> <tr class="row-3 odd"> <td class="column-1">Circle 3 - 5</td> <td class="column-2">28-110</td> <td class="column-3">21500</td> </tr> <tr class="row-4 even"> <td class="column-1">Circle 3 - 5</td> <td class="column-2">115-180</td> <td class="column-3">20700</td> </tr> <tr class="row-5 odd"> <td class="column-1">Cube 3 - 5</td> <td class="column-2">63-80</td> <td class="column-3">21500</td> </tr> <tr class="row-6 even"> <td class="column-1">Cube 3 - 5</td> <td class="column-2">100-220</td> <td class="column-3">20700</td> </tr> <tr class="row-7 odd"> <td class="column-1">Line 3 - 5</td> <td class="column-2">10-50 ? 40-200</td> <td class="column-3">27000</td> </tr> </table> in the end it should look like this: <table id="table"> <tr class="row-1 odd parent"> <th class="column-1">st. 3 - 5</th> <th class="column-2">Profile</th> <th class="column-3">Purpose</th> </tr> <tr class="row-2 even child-row-1"> <td class="column-1">Metal Stamp</td> <td class="column-2">Width</td> <td class="column-3">Price</td> </tr> <tr class="row-3 odd child-row-1"> <td class="column-1">Circle 3 - 5</td> <td class="column-2">28-110</td> <td class="column-3">21500</td> </tr> <tr class="row-4 even child-row-1"> <td class="column-1">Circle 3 - 5</td> <td class="column-2">115-180</td> <td class="column-3">20700</td> </tr> <tr class="row-5 odd child-row-1"> <td class="column-1">Cube 3 - 5</td> <td class="column-2">63-80</td> <td class="column-3">21500</td> </tr> <tr class="row-6 even child-row-1"> <td class="column-1">Cube 3 - 5</td> <td class="column-2">100-220</td> <td class="column-3">20700</td> </tr> <tr class="row-7 odd child-row-1"> <td class="column-1">Line 3 - 5</td> <td class="column-2">10-50 ? 40-200</td> <td class="column-3">27000</td> </tr> </table>

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• design patterns for hierarchical structures

  - by JLBarros

  Anyone knows some design patterns for hierarchical structures? For example, to manage inventory categories, accounting chart of accounts, divisions of human resources, etc.. Thank you very much in advance EDIT: Thanks for your interest. I am looking for a better way of dealing with hierarchical items to which they should apply operations depending on the level of hierarchy. I have been studying the patterns by Martin Fowler, for example Accounting, but I wonder if there are other more generic. The problem is that operations apply to the items must be possible to change even at run time and may depend on other external variables. I thought of a kind of strategy pattern but would like to combine it with the fact that it is a hierarchical scheme. I would appreciate any reference to hierarchical patterns and you'll take care of them in depth.

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• Object model design choice

  - by spinon

  I am currently working on a ASP.NET MVC reporting application using C#. This is a redesign from a PHP application that was just initially thrown together and is now starting to gain some more traction. SowWe are in the process of reworking the backend to have a more OO approach. One of the descisions I am currently wrestling with is how to structure the domain objects. Since 95% of the site is readonly I am not sure if the typical approaches are practical. Should I create domain objects for the primary pieces of the application (ticket, assignment, assignee) and then create static methods off of these areas to pull the reporting data? Or should I just skip that part and create the chart data classes and have some get method off of these classes? It's not a real big application and currenlty I am the only one developing on it. But I feel torn as to which approach. I feel that the first one is the better choice but maybe overkill given that the majority of uses is for aggregate reporting. Anybody have some good insight on why I should go one way or another?

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• What are the differences between struct and class in C++

  - by palm3D

  This question was already asked in the context of C#/.Net. Now I'd like to learn the differences between a struct and a class in (unmanaged) C++. Please discuss the technical differences as well as reasons for choosing one or the other in OO design. I'll start with an obvious difference: If you don't specify public: or private:, members of a struct are public by default; members of a class are private by default. I'm sure there are other differences to be found in the obscure corners of the C++ specification.

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• Need advice on framework design: how to make extending easy

  - by beginner_

  I'm creating a framework/library for a rather specific use-case (data type). It uses diverse spring components, including spring-data. The library has a set of entity classes properly set up and according service and dao layers. The main work or main benefit of the framework lies in the dao and service layer. Developers using the framework should be able to extend my entity classes to add additional fields they require. Therefore I made dao and service layer generic so it can be used by such extended entity classes. I now face an issue in the IO part of the framework. It must be able to import the according "special data type" into the database. In this part I need to create a new entity instance and hence need the actual class used. My current solution is to configure in spring a bean of the actual class used. The problem with this is that an application using the framework could only use 1 implementation of the entity (the original one from me or exactly 1 subclass but not 2 different classes of the same hierarchy. I'm looking for suggestions / desgins for solving this issue. Any ideas?

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• Android From Local DB (DAO) to Server sync (JSON) - Design issue

  - by Taiko

  I sync data between my local DB and a Server. I'm looking for the cleanest way to modelise all of this. I have a com.something.db package That contains a Data Helper and couple of DAO classes that represents objects stored in the db (I didn't write that part) com.something.db --public DataHelper --public Employee @DatabaseField e.g. "name" will be an actual column name in the DB -name @DatabaseField -salary etc... (all in all 50 fields) I have a com.something.sync package That contains all the implementation detail on how to send data to the server. It boils down to a ConnectionManager that is fed by different classes that implements a 'Request' interface com.something.sync --public interface ConnectionManager --package ConnectionManagerImpl --public interface Request --package LoginRequest --package GetEmployeesRequest My issue is, at some point in the sync process, I have to JSONise and de-JSONise my data (E.g. the Employee class). But I really don't feel like having the same Employee class be responsible for both his JSONisation and his actual representation inside the local database. It really doesn't feel right, because I carefully decoupled the rest, I am only stuck on this JSON thing. What should I do ? Should I write 3 Employee classes ? EmployeeDB @DatabaseField e.g. "name" will be an actual column name in the DB -name @DatabaseField -salary -etc... 50 fields EmployeeInterface -getName -getSalary -etc... 50 fields EmployeeJSON -JSON_KEY_NAME = "name" The JSON key happens to be the same as the table name, but it isn't requirement -name -JSON_KEY_SALARY = "salary" -salary -etc... 50 fields It feels like a lot of duplicates. Is there a common pattern I can use there ?

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• Best design for a "Command Executer" class

  - by Justin984

  Sorry for the vague title, I couldn't think of a way to condense the question. I am building an application that will run as a background service and intermittently collect data about the system its running on. A second Android controller application will query the system over tcp/ip for statistics about the system. Currently, the background service has a tcp listener class that reads/writes bytes from a socket. When data is received, it raises an event to notify the service. The service takes the bytes, feeds them into a command parser to figure out what is being requested, and then passes the parsed command to a command executer class. When the service receives a "query statistics" command, it should return statistics over the tcp/ip connection. Currently, all of these classes are fully decoupled from each other. But in order for the command executer to return statistics, it will obviously need access to the socket somehow. For reasons I can't completely articulate, it feels wrong for the command executer to have a direct reference to the socket. I'm looking for strategies and/or design patterns I can use to return data over the socket while keeping the classes decoupled, if this is possible. Hopefully this makes sense, please let me know if I can include any info that would make the question easier to understand.

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• General ORM design question

  - by Calvin

  Suppose you have 2 classes, Person and Rabbit. A person can do a number of things to a rabbit, s/he can either feed it, buy it and become its owner, or give it away. A rabbit can have none or at most 1 owner at a time. And if it is not fed for a while, it may die. Class Person { Void Feed(Rabbit r); Void Buy(Rabbit r); Void Giveaway(Person p, Rabbit r); Rabbit[] rabbits; } Class Rabbit { Bool IsAlive(); Person pwner; } There are a couple of observations from the domain model: Person and Rabbit can have references to each other Any actions on 1 object can also change the state of the other object Even if no explicit actions are invoked, there can still be a change of state in the objects (e.g. Rabbit can be starved to death, and that causes it to be removed from the Person.rabbits array) As DDD is concerned, I think the correct approach is to synchronize all calls that may change the states in the domain model. For instance, if a Person buys a Rabbit, s/he would need to acquire a lock in Person to make a change to the rabbits array AND also another lock in Rabbit to change its owner before releasing the first one. This would prevent a race condition where 2 Persons claim to be the owner of the little Rabbit. The other approach is to let the database to handle all these synchronizations. Who makes the first call wins, but then the DB needs to have some kind of business logics to figure out if it is a valid transaction (e.g. if a Rabbit already has an owner, it cannot change its owner unless the Person gives it away). There are both pros/cons in either approach, and I’d expect the “best” solution would be somewhere in-between. How would you do it in real life? What’s your take and experience? Also, is it a valid concern that there can be another race condition the domain model has committed its change but before it is fully committed in the database? And for the 3rd observation (i.e. state change due to time factor). How will you do it?

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