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• Keeping a domain model consistent with actual data

  - by fstuijt

  Recently domain driven design got my attention, and while thinking about how this approach could help us I came across the following problem. In DDD the common approach is to retrieve entities (or better, aggregate roots) from a repository which acts as a in-memory collection of these entities. After these entities have been retrieved, they can be updated or deleted by the user, however after retrieval they are essentially disconnected from the data source and one must actively inform the repository to update the data source and make is consistent again with our in-memory representation. What is the DDD approach to retrieving entities that should remain connected to the data source? For example, in our situation we retrieve a series of sensors that have a specific measurement during retrieval. Over time, these measurement values may change and our business logic in the domain model should respond to these changes properly. E.g., domain events may be raised if a sensor value exceeds a predefined threshold. However, using the repository approach, these sensor values are just snapshots, and are disconnected from the data source. Does any of you have an idea on how to solve this following the DDD approach?

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• Depending on fixed version of a library and ignore its updates

  - by Moataz Elmasry

  I was talking to a technical boss yesterday. Its about a project in C++ that depends on opencv and he wanted to include a specific opencv version into the svn and keep using this version ignoring any updates which I disagreed with.We had a heated discussion about that. His arguments: Everything has to be delivered into one package and we can't ask the client to install external libraries. We depend on a fixed version so that new updates of opencv won't screw our code. We can't guarantee that within a version update, ex from 3.2.buildx to 3.2.buildy. Buildy the function signatures won't change. My arguments: True everything has to be delivered to the client as one package,but that's what build scripts are for. They download the external libraries and create a bundle. Within updates of the same version 3.2.buildx to 3.2.buildy its impossible that a signature change, unless it is a really crappy framework, which isn't the case with opencv. We deprive ourselves from new updates and features of that library. If there's a bug in the version we took, and even if there's a bug fix later, we won't be able to get that fix. Its simply ineffiecient and anti design to depend on a certain version/build of an external library as it makes our project difficult in the future to adopt to new changes. So I'd like to know what you guys think. Does it really make sense to include a specific version of external library in our svn and keep using it ignoring all updates?

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• How can we best petition to bring Adobe creative software to Ubuntu?

  - by Sixthlaw

  Now I know its not as simple as asking for Adobe to support their design software on Ubuntu, but is there a way for the community and Canonical to make known to Adobe the rapidly growing amount of Linux users, and their desire for this great set of tools OFFICIALLY? I know that many of the answers I receive might be of the fashion "Its not going to happen", "use the free tools provided" or "Who knows it might happen in the near future", but this IS not what I am looking for. I have noticed, on sites like www.OmgUbuntu.com, there are links to pages where people can "like" the idea. Is there a way to try and get the whole community on board with this one, even Canonical, and as stated above, put forward this proposal to Adobe. The current requests for an Adobe CS, for Linux, are in dribs and drabs scattered all of the internet. Now is the best time to come up with productive solutions on how we can best gather statistics on the amount of people willing to buy the Adobe CS. These are the words of an Adobe employee: "I have forwarded this feedback on to the appropriate team who will consider it for future releases of Adobe software." The larger amount of people we have unified in the ONE community proposal, the greater chance we have of getting the software. How can we make this happen?

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• Is there a common programming term for the problems of adding features to an already-featureful program?

  - by Jeremy Friesner

  I'm looking for a commonly used programming term to describe a software-engineering phenomenon, which (for lack of a better way to describe it) I'll illustrate first with a couple of examples-by-analogy: Scenario 1: We want to build/extend a subway system on the outskirts of a small town in Wyoming. There are the usual subway-problems to solve, of course (hiring the right construction company, choosing the best route, buying the subway cars), but other than that it's pretty straightforward to implement the system because there aren't a huge number of constraints to satisfy. Scenario 2: Same as above, except now we need to build/extend the subway system in downtown Los Angeles. Here we face all of the problems we did in case (1), but also additional problems -- most of the applicable space is already in use, and has a vocal constituency which will protest loudly if we inconvenience them by repurposing, redesigning, or otherwise modifying the infrastructure that they rely on. Because of this, extensions to the system happen either very slowly and expensively, or they don't happen at all. I sometimes see a similar pattern with software development -- adding a new feature to a small/simple program is straightforward, but as the program grows, adding further new features becomes more and more difficult, if only because it is difficult to integrate the new feature without adversely affecting any of the large number of existing use-cases or user-constituencies. (even with a robust, adaptable program design, you run into the problem of the user interface becoming so elaborate that the program becomes difficult to learn or use) Is there a term for this phenomenon?

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• Is wrapping a third party code the only solution to unit test its consumers? [closed]

  - by Songo

  I'm doing unit testing and in one of my classes I need to send a mail from one of the methods, so using constructor injection I inject an instance of Zend_Mail class which is in Zend framework. Now some people argue that if a library is stable enough and won't change often then there is no need to wrap it. So assuming that Zend_Mail is stable and won't change and it fits my needs entirely, then I won't need a wrapper for it. Now take a look at my class Logger that depends on Zend_Mail: class Logger{ private $mailer; function __construct(Zend_Mail $mail){ $this->mail=$mail; } function toBeTestedFunction(){ //Some code $this->mail->setTo('some value'); $this->mail->setSubject('some value'); $this->mail->setBody('some value'); $this->mail->send(); //Some } } However, Unit testing demands that I test one component at a time, so I need to mock the Zend_Mail class. In addition I'm violating the Dependency Inversion principle as my Logger class now depends on concretion not abstraction. Now is wrapping Zend_Mail the only solution or is there a better approach to this problem? The code is in PHP, but answers doesn't have to be. This is more of a design issue than a language specific feature

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• Static / Shared Helper Functions vs Built-In Methods

  - by Nathan

  This is a simple question but a design consideration that I often run across in my day to day development work. Lets say that you have a class that represents some kinds of collection. Public Class ModifiedCustomerOrders Public Property Orders as List(Of ModifiedOrders) End Class Within this class you do all kinds of important work, such as combining many different information sources and, eventually, build the Modified Customer Orders. Now, you have different processes that consume this class, each of which needs a slightly different slice of the ModifiedCustomerOrders items. To enable this, you want to add filtering functionality. How do you go about this? Do you: Add Filtering calls to the ModifiedCustomerOrders class so that you can say: MyOrdersClass.RemoveCanceledOrders() Create a Static / Shared "tooling" class that allows you to call: OrdersFilters.RemoveCanceledOrders(MyOrders) Create an extension method to accomplish the same feat as #2 but with less typing: MyOrders.RemoveCanceledOrders() Create a "Service" method that handles the getting of Orders as appropriate to the calling function, while using one of the previous approaches "under the hood". OrdersService.GetOrdersForProcessA() Others? I tend to prefer the tooling / extension method approaches as they make testing a little bit simpler. Although I dependency inject all my sourcing data into the ModifiedCustomerOrders, having it as part of the class makes it a little bit more complicated to test. Typically, I choose to use extension methods where I am doing parameterless transformations / filters. As they get more complex, I will move it into a static class instead. Thoughts on this approach? How would you approach it?

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• What are solutions and tradeoffs to maintain search result consistency in a web application

  - by iammichael

  Consider a web application with a custom search function that must display the results in a paged manner (twenty per page with up to hundreds of thousands of total results) and the ability to drill down to individual results that maintain next/previous links to navigate through the results. Re-executing the search on each page request to get the appropriate results for that page of data can be too expensive (up to 15s per search). Also, since the underlying data can change frequently (e.g. addition of new results), re-executing could cause the next/previous functionality to result in inconsistent behavior (e.g. the same results reappearing on a later page after having been viewed on an earlier page). What options exist to ensure the search results can be viewed across multiple pages in a consistent manner, and what tradeoffs does each option have in terms of network, CPU, memory, and storage requirements? EDIT: I thought caching the query search results was an obvious necessity. The question is really asking about where to cache the result set and what tradeoffs might exist to each. For example, storing the ids of the entities in the result set on the client, or storing the IDs of the entities themselves in the users session on the web server, or in a temporary table in the database. I'm not looking specifically for a single solution as different scenarios may result in different approaches (and such a question would be more suited for stackoverflow.com rather than here), but more of a design comparison between the possible approaches.

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• Should I think about switching to another platform as a .Net developer? [closed]

  - by A. Karimi

  I’ve been a developer for about 10 years and I’ve almost worked on Microsoft stack. At the last several years I’ve been introduced to some good practices such as IoC and other primary design patterns. Now I feel so much comfortable using these patterns and concepts and I’m very angry why we didn’t do that earlier! They exist and used by many developers since more than 5 years ago but why I and many of my colleagues began using them a little later. As you may know Java developers are more ahead in these fields (concepts, patterns and …) than .Net developers. Am I right? Now the question is, “Why we (as .NET developers) weren’t ahead so much? Isn’t it because we are using Microsoft stack?”. I know ALT.NET but why we are trying make a closed ecosystem open and finding alternatives for Microsoft Echo Chamber, while there are natively open ecosystems like Java!? I've always liked most of the Microsoft works very much but I’m worried about this issue. I am even ask myself should I move to another platform?

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• Correct way to inject dependencies in Business logic service?

  - by Sri Harsha Velicheti

  Currently the structure of my application is as below Web App -- WCF Service (just a facade) -- Business Logic Services -- Repository - Entity Framework Datacontext Now each of my Business logic service is dependent on more than 5 repositories ( I have interfaces defined for all the repos) and I am doing a Constructor injection right now(poor mans DI instead of using a proper IOC as it was determined that it would be a overkill for our project). Repositories have references to EF datacontexts. Now some of the methods in the Business logic service require only one of the 5 repositories, so If I need to call that method I would end up instantiating a Service which will instatiate all 5 repositories which is a waste. An example: public class SomeService : ISomeService { public(IFirstRepository repo1, ISecondRepository repo2, IThirdRepository repo3) {} // My DoSomething method depends only on repo1 and doesn't use repo2 and repo3 public DoSomething() { //uses repo1 to do some stuff, doesn't use repo2 and repo3 } public DoSomething2() { //uses repo2 and repo3 to do something, doesn't require repo1 } public DoSomething3() { //uses repo3 to do something, doesn't require repo1 and repo2 } } Now if my I have to use DoSomething method on SomeService I end up creating both IFirstRepository,ISecondRepository and IThirdRepository but using only IFirstRepository, now this is bugging me, I can seem to accept that I am un-necessarily creating repositories and not using them. Is this a correct design? Are there any better alternatives? Should I be looking at Lazy instantiation Lazy<T> ?

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• How to implement isValid correctly?

  - by Songo

  I'm trying to provide a mechanism for validating my object like this: class SomeObject { private $_inputString; private $_errors=array(); public function __construct($inputString) { $this->_inputString = $inputString; } public function getErrors() { return $this->_errors; } public function isValid() { $isValid = preg_match("/Some regular expression here/", $this->_inputString); if($isValid==0){ $this->_errors[]= 'Error was found in the input'; } return $isValid==1; } } Then when I'm testing my code I'm doing it like this: $obj = new SomeObject('an INVALID input string'); $isValid = $obj->isValid(); $errors=$obj->getErrors(); $this->assertFalse($isValid); $this->assertNotEmpty($errors); Now the test passes correctly, but I noticed a design problem here. What if the user called $obj->getErrors() before calling $obj->isValid()? The test will fail because the user has to validate the object first before checking the error resulting from validation. I think this way the user depends on a sequence of action to work properly which I think is a bad thing because it exposes the internal behaviour of the class. How do I solve this problem? Should I tell the user explicitly to validate first? Where do I mention that? Should I change the way I validate? Is there a better solution for this? UPDATE: I'm still developing the class so changes are easy and renaming functions and refactoring them is possible.

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• Need ideas on how to give my levels structure

  - by akuritsu

  I am making an iOS game for a project at school. It is going to be a tiny bit like Fruit Ninja, as in it will have different things on the screen, and when you hit them, they die, and you get points. The trouble is that unlike Fruit Ninja, my game will have different types of sprites, all doing different things (moving different places, doing different things, etc). The one thing that is bad about having all of these sprites that do different things is that it is hard for them to look neat on the screen all together. I was planning on having a couple of different gamemodes: Time Trial You have 120 seconds to kill as many sprites as possible. Survival You have three lives, every time you try to hit a sprite and miss, you lose a life. ???? Whatever I think of. I am a rookie to game design in general, and I don't know the best way to make my game look good, and play well. I could have all of these sprites on the screen at the same time, or I could have them come in waves, for example 10 of sprite_a come on, and once they are killed, 10 of sprite_b come on, etc... Please give me your opinion about which one I should code. If you have any other suggestions for either a third gamemode, or a completely different way to make the levels, feel free to tell me.

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• Motivation for service layer (instead of just copying dlls)?

  - by BornToCode

  I'm creating an application which has 2 different UIs so I'm making it with a service layer which I understood is appropriate for such case. However I found myself just creating web methods for every single method I have in the BL layer, so the services basically built from methods that looks like this: return customers_bl.Get_Customer_Prices(customer_id); I understood that a main point of the service layer is to prevent duplication of code so I asked myself - well, why not just import the BL.dll (and the DAL.dll) to the other UI, and whenever making a change re-copy the dll files, it might not be so 'neat', but is the all purpose of the service layer to prevent this? {I know something is wrong in my approach, I'm probably missing the importance of service layer, I'd like to get more motivation to create another layer, especially because as it is I found that many of my BL functions ALREADY looks like: return customers_dal.Get_Customer_Prices(cust_id) which led me to ask: was it really necessary to create the BL just because on several functions I actually have LOGIC inside the BL?} so I'm looking for more motivation to creating ONE MORE layer, I'm sure it's not just to make it more convenient that I won't have to re-copy the dlls on changes? Am I grasping it wrong? Any simple guidelines on how to design service layer (corresponding to all the BL layer functions or not? any simple example?) any enlightenment on the subject?

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• Did I Inadvertently Create a Mediator in my MVC?

  - by SoulBeaver

  I'm currently working on my first biggish project. It's a frontend facebook application that has, since last Tuesday, spanned some 6000-8000 LOC. I say this because I'm using the MVC, an architecture I have never rigidly enforced in any of my hobby projects. I read part of the PureMVC book, but I didn't quite grasp the concept of the Mediator. Since I didn't understand and didn't see the need for it, my project has yet to use a single mediator. Yesterday I went back to the design board because of some requirement changes and noticed that I could move all UI elements out of the View and into its own class. The View essentially only managed the lifetime of the UI and all events from the UI or Model. Technically, the View has now become a 'Mediator' between the Model and UI. Therefore, I realized today, I could just move all my UI stuff back into the View and create a mediator class that handles all events from the view and model. Is my understanding correct in thinking that I have devolved my View as it currently is (handling events from the Model and UI) into a Mediator and that the UI class is what should be the View?

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• Override methods should call base method?

  - by Trevor Pilley

  I'm just running NDepend against some code that I have written and one of the warnings is Overrides of Method() should call base.Method(). The places this occurs are where I have a base class which has virtual properties and methods with default behaviour but which can be overridden by a class which inherits from the base class and doesn't call the overridden method. For example, in the base class I have a property defined like this: protected virtual char CloseQuote { get { return '"'; } } And then in an inheriting class which uses a different close quote: protected override char CloseQuote { get { return ']'; } } Not all classes which inherit from the base class use different quote characters hence my initial design. The alternatives I thought of were have get/set properties in the base class with the defaults set in the constructor: protected BaseClass() { this.CloseQuote = '"'; } protected char CloseQuote { get; set; } public InheritingClass() { this.CloseQuote = ']'; } Or make the base class require the values as constructor args: protected BaseClass(char closeQuote, ...) { this.CloseQuote = '"'; } protected char CloseQuote { get; private set; } public InheritingClass() base (closeQuote: ']', ...) { } Should I use virtual in a scenario where the base implementation may be replaced instead of extended or should I opt for one of the alternatives I thought of? If so, which would be preferable and why?

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• Motivation for a service layer (instead of just copying dlls)?

  - by BornToCode

  I'm creating an application which has 2 different UIs so I'm making it with a service layer which I understood is appropriate for such scenario. However I found myself just creating web methods for every single method I have in the BL layer, so the services basically built from methods that looks like this: return customers_bl.Get_Customer_Prices(customer_id); I understood that a main point of the service layer is to prevent duplication of code so I asked myself - why not just import the BL.DLL (and the dal.dll) to the other UI, and whenever making a change re-copy the dlls, it might not be so 'neat', but still less hassle than one more layer? {I know something is wrong in my approach, I'm probably missing the importance of service layer, I'd like to get more motivation to create another layer, especially because as it is I found that many of my BL functions ALREADY looks like: return customers_dal.Get_Customer_Prices(cust_id) which led me to ask: was it really necessary to create the BL just because on several functions I actually have LOGIC inside the BL?} so I'm looking for more motivation to creating ONE MORE layer, I'm sure it's not just to make it more convenient that I won't have to re-copy the dlls on changes? Am I grasping it wrong? Any simple guidelines on how to design service layer (corresponding to all the BL layer functions or not? any simple example?) any enlightenment on the subject?

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• How to pass dynamic information between a form and a service? [closed]

  - by qminator

  I have a design problem and hopefully the braintrust which is stack exchange can help. I have a generic form, which loads a dataset and displays it. It never has direct knowledge of what it contains but can pass it to a service for manipulation (via an Onclick event for example). However, the form might need to alter its behaviour based on the manipulation by the service. Example: The service realises this dataset requires sending of an email by the user and needs to send an instruction to the form to open up a mail form. My idea is thus: I'm thinking about passing back some type of key/name dictionary, filled with commands which the service requires. They could then be interpeted by the form without it need to reference something specific. Example: IF the service decides that the dataset needs to refresh it would send back a key/name pair, I might even be able to chain commands. Refreshing the dataset and sending a mail. Refresh / "Foo" Mail / "[email protected]" The form would reference an action explicitly (Refresh or Mail) but not the instructions themselves. Is this a valid idea or am I wasting time?

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• How to avoid the GameManager god object?

  - by lorancou

  I just read an answer to a question about structuring game code. It made me wonder about the ubiquitous GameManager class, and how it often becomes an issue in a production environment. Let me describe this. First, there's prototyping. Nobody cares about writing great code, we just try to get something running to see if the gameplay adds up. Then there's a greenlight, and in an effort to clean things up, somebody writes a GameManager. Probably to hold a bunch of GameStates, maybe to store a few GameObjects, nothing big, really. A cute, little, manager. In the peaceful realm of pre-production, the game is shaping up nicely. Coders have proper nights of sleep and plenty of ideas to architecture the thing with Great Design Patterns. Then production starts and soon, of course, there is crunch time. Balanced diet is long gone, the bug tracker is cracking with issues, people are stressed and the game has to be released yesterday. At that point, usually, the GameManager is a real big mess (to stay polite). The reason for that is simple. After all, when writing a game, well... all the source code is actually here to manage the game. It's easy to just add this little extra feature or bugfix in the GameManager, where everything else is already stored anyway. When time becomes an issue, no way to write a separate class, or to split this giant manager into sub-managers. Of course this is a classical anti-pattern: the god object. It's a bad thing, a pain to merge, a pain to maintain, a pain to understand, a pain to transform. What would you suggest to prevent this from happening?

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• Which are the best ways to organize view hierarchies in GUI interfaces?

  - by none

  I'm currently trying to figure out the best techniques for organizing GUI view hierarchies, that is dividing a window into several panels which are in turn divided into other components. I've given a look to the Composite Design Pattern, but I don't know if I can find better alternatives, so I'd appreciate to know if using the Composite is a good idea, or it would be better looking for some other techniques. I'm currently developing in Java Swing, but I don't think that the framework or the language can have a great impact on this. Any help will be appreciated. ---------EDIT------------ I was currently developing a frame containing three labels, one button and a text field. At the button pressed, the content inside the text field would be searched, and the results written inside the three labels. One of my typical structure would be the following: MainWindow | Main panel | Panel with text field and labels. | Panel with search button Now, as the title explains, I was looking for a suitable way of organizing both the MainPanel and the other two panels. But here came problems, since I'm not sure whether organizing them like attributes or storing inside some data structure (i.e. LinkedList or something like this). Anyway, I don't really think that both my solution are really good, so I'm wondering if there are really better approaches for facing this kind of problems. Hope it helps

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• On Developing Web Services with Global State

  - by user74418

  I'm new to web programming. I'm more experienced and comfortable with client-side code. Recently, I've been dabbling in web programming through Python's Google App Engine. I ran into some difficulty while trying to write some simple apps for the purposes of learning, mainly involving how to maintain some kind of consistent universally-accessible state for the application. I tried to write a simple queueing management system, the kind you would expect to be used in a small clinic, or at a cafeteria. Typically, this is done with hardware. You take a number from a ticketing machine, and when your number is displayed or called you approach the counter for service. Alternatively, you could be given a small pager, which will beep or vibrate when it is your turn to receive service. The former is somewhat better in that you have an idea of how many people are still ahead of you in the queue. In this situation, the global state is the last number in queue, which needs to be updated whenever a request is made to the server. I'm not sure how to best to store and maintain this value in a GAE context. The solution I thought of was to keep the value in the Datastore, attempt to query it during a ticket request, update the value, and then re-store it with put. My problem is that I haven't figured out how to lock the resource so that other requests do not check the value while it is in the middle of being updated. I am concerned that I may end up ticket requests that have the same queue number. Also, the whole solution feels awkward to me. I was wondering if there was a more natural way to accomplish this without having to go through the Datastore. Can anyone with more experience in this domain provide some advice on how to approach the design of the above application?

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• Should sanity be a property of a programmer or a program?

  - by toplel32

  I design and implement languages, that can range from object notations to markup languages. In many cases I have considered restrictions in favor of sanity (common knowledge), like in the case of control characters in identifiers. There are two consequences to consider before doing this: It takes extra computation It narrows liberty I'm interested to learn how developers think of decisions like this. As you may know Microsoft C# is very open on the contrary. If you really want to prefix your integer as Long with 'l' instead of 'L' and so risk other developers of confusing '1' and 'l', no problem. If you want to name your variables in non-latin script so they will contrast with C#'s latin keywords, no problem. Or if you want to distribute a string over multiple lines and so break a series of indentation, no problem. It is cheap to ensure consistency with restrictions and this makes it tempting to implement. But in the case of disallowing non-latin characters (concerning the second example), it means a discredit to Unicode, because one would not take full advantage of its capacity.

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• Getting Requirements Right

  - by Tim Murphy

  Originally posted on: http://geekswithblogs.net/tmurphy/archive/2013/10/28/getting-requirements-right.aspxI had a meeting with a stakeholder who stated “I bet you wish I wasn’t in these meetings”.  She said this because she kept changing what we thought the end product should look like.  My reply was that it would be much worse if she came in at the end of the project and told us we had just built the wrong solution. You have to take the time to get the requirements right.  Be honest with all involved parties as to the amount of time it is taking to refine the requirements.  The only thing worse than wrong requirements is a surprise in budget overages.  If you give open visibility to your progress then management has the ability to shift priorities if needed. In order to capture the best requirements use different approaches to help your stakeholders to articulate their needs.  Use mock ups and matrix spread sheets to allow them to visualize and confirm that everyone has the same understanding.  The goals isn’t to record every last detail, but to have the major landmarks identified so there are fewer surprises along the way. Help the team members to understand that you all have the same goal.  You want to create the best possible solution for the given business problem.  If you do this everyone involved will do there best to outline a picture of what is to be built and you will be able to design an appropriate solution to fill those needs more easily. Technorati Tags: requirements gathering,PSC Group,PSC

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• Redesigning my website has destroyed my SEO

  - by user20721

  Unfortunately i read an article on how to avoid destroying your websites SEO from a redesign article AFTER its was too late! Here is the article (http://www.searchenginejournal.com/how-to-avoid-seo-disaster-during-a-website-redesign/42824/) On 20 November 12 completely redesigned our www.retromodern.com.au . We get ALL our customers from our website as we do not have a shop. Since that dreaded day a month ago the phone pretty much stopped, basically no emails, Google rankings down and Google analytics have halved by 50%. Yesterday i did some research into as as i had no idea that a re-design of a website could have such a damaging effect - yes i am a novice and use a WYSIWYG type web builder. There are lots of info on how to AVOID this from happening BUT what do i do as i have already made the mistake? Yesterday i reloaded my OLD site with my new pages in the background hoping this would be a start. I really have no idea of how to get out of this mess. Please please help. Thanks in Advance. Monique

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• Hide or Show singleton?

  - by Sinker

  Singleton is a common pattern implemented in both native libraries of .NET and Java. You will see it as such: C#: MyClass.Instance Java: MyClass.getInstance() The question is: when writing APIs, is it better to expose the singleton through a property or getter, or should I hide it as much as possible? Here are the alternatives for illustrative purposes: Exposed(C#): private static MyClass instance; public static MyClass Instance { get { if (instance == null) instance = new MyClass(); return instance; } } public void PerformOperation() { ... } Hidden (C#): private static MyClass instance; public static void PerformOperation() { if (instance == null) { instance = new MyClass(); } ... } EDIT: There seems to be a number of detractors of the Singleton design. Great! Please tell me why and what is the better alternative. Here is my scenario: My whole application utilises one logger (log4net/log4j). Whenever, the program has something to log, it utilises the Logger class (e.g. Logger.Instance.Warn(...) or Logger.Instance.Error(...) etc. Should I use Logger.Warn(...) or Logger.Warn(...) instead? If you have an alternative to singletons that addresses my concern, then please write an answer for it. Thank you :)

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• How should I implement Transaction database EJB 3.0

  - by JamesBoyZ

  In the CustomerTransactions entity, I have the following field to record what the customer bought: @ManyToMany private List<Item> listOfItemsBought; When I think more about this field, there's a chance it may not work because merchants are allowed to change item's information (e.g. price, discount, etc...). Hence, this field will not be able to record what the customer actually bought when the transaction occurred. At the moment, I can only think of 2 ways to make it work. I will record the transaction details into a String field. I feel that this way would be messy if I need to extract some information about the transaction later on. Whenever the merchant changes an item's information, I will not update directly to that item's fields. Instead, I will create another new item with all the new information and keep the old item untouched. I feel that this way is better because I can easily extract information about the transaction later on. However, the bad side is that my Item table may contain a lot of rows. I'd be very grateful if someone could give me an advice on how I should tackle this problem. UPDATE: I'd like to add more information about the current design. public class Customer implements Serializable { @OneToMany private List<CustomerTransactions> listOfTransactions; } public class CustomerTransactions implements Serializable { @ManyToMany private List<Item> listOfItemsBought; } public class Merchant implements Serializable { @OneToMany private List<Item> listOfSellingItems; }

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• Why using Fragments?

  - by ahmed_khan_89

  I have read the documentation and some other questions' threads about this topic and I don't really feel convinced; I don't see clearly the limits of use of this technique. Fragments are now seen as a Best Practice; every Activity should be basically a support for one or more Fragments and not call a layout directly. Fragments are created in order to: allow the Activity to use many fragments, to change between them, to reuse these units... == the Fragment is totally dependent to the Context of an activity , so if I need something generic that I can reuse and handle in many Activities, I can create my own custom layouts or Views ... I will not care about this additional Complexity Developing Layer that fragments would add. a better handling to different resolution == OK for tablets/phones in case of long process that we can show two (or more) fragments in the same Activity in Tablets, and one by one in phones. But why would I use fragments always ? handling callbacks to navigate between Fragments (i.e: if the user is Logged-in I show a fragment else I show another fragment). === Just try to see how many bugs facebook SDK Log-in have because of this, to understand that it is really (?) ... considering that an Android Application is based on Activities... Adding another life cycles in the Activity would be better to design an Application... I mean the modules, the scenarios, the data management and the connectivity would be better designed, in that way. === This is an answer of someone who's used to see the Android SDK and Android Framework with a Fragments vision. I don't think it's wrong, but I am not sure it will give good results... And it is really abstract... ==== Why would I complicate my life, coding more, in using them always? else, why is it a best practice if it's just a tool for some cases? what are these cases?

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