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  • Optimal communication pattern to update subscribers

    - by hpc
    What is the optimal way to update the subscriber's local model on changes C on a central model M? ( M + C - M_c) The update can be done by the following methods: Publish the updated model M_c to all subscribers. Drawback: if the model is big in contrast to the change it results in much more data to be communicated. Publish change C to all subscribes. The subscribers will then update their local model in the same way as the server does. Drawback: The client needs to know the business logic to update the model in the same way as the server. It must be assured that the subscribed model stays equal to the central model. Calculate the delta (or patch) of the change (M_c - M = D_c) and transfer the delta. Drawback: This requires that calculating and applying the delta (M + D_c = M_c) is an cheap/easy operation. If a client newly subscribes it must be initialized. This involves sending the current model M. So method 1 is always required. Think of playing chess as a concrete example: Subscribers send moves and want to see the latest chess board state. The server checks validity of the move and applies it to the chess board. The server can then send the updated chessboard (method 1) or just send the move (method 2) or send the delta (method 3): remove piece on field D4, put tower on field D8.

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  • Help identify the pattern for reacting on updates

    - by Mike
    There's an entity that gets updated from external sources. Update events are at random intervals. And the entity has to be processed once updated. Multiple updates may be multiplexed. In other words there's a need for the most current state of entity to be processed. There's a point of no-return during processing where the current state (and the state is consistent i.e. no partial update is made) of entity is saved somewhere else and processing goes on independently of any arriving updates. Every consequent set of updates has to trigger processing i.e. system should not forget about updates. And for each entity there should be no more than one running processing (before the point of no-return) i.e. the entity state should not be processed more than once. So what I'm looking for is a pattern to cancel current processing before the point of no return or abandon processing results if an update arrives. The main challenge is to minimize race conditions and maintain integrity. The entity sits mainly in database with some files on disk. And the system is in .NET with web-services and message queues. What comes to my mind is a database queue-like table. An arriving update inserts row in that table and the processing is launched. The processing gathers necessary data before the point of no-return and once it reaches this barrier it looks into the queue table and checks whether there're more recent updates for the entity. If there are new updates the processing simply shuts down and its data is discarded. Otherwise the processing data is persisted and it goes beyond the point of no-return. Though it looks like a solution to me it is not quite elegant and I believe this scenario may be supported by some sort of middleware. If I would use message queues for this then there's a need to access the queue API in the point of no-return to check for the existence of new messages. And this approach also lacks elegance. Is there a name for this pattern and an existing solution?

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  • Javascript: Avoid this and new - further reading? [closed]

    - by Thomas Deutsch
    I do not want this to end in a sort of religious discussion, i want to collect some sources for further reading on this topic. As shown here: Node.js Style and Structure Point 1: Avoid this and new you can find a good example when it could be better to use closures instead of a prototype, and to make every argument explicit. Ok, i agree - could be nice, but i need to know more. Can anyone recommend a good link? Would this make my code 100% object-pattern-free ? (no factory-, repository-, module- pattern?)

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  • Is implementing an interface defined in a subpackage an anti-pattern?

    - by Michael Kjörling
    Let's say I have the following: package me.my.pkg; public interface Something { /* ... couple of methods go here ... */ } and: package me.my; import me.my.pkg.Something; public class SomeClass implements Something { /* ... implementation of Something goes here ... */ /* ... some more method implementations go here too ... */ } That is, the class implementing an interface lives closer to the package hierarchy root than does the interface it implements but they both belong in the same package hierarchy. The reason for this in the particular case I have in mind is that there is a previously-existing package that groups functionality which the Something interface logically belongs to, and the logical (as in both "the one you'd expect" and "the one where it needs to go given the current architecture") implementation class exists previously and lives one level "up" from the logical placement of the interface. The implementing class does not logically belong anywhere under me.my.pkg. In my particular case, the class in question implements several interfaces, but that feels like it doesn't make any (or at least no significant) difference here. I can't decide if this is an acceptable pattern or not. Is it or is it not, and why?

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  • Is the Entity Component System architecture object oriented by definition?

    - by tieTYT
    Is the Entity Component System architecture object oriented, by definition? It seems more procedural or functional to me. My opinion is that it doesn't prevent you from implementing it in an OO language, but it would not be idiomatic to do so in a staunchly OO way. It seems like ECS separates data (E & C) from behavior (S). As evidence: The idea is to have no game methods embedded in the entity. And: The component consists of a minimal set of data needed for a specific purpose Systems are single purpose functions that take a set of entities which have a specific component I think this is not object oriented because a big part of being object oriented is combining your data and behavior together. As evidence: In contrast, the object-oriented approach encourages the programmer to place data where it is not directly accessible by the rest of the program. Instead, the data is accessed by calling specially written functions, commonly called methods, which are bundled in with the data. ECS, on the other hand, seems to be all about separating your data from your behavior.

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  • Object Design catalog and resources

    - by Tauren
    I'm looking for web sites, books, or other resources that provide a catalog of object designs used in common scenarios. I'm not looking for generic design patterns, but for samples of actual object designs that were used to solve real problems. For instance, I'm about to build an internal messaging system for a web application, similar to Facebook's messaging system. This system will allow administrators to send messages to all members, to selected groups of members, or to individuals. Members can send messages to other members or groups of members. Fairly common stuff and a feature that I'm sure thousands of web applications require. I know each situation is different and there are a million ways to design this solution. Although this scenario isn't really all that complex, I'm sure the basic design of the necessary objects and relationships for a system like this has already been done many times. It would be nice to review other similar designs before building my own. Is there a place where people can share their designs and others can browse/search through the catalog to review and provide feedback on them? StackOverflow could be used to a degree for this, but doesn't really provide a catalog of designs. Any other resources that would relate?

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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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  • 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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  • design an extendible and pluggable business logic flow handler in php

    - by Broncha
    I am working on a project where I need to allow a pluggable way to inject business processes in the normal data flow. eg There is an ordering system. The standard flow of the application is A consumer orders an item. Pays for it and card is authorized. Admin captures the payment. Order is marked as complete and item is shipped. But this process may vary (extra steps in between) for different clients. Say a client would need to validate the location of the consumer before he is presented with a credit card form, OR his policies might require some other processes in between. I am thinking of using State Pattern for processing orders, saving the current state of the order in database, and initializing the state of order from the saved state. I would also need some mechanism, where a small plugin would be able to inject business specific states in the state machine. Am I thinking the right way? Are there already implemented patterns for this kind of situation? I am working with Codeigniter and basically this would mean for me, to redirect to proper controller according to the current state of the order. Like, if the state of the order is unconfirmed then redirect the user to details page and then change the state to pending. If some client would need to do some validation, then register an intermediate state between unconfirmed and pending Please suggest.

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  • Design Pattern for Social Game Mission Mechanics

    - by Furkan ÇALISKAN
    When we want to design a mission sub-system like in the The Ville or Sims Social, what kind of design pattern / idea would fit the best? There may be relation between missions (first do this then this etc...) or not. What do you think sims social or the ville or any other social games is using for this? I'm looking for a best-practise method to contruct a mission framework for tha game. How the well-known game firms do this stuff for their large scale social facebook games? Giving missions to the players and wait players to complete them. when they finished the missions, providing a method to catch this mission complete events considering large user database by not using server-side not so much to prevent high-traffic / resource consumption. how should i design the database and server-client communication to achive this design condidering this trade-off.

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  • New book in the style of Advanced Programming Language Design by R. A. Finkel [closed]

    - by mfellner
    I am currently researching visual programming language design for a university paper and came across Advanced Programming Language Design by Raphael A. Finkel from 1996. Other, older discussions in the same vein on Stackoverflow have mentioned Language Implementation Patterns by Terence Parr and Programming Language Pragmatics* by Michael L. Scott. I was wondering if there is even more (and especially up-to-date) literature on the general topic of programming language design. *) http://www.cs.rochester.edu/~scott/pragmatics/

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  • Does TDD lead to the good design?

    - by Eugen Martynov
    I'm in transition from "writing unit tests" state to TDD. I saw as Johannes Brodwall creates quite acceptable design from avoiding any of architecture phase before. I'll ask him soon if it was real improvisation or he had some thoughts upfront. I also clearly understand that everyone has experience that prevents to write explicit design bad patterns. But after participating in code retreat I hardly believe that writing test first could save us from mistakes. But I also believe that tests after code will lead to mistakes much faster. So this night question is asking for people who is using TDD for a long time share their experience about results of design without upfront thinking. If they really practice it and get mostly suitable design. Or it's my small understanding about TDD and probably agile.

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  • Functional/nonfunctional requirements VS design ideas

    - by Nicholas Chow
    Problem domain Functional requirements defines what a system does. Non-Functional requirements defines quality attributes of what the system does as a whole.(performance, security, reliability, volume, useability, etc.) Constraints limits the design space, they restrict designers to certain types of solutions. Solution domain Design ideas , defines how the system does it. For example a stakeholder need might be we want to increase our sales, therefore we must improve the usability of our webshop so more customers will purchase, a requirement can be written for this. (problem domain) Design takes this further into the solution domain by saying "therefore we want to offer credit card payments in addition to the current prepayment option". My problem is that the transition phase from requirement to design seems really vague, therefore when writing requirements I am often confused whether or not I incorporated design ideas in my requirements, that would make my requirement wrong. Another problem is that I often write functional requirements as what a system does, and then I also specify in what timeframe it must be done. But is this correct? Is it then a still a functional requirement or a non functional one? Is it better to seperate it into two distinct requirements? Here are a few requirements I wrote: FR1 Registration of Organizer FR1 describes the registration of an Organizer on CrowdFundum FR1.1 The system shall display a registration form on the website. FR1.2 The system shall require a Name, Username, Document number passport/ID card, Address, Zip code, City, Email address, Telephone number, Bank account, Captcha code on the registration form when a user registers. FR1.4 The system shall display an error message containing: “Registration could not be completed” to the subscriber within 1 seconds after the system check of the registration form was unsuccessful. FR1.5 The system shall send a verification email containing a verification link to the subscriber within 30 seconds after the system check of the registration form was successful. FR1.6 The system shall add the newly registered Organizer to the user base within 5 seconds after the verification link was accessed. FR2 Organizer submits a Project FR2 describes the submission of a Project by an Organizer on CrowdFundum - FR2 The system shall display a submit Project form to the Organizer accounts on the website.< - FR2.3 The system shall check for completeness the Name of the Project, 1-3 Photo’s, Keywords of the Project, Punch line, Minimum and maximum amount of people, Funding threshold, One or more reward tiers, Schedule of when what will be organized, Budget plan, 300-800 Words of additional information about the Project, Contact details within 1 secondin after an Organizer submits the submit Project form. - FR2.8 The system shall add to the homepage in the new Projects category the Project link within 30 seconds after the system made a Project webpage - FR2.9 The system shall include in the Project link for the homepage : Name of the Project, 1 Photo, Punch line within 30 seconds after the system made a Project webpage. Questions: FR 1.1 : Have I incorporated a design idea here, would " the system shall have a registration form" be a better functional requirement? F1.2 ,2.3 : Is this not singular? Would the conditions be better written for each its own separate requirement FR 1.4: Is this a design idea? Is this a correct functional requirement or have I incorporated non functional(performance) in it? Would it be better if I written it like this: FR1 The system shall display an error message when check is unsuccessful. NFR: The system will respond to unsuccesful registration form checks within 1 seconds. Same question with FR 2.8 and 2.9. FR2.3: The system shall check for "completeness", is completeness here used ambigiously? Should I rephrase it? FR1.2: I added that the system shall require a "Captcha code" is this a functional requirement or does it belong to the "security aspect" of a non functional requirement. I am eagerly waiting for your response. Thanks!

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  • Good resources for language design

    - by Aaron Digulla
    There are lots of books about good web design, UI design, etc. With the advent of Xtext, it's very simple to write your own language. What are good books and resources about language design? I'm not looking for a book about compiler building (like the dragon book) but something that answers: How to create a grammar that is forgiving (like adding optional trailing commas)? Which grammar patterns cause problems for users of a language? How create a compact grammar without introducing ambiguities

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  • String patterns that can be used to filter and group files

    - by Louis Rhys
    One of our application filters files in certain directory, extract some data from it and export a document from the extracted data. The algorithm for extracting the data depends on the file, and so far we use regex to select the algorithm to be used, for example .*\.txt will be processed by algorithm A, foo[0-5]\.xml will be processed by algo B, etc. However now we need some files to be processed together. For example, in one case we need two files, foo.*\.xml and bar.*\.xml. Part of the information to be extracted exist in the foo file, and the other part in the bar file. Moreover, we need to make sure the wild card is compatible. For example, if there are 6 files foo1.xml foo23.xml bar1.xml bar9.xml bar23.xml foo4.xml I would expect foo1 and bar1 to be identified as a group, and foo23 and bar23 as another group. bar9 and foo4 has no pair, so they will not be treated. Now, since the filter is configured by user, we need to have a pattern that can express the above requirement. I don't think you can express meaning like above in standard regex. (foo|bar).*\.xml will match all 6 file above and we can't identify which file is paired for a particular file. Is there any standard pattern that can express it? Or any idea how to modify regex to support this, that can be implemented easily?

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  • How to explain why design choices are good?

    - by Telastyn
    As I've become a better developer, I find that much of my design skill comes more from intuition than mechanical analysis. This is great. It lets me read code and get a feel for it quicker. It lets me translate designs between languages and abstractions much easier. And it let's me get stuff done faster. The downside is that I find it harder to explain to teammates (and worse, management) why a particular design is advantageous; especially teammates that are behind the times on best practices. "This design is more testable!" or "You should favor composition over inheritance." go right over their heads, and lead into the rabbit hole of me trying to clue everyone in to the last decade of software engineering advances. I'll get better at it with practice of course, but in the mean time it involves a lot of wasted time and/or bad design (that will lead to wasted time fixing it later). How can I better explain why a certain design is superior, when the benefits aren't completely obvious to the audience?

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  • Any recommended books/resources on component-based design?

    - by user1163640
    I come from a background with heavy use of the classical object-oriented paradigm for software development. The company I am a part of switched to Unity not too long ago, and we're all very excited to get started using it However, one aspect that have sparked my interested, and which I think will become a very important part of our future development, is Unity's approach to component-based design with scripting; with less focus on typical hierarchical aspect. Question I was wondering if anyone could recommend any good books on this subject? I have had trouble finding any books or books with reliable reviews, and was wondering if anyone more experienced here had something to say on the issue? Any other kind of resource would be excellent too, I'm just interested in getting to learn everything I can about it. This is not meant as a discussion about best books or resources on the topic, but simply a question regarding any resources that any of you find useful. Thank you all for your time!

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  • Guidelines or Design pattern to develop configurable software

    - by Rumit Parakhiya
    I want to develop an application which would have it's own framework, using which developer can implement functionality very easily. Developer shouldn't have to code for each and every page or report. But, he can do it very easily by just configuring it using the framework provided. Some nice examples of it is SAP and Tally. They have got their own framework, using which anybody having knowledge of it can customize or extend functionality of the product. But, as I am beginner in this direction, I don't have any idea about where to start. Can anybody point me to some design pattern which I can follow or some similar open source software which I can refer?

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  • design for interruptable operations

    - by tpaksu
    I couldn't find a better topic but here it is; 1) When user clicks a button, code starts t work, 2) When another button is clicked, it would stop doing whatever it does and start to run the second button's code, 3) Or with not user interaction, an electrical power down detected from a connected device, so our software would cancel the current event and start doing the power down procedure. How is this design mostly applied to code? I mean "stop what you are doing" part? If you would say events, event handlers etc. how do you bind a condition to the event? and how do you tell the program without using laddered if's to end it's process? method1(); if (powerdown) return; method2(); if (powerdown) return; etc.

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  • Business Layer Design in J2EE Project

    - by user63157
    Currently the project on which I am working is being developed with Spring, Hibernate and struts. The business layer consists of simple java beans with no behavior in them only properties and getter and setter methods, the services are written on them which operates on them and call DAO layer methods and all. My questions is that is it object oriented way of designing or simply the procedure way in which the data and the functions on which they operate are not together. Please provide your thoughts and inputs on how the business logic is design and implemented in j2ee application, is the domain model contains business methods or are they simply dumb objects which have only data and services written on to them.

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  • AntFarm anti-pattern -- strategies to avoid, antidotes to help heal from

    - by alchemical
    I'm working on a 10 page web site with a database back-end. There are 500+ objects in use, trying to implement the MVP pattern in ASP.Net. I'm tracing the code-execution from a single-page, my finger has been on F-11 in Visual Studio for about 40 minutes, there seems to be no end, possibly 1000+ method calls for one web page! If it was just 50 objects that would be one thing, however, code execution snakes through all these objects just like millions of ants frantically woring in their giant dirt mound house, riddled with object tunnels. Hence, a new anti-pattern is born : AntFarm. AntFarm is also known as "OO-Madnes", "OO-Fever", OO-ADD, or simply design-pattern junkie. This is not the first time I've seen this, nor my associates at other companies. It seems that this style is being actively propogated, or in any case is a misunderstanding of the numerous OO/DP gospels going around... I'd like to introduce an anti-pattern to the anti-pattern: GST or "Get Stuff Done" AKA "Get Sh** done" AKA GRD (GetRDone). This pattern focused on just what it says, getting stuff done, in a simple way. I may try to outline it more in a later post, or please share your ideas on this antidote pattern. Anyway, I'm in the midst of a great example of AntFarm anti-pattern as I write (as a bonus, there is no documentation or comments). Please share you thoughts on how this anti-pattern has become so prevelant, how we can avoid it, and how can one undo or deal with this pattern in a live system one must work with!

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  • A good design pattern for almost similar objects

    - by Sam
    Hello, I have two websites that have an almost identical database schema. the only difference is that some tables in one website have 1 or 2 extra fields that the other and vice versa. I wanted to the same Database Access layer classes to will manipulate both websites. What can be a good design pattern that can be used to handle that little difference. for example, I have a method createAccount(Account account) in my DAO class but the implementation will be slightly different between website A and website B. I know design patterns don't depend on the language but FYI i m working with Perl. Thanks

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  • C# Domain-Driven Design Sample Released

    - by Artur Trosin
    In the post I want to declare that NDDD Sample application(s) is released and share the work with you. You can access it here: http://code.google.com/p/ndddsample. NDDDSample from functionality perspective matches DDDSample 1.1.0 which is based Java and on joint effort by Eric Evans' company Domain Language and the Swedish software consulting company Citerus. But because NDDDSample is based on .NET technologies those two implementations could not be matched directly. However concepts, practices, values, patterns, especially DDD, are cross-language and cross-platform :). Implementation of .NET version of the application was an interesting journey because now as .NET developer I better understand the differences positive and negative between these two platforms. Even there are those differences they can be overtaken, in many cases it was not so hard to match a java libs\framework with .NET during the implementation. Here is a list of technology stack: 1. .net 3.5 - framework 2. VS.NET 2008 - IDE 3. ASP.NET MVC2.0 - for administration and tracking UI 4. WCF - communication mechanism 5. NHibernate - ORM 6. Rhino Commons - Nhibernate session management, base classes for in memory unit tests 7. SqlLite - database 8. Windsor - inversion of control container 9. Windsor WCF facility - for better integration with NHibernate 10. MvcContrib - and in particular its Castle WindsorControllerFactory in order to enable IoC for controllers 11. WPF - for incident logging application 12. Moq - mocking lib used for unit tests 13. NUnit - unit testing framework 14. Log4net - logging framework 15. Cloud based on Azure SDK These are not the latest technologies, tools and libs for the moment but if there are someone thinks that it would be useful to migrate the sample to latest current technologies and versions please comment. Cloud version of the application is based on Azure emulated environment provided by the SDK, so it hasn't been tested on ‘real' Azure scenario (we just do not have access to it). Thanks to participants, Eugen Gorgan who was involved directly in development, Ruslan Rusu and Victor Lungu spend their free time to discuss .NET specific decisions, Eugen Navitaniuc helped with Java related questions. Also, big thank to Cornel Cretu, he designed a nice logo and helped with some browser incompatibility issues. Any review and feedback are welcome! Thank you, Artur Trosin

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  • Design pattern for window management in a Java Swing app

    - by Lord Torgamus
    I've just started creating my very first little Java Swing app. When the program opens, it brings up a single, simple window with a label and a couple buttons. Clicking one of those buttons is supposed to wipe out the welcome screen and replace it with a totally different panel. I'm not sure what the best way to create that functionality is. One method would be to pass my JFrame as an argument into... just about every other component, but that feels hacky to me. Or, there's making each panel double as an action listener, but that doesn't seem right, either. Is there a design pattern I should be applying here? "Replace the contents of the main — and only — window" must be a reasonably common operation. A name for the pattern would be enough; I can use Google on my own from there. (I wouldn't say no to a longer explanation, though.)

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