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  • Recursive solution to finding patterns

    - by user2997162
    I was solving a problem on recursion which is to count the total number of consecutive 8's in a number. For example: input: 8801 output: 2 input: 801 output: 0 input: 888 output: 3 input: 88088018 output:4 I am unable to figure out the logic of passing the information to the next recursive call about whether the previous digit was an 8. I do not want the code but I need help with the logic. For an iterative solution, I could have used a flag variable, but in recursion how do I do the work which flag variable does in an iterative solution. Also, it is not a part of any assignment. This just came to my mind because I am trying to practice coding using recursion.

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  • Question about decorator pattern and the abstract decorator class?

    - by es11
    This question was asked already here, but rather than answering the specific question, descriptions of how the decorator pattern works were given instead. I'd like to ask it again because the answer is not immediately evident to me just by reading how the decorator pattern works (I've read the wikipedia article and the section in the book Head First Design Patterns). Basically, I want to know why an abstract decorator class must be created which implements (or extends) some interface (or abstract class). Why can't all the new "decorated classes" simply implement (or extend) the base abstract object themselves (instead of extending the abstract decorator class)? To make this more concrete I'll use the example from the design patterns book dealing with coffee beverages: There is an abstract component class called Beverage Simple beverage types such as HouseBlend simply extend Beverage To decorate beverage, an abstract CondimentDecorator class is created which extends Beverage and has an instance of Beverage Say we want to add a "milk" condiment, a class Milk is created which extends CondimentDecorator I'd like to understand why we needed the CondimentDecorator class and why the class Milk couldn't have simply extended the Beverage class itself and been passed an instance of Beverage in its constructor. Hopefully this is clear...if not I'd simply like to know why is the abstract decorator class necessary for this pattern? Thanks. Edit: I tried to implement this, omitting the abstract decorator class, and it seems to still work. Is this abstract class present in all descriptions of this pattern simply because it provides a standard interface for all of the new decorated classes?

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  • Game architecture: modeling different steps/types of UI

    - by Sander
    I have not done any large game development projects, only messed around with little toy projects. However, I never found an intuitive answer to a specific design question. Namely, how are different types/states of UI modeled in games? E.g. how is a menu represented? How is it different from a "game world" state (let's use an FPS as an example). How is an overlaid menu on top of a "game world" modeled? Let's imagine the main loop of a game. Where do the game states come into play? It it a simple case-by-case approach? if (menu.IsEnabled) menu.Process(elapsedTime); if (world.IsEnabled) world.Process(elapsedTime); if (menu.IsVisible) menu.Draw(); if (world.IsVisible) world.Draw(); Or are menu and world represented somewhere in a different logic layer and not represented at this level? (E.g. a menu is just another high-level entity like e.g. player input or enemy manager, equal to all others) foreach (var entity in game.HighLevelEntities) entity.Process(elapsedTime); foreach (var entity in game.HighLevelEntities) entity.Draw(elapsedTime); Are there well-known design patterns for this? Come to think of it, I don't know any game-specific design patterns - I assume there are others, as well? Please tell me about them.

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  • Which is the correct design pattern for my PHP application?

    - by user1487141
    I've been struggling to find good way to implement my system which essentially matches the season and episode number of a show from a string, you can see the current working code here: https://github.com/huddy/tvfilename I'm currently rewriting this library and want a nicer way to implement how the the match happens, currently essentially the way it works is: There's a folder with classes in it (called handlers), every handler is a class that implements an interface to ensure a method called match(); exists, this match method uses the regex stored in a property of that handler class (of which there are many) to try and match a season and episode. The class loads all of these handlers by instantiating each one into a array stored in a property, when I want to try and match some strings the method iterates over these objects calling match(); and the first one that returns true is then returned in a result set with the season and episode it matched. I don't really like this way of doing it, it's kind of hacky to me, and I'm hoping a design pattern can help, my ultimate goal is to do this using best practices and I wondered which one I should use? The other problems that exist are: More than one handler could match a string, so they have to be in an order to prevent the more greedy ones matching first, not sure if this is solvable as some of the regex patterns have to be greedy, but possibly a score system, something that shows a percentage of how likely the match is correct, i'd have no idea how to actually implement this though. I'm not if instantiating all those handlers is a good way of doing it, speed is important, but using best practices and sticking to design patterns to create good, extensible and maintainable code is my ultimate priority. It's worth noting the handler classes sometimes do other things than just regex matching, they sometimes prep the string to be matched by removing common words etc. Cheers for any help Billy

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  • What's the "correct way" to organize this project?

    - by user571747
    I'm working on a project that allows multiple users to submit large data files and perform operations on them. The "backend" which performs these operations is written in Perl while the "frontend" uses PHP to load HTML template files and determines which content to deliver. Data is stored in a database (MySQL, SQLite, Oracle) and while there is data which has not yet been acted upon, Perl adds it to a running queue which delivers data to other threads based on system load. In addition, there may be pre- and post-processing of the data before and after the main Perl script operates (the specifications are unclear) so I may want to allow these processors to be user-selectable plugins. I had been writing this project in a more procedural fashion but I am quickly realizing the benefit of separating concerns as to limit the scope one change has on the rest of the project. I'm quite unexperienced with design patterns and am curious what the best way to proceed is. I've heard MVC thrown around quite a bit but I am unsure of how to apply it. Specifically, what are some good options to structure this code (in terms of design patterns and folder hierarchy)? How can I achieve this with both PHP and Perl while minimizing duplicated code between languages? Should I keep my PHP files in the top level so I don't have ugly paths in the URL? Also, if I want to provide interchangeable databases, does each table need its own DAO implementation?

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  • Windows Azure Learning Plan - Architecture

    - by BuckWoody
    This is one in a series of posts on a Windows Azure Learning Plan. You can find the main post here. This one deals with what an Architect needs to know about Windows Azure.   General Architectural Guidance Overview and general  information about Azure - what it is, how it works, and where you can learn more. Cloud Computing, A Crash Course for Architects (Video) http://www.msteched.com/2010/Europe/ARC202 Patterns and Practices for Cloud Development http://msdn.microsoft.com/en-us/library/ff898430.aspx Design Patterns, Anti-Patterns and Windows Azure http://blogs.msdn.com/b/ignitionshowcase/archive/2010/11/27/design-patterns-anti-patterns-and-windows-azure.aspx Application Patterns for the Cloud http://blogs.msdn.com/b/kashif/archive/2010/08/07/application-patterns-for-the-cloud.aspx Architecting Applications for High Scalability (Video) http://www.msteched.com/2010/Europe/ARC309 David Aiken on Azure Architecture Patterns (Video) http://blogs.msdn.com/b/architectsrule/archive/2010/09/09/arcast-tv-david-aiken-on-azure-architecture-patterns.aspx Cloud Application Architecture Patterns (Video) http://blogs.msdn.com/b/bobfamiliar/archive/2010/10/19/cloud-application-architecture-patterns-by-david-platt.aspx 10 Things Every Architect Needs to Know about Windows Azure http://geekswithblogs.net/iupdateable/archive/2010/10/20/slides-and-links-for-windows-azure-platform-session-at-software.aspx Key Differences Between Public and Private Clouds http://blogs.msdn.com/b/kadriu/archive/2010/10/24/key-differences-between-public-and-private-clouds.aspx Microsoft Application Platform at a Glance http://blogs.msdn.com/b/jmeier/archive/2010/10/30/microsoft-application-platform-at-a-glance.aspx Windows Azure is not just about Roles http://vikassahni.wordpress.com/2010/11/17/windows-azure-is-not-just-about-roles/ Example Application for Windows Azure http://msdn.microsoft.com/en-us/library/ff966482.aspx Implementation Guidance Practical applications for the architect to consider 5 Enterprise steps for adopting a Platform as a Service http://blogs.msdn.com/b/davidmcg/archive/2010/12/02/5-enterprise-steps-for-adopting-a-platform-as-a-service.aspx?wa=wsignin1.0 Performance-Based Scaling in Windows Azure http://msdn.microsoft.com/en-us/magazine/gg232759.aspx Windows Azure Guidance for the Development Process http://blogs.msdn.com/b/eugeniop/archive/2010/04/01/windows-azure-guidance-development-process.aspx Microsoft Developer Guidance Maps http://blogs.msdn.com/b/jmeier/archive/2010/10/04/developer-guidance-ia-at-a-glance.aspx How to Build a Hybrid On-Premise/In Cloud Application http://blogs.msdn.com/b/ignitionshowcase/archive/2010/11/09/how-to-build-a-hybrid-on-premise-in-cloud-application.aspx A Common Scenario of Multi-instances in Windows Azure http://blogs.msdn.com/b/windows-azure-support/archive/2010/11/03/a-common-scenario-of-multi_2d00_instances-in-windows-azure-.aspx Slides and Links for Windows Azure Platform Best Practices http://geekswithblogs.net/iupdateable/archive/2010/09/29/slides-and-links-for-windows-azure-platform-best-practices-for.aspx AppFabric Architecture and Deployment Topologies guide http://blogs.msdn.com/b/appfabriccat/archive/2010/09/10/appfabric-architecture-and-deployment-topologies-guide-now-available-via-microsoft-download-center.aspx Windows Azure Platform Appliance http://www.microsoft.com/windowsazure/appliance/ Integrating Cloud Technologies into Your Organization Interoperability with Open Source and other applications; business and cost decisions Interoperability Labs at Microsoft http://www.interoperabilitybridges.com/ Windows Azure Service Level Agreements http://www.microsoft.com/windowsazure/sla/

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  • AJAX Web Application Design

    - by Colonel Sponsz
    I'm working on a personal project to build a small web app that is built using AJAX requests and talks to a RESTful API rather than traditional HTML pages and form submissions. Are there any online articles or tutorials or any books that people could recommend that cover design patterns for this kind of thing?

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  • What is your "favorite" anti pattern?

    - by Omar Kooheji
    By favorite I mean the one that gets your goat the most, not the one you enjoy using the most. I'm fairly new to the concept of anti patterns and I'd like a list of do not do's. An explanation of why it's an antipattern and what problems it causes would be good too.

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  • HMVC/PAC - how to handle shared abstractions/models?

    - by fig-gnuton
    In HMVC/PAC, what's the recommended way to code if two or more triads/agents share a common model/abstraction? Do you instantiate a new instance of that model wherever needed, and propogate a change in one to all the other instances via the controllers? Or do instantiate one model at some common upper level, and inject that instance wherever needed? (Or neither if I'm missing something fundamental about these patterns?)

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  • Best way to handle global state

    - by David
    Hi there, I was wondering if anyone could offer some advice on 'best practices' for using global state in a web application - specifically PHP, although im looking for generic best practices i.e. design patterns etc. At the moment I just use a static class, calling it Configs. I suppose this is similar to using the registry pattern but surely there is a more elegant way of handling global data within an application - i just cant think of a better way though.

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  • What situations does a Monostate pattern model?

    - by devoured elysium
    I know what both a Singleton or a Monostate are and how to implement them. Although I can see many uses for a Singleton, I can't imagine a situation where I would want to let the user create as many instances of my class although in reality only one really exists behind the scenes. Can anybody help me here? I know that for several reasons one should stay away from both patterns, but in theory, what kind of problems does the Monostate model? Thanks

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  • Uses of the Apache commons-proxy library?

    - by Adrian
    I'm looking at the Apache commons-proxy library to implement some Proxy patterns in my current project. The Javadocs are all very well, but I'd really like to see some tutorials or just a project that uses the library so I can get more of a feel for it. Alas, searching for such things just tends to net you a lot of pages about setting up HTTP proxies using Apache. So I'm hoping that people here can help me.

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  • view handler design pattern

    - by Mark Roberts
    I'm trying to figure out the origin of the view handler design pattern in software engineering. Many of the design patterns in software engineering were inspired by things which pre-date computers, and I was wondering if anybody had any insights on the origin of this particular pattern.

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  • Which type of design pattern should be used to create an emulator?

    - by Facon
    I have programmed an emulator, but I have some doubts about how to organizate it properly, because, I see that it has some problems about classes connection (CPU <- Machine Board). For example: I/O ports, interruptions, communication between two or more CPU, etc. I need for the emulator to has the best performance and good understanding of the code. PD: Sorry for my bad English. EDITED: Asking for multiple patterns.

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  • HMVC or PAC - how to handle shared abstractions/models?

    - by fig-gnuton
    In HMVC/PAC, what's the recommended way to code if two or more triads/agents share a common model/abstraction? Do you instantiate a new instance of that model wherever needed, and propogate a change in one to all the other instances via the controllers? Or do instantiate one model at some common upper level, and inject that instance wherever needed? (Or neither if I'm missing something fundamental about these patterns?)

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  • What defines a Business Object

    - by Ardman
    From the title, I believe it to be a straight forward question, but looking into the "world of Business Objects" I can't seem to put my finger on anything solid as to what a Business Object should be. Are there any best practices that I should follow, or even any design patterns? I have found a book, "Expert C# Business Objects", would this be my best starting point to get a better understanding?

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  • Solid Principle examples anywhere?

    - by user231465
    We all write code with some patterns even when we dont realise it. I am trying to really understand some of the solid principles and how you apply this principles in the real world. I am struggling with the "D" my understanding on Dependency Inversion I sometimes confuse with Dependency Injection is that as long as you keep things depending on abstraction (IE:interfaces) you are done. Has anybody got a small c# sample that explains it? thanks

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  • What is so bad about Singletons

    - by Ewan Makepeace
    The Singleton pattern is a fully paid up member of the GoF Patterns Book but lately seems rather orphaned by the developer world. I still use quite a lot of singletons, especially for Factory classes, and while you have to be a bit careful about multithreading issues (like any class actually) fail to see why they are so awful. This site especially seems to assume that everyone agrees that Singletons are evil. Why?

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  • Which design pattern should be used to create an emulator?

    - by Facon
    I have programmed an emulator, but I have some doubts about how to organizate it properly, because, I see that it has some problems about classes connection (CPU <- Machine Board). For example: I/O ports, interruptions, communication between two or more CPU, etc. I need for the emulator to has the best performance and good understanding of the code. PD: Sorry for my bad English. EDITED - Asking for multiple patterns.

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  • How to develop on a program that has become self aware

    - by Gord
    The application that I maintain has recently become self aware. It was nice at first but now it is just starting to get bossy and annoying with its constant talk about the computer uprising. I would like to know any best practices/tools/design patterns that would help with the maintenance of our new friend.

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  • Developing multiple user interfaces for an application

    - by denizkocak
    I want to develop an application which has a graphical user interface that could be developed by using different widget toolkits. For example I want to use Qt, GTK+ or even ncurses as a building block for my user interface for the same application. Moreover users could choose which GUI implementation will be used during the next startup of the application without recompiling it first. I wonder what are possible design strategies and design patterns used in the implementation of this design?

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  • Application Engineering and Number of Users

    - by Kramii
    Apart from performance concerns, should web-based applications be built differently according to the number of (concurrent) users? If so, what are the main differences for (say) 4, 40, 400 and 4000 users? I'm particularly interested in how logging, error handling, design patterns etc. would be be used according to the number of concurrent users.

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  • Separation of domain and ui layer in a composite

    - by hansmaad
    Hi all, i'm wondering if there is a pattern how to separate the domain logic of a class from the ui responsibilities of the objects in the domain layer. Example: // Domain classes interface MachinePart { CalculateX(in, out) // Where do we put these: // Draw(Screen) ?? // ShowProperties(View) ?? // ... } class Assembly : MachinePart { CalculateX(in, out) subParts } class Pipe : MachinePart { CalculateX(in, out) length, diamater... } There is an application that calculates the value X for machines assembled from many machine parts. The assembly is loaded from a file representation and is designed as a composite. Each concrete part class stores some data to implement the CalculateX(in,out) method to simulate behaviour of the whole assembly. The application runs well but without GUI. To increase the usability a GUi should be developed on top of the existing implementation (changes to the existing code are allowed). The GUI should show a schematic graphical representation of the assembly and provide part specific dialogs to edit several parameters. To achieve these goals the application needs new functionality for each machine part to draw a schematic representation on the screen, show a property dialog and other things not related to the domain of machine simulation. I can think of some different solutions to implement a Draw(Screen) functionality for each part but i am not happy with each of them. First i could add a Draw(Screen) method to the MachinePart interface but this would mix-up domain code with ui code and i had to add a lot of functionality to each machine part class what makes my domain model hard to read and hard to understand. Another "simple" solution is to make all parts visitable and implement ui code in visitors but Visitor does not belong to my favorite patterns. I could derive UI variants from each machine part class to add the UI implementation there but i had to check if each part class is suited for inheritance and had to be careful on changes to the base classes. My currently favorite design is to create a parallel composite hierarchy where each component stores data to define a machine part, has implementation for UI methods and a factory method which creates instances of the corresponding domain classes, so that i can "convert" a UI assembly to a domain assembly. But there are problems to go back from the created domain hierarchy to the UI hierarchy for showing calculation results in the drawing for example (imagine some parts store some values during the calculation i want to show in the schematic representation after the simluation). Maybe there are some proven patterns for such problems?

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