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• What type of pattern would be used in this case

  - by Admiral Kunkka

  I want to know how to tackle this type of scenario. We are building a person's background, from scratch, and I want to know, conceptually, how to proceed with a secure object pattern in both design and execution... I've been reading on Factory patterns, Model-View-Controller types, Dependency injection, Singleton approaches... and I can't seem to grasp or 'fit' these types of designs decisions into what I'm trying to do.. First and foremost, I started with having a big jack-of-all-trades class, then I read some more, and some tips were to make sure your classes only have a single purpose.. which makes sense and I started breaking down certain things into other classes. Okay, cool. Now I'm looking at dependency injection and kind of didn't really know what's going on. Example/insight of what kind of heirarchy I need to accomplish... class Person needs to access and build from a multitude of different classes. class Culture needs to access a sub-class for culture benefits class Social needs to access class Culture, and other sub-classes class Birth needs to access Social, Culture, and other sub-classes class Childhood/Adolescence/Adulthood need to access everything. Also, depending on different rolls, this class heirarchy needs to create multiple people as well, such as Family, and their backgrounds using some, if not all, of these same classes. Think of it as a people generator, all random, with backgrounds and things that happen to them. Ageing, death of loved ones, military careers, e.t.c. Most of the generation is done randomly, making calls to a mt_rand function to pick from most of the selections inside the classes, guaranteeing the data to be absolutely random. I have most of the bulk-data down, and was looking for some insight from fellow programmers, what do you think?

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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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• USE case to Class Diagram - How do I?

  - by 01010011

  Hi, I would like your guidance on how to create classes and their relationships (generalization, association, aggregation and composition) accurately from my USE case diagram (please see below). I am trying to create this class diagram so I can use it to create a simple online PHP application that allows the user to register an account, login and logout, and store, search and retrieve data from a MySQL database. Are my classes correct? Or should I create more classes? And if so, what classes are missing? What relationships should I use when connecting the register, login, logout, search_database and add_to_database to the users? I'm new to design patterns and UML class diagrams but from my understanding, the association relationship relates one object with another object; the aggregation relationship is a special kind of association that allows "a part" to belong to more than one "whole" (e.g. a credit card and its PIN - the PIN class can also be used in a debit card class); and a composition relationship is a special form of aggregation that allows each part to belong to only one whole at a time. I feel like I have left out some classes or something because I just can't seem to find the relationships from my understanding of relationships. Any assistance will be really appreciated. Thanks in advance. USE CASE DIAGRAM CLASS DIAGRAM

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• Avoiding Object Oriented Pitfalls, Migrating from C, What Worked for You?

  - by Stephen

  I've been programming in procedural languages for quite some time now, and my first reaction to a problem is to start breaking it down into tasks to perform rather than to consider the different entities (objects) that exist and their relationships. I have had a university course in OOP, and understand the fundamentals of encapsulation, data abstraction, polymorphism, modularity and inheritance. I read Learning to think in the Object Oriented Way and Learning object oriented thinking, and will be looking at some of the books pointed to in those answers. I think that several of my medium to large sized projects will benefit from effective use of OOP but as a novice I would like to avoid time consuming, common errors. Based on your experiences, what are these pitfalls and what are reasonable ways around them? If you could explain why they are pitfalls, and how your suggestion is effective in addressing the issue it'd be appreciated. I'm thinking along the lines of something like "Is it common to have a fair number of observer and modifier methods and use private variables or are there techniques for consolidating/reducing them?" I'm not worried about using C++ as a pure OO language, if there are good reasons to mix methods. (Reminiscent of the reasons to use GOTOs, albeit sparingly.) Thank you!

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• Pattern for managing reference count and object life

  - by Gopalakrishnan Subramani

  We have a serial port which is connected to hundreds of physical devices on the same wire. We have protocols like Modbus and Hart to handle the request and response between the application and devices. The question is related to managing the reference count of the channel. When no device is using the channel, the channel should be closed. public class SerialPortChannel { int refCount = 0; public void AddReference() { refCount++; } public void ReleaseReference() { refCount--; if (refCount <= 0) this.ReleasePort(); //This close the serial port } } For each device connected, we create a object for the device like device = new Device(); device.Attach(channel); //this calls channel.AddReference() When the device disconnect, device.Detach(channel); //this calls channel.ReleaseReference() I am not convinced by the reference count model. Are there any better way to handle this problem in .NET World?

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• who are software design engineers?

  - by Sepala

  My question is, who are software design engineers? And, what is the meaning of the following statement (from a software design engineer job ad)? "Application domain knowledge is essential and....." What is application domain? SDLC? My hope is to become a software engineer one day (OK, to be honest, more than that. I need to be a legend), that who do programming (They say this job has no programming). I am following final year of my Bsc(Hons) in computing and I have completed a foreign diploma, majoring software engineering - Java technologies. Will this job experience help me out to get a job in my desired position, which is mentioned above, after the degree? Wikipedia and google never gave a clear straight forward answer!! Please help!

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• Code Structure / Level Design: Plants vs Zombies game level dissection

  - by lalan

  Hi Friends, I am interested in learning the class structure of Plants vs Zombies, particularly level design; for those who haven't played it - this video contains nice play-through: http://www.youtube.com/watch?v=89DfdOIJ4xw. How would I go ahead and design the code, mostly structure & classes, which allows for maximum flexibility & clean development? I am familiar with data driven design concepts, and would use events to handle most of dynamic behavior. Dissection at macro level: (Once every Level) Load tilemap, props, etc -- basically build the map (Once every Level) Camera Movement - might consider it as short cut-scene (Once every Level) Show Enemies you'll face during present level (Once every Level) Unit Selection Window/Panel - selection of defensive plants (Once every Level) Camera Movement - might consider it as short cut-scene (Once every Level) HUD Creation - based on unit selection (Level Loop) Enemy creation - based on types of zombies allowed (Level Loop) Sun/Resource generation (Level Loop) Show messages like 'huge wave of zombies coming', 'final wave' (Level Loop) Other unique events - Spawn gifts, money, tombstones, etc (Once every Level) Unlock new plant Potential game scripts: a) Level definitions: Level_1_1.xml, Level_1_2.xml, etc. Level_1_1.xml :: Sample script <map> <tilemap>tilemapFrontLawn</tilemap> <SpawnPoints> tiles where particular type of zombies (land vs water) may spawn</spawnPoints> <props> position, entity array -- lawnmower, </props> </map> <zombies> <... list of zombies who gonna attack by ids...> </zombies> <plants> <... list by plants which are available for defense by ids...> </plants> <progression> <ZombieWave name='first wave' spawnScript='zombieLightWave.lua' unlock='null'> <startMessages time=1.5>Ready</startMessages> <endMessages time=1.5>Huge wave of zombies incoming</endMessages> </ZombieWave> </progression> b) Entities definitions: .xmls containing zombies, plants, sun, lawnmower, coins, etc description. Potential classes: //LevelManager - Based on the level under play, it will load level script. Few of the // functions it may have: class LevelManager { public: bool load(string levelFileName); bool enter(); bool update(float deltatime); bool exit(); private: LevelData* mLevelData; } // LevelData - Contains the details of level loaded by LevelManager. class LevelData { private: string file; // array of camera,dialog,attackwaves, etc in active level LevelCutSceneCamera** mArrayCutSceneCamera; LevelCutSceneDialog** mArrayCutSceneDialog; LevelAttackWave** mArrayAttackWave; .... // which camera,dialog,attackwave is active in level uint mCursorCutSceneCamera; uint mCursorCutSceneDialog; uint mCursorAttackWave; public: // based on cursor, get the next camera,dialog,attackwave,etc in active level // return false/true based on failure/success bool nextCutSceneCamera(LevelCutSceneCamera**); bool nextCutSceneDialog(LevelCutSceneDialog**); } // LevelUnderPlay- LevelManager class LevelUnderPlay { private: LevelCutSceneCamera* mCutSceneCamera; LevelCutSceneDialog* mCutSceneDialog; LevelAttackWave* mAttackWave; Entities** mSelectedPlants; Entities** mAllowedZombies; bool isCutSceneCameraActive; public: bool enter(); bool update(float deltatime); bool exit(); } I am totally confused.. :( Does it make sense of using class composition (have flat class hierarchy) for managing levels. Is it a good idea to just add/remove/update sprites (or any drawable stuff) to current scene from LevelManager or LevelUnderPlay? If I want to make non-linear level design, how should I go ahead? Perhaps I would need a LevelProgression class, which would decide what to do based on decision tree. Any suggestions would be appreciated very much. Thank for your time, lalan

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• Relationship between TDD and Software Architecture/Design

  - by Christopher Francisco

  I'm new to TDD and have been reading the theory since applying it is more complicated than it sounds when you're learning by yourself. As far as I know, the objective is to write test cases for each requirement and run the test so it fails (to prevent a false positive). Afterward, you should write the minimum amount of code that can pass the test and move to the next one. That being said, is it true that you get a fast development, but what about the code itself? this theory makes me think you are not considering things like abstraction, delegation of responsibilities, design patterns, architecture and others since you're just writing "the minimum amount of code that can pass the test". I know I'm probably wrong because if this were true, we'd have a lot of crappy developers with poor software architecture and documentation so I'm asking for a guide here, what's the relationship between TDD and Software Architecture/Design?

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• Design patterns frequently seen in embedded systems programming

  - by softwarelover

  I don't have any question related to coding. My concerns are about embedded systems programming independent of any particular programming language. Because I am new in the realm of embedded programming, I would quite appreciate responses from those who consider themselves experienced embedded systems programmers. I basically have 2 questions. Of the design patterns listed below are there any seen frequently in embedded systems programming? Abstraction-Occurrence pattern General Hierarchy pattern Player-Role pattern Singleton pattern Observer pattern Delegation pattern Adapter pattern Facade pattern Immutable pattern Read-Only Interface pattern Proxy pattern As an experienced embedded developer, what design patterns have you, as an individual, come across? There is no need to describe the details. Only the pattern names would suffice. Please share your own experience. I believe the answers to the above questions would work as a good starting point for any novice programmers in the embedded world.

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• Modified Strategy Design Pattern

  - by Samuel Walker

  I've started looking into Design Patterns recently, and one thing I'm coding would suit the Strategy pattern perfectly, except for one small difference. Essentially, some (but not all) of my algorithms, need an extra parameter or two passed to them. So I'll either need to pass them an extra parameter when I invoke their calculate method or store them as variables inside the ConcreteAlgorithm class, and be able to update them before I call the algorithm. Is there a design pattern for this need / How could I implement this while sticking to the Strategy Pattern? I've considered passing the client object to all the algorithms, and storing the variables in there, then using that only when the particular algorithm needs it. However, I think this is both unwieldy, and defeats the point of the strategy pattern. Just to be clear I'm implementing in Java, and so don't have the luxury of optional parameters (which would solve this nicely).

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• Adventures in Windows 8: Understanding and debugging design time data in Expression Blend

  - by Laurent Bugnion

  One of my favorite features in Expression Blend is the ability to attach a Visual Studio debugger to Blend. First let’s start by answering the question: why exactly do you want to do that? Note: If you are familiar with the creation and usage of design time data, feel free to scroll down to the paragraph titled “When design time data fails”. Creating design time data for your app When a designer works on an app, he needs to see something to design. For “static” UI such as buttons, backgrounds, etc, the user interface elements are going to show up in Blend just fine. If however the data is fetched dynamically from a service (web, database, etc) or created dynamically, most probably Blend is going to show just an empty element. The classical way to design at that stage is to run the application, navigate to the screen that is under construction (which can involve delays, need to log in, etc…), to measure what is on the screen (colors, margins, width and height, etc) using various tools, going back to Blend, editing the properties of the elements, running again, etc. Obviously this is not ideal. The solution is to create design time data. For more information about the creation of design time data by mocking services, you can refer to two talks of mine “Deep dive MVVM” and “MVVM Applied From Silverlight to Windows Phone to Windows 8”. The source code for these talks is here and here. Design time data in MVVM Light One of the main reasons why I developed MVVM Light is to facilitate the creation of design time data. To illustrate this, let’s create a new MVVM Light application in Visual Studio. Install MVVM Light from here: http://mvvmlight.codeplex.com (use the MSI in the Download section). After installing, make sure to read the Readme that opens up in your favorite browser, you will need one more step to install the Project Templates. Start Visual Studio 2012. Create a new MvvmLight (Win8) app. Run the application. You will see a string showing “Welcome to MVVM Light”. In the Solution explorer, right click on MainPage.xaml and select Open in Blend. Now you should see “Welcome to MVVM Light [Design]” What happens here is that Expression Blend runs different code at design time than the application runs at runtime. To do this, we use design-time detection (as explained in a previous article) and use that information to initialize a different data service at design time. To understand this better, open the ViewModelLocator.cs file in the ViewModel folder and see how the DesignDataService is used at design time, while the DataService is used at runtime. In a real-life applicationm, DataService would be used to connect to a web service, for instance. When design time data fails Sometimes however, the creation of design time data fails. It can be very difficult to understand exactly what is happening. Expression Blend is not giving a lot of information about what happened. Thankfully, we can use a trick: Attaching a debugger to Expression Blend and debug the design time code. In WPF and Silverlight (including Windows Phone 7), you could simply attach the debugger to Blend.exe (using the “Managed (v4.5, v4.0) code” option even for Silverlight!!) In Windows 8 however, things are just a bit different. This is because the designer that renders the actual representation of the Windows 8 app runs in its own process. Let’s illustrate that: Open the file DesignDataService in the Design folder. Modify the GetData method to look like this: public void GetData(Action<DataItem, Exception> callback) { throw new Exception(); // Use this to create design time data var item = new DataItem("Welcome to MVVM Light [design]"); callback(item, null); } Go to Blend and build the application. The build succeeds, but now the page is empty. The creation of the design time data failed, but we don’t get a warning message. We need to investigate what’s wrong. Close MainPage.xaml Go to Visual Studio and select the menu Debug, Attach to Process. Update: Make sure that you select “Managed (v4.5, v4.0) code” in the “Attach to” field. Find the process named XDesProc.exe. You should have at least two, one for the Visual Studio 2012 designer surface, and one for Expression Blend. Unfortunately in this screen it is not obvious which is which. Let’s find out in the Task Manager. Press Ctrl-Alt-Del and select Task Manager Go to the Details tab and sort the processes by name. Find the one that says “Blend for Microsoft Visual Studio 2012 XAML UI Designer” and write down the process ID. Go back to the Attach to Process dialog in Visual Studio. sort the processes by ID and attach the debugger to the correct instance of XDesProc.exe. Open the MainViewModel (in the ViewModel folder) Place a breakpoint on the first line of the MainViewModel constructor. Go to Blend and open the MainPage.xaml again. At this point, the debugger breaks in Visual Studio and you can execute your code step by step. Simply step inside the dataservice call, and find the exception that you had placed there. Visual Studio gives you additional information which helps you to solve the issue. More info and Conclusion I want to thank the amazing people on the Expression Blend team for being very fast in guiding me in that matter and encouraging me to blog about it. More information about the XDesProc.exe process can be found here. I had to work on a Windows 8 app for a few days without design time data because of an Exception thrown somewhere in the code, and it was really painful. With the debugger, finding the issue was a simple matter of stepping into the code until it threw the exception.   Laurent Bugnion (GalaSoft) Subscribe | Twitter | Facebook | Flickr | LinkedIn

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• Design review for application facing memory issues

  - by Mr Moose

  I apologise in advance for the length of this post, but I want to paint an accurate picture of the problems my app is facing and then pose some questions below; I am trying to address some self inflicted design pain that is now leading to my application crashing due to out of memory errors. An abridged description of the problem domain is as follows; The application takes in a “dataset” that consists of numerous text files containing related data An individual text file within the dataset usually contains approx 20 “headers” that contain metadata about the data it contains. It also contains a large tab delimited section containing data that is related to data in one of the other text files contained within the dataset. The number of columns per file is very variable from 2 to 256+ columns. The original application was written to allow users to load a dataset, map certain columns of each of the files which basically indicating key information on the files to show how they are related as well as identify a few expected column names. Once this is done, a validation process takes place to enforce various rules and ensure that all the relationships between the files are valid. Once that is done, the data is imported into a SQL Server database. The database design is an EAV (Entity-Attribute-Value) model used to cater for the variable columns per file. I know EAV has its detractors, but in this case, I feel it was a reasonable choice given the disparate data and variable number of columns submitted in each dataset. The memory problem Given the fact the combined size of all text files was at most about 5 megs, and in an effort to reduce the database transaction time, it was decided to read ALL the data from files into memory and then perform the following; perform all the validation whilst the data was in memory relate it using an object model Start DB transaction and write the key columns row by row, noting the Id of the written row (all tables in the database utilise identity columns), then the Id of the newly written row is applied to all related data Once all related data had been updated with the key information to which it relates, these records are written using SqlBulkCopy. Due to our EAV model, we essentially have; x columns by y rows to write, where x can by 256+ and rows are often into the tens of thousands. Once all the data is written without error (can take several minutes for large datasets), Commit the transaction. The problem now comes from the fact we are now receiving individual files containing over 30 megs of data. In a dataset, we can receive any number of files. We’ve started seen datasets of around 100 megs coming in and I expect it is only going to get bigger from here on in. With files of this size, data can’t even be read into memory without the app falling over, let alone be validated and imported. I anticipate having to modify large chunks of the code to allow validation to occur by parsing files line by line and am not exactly decided on how to handle the import and transactions. Potential improvements I’ve wondered about using GUIDs to relate the data rather than relying on identity fields. This would allow data to be related prior to writing to the database. This would certainly increase the storage required though. Especially in an EAV design. Would you think this is a reasonable thing to try, or do I simply persist with identity fields (natural keys can’t be trusted to be unique across all submitters). Use of staging tables to get data into the database and only performing the transaction to copy data from staging area to actual destination tables. Questions For systems like this that import large quantities of data, how to you go about keeping transactions small. I’ve kept them as small as possible in the current design, but they are still active for several minutes and write hundreds of thousands of records in one transaction. Is there a better solution? The tab delimited data section is read into a DataTable to be viewed in a grid. I don’t need the full functionality of a DataTable, so I suspect it is overkill. Is there anyway to turn off various features of DataTables to make them more lightweight? Are there any other obvious things you would do in this situation to minimise the memory footprint of the application described above? Thanks for your kind attention.

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• C++ Library API Design

  - by johannes

  I'm looking for a good resource for learning about good API design for C++ libraries, looking at shared objects/dlls etc. There are many resources on writing nice APIs, nice classes, templates and so on at source level, but barely anything about putting things together in shared libs and executables. Books like Large-Scale C++ Software Design by John Lakos are interesting but massively outdated. What I'm looking for is advice i.e. on handling templates. With templates in my API I often end up with library code in my executable (or other library) so if I fix a bug in there I can't simply roll out the new library but have to recompile and redistribute all clients of that code. (and yes, I know some solutions like trying to instantiate at least the most common versions inside the library etc.) I'm also looking for other caveats and things to mind for keeping binary compatibility while working on C++ libraries. Is there a good website or book on such things?

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• When should a method of a class return the same instance after modifying itself?

  - by modiX

  I have a class that has three methods A(), B() and C(). Those methods modify the own instance. While the methods have to return an instance when the instance is a separate copy (just as Clone()), I got a free choice to return void or the same instance (return this;) when modifying the same instance in the method and not returning any other value. When deciding for returning the same modified instance, I can do neat method chains like obj.A().B().C();. Would this be the only reason for doing so? Is it even okay to modify the own instance and return it, too? Or should it only return a copy and leave the original object as before? Because when returning the same modified instance the user would maybe admit the returned value is a copy, otherwise it would not be returned? If it's okay, what's the best way to clarify such things on the method?

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• How do you approach database design?

  - by bron

  I am primarily a web developer and I have a couple of personal projects which I want to kick off. One thing that is bugging me is database design. I have gone through in school db normalization and stuff like that but it has been a couple of years ago and I have never had experience with relational database design except for school. So how you do you approach database from a web app perspective? How do you begin and what do you look out for? What are flags for caution?

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• How to design software when using BDD?

  - by Léster

  I'm working on a project right now and it's my first project using BDD. Up till now, the user stories have proven themselves a very valuable weapon to understand requirements and to specify the solution in a comprehensive, easy to understand language. My question is this: now that my user stories are complete, how do I design my solution? I understand that I derive behavior tests from my user stories, and I have to do UI design, but am I supposed to use good ol' UML? I'm under the impression that when using user stories, UML is left out; is this correct? Léster

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• design pattern for unit testing? [duplicate]

  - by Maddy.Shik

  This question already has an answer here: Unit testing best practices for a unit testing newbie 4 answers I am beginner in developing test cases, and want to follow good patterns for developing test cases rather than following some person or company's specific ideas. Some people don't make test cases and just develop the way their senior have done in their projects. I am facing lot problems like object dependencies (when want to test method which persist A object i have to first persist B object since A is child of B). Please suggest some good books or sites preferably for learning design pattern for unit test cases. Or reference to some good source code or some discussion for Dos and Donts will do wonder. So that i can avoid doing mistakes be learning from experience of others.

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• How to fill certain application design learning "gaps"?

  - by e4rthdog

  In life it doesnt matter if you do one thing for 15 years. You will end up waking one day and asking stuff that are equal to "how do i walk?" :) My specific question is that as a new entrant to C# and OOP i am stepping into many little "details" that need to be addressed. Written a lot of code in VB.NET / cobol / simple php e.t.c surely does not help much into the OOP world... So , even after reading entry level books for C# and watching some videos i recently found out about the "factory model design" for applications. I would appreciate if any of you guys recomment some reading on application design architecture for further reading...

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• design pattern for unit testing?

  - by Maddy.Shik

  I am beginner in developing test cases, and want to follow good patterns for developing test cases rather than following some person or company's specific ideas. Some people don't make test cases and just develop the way their senior have done in their projects. I am facing lot problems like object dependencies (when want to test method which persist A object i have to first persist B object since A is child of B). Please suggest some good books or sites preferably for learning design pattern for unit test cases. Or reference to some good source code or some discussion for Dos and Donts will do wonder. So that i can avoid doing mistakes be learning from experience of others.

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• Online examples for software design diagrams

  - by Gerenuk

  Do you know where I can find a good example of software design diagrams and specs on the internet? Like UML, specs and similar. I'd like to understand this approach better. Before I just started coding and now I'd like plan more in advance. By diagrams I don't mean made-up examples, but something that would actually be used. Also it shouldn't be so trivial that there is no use of using diagrams. Ideally it shouldn't be too large either. Do you know a good online source? (this question is about online resources and specific examples only. it is not asking about books or advise how to learn software design.)

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• C# Open Source software that is useful for learning Design Patterns

  - by Fathom Savvy

  In college I took a class in Expert Systems. The language the book taught (CLIPS) was esoteric - Expert Systems: Principles and Programming, Fourth Edition. I remember having a tough time with it. So, after almost failing the class, I needed to create the most awesome Expert System for my final presentation. I chose to create an expert system that would calculate risk analysis for a person's retirement portfolio. In short, the system would provide the services normally performed by one's financial adviser. In other words, based on personality, age, state of the macro economy, and other factors, should one's portfolio be conservative, moderate, or aggressive? In the appendix of the book (or on the CD-ROM), there was this in-depth example program for something unrelated to my presentation. Over my break, I read and re-read every line of that program until I understood it to the letter. Even though it was unrelated, I learned more than I ever could by reading all of the chapters. My presentation turned out to be pretty damn good and I received praises from my professor and classmates. So, the moral of the story is..., by understanding other people's code, you can gain greater insight into a language/paradigm than by reading canonical examples. Still, to this day, I am having trouble with everyday design patterns such as the Factory Pattern. I would like to know if anyone could recommend open source software that would help me understand the Gang of Four design patterns, at the very least. I have read the books, but I'm having trouble writing code for the concepts in the real world. Perhaps, by studying code used in today's real world applications, it might just "click". I realize a piece of software may only implement one kind of design pattern. But, if the pattern is an implementation you think is good for learning, and you know what pattern to look for within the source, I'm hoping you can tell me about it. For example, the System.Linq.Expressions namespace has a good example of the Visitor Pattern. The client calls Expression.Accept(new ExpressionVisitor()), which calls ExpressionVisitor (VisitExtension), which calls back to Expression (VisitChildren), which then calls Expression (Accept) again - wooah, kinda convoluted. The point to note here is that VisitChildren is a virtual method. Both Expression and those classes derived from Expression can implement the VisitChildren method any way they want. This means that one type of Expression can run code that is completely different from another type of derived Expression, even though the ExpressionVisitor class is the same in the Accept method. (As a side note Expression.Accept is also virtual). In the end, the code provides a real world example that you won't get in any book because it's kinda confusing. To summarize, If you know of any open source software that uses a design pattern implementation you were impressed by, please list it here. I'm sure it will help many others besides just me. public class VisitorPatternTest { public void Main() { Expression normalExpr = new Expression(); normalExpr.Accept(new ExpressionVisitor()); Expression binExpr = new BinaryExpression(); binExpr.Accept(new ExpressionVisitor()); } } public class Expression { protected internal virtual Expression Accept(ExpressionVisitor visitor) { return visitor.VisitExtension(this); } protected internal virtual Expression VisitChildren(ExpressionVisitor visitor) { if (!this.CanReduce) { throw Error.MustBeReducible(); } return visitor.Visit(this.ReduceAndCheck()); } public virtual Expression Visit(Expression node) { if (node != null) { return node.Accept(this); } return null; } public Expression ReduceAndCheck() { if (!this.CanReduce) { throw Error.MustBeReducible(); } Expression expression = this.Reduce(); if ((expression == null) || (expression == this)) { throw Error.MustReduceToDifferent(); } if (!TypeUtils.AreReferenceAssignable(this.Type, expression.Type)) { throw Error.ReducedNotCompatible(); } return expression; } } public class BinaryExpression : Expression { protected internal override Expression Accept(ExpressionVisitor visitor) { return visitor.VisitBinary(this); } protected internal override Expression VisitChildren(ExpressionVisitor visitor) { return CreateDummyExpression(); } protected internal Expression CreateDummyExpression() { Expression dummy = new Expression(); return dummy; } } public class ExpressionVisitor { public virtual Expression Visit(Expression node) { if (node != null) { return node.Accept(this); } return null; } protected internal virtual Expression VisitExtension(Expression node) { return node.VisitChildren(this); } protected internal virtual Expression VisitBinary(BinaryExpression node) { return ValidateBinary(node, node.Update(this.Visit(node.Left), this.VisitAndConvert<LambdaExpression>(node.Conversion, "VisitBinary"), this.Visit(node.Right))); } }

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• Software design methods for Java or any other programming language

  - by IkerB

  I'm junior programmer and I would like to know how professionals write their code or which steps they follow when they are creating new software. I mean, which steps they follow, which programming methodology, software architecture design application software, etc. I would like to find a tutorial where they explain from the beginning which steps I have to follow from The Idea I have in my mind to the final version of the application in any language. Or perhaps how is your programming steps or rules that you used to follow. Because everytime I want to create the an application I spend few time on the design and a lot of time coding (I know, that's not good).

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• Design Patterns - do you use them?

  - by seth

  Being an IT student, I was recently given some overview about design patterns by one of our teachers. I understood what they are for but some aspects still keep bugging me. Are they really used by the majority of programmers? Speaking of experience, I've had some troubles while programming, things I could not solve for a while, but google and some hours of research solved my problem. If somewhere in the web I find a way to solve my problem, is this a design pattern? Am I using it? And also, do you (programmers) find yourself looking for patterns (where am I supposed to look btw?) when you start the development? If so, this is certainly a habit that I must start to embrace.

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• Design documents as part of Agile

  - by syrion

  At my workplace, we face a challenge in that "agile" too often has meant "vague requirements, bad acceptance criteria, good luck!" We're trying to address that, as a general improvement effort. So, as part of that, I am proposing that we generate design documents that, above and beyond the user story level, accurately reflect the outcome of preliminary investigations of the effect of a given feature within the system and including answers to questions that we have asked the business. Is there an effective standard for this? We currently face a situation where a new feature may impact multiple areas in our "big ball of mud" system, and estimates are starting to climb due to this technical debt. Hopefully more thoughtful design processes can help.

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• How do we know to favour composition over generalisation is always the right choice?

  - by Carnotaurus

  Whether an object physically exists or not, we can choose to model it in different ways. We could arbitarily use generalisation or composition in many cases. However, the GoF principle of "favour composition over generalisation [sic]" guides us to use composition. So, when we model, for example, a line then we create a class that contains two members PointA and PointB of the type Point (composition) instead of extending Point (generalisation). This is just a simplified example of how we can arbitarily choose composition or inheritance to model, despite that objects are usually much more complex. How do we know that this is the right choice? It matters at least because there could be a ton of refactoring to do if it is wrong?

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