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  • LSP vs OCP / Liskov Substitution VS Open Close

    - by Kolyunya
    I am trying to understand the SOLID principles of OOP and I've come to the conclusion that LSP and OCP have some similarities (if not to say more). the open/closed principle states "software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification". LSP in simple words states that any instance of Foo can be replaced with any instance of Bar which is derived from Foo and the program will work the same very way. I'm not a pro OOP programmer, but it seems to me that LSP is only possible if Bar, derived from Foo does not change anything in it but only extends it. That means that in particular program LSP is true only when OCP is true and OCP is true only if LSP is true. That means that they are equal. Correct me if I'm wrong. I really want to understand these ideas. Great thanks for an answer.

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  • how do you read from system.out in Java [closed]

    - by Dan
    I'm trying to create a word scramble game and so far I have taken a vector of randomly assorted strings that contains both words and hints and split them into two vectors. I have randomly scrambled the word and set this all up in text boxes. Right now I'm stuck because I have a text box that takes input but I'm not sure how to read that in? I want the user to type the unscrambled word into the text box and have it calculate as correct and move on to the next word immediately. I also don't know how to get the keys working. I want the "?" character to be the hint button that shows the hint. At the moment the hint box works if I type the question mark in using the System.in but it doesn't work if I type it directly in to the text box. The characters are showing up in the text box but nothing is working after that.

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  • Dependency injection in constructor, method or just use a static class instead?

    - by gaetanm
    What is the best between: $dispatcher = new Dispatcher($request); $dispatcher->dispatch(); and $dispatcher = new Dispatcher(); $dispatcher->dispatch($request); or even Dispatcher::dispatch($request); Knowing that only one method of this class uses the $request instance. I naturally tend to the last solution because the class have no other states, but by I feel that it may not be the best OOP solution.

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  • Looking for some OO design advice

    - by Andrew Stephens
    I'm developing an app that will be used to open and close valves in an industrial environment, and was thinking of something simple like this:- public static void ValveController { public static void OpenValve(string valveName) { // Implementation to open the valve } public static void CloseValve(string valveName) { // Implementation to close the valve } } (The implementation would write a few bytes of data to the serial port to control the valve - an "address" derived from the valve name, and either a "1" or "0" to open or close the valve). Another dev asked whether we should instead create a separate class for each physical valve, of which there are dozens. I agree it would be nicer to write code like PlasmaValve.Open() rather than ValveController.OpenValve("plasma"), but is this overkill? Also, I was wondering how best to tackle the design with a couple of hypothetical future requirements in mind:- We are asked to support a new type of valve requiring different values to open and close it (not 0 and 1). We are asked to support a valve that can be set to any position from 0-100, rather than simply "open" or "closed". Normally I would use inheritance for this kind of thing, but I've recently started to get my head around "composition over inheritance" and wonder if there is a slicker solution to be had using composition?

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  • What simple game is good to learn OO principles?

    - by Bogdan Gavril
    I have to come up with a project propsal for my students, here are some details: The design should be gove over OO concepts: encapsulation, interfaces, inheritance, abstract classes Idealy a game, to keep interest high No GUI, just the console Effective time to finish this: ~ 6 days (1 person per proj) I have found one nice example of a game with carnivore and herbivore cells in a drop of water (array), it's a game of life twist. It is a bit too simple. Any ideeas? Aditional info: - language is C#

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  • Question about SDLC. How to answer this?

    - by pirzada
    I have seen this asked many times in job interviews but I am still not sure how to answer this. I am a web developer for quite some time but I still have problem with explaining OOP and SDLC (Familiar with system development life cycle) . How to prepare for above 2 topics for an interview point of view. Still I use both all the time during development. I am not clear on OOP SDLC Is there any simplest answer to both of these? Thanks

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  • Which topics should be covered in a basic undergraduate C++ course?

    - by Gulshan
    I have a young lecturer friend who is going to teach the undergraduate C++ course in CS. He asked me for some suggestions regarding how the course should be organized. Now I am asking you. I have seen many trends in universities which leads to a nasty experience of C++. So, please suggest from a professional programmer's point of view. For your information, the students going to take the course, have taken course like "Introduction to programming with C" in previous semester.

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  • Identity Map Pattern and the Entity Framework

    - by nikolaosk
    This is going to be the seventh post of a series of posts regarding ASP.Net and the Entity Framework and how we can use Entity Framework to access our datastore. You can find the first one here , the second one here and the third one here , the fourth one here , the fifth one here and the sixth one here . I have a post regarding ASP.Net and EntityDataSource. You can read it here .I have 3 more posts on Profiling Entity Framework applications. You can have a look at them here , here and here . In...(read more)

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  • Is there any reason to use "container" classes?

    - by Michael
    I realize the term "container" is misleading in this context - if anyone can think of a better term please edit it in. In legacy code I occasionally see classes that are nothing but wrappers for data. something like: class Bottle { int height; int diameter; Cap capType; getters/setters, maybe a constructor } My understanding of OO is that classes are structures for data and the methods of operating on that data. This seems to preclude objects of this type. To me they are nothing more than structs and kind of defeat the purpose of OO. I don't think it's necessarily evil, though it may be a code smell. Is there a case where such objects would be necessary? If this is used often, does it make the design suspect?

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  • Describe business logic with diagrams

    - by Nikos M.
    I am currently developing a web application for my thesis.I was asked by my professor to make diagrams to describe the business logic. Since I don't have a prior experience, I am pretty confused with all the terminology. I managed to clarify,I think, what business rules and business logic are, but I can't find out how you describe the business logic. Is it something particular or is it something more general? Do I need to learn UML? Does the fact that I use MVC affects the way I'll describe it?

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  • How much is modern programming still tied to underyling digital logic?

    - by New Talk
    First of all: I've got no academic background. I'm working primarily with Java and Spring and I'm also fond of web programming and relational databases. I hope I'm using the right terms and I hope that this vague question makes some sense. Today the following question came to my mind: How much is modern programming still tied to the underlying digital logic? With modern programming I mean concepts like OOP, AOP, Java 7, AJAX, … I hope you get the idea. Do they no longer need the digital logic with which computers are working internally? Or is binary logic still ubiquitous when programming this way? If I'd change the inner workings of a computer overnight, would it matter, because my programming techniques are already that abstract? P. S.: With digital logic I mean the physical representation of everything "inside" the computer as zeroes and ones. Changed "binary" to "digital".

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  • Good Software Architecture book or material?

    - by Inder Kumar Rathore
    I am a programmer and there is always a word going around about the architecture of the application/software. I want to gain some knowledge about how to develop good architecture. I know it is something that comes with the experience but I need some start so that I can practice it and get some good experience. So Please refer a good book for architecture. I know "Head first design patterns" is there, should I go for it or is there some good books also. Thanks

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  • Is it better to load up a class with methods or extend member functionality in a local subclass?

    - by Calvin Fisher
    Which is better? Class #1: public class SearchClass { public SearchClass (string ProgramName) { /* Searches LocalFile objects, handles exceptions, and puts results into m_Results. */ } DateTime TimeExecuted; bool OperationSuccessful; protected List<LocalFile> m_Results; public ReadOnlyCollection<LocalFile> Results { get { return new ReadOnlyCollection<LocalFile>(m_Results); } } #region Results Filters public DateTime OldestFileModified { get { /* Does what it says. */ } } public ReadOnlyCollection<LocalFile> ResultsWithoutProcessFiles() { return new ReadOnlyCollection<LocalFile> ((from x in m_Results where x.FileTypeID != FileTypeIDs.ProcessFile select x).ToList()); } #endregion } Or class #2: public class SearchClass { public SearchClass (string ProgramName) { /* Searches LocalFile objects, handles exceptions, and puts results into m_Results. */ } DateTime TimeExecuted; bool OperationSuccessful; protected List<LocalFile> m_Results; public ReadOnlyCollection<LocalFile> Results { get { return new ReadOnlyCollection<LocalFile>(m_Results); } } public class SearchResults : ReadOnlyCollection<LocalFile> { public SearchResults(IList<LocalFile> iList) : base(iList) { } #region Results Filters public DateTime OldestFileModified { get { /* Does what it says. */ } } public ReadOnlyCollection<LocalFile> ResultsWithoutProcessFiles() { return new ReadOnlyCollection<LocalFile> ((from x in this where x.FileTypeID != FileTypeIDs.ProcessFile select x).ToList()); } #endregion } } ...with the implication that OperationSuccessful is accompanied by a number of more interesting properties on how the operation went, and OldestFileModified and ResultsWithoutProcessFiles() also have several more siblings in the Results Filters section.

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  • Something similar to Objective-C categories in other languages?

    - by adig
    I understand Objective-C categories and how they become useful, but I always have a hard time explaining the concept to other programmers that are not familiar with Objective C. Maybe I'm just bad at explaining things, but I was thinking at another way to explain it by comparing to similar features offered by other (more popular) languages. (ex : I can explain the similarities between Objective C protocols and Java Interfaces) Any examples similar to Categories ?

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  • Make my website dynamically loaded data available to Facebook Open Graph Object Scrapper

    - by fvaliquette
    Here is the design of my web site: The user enter myWebsite.com/a/1 .htaccess rules redirect to myWebsite.com/b Now the JavaScript ExtJS library is loading. Extracting the value from the URL (in this case it is “1”) Loading ./xml/1.xml From 1.xml setting the Open Graph data (Title, type, image, etc) Loading data that will be shown to the user from 1.xml into the website. My question is: How can I make the Open Graph data available to Facebook? Facebook do not to load my ExtJS JavaScript Library before extracting the Open Graph Object values from the HTML. Is there an easy solution to this problem? The only solutions I found is to make statics web pages or dynamically pages rendered on the server side but I would like to avoid these since my web page implementation is already finished and I would like to avoid re working on it.

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  • what is message passing in OO?

    - by Tom
    I've been studying OO programming, primarily in C++, C# and Java. I thought I had a good grasp on it with my understanding of encapsulation, inheritance and polymorphism (as well as reading a lot of questions on this site). One thing that seems to popup up here and there is the concept of "message passing". Apparently, this is something that is not used whilst OO programming in today's mainstream languages, but is supported by Smalltalk. My questions are: What is message passing? (Can someone give a practical example?) Is there any support for this "message passing" in C++, C# or Java?

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  • Determine percentage of screen covered by an object without using frustum culling

    - by Meltac
    On the CPU-side of an 3D first-person / ego perspective game I need to check whether what the players currently sees on screen is the inside of a box object defined by world space coordinates (the player might be outside of that box but on screen sees only/mostly the inside of the box, or vice-versa, looks from within the box to the outside). The "casual" way of performing such a check would incorporate frustum culling but such an approach would be hard to achieve with my given set of engine parameters which I'd like to avoid if there is a simpler way. What I actually have at the point where I would like to do the check (high-level script on CPU, not GPU side): Camera world position Camera direction Camera FOV Two Box corner world coordinates (left-bottom-front, right-top-back) What I do not have right away: View frustrum definition (near/far plane or say 6 planes defining frustum) Any specific pixel information (uv, view space position, depth or the like) What I would like to calculate: Percentage of screen "covered" by box. Any hints on how to perform such calculation?

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  • How to refactor an OO program into a functional one?

    - by Asik
    I'm having difficulty finding resources on how to write programs in a functional style. The most advanced topic I could find discussed online was using structural typing to cut down on class hierarchies; most just deal with how to use map/fold/reduce/etc to replace imperative loops. What I would really like to find is an in-depth discussion of an OOP implementation of a non-trivial program, its limitations, and how to refactor it in a functional style. Not just an algorithm or a data structure, but something with several different roles and aspects - a video game perhaps. By the way I did read Real-World Functional Programming by Tomas Petricek, but I'm left wanting more.

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  • Explanation on how "Tell, Don't Ask" is considered good OO

    - by Pubby
    This blogpost was posted on Hacker News with several upvotes. Coming from C++, most of these examples seem to go against what I've been taught. Such as example #2: Bad: def check_for_overheating(system_monitor) if system_monitor.temperature > 100 system_monitor.sound_alarms end end versus good: system_monitor.check_for_overheating class SystemMonitor def check_for_overheating if temperature > 100 sound_alarms end end end The advice in C++ is that you should prefer free functions instead of member functions as they increase encapsulation. Both of these are identical semantically, so why prefer the choice that has access to more state? Example 4: Bad: def street_name(user) if user.address user.address.street_name else 'No street name on file' end end versus good: def street_name(user) user.address.street_name end class User def address @address || NullAddress.new end end class NullAddress def street_name 'No street name on file' end end Why is it the responsibility of User to format an unrelated error string? What if I want to do something besides print 'No street name on file' if it has no street? What if the street is named the same thing? Could someone enlighten me on the "Tell, Don't Ask" advantages and rationale? I am not looking for which is better, but instead trying to understand the author's viewpoint.

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  • What is the difference between Java 6 and PHP 5.4? [closed]

    - by Mashael
    First of all, let me explain the matter. I'm in a class where we learn Java 6 OOP fundamentals. However, my goal is to learn PHP (the last version) next. So, my question: Is there a big difference between PHP and Java 6 in OOP concepts? Meaning that after I finish the OOP class in Java will I find a lot of things that need to be learned in PHP regarding OOP? Update: *My goal of learning PHP next is to build dynamic sites* (I'm not sure of other options) and to follow OOP.

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  • OOP - Composition, Components and Composites Example?

    - by coder3
    I've been reading a bit about OOP in relation to Composition, Components and Composites. I believe I understand the fundamental principle (not sure). Can some one please provide a code example of a person or car (both have many properties) using Composition, Components and Composites. I think seeing it in code would clear up the confusion I have regarding this pattern. Preferably in Java or PHP - many thanks!

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  • software architecture (OO design) refresher course

    - by PeterT
    I am lead developer and team lead in a small RAD team. Deadlines are tight and we have to release often, which we do, and this is what keep the business happy. While we (the development team) are trying to maintain the quality of the code (clean and short methods), I can't help but notice that the overall quality of the OO design&architecture is getting worse over the time - the library we are working on is gradually reducing itself to a "bag of functions". Well, we try to use the design patterns, but since we don't really have much time for a design as such we are mostly using the creational ones. I have read Code Complete / Design Patterns (GOF & enterprise) / Progmatic Programmer / and many books from Effective XXX series. Should I re-read them again as I have read them a long time ago and forgotten quite a lot, or there are other / better OO design / software architeture books been published since then which I should definitely read? Any ideas, recommendations on how can I get the situation under control and start improving the architecture. The way I see it - I will start improving the architectural / design quality of software components I am working on and then will start helping other team members once I find what is working for me.

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  • Which paradigm to use for writing chess engine?

    - by poke
    If you were going to write a chess game engine, what programming paradigm would you use (OOP, procedural, etc) and why whould you choose it ? By chess engine, I mean the portion of a program that evaluates the current board and decides the computer's next move. I'm asking because I thought it might be fun to write a chess engine. Then it occured to me that I could use it as a project for learning functional programming. Then it occured to me that some problems aren't well suited to the functional paradigm. Then it occured to me that this might be good discussion fodder.

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  • How does a search functionality fit in DDD with CQRS?

    - by Songo
    In Vaughn Vernon's book Implementing domain driven design and the accompanying sample application I found that he implemented a CQRS approach to the iddd_collaboration bounded context. He presents the following classes in the application service layer: CalendarApplicationService.java CalendarEntryApplicationService.java CalendarEntryQueryService.java CalendarQueryService.java I'm interested to know if an application will have a search page that feature numerous drop downs and check boxes with a smart text box to match different search patterns; How will you structure all that search logic? In a command service or a query service? Taking a look at the CalendarQueryService.java I can see that it has 2 methods for a huge query, but no logic at all to mix and match any search filters for example. I've heard that the application layer shouldn't have any business logic, so where will I construct my dynamic query? or maybe just clutter everything in the Query service?

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  • Hadoop and Object Reuse, Why?

    - by Andrew White
    In Hadoop, objects passed to reducers are reused. This is extremely surprising and hard to track down if you're not expecting it. Furthermore, the original tracker for this "feature" doesn't offer any evidence that this change actually improved performance (unless I missed it). It would speed up the system substantially if we reused the keys and values [...] but I think it is worth doing. This seems completely counter to this very popular answer. Is there some credence to the Hadoop developer's claim? Is there something "special" about Hadoop that would invalidate the notion of object creation being cheap?

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