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  • If I define a property to prototype appears in the constructor of object, why?

    - by Eduard Florinescu
    I took the example from this question modified a bit: What is the point of the prototype method? function employee(name,jobtitle,born) { this.name=name; this.jobtitle=jobtitle; this.born=born; this.status="single" } employee.prototype.salary=10000000; var fred=new employee("Fred Flintstone","Caveman",1970); console.log(fred.salary); fred.salary=20000; console.log(fred.salary) And the output in console is this: What is the difference salary is in constructor but I still can access it with fred.salary, how can I see if is in constructor from code, status is still employee property how can I tell for example if name is the one of employee or has been touch by initialization? Why is salary in constructor, when name,jobtitle,born where "touched" by employee("Fred Flintstone","Caveman",1970); «constructor»?

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  • Manager/Container class vs static class methods

    - by Ben
    Suppose I a have a Widget class that is part of a framework used independently by many applications. I create Widget instances in many situations and their lifetimes vary. In addition to Widget's instance specified methods, I would like to be able to perform the follow class wide operations: Find a single Widget instance based on a unique id Iterate over the list of all Widgets Remove a widget from the set of all widgets In order support these operations, I have been considering two approaches: Container class - Create some container or manager class, WidgetContainer, which holds a list of all Widget instances, support iteration and provides methods for Widget addition, removal and lookup. For example in C#: public class WidgetContainer : IEnumerable<Widget { public void AddWidget(Widget); public Widget GetWidget(WidgetId id); public void RemoveWidget(WidgetId id); } Static class methods - Add static class methods to Widget. For example: public class Widget { public Widget(WidgetId id); public static Widget GetWidget(WidgetId id); public static void RemoveWidget(WidgetId id); public static IEnumerable<Widget AllWidgets(); } Using a container class has the added problem of how to access the container class. Make it a singleton?..yuck! Create some World object that provides access to all such container classes? I have seen many frameworks that use the container class approach, so what is the general consensus?

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  • When are Getters and Setters Justified

    - by Winston Ewert
    Getters and setters are often criticized as being not proper OO. On the other hand most OO code I've seen has extensive getters and setters. When are getters and setters justified? Do you try to avoid using them? Are they overused in general? If your favorite language has properties (mine does) then such things are also considered getters and setters for this question. They are same thing from an OO methodology perspective. They just have nicer syntax. Sources for Getter/Setter Criticism (some taken from comments to give them better visibility): http://www.javaworld.com/javaworld/jw-09-2003/jw-0905-toolbox.html http://typicalprogrammer.com/?p=23 http://c2.com/cgi/wiki?AccessorsAreEvil http://www.darronschall.com/weblog/2005/03/no-brain-getter-and-setters.cfm http://www.adam-bien.com/roller/abien/entry/encapsulation_violation_with_getters_and To state the criticism simply: Getters and Setters allow you to manipulate the internal state of objects from outside of the object. This violates encapsulation. Only the object itself should care about its internal state. And an example Procedural version of code. struct Fridge { int cheese; } void go_shopping(Fridge fridge) { fridge.cheese += 5; } Mutator version of code: class Fridge { int cheese; void set_cheese(int _cheese) { cheese = _cheese; } int get_cheese() { return cheese; } } void go_shopping(Fridge fridge) { fridge.set_cheese(fridge.get_cheese() + 5); } The getters and setters made the code much more complicated without affording proper encapsulation. Because the internal state is accessible to other objects we don't gain a whole lot by adding these getters and setters. The question has been previously discussed on Stack Overflow: http://stackoverflow.com/questions/565095/java-are-getters-and-setters-evil http://stackoverflow.com/questions/996179

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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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  • OO Design, how to model Tonal Harmony?

    - by David
    I have started to write a program in C++ 11 that would analyse chords, scales, and harmony. The biggest problem I am having in my design phase, is that the note 'C' is a note, a type of chord (Cmaj, Cmin, C7, etc), and a type of key (the key of Cmajor, Cminor). The same issue arises with intervals (minor 3rd, major 3rd). I am using a base class, Token, that is the base class for all 'symbols' in the program. so for example: class Token { public: typedef shared_ptr<Token> pointer_type; Token() {} virtual ~Token() {} }; class Command : public Token { public: Command() {} pointer_type execute(); } class Note : public Token; class Triad : public Token; class MajorTriad : public Triad; // CMajorTriad, etc class Key : public Token; class MinorKey : public Key; // Natural Minor, Harmonic minor,etc class Scale : public Token; As you can see, to create all the derived classes (CMajorTriad, C, CMajorScale, CMajorKey, etc) would quickly become ridiculously complex including all the other notes, as well as enharmonics. multiple inheritance would not work, ie: class C : public Note, Triad, Key, Scale class C, cannot be all of these things at the same time. It is contextual, also polymorphing with this will not work (how to determine which super methods to perform? calling every super class constructors should not happen here) Are there any design ideas or suggestions that people have to offer? I have not been able to find anything on google in regards to modelling tonal harmony from an OO perspective. There are just far too many relationships between all the concepts here.

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  • Which open source PHP project has the 'perfect' OOP design I can learn from?

    - by aditya menon
    I am a newbie to OOP, and I learn best by example. You could say this question is similar to Which Scala open source projects should I study to learn best coding practices - but in PHP. I have heard-tell that Symfony has the best 'architecture' (I will not pretend I know what that exactly means), as well as Doctrine ORM. Is it worth it to spend many months reading the source code of these projects, trying to deduce the patterns used and learning new tricks? I have seen equal number of web pages dissing and liking Zend's codebase (will provide links if deemed necessary). Do you know of any other project that would make any veteran OOP developer shed tears of joy? Please let me add that practicality and scope of use is not a concern at all here - I just want to do: Pick a project that has a codebase deemed awesome by devs way better and greater than me. Write code that achieves what the project does. Compare results and try to learn what I don't know. Basically, an academic interest codebase. Any recommendations please?

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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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  • 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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  • Design patterns and multiple programming languages

    - by Eduard Florinescu
    I am referring here to the design patterns found in the GOF book. First, how I see it, there are a few peculiarities to design pattern and knowing multiple languages, for example in Java you really need a singleton but in Python you can do without it you write a module, I saw somewhere a wiki trying to write all GOF patterns for JavaScript and all the entries were empty, I guess because it might be a daunting task to do that adaptation. If there is someone who is using design patterns and is programming multiple languages supporting the OOP paradigm and can give me a hint on how should I approach design patterns. An approach that might help me in all languages I use(Java, JavaScript, Python, Ruby): Can I write good application without knowing exactly the GOF design patterns or I might need just some of them which might be crucial and if yes which one, are there alternatives to GOF for specific languages, and should a programmer or a team make their own design patterns set?

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • How do game programmers design their classes to reuse in AI, network and play and pass mode?

    - by Amogh Talpallikar
    For a two player game where, your opponent could be on the network, CPU itself or near you where you would play turn by turn on the same machine. How do people design classes for re-use ? I am in a similar situation and have no experience in making such complex games. But here is what I have thought, If I am a player object , I should only be interacting with the GameManager or GameEngine Singleton , from which I will get various notifications about the game status. I dont care where and who my opponent is, this GameManager depending upon the game mode, will interact with gameNetworkManager , or AI tell me what the opponent played. I am not sure about the scenario where we play and pass [turn by turn on same machine]. Hoping for a brief but clear explanation or at least a link to a similar resource.:)

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  • Does command/query separation apply to a method that creates an object and returns its ID?

    - by Gilles
    Let's pretend we have a service that calls a business process. This process will call on the data layer to create an object of type A in the database. Afterwards we need to call again on another class of the data layer to create an instance of type B in the database. We need to pass some information about A for a foreign key. In the first method we create an object (modify state) and return it's ID (query) in a single method. In the second method we have two methods, one (createA) for the save and the other (getId) for the query. public void FirstMethod(Info info) { var id = firstRepository.createA(info); secondRepository.createB(id); } public void SecondMethod(Info info) { firstRepository.createA(info); var key = firstRepository.getID(info); secondRepository.createB(key); } From my understanding the second method follows command query separation more fully. But I find it wasteful and counter-intuitive to query the database to get the object we have just created. How do you reconcile CQS with such a scenario? Does only the second method follow CQS and if so is it preferable to use it in this case?

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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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  • Any language where every class instance is a class too?

    - by Dokkat
    Taking inspiration from Javascript prototypes, I had the idea of a language where every instance can be used as a class. Before I potentially reinvent the wheel, I would like to ask if there is a language already using this concept: //To declare a Class, extend the base class (in this case, Type) Type(Weapon,{price:0}); //Same syntax to inherit; simply extend the parent: Weapon(Sword,{price:3}); Weapon(Axe,{price:4}); Sword(Katana,{price:7}); Sword(Dagger,{price:3}); //And the same to create an instance: Katana(myKatana,{nickname:"Leon"}); myKatana.price; // 7 myKatana.nickname; // Leon // An operator to return children of a class; Sword_; // [Katana, Dagger] // An operator to return array of descendants; Sword__; // [Katana, Dagger, myKatana] // An operator to return array of parents; Sword^; // Weapon // Arrays can be used as elements Sword__.price += 1; //increases price of Sword's descendants by 1 mySword.price; //8 // And to access specific element (using its name instead of index) var name = "mySword" Katana_[name]; // [mySword] Katana_[name].nickname; // Leon Has this kind of approach been already studied/implemented?

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  • What should be allowed inside getters and setters?

    - by Botond Balázs
    I got into an interesting internet argument about getter and setter methods and encapsulation. Someone said that all they should do is an assignment (setters) or a variable access (getters) to keep them "pure" and ensure encapsulation. Am I right that this would completely defeat the purpose of having getters and setters in the first place and validation and other logic (without strange side-effects of course) should be allowed? When should validation happen? When setting the value, inside the setter (to protect the object from ever entering an invalid state - my opinion) Before setting the value, outside the setter Inside the object, before each time the value is used Is a setter allowed to change the value (maybe convert a valid value to some canonical internal representation)?

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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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