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  • How to change the state of a singleton in runtime

    - by user34401
    Consider I am going to write a simple file based logger AppLogger to be used in my apps, ideally it should be a singleton so I can call it via public class AppLogger { public static String file = ".."; public void logToFile() { // Write to file } public static log(String s) { AppLogger.getInstance().logToFile(s); } } And to use it AppLogger::log("This is a log statement"); The problem is, what is the best time I should provide the value of file since it is a just a singleton? Or how to refactor the above code (or skip using singleton) so I can customize the log file path? (Assume I don't need to write to multiple at the same time) p.s. I know I can use library e.g. log4j, but consider it is just a design question, how to refactor the code above?

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  • Use decorator and factory together to extend objects?

    - by TheClue
    I'm new to OOP and design pattern. I've a simple app that handles the generation of Tables, Columns (that belong to Table), Rows (that belong to Column) and Values (that belong to Rows). Each of these object can have a collection of Property, which is in turn defined as an enum. They are all interfaces: I used factories to get concrete instances of these products, depending on circumnstances. Now I'm facing the problem of extending these classes. Let's say I need another product called "SpecialTable" which in turn has some special properties or new methods like 'getSomethingSpecial' or an extended set of Property. The only way is to extend/specialize all my elements (ie. build a SpecialTableFactory, a SpecialTable interface and a SpecialTableImpl concrete)? What to do if, let's say, I plan to use standard methods like addRow(Column column, String name) that doesn't need to be specialized? I don't like the idea to inherit factories and interfaces, but since SpecialTable has more methods than Table i guess it cannot share the same factory. Am I wrong? Another question: if I need to define product properties at run time (a Table that is upgraded to SpecialTable at runtime), i guess i should use a decorator. Is it possible (and how) to combine both factory and decorator design? Is it better to use a State or Strategy pattern, instead?

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  • Passing functions into other functions as parameters, bad practice?

    - by BlueHat
    We've been in the process of changing how our AS3 application talks to our back end and we're in the process of implementing a REST system to replace our old one. Sadly the developer who started the work is now on long term sick leave and it's been handed over to me. I've been working with it for the past week or so now and I understand the system, but there's one thing that's been worrying me. There seems to be a lot of passing of functions into functions. For example our class that makes the call to our servers takes in a function that it will then call and pass an object to when the process is complete and errors have been handled etc. It's giving me that "bad feeling" where I feel like it's horrible practice and I can think of some reasons why but I want some confirmation before I propose a re-work to system. I was wondering if anyone had any experience with this possible problem?

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  • How do I decide to which class a method should belong

    - by Eleeist
    I have TopicBusiness.class and PostBusiness.class. I have no problem with deciding into which class methods such as addPostToDatabase() or getAllPostsFromDatabase() should go. But what about getAllPostsFromTopic(TopicEntity topic) or getNumberOfPostsInTopic(TopicEntity topic)? Should the parameter be the deciding factor? So when the method takes TopicEntity as parameter it should belong to TopicBusiness.class? I am quite puzzled by this. EDIT: Some more info as requested. TopicBusiness.class and PostBusiness.class are classes holding all the business logic of the application concerning topics and posts respectively - that is fetching the data from database and/or performing some operations on them. TopicEntity is data (in this case representing single topic) fetched from database. getAllPostFromTopic(TopicEntity topic) gets all posts from database that belong to particular topic, while getNumberOfPostsInTopic(TopicEntity topic) performs database query and returns the number of posts that topic passed as parameter consists of.

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  • Interfaces on an abstract class

    - by insta
    My coworker and I have different opinions on the relationship between base classes and interfaces. I'm of the belief that a class should not implement an interface unless that class can be used when an implementation of the interface is required. In other words, I like to see code like this: interface IFooWorker { void Work(); } abstract class BaseWorker { ... base class behaviors ... public abstract void Work() { } protected string CleanData(string data) { ... } } class DbWorker : BaseWorker, IFooWorker { public void Work() { Repository.AddCleanData(base.CleanData(UI.GetDirtyData())); } } The DbWorker is what gets the IFooWorker interface, because it is an instantiatable implementation of the interface. It completely fulfills the contract. My coworker prefers the nearly identical: interface IFooWorker { void Work(); } abstract class BaseWorker : IFooWorker { ... base class behaviors ... public abstract void Work() { } protected string CleanData(string data) { ... } } class DbWorker : BaseWorker { public void Work() { Repository.AddCleanData(base.CleanData(UI.GetDirtyData())); } } Where the base class gets the interface, and by virtue of this all inheritors of the base class are of that interface as well. This bugs me but I can't come up with concrete reasons why, outside of "the base class cannot stand on its own as an implementation of the interface". What are the pros & cons of his method vs. mine, and why should one be used over another?

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  • Law of Demeter in MVC regarding Controller-View communication

    - by Antonio MG
    The scenario: Having a Controller that controls a view composed of complex subviews. Each one of those subviews is a separated class in a separate file. For example, one of those subviews is called ButtonsView, and has a bunch of buttons. The Controller has to access those buttons. Would accessing those buttons like this: controllerMainView.buttonsView.firstButton.state(); be a violation of the LOD? On one hand, it could be yes because the controller is accessing the inner hierarchy of the view. On the other, a Controller should be aware of what happens inside the view and how is composed. Any thoughts?

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  • How to decide to which class does a method belong

    - by Eleeist
    I have TopicBusiness.class and PostBusiness.class. I have no problem with deciding into which class methods such as addPostToDatabase() or getAllPostsFromDatabase() should go. But what about getAllPostsFromTopic(TopicEntity topic) or getNumberOfPostsInTopic(TopicEntity topic)? Should the parameter be the deciding factor? So when the method takes TopicEntity as parameter it should belong to TopicBusiness.class? I am quite puzzled by this.

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  • Is it better to return NULL or empty values from functions/methods where the return value is not present?

    - by P B
    I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take the following two methods as an examples: string ReverseString(string stringToReverse) // takes a string and reverses it. Person FindPerson(int personID) // finds a Person with a matching personID. In ReverseString(), I would say return an empty string because the return type is string, so the caller is expecting that. Also, this way, the caller would not have to check to see if a NULL was returned. In FindPerson(), returning NULL seems like a better fit. Regardless of whether or not NULL or an empty Person Object (new Person()) is returned the caller is going to have to check to see if the Person Object is NULL or empty before doing anything to it (like calling UpdateName()). So why not just return NULL here and then the caller only has to check for NULL. Does anyone else struggle with this? Any help or insight is appreciated.

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  • Any tips/tricks/resources on actually TEACHING a class on OOP? [closed]

    - by Sempus
    I may slowly be getting into teaching an Object-Orientated Programming class at my school in a year or two. I just graduated and work at my school as an Application Programmer. I'd first start off as a TA/grader and then slowly move into the Professor role. The class would be in Java. I always see resources on this fine site about HOW to program, but does anyone know any tips/tricks/resources on how to TEACH a programming class? It would be full of all different skills levels(but still semi-technical) so it would have to be a little more understandable than if it was just CS kids.

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  • is it valid that a state machine can have more than one possible state for some transition?

    - by shankbond
    I have a requirement for a workflow which I am trying to model as a state machine, I see that there is more than one outcome of a given transition(or activity). Is it valid for a state machine to have more than one possible states, but only one state will be true at a given time? Note: This is my first attempt to model a state machine. Eg. might be: s1-t1-s2 s1-t1-s3 s1-t1-s4 where s1, s2, s3, s4 are states and t1 is transition/activity. A fictitious real world example might be: For a human, there can be two states: hungry, not hungry A basket can have only one item from: apple, orange. So, to model it we will have: hungry-pick from basket-apple found hungry-pick from basket-orange found apple found-eat-not hungry orange found-take juice out of it and then drink- not hungry

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  • Separation of memory oriented process and CPU oriented process

    - by Jeevan Dongre
    I am develops guy working for an e-commerce company I am running my e-commerce application built using ruby on rails spree commerce. I am presently running 2 medium instances in the production. One is a high memory instance which has 3.8 RAM and single Core CPU and another one is high CPU instance which has Dual Core CPU. Basically AWS calls it has m1.medium and c1.medium instance respectively. My question is it possible to separate the processes according the cpu intense and memory intense? So that all the cpu intense process can be made run in high cpu instance and all the memory intense process can be made to run in the high memory instances. Is any tool available to identify those process. Kindly give me some heads up. Thank you

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  • getting aspect related information reg

    - by GowthamanSS
    Suppose i have these structure as class ss { public void createfile() { StreamWriter sw= new StreamWriter("d:/test.txt"); } } i need to do aspect where ever i use StreamWriter? as for as consideration i already used the below code as [assembly: MyAspect(AttributeTargetAssembly="mscorlib", AttributeTargetTypes="System.IO.File", AttributeTargetMembers="Create"] for file.create method .. it works fine .. Is there any way to solve this problem ... waiting for your response

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  • Resizing image with Python with locked aspect ratio

    - by David Vinklar
    How should I resize an image with Python script so that it would automatically adjust the Height ratio to the Width used? I'm using the following code: def Do(Environment): # Resize App.Do( Environment, 'Resize', { 'AspectRatio': 1.33333, 'CurrentDimensionUnits': App.Constants.UnitsOfMeasure.Pixels, 'CurrentResolutionUnits': App.Constants.ResolutionUnits.PixelsPerIn, 'Height': 1440, 'MaintainAspectRatio': True, 'Resample': True, 'ResampleType': App.Constants.ResampleType.SmartSize, 'ResizeAllLayers': True, 'Resolution': 72, 'Width': 1920, }) Using this code works perfectly if the aspect ratio of an image is the same as the one defined in the code - i.e. 1.33333. But how should I make it work with images that do not have this ratio? For me, what is important is that the new Width is 1920; Height has to be able to adjust automatically. Any ideas which part of my code should be altered and how?

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  • Object Oriented Database - why most of the companies do not use them

    - by GigaPr
    Hi, I am pretty new to programming(just finished University). I have been thought in the last 4 years about Object Oriented development and the numerous advantages of this approach. My question is Isn't it easier to use a pure Object Oriented database in development applications? Why Object Oriented database are not as much diffuse as relational? From my point of view makes sense to use OO database, the latter will avoid the numerous construction necessary for the mapping of complex objects on the tables.

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  • Looking for early paper about compiling object-oriented code

    - by Robert Kosara
    I remember reading a paper a long time ago that talked about object-oriented programming. I believe that this was from the early 1980s or perhaps even before then. This was at the time when object-oriented programming was still done through pre-processors, and one thing that stuck with me is this: it argued that you could write code in either procedural or object-oriented fashion, and after preprocessing/compiling, you would end up with the exact same machine code. Does anybody know which paper I'm talking about?

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  • Unittesting aspect-oriented features.

    - by Tomas Brambora
    Hi, I'd like to know what would you propose as the best way to unit test aspect-oriented application features (well, perhaps that's not the best name, but it's the best I was able to come up with :-) ) such as logging or security? These things are sort of omni-present in the application, so how to test them properly? E.g. say that I'm writing a Cherrypy web server in Python. I can use a decorator to check whether the logged-in user has the permission to access a given page. But then I'd need to write a test for every page to see whether it works oK (or more like to see that I had not forgotten to check security perms for that page). This could maybe (emphasis on maybe) be bearable if logging and/or security were implemented during the web server "normal business implementation". However, security and logging usually tend to be added to the app as an afterthough (or maybe that's just my experience, I'm usually given a server and then asked to implement security model :-) ). Any thoughts on this are very welcome. I have currently 'solved' this issue by, well - not testing this at all. Thanks.

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  • I'm interested in checking out a stack-oriented programming language. Which one would you recommend?

    - by Anto
    I'm interested in learning a stack-oriented programming language (such as Forth), which one would you recommend? The qualities I want are: You should be able to develop non-trivial software in it, but it mustn't be a great language for that as: I want to learn the language so I can try out a new paradigm (that is, not because I (think) that I will have great use of it). The reason I want to learn another paradigm is that I want to broaden my views on different approaches (learn to think in new ways, different from OOP, functional and structured). The language should let me do that (learn to think differently). The language should have available and good resources to learn from. The resources should also approach stack-oriented programming in a way that you understand the paradigm (after all, I do this for the paradigm).

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  • So what *did* Alan Kay really mean by the term "object-oriented"?

    - by Charlie Flowers
    Reportedly, Alan Kay is the inventor of the term "object oriented". And he is often quoted as having said that what we call OO today is not what he meant. For example, I just found this on Google: I made up the term 'object-oriented', and I can tell you I didn't have C++ in mind -- Alan Kay, OOPSLA '97 I vaguely remember hearing something pretty insightful about what he did mean. Something along the lines of "message passing". Do you know what he meant? Can you fill in more details of what he meant and how it differs from today's common OO? Please share some references if you have any. Thanks.

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  • Can an object oriented program be seen as a Finite State Machine?

    - by Peretz
    This might be a philosophical/fundamental question, but I just want to clarify it. In my understanding a Finite State Machine is a way of modeling a system in which the system's output will not only depend on the current inputs, but also the current state of the system. Additionally, as the name suggests it, a finite state machine can be segmented in a finite N number of states with its respective state and behavior. If this is correct, shouldn't every single object with data and function members be a state in our object oriented model, making any object oriented design a finite state machine? If that is not the interpretation of a FSM in object design, what exactly people mean when they implement a FSM in software? am I missing something? Thanks

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  • Where, in an object oriented system should you, if at all, choose (C-style) structs over classes?

    - by Anto
    C and most likely many other languages provide a struct keyword for creating structures (or something in a similar fashion). These are (at least in C), from a simplified point of view like classes, but without polymorphism, inheritance, methods, and so on. Think of an object-oriented (or multi paradigm) language with C-style structs. Where would you choose them over classes? Now, I don't believe they are to be used with OOP as classes seem to replace their purposes, but I wonder if there are situations where they could be preferred over classes in otherwise object-oriented programs and in what kind of situations. Are there such situations?

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  • How to design this procedural application into object oriented format?

    - by DavidL
    I'm building an application that basically pulls json data from a bunch of websites, processes it in some way and then writes it to a file. It is very easy to write this in a procedural way. I was wondering how this could be done in an object oriented way. Currently, the application looks something like this: res = get_json(link); process(res); write(res); Even if writing this in an object oriented way is not the best idea, tell me how it could be done because I have trouble with it.

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  • Criteria for a language to be considered "object oriented"

    - by nist
    I had a discussion about OO programming today and by browsing the internet I found a lot of different specifications for object oriented languages. What are the requirements for a language to be object oriented? For myself an object oriented language must have classes, inheritance and encapsulation. Is C an object oriented language just because you can use structs and program with an object oriented design? Why/ why not? Are there any good sites/articles about this? And please, no Wikipedia links because I've already been there.

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  • Aspect Oriented Programming Library/Framework for Actionscript 3?

    - by Tom
    I'm looking for a full featured AOP Library for Actionscript 3. The following projects I noticed so far, but they all seem to have their problems: - http://farmcode.org/page/Sodality.aspx (looks most promising so far, however it requires you to create a whole new class for every AOP "call" I believe, and it forces you to follow quite a lot of restrictions, anyone has experience with it? - http://code.google.com/p/loom-as3/ (this one is discontinued) - http://code.google.com/p/floxy/ (dynamic proxy generation? this isn't really AOP as I know it, right?) - http://code.google.com/p/flemit/ (dynamic byte code generation? this is something AOP needs I think, but not the full featured AOP framework I am looking for) Does anyone know of a better solution? Or does anyone have any experiences with AOP in Actionscript 3? Best regards, Tom

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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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