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• Defining formula through user interface in user form

  - by BriskLabs Pakistan

  I am a student and developing a simple assignment - windows form application in visual studio 2010. The application is suppose to construct formulas as per user requirement. The process: It has to pick data from columns of Microsoft Access database and the user should be able to pick the data by column name like we do in a drop down menu. and create reusable formulas in it ( configure it once and can change it again). followings are column titles from database that can be picked for example. e.g Col -1 : Marks in Maths Col -2 : Total Marks in Maths Col -3 : Marks in science Col -4 : Total marks in science Finally we should be able to construct any formula in the UI like (Col 1 + Col 3 ) / ( col 2 + col 4) = Formula 1 once this is formula is set saved and a name is assigned to it by user. he/she can use the formula and results shall appear in a window below. i.e He would be able to calculate his desired figures (formula) by only manipulating underlying data on the UI layer....choose the data for a period and apply the formula and get the answer Problem: It looks like I have to create an app where rules are set through UI....... this means no stored procedures are required in SQL.... please suggest the right approach.

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• Should all, none, or some overriden methods call Super?

  - by JoJo

  When designing a class, how do you decide when all overridden methods should call super or when none of the overridden methods should call super? Also, is it considered bad practice if your code logic requires a mixture of supered and non-supered methods like the Javascript example below? ChildClass = new Class.create(ParentClass, { /** * @Override */ initialize: function($super) { $super(); this.foo = 99; }, /** * @Override */ methodOne: function($super) { $super(); this.foo++; }, /** * @Override */ methodTwo: function($super) { this.foo--; } }); After delving into the iPhone and Android SDKs, I noticed that super must be called on every overridden method, or else the program will crash because something wouldn't get initialized. When deriving from a template/delegate, none of the methods are supered (obviously). So what exactly are these "je ne sais quoi" qualities that determine whether a all, none, or some overriden methods should call super?

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• Why to say, my function is of IFly type rather than saying it's Airplane type

  - by Vishwas Gagrani

  Say, I have two classes: Airplane and Bird, both of them fly. Both implement the interface IFly. IFly declares a function StartFlying(). Thus both Airplane and Bird have to define the function, and use it as per their requirement. Now when I make a manual for class reference, what should I write for the function StartFlying? 1) StartFlying is a function of type IFly . 2) StartFlying is a function of type Airplane 3) StartFlying is a function of type Bird. My opinion is 2 and 3 are more informative. But what i see is that class references use the 1st one. They say what interface the function is declared in. Problem is, I really don't get any usable information from knowing StartFlying is IFly type. However, knowing that StartFlying is a function inside Airplane and Bird, is more informative, as I can decide which instance (Airplane or Bird ) to use. Any lights on this: how saying StartFlying is a function of type IFly, can help a programmer understanding how to use the function?

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• Render 3d object to 2d surface (embedded system)

  - by Martin Berger

  i am working on an embedded system of a sort, and in some free time i would like to test its drawing capabilities. System in question is ARM Cortex M3 microcontroller attached to EasyMX Stellaris board. And i have a small 320x240 TFT screen :) Now, i have some free time each day and i want to create rotating cube. Micro C PRO for ARM doesnt have 3d drawing capabilities, which means it must be done in software. From the book Introduction to 3D Game Programming with DirectX 10 i know matrix algebra for transformations but that is cool when you have DirectX to set camera right. I gues i could make 2d object to rotate, but how would i go with 3d one? Any ideas and examples are welcome. Although i would prefer advices. I'd like to understand this.

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• Where can I learn about every OOP concept?

  - by Mel

  I'm looking for some material that can explain all the concepts related to OOP that doesn't deviate too much from the point. I want something short and understandable for a beginner. I know some of these can be found on wikipedia, but wikipedia is full of minor and sometimes big mistakes and I don't think that is the best choice for learning something. Where should I start ? Also, please don't recommend books of 1000 pages or such.

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• What's the equivalent name of "procedure" in OOP?

  - by AeroCross

  In several of my programming courses in the University, my teachers always told me the following: A function and a procedure are basically the same thing: the only difference is that a function returns a value, and the procedure doesn't. That means that this: function sum($a, $b) { return $a + $b; } ... is a function, and this: function sum($a, $b) { echo $a + $b; } ... is a procedure. In the same train of thought, I've seen that a method is the equivalent of a function in the OOP world. That means that this: class Example { function sum($a, $b) { return $a + $b; } } Is a method — but how do you call this? class Example { function sum($a, $b) { echo $a + $b; } } What's the equivalent name, or how do you call a method that doesn't returns anything?

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• How do I start correctly in building database classes in c#?

  - by e4rthdog

  I am new in C# programming and in OOP. I need to dive into web applications for my company, and I need to do it fast and correct. So even that I know ASP.NET MVC is the way to go, I want to start with some simple applications with ASP.NET Webforms and then advance to MVC logic. Also regarding my db classes: I plan to create common database classes in order to be able to use them either from WinForms or ASP.NET applications. I also know that the way to go is to learn about ORM and EF. BUT I also want to start from where I am feeling comfortable and that is the traditional ADO.NET way. So about my Data Access Layer classes: Should I return my results in datasets or arraylists/lists? Should my methods do their own connect/disconnect from the db, or have separate methods and let the application maintain the connection?

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• Share Mulitple Classes as one dll or a lib with Mulitple Projects

  - by JNL

  Currently I have some shared class files(.cpp and .h) which I include them in around 20 Projects. Currently I have to include them in all of the projects. So if I get some business requirments and I change some of the shared(.cpp or .h) files I have to include them in all the 20 Projects which is kind of tedious. Is there a way where I can create a shared dll or library and include it all of my Projects. So if I have to change it, I just have to change it once and then just Add Reference to include that dll or library which contains all the shared(.cpp, .h) files. Any help/recommendations regarding the same, will be highly appreciated. I am using VS2012 for VC++.

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• Parallel Class/Interface Hierarchy with the Facade Design Pattern?

  - by Mike G

  About a third of my code is wrapped inside a Facade class. Note that this isn't a "God" class, but actually represents a single thing (called a Line). Naturally, it delegates responsibilities to the subsystem behind it. What ends up happening is that two of the subsystem classes (Output and Timeline) have all of their methods duplicated in the Line class, which effectively makes Line both an Output and a Timeline. It seems to make sense to make Output and Timeline interfaces, so that the Line class can implement them both. At the same time, I'm worried about creating parallel class and interface structures. You see, there are different types of lines AudioLine, VideoLine, which all use the same type of Timeline, but different types of Output (AudioOutput and VideoOutput, respectively). So that would mean that I'd have to create an AudioOutputInterface and VideoOutputInterface as well. So not only would I have to have parallel class hierarchy, but there would be a parallel interface hierarchy as well. Is there any solution to this design flaw? Here's an image of the basic structure (minus the Timeline class, though know that each Line has-a Timeline): NOTE: I just realized that the word 'line' in Timeline might make is sound like is does a similar function as the Line class. They don't, just to clarify.

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• Learning good OOP design & unlearning some bad habits

  - by Nick

  I have been mostly a C programmer so far in my career with knowledge of C++. I rely on C++ mostly for the convenience STL provides and I hardly ever focus on good design practices. As I have started to look for a new job position, this bad habit of mine has come back to haunt me. During the interviews, I have been asked to design a problem (like chess, or some other scenario) using OOP and I doing really badly at that (I came to know this through feedback from one interview). I tried to google stuff and came up with so many opinions and related books that I don't know where to begin. I need a good through introduction to OOP design with which I can learn practical design, not just theory. Can you point me to any book which meets my requirements ? I prefer C++, but any other language is fine as long as I can pick-up good practices. Also, I know that books can only go so far. I would also appreciate any good practice project ideas that helped you learn and improve your OOP concepts. Thanks.

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• design for supporting entities with images

  - by brainydexter

  I have multiple entities like Hotels, Destination Cities etc which can contain images. The way I have my system setup right now is, I think of all the images belonging to this universal set (a table in the DB contains filePaths to all the images). When I have to add an image to an entity, I see if the entity exists in this universal set of images. If it exists, attach the reference to this image, else create a new image. E.g.: class ImageEntityHibernateDAO { public void addImageToEntity(IContainImage entity, String filePath, String title, String altText) { ImageEntity image = this.getImage(filePath); if (image == null) image = new ImageEntity(filePath, title, altText); getSession().beginTransaction(); entity.getImages().add(image); getSession().getTransaction().commit(); } } My question is: Earlier I had to write this code for each entity (and each entity would have a Set collection). So, instead of re-writing the same code, I created the following interface: public interface IContainImage { Set<ImageEntity> getImages(); } Entities which have image collections also implements IContainImage interface. Now, for any entity that needs to support adding Image functionality, all I have to invoke from the DAO looks something like this: // in DestinationDAO::addImageToDestination { imageDao.addImageToEntity(destination, imageFileName, imageTitle, imageAltText); // in HotelDAO::addImageToHotel { imageDao.addImageToEntity(hotel, imageFileName, imageTitle, imageAltText); It'd be great help if someone can provide me some critique on this design ? Are there any serious flaws that I'm not seeing right away ?

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• Why should I declare a class as an abstract class?

  - by Pied Piper

  I know the syntax, rules applied to abstract class and I want know usage of an abstract class Abstract class can not be instantiated directly but can be extended by other class What is the advantage of doing so? How it is different from an Interface? I know that one class can implement multiple interfaces but can only extend one abstract class. Is that only difference between an interface and an abstract class? I am aware about usage of an Interface. I have learned that from Event delegation model of AWT in Java. In which situations I should declare class as an abstract class? What is benefits of that?

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• Should all, none, or some overridden methods call Super?

  - by JoJo

  When designing a class, how do you decide when all overridden methods should call super or when none of the overridden methods should call super? Also, is it considered bad practice if your code logic requires a mixture of supered and non-supered methods like the Javascript example below? ChildClass = new Class.create(ParentClass, { /** * @Override */ initialize: function($super) { $super(); this.foo = 99; }, /** * @Override */ methodOne: function($super) { $super(); this.foo++; }, /** * @Override */ methodTwo: function($super) { this.foo--; } }); After delving into the iPhone and Android SDKs, I noticed that super must be called on every overridden method, or else the program will crash because something wouldn't get initialized. When deriving from a template/delegate, none of the methods are supered (obviously). So what exactly are these "je ne sais quoi" qualities that determine whether a all, none, or some overriden methods should call super?

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• What alternative is better to diagram this scenario?

  - by Mosty Mostacho

  I was creating and discussing a class diagram with a partner of mine. To simplify things, I've modify the real domain we're working on and made up the following diagram: Basically, a company works on constructions that are quite different one from each other but are still constructions. Note I've added one field for each class but there should be many more. Now, I thought this was the way to go but my partner told me that if in the future new construction classes appear we would have to modify the Company class, which is correct. So the new proposed class diagram would be this: Now I've been wondering: Should the fact that in no place of the application will there be mixed lists of planes and bridges affect the design in any way? When we have to list only planes for a company, how are we supposed to distinguish them from the other elements in the list without checking for their class names? Related to the previous question, is it correct to assume that this type of diagram should be high-level and this is something it shouldn't matter at this stage but rather be thought and decided at implementation time? Any comment will be appreciated.

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• What are the differences between abstract classes, interfaces, and when to use them

  - by user66662

  Recently I have started to wrap my head around OOP, and I am now to the point where the more I read about the differences between Abstract classes and Interfaces the more confused I become. So far, neither can be instantiated. Interfaces are more or less structural blueprints that determine the skeleton and abstracts are different by being able to partially develop code. I would like to learn more about these through my specific situation. Here is a link to my first question if you would like a little more background information: What is a good design model for my new class? Here are two classes I created: class Ad { $title; $description $price; function get_data($website){ } function validate_price(){ } } class calendar_event { $title; $description $start_date; function get_data($website){ //guts } function validate_dates(){ //guts } } So, as you can see these classes are almost identical. Not shown here, but there are other functions, like get_zip(), save_to_database() that are common across my classes. I have also added other classes Cars and Pets which have all the common methods and of course properties specific to those objects (mileage, weight, for example). Now I have violated the DRY principle and I am managing and changing the same code across multiple files. I intend on having more classes like boats, horses, or whatever. So is this where I would use an interface or abstract class? From what I understand about abstract classes I would use a super class as a template with all of the common elements built into the abstract class, and then add only the items specifically needed in future classes. For example: abstract class content { $title; $description function get_data($website){ } function common_function2() { } function common_function3() { } } class calendar_event extends content { $start_date; function validate_dates(){ } } Or would I use an interface and, because these are so similar, create a structure that each of the subclasses are forced to use for integrity reasons, and leave it up to the end developer who fleshes out that class to be responsible for each of the details of even the common functions. my thinking there is that some 'common' functions may need to be tweaked in the future for the needs of their specific class. Despite all that above, if you believe I am misunderstanding the what and why of abstracts and interfaces altogether, by all means let a valid answer to be stop thinking in this direction and suggest the proper way to move forward! Thanks!

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• Java word scramble game [closed]

  - by Dan

  I'm working on code for a word scramble game in Java. I know the code itself is full of bugs right now, but my main focus is getting a vector of strings broken into two separate vectors containing hints and words. The text file that the strings are taken from has a colon separating them. So here is what I have so far. public WordApp() { inputRow = new TextInputBox(); inputRow.setLocation(200,100); phrases = new Vector <String>(FileUtilities.getStrings()); v_hints = new Vector<String>(); v_words = new Vector<String>(); textBox = new TextBox(200,100); textBox.setLocation(200,200); textBox.setText(scrambled + "\n\n Time Left: \t" + seconds/10 + "\n Score: \t" + score); hintBox = new TextBox(200,200); hintBox.setLocation(300,400); hintBox.hide(); Iterator <String> categorize = phrases.iterator(); while(categorize.hasNext()) { int index = phrases.indexOf(":"); String element = categorize.next(); v_words.add(element.substring(0,index)); v_hints.add(element.substring(index +1)); phrases.remove(index); System.out.print(index); } The FileUtilities file was given to us by the pofessor, here it is. import java.util.*; import java.io.*; public class FileUtilities { private static final String FILE_NAME = "javawords.txt"; //------------------ getStrings ------------------------- // // returns a Vector of Strings // Each string is of the form: word:hint // where word contains no spaces. // The words and hints are read from FILE_NAME // // public static Vector<String> getStrings ( ) { Vector<String> words = new Vector<String>(); File file = new File( FILE_NAME ); Scanner scanFile; try { scanFile = new Scanner( file); } catch ( IOException e) { System.err.println( "LineInput Error: " + e.getMessage() ); return null; } while ( scanFile.hasNextLine() ) { // read the word and follow it by a colon String s = scanFile.nextLine().trim().toUpperCase() + ":"; if( s.length()>1 && scanFile.hasNextLine() ) { // append the hint and add to collection s+= scanFile.nextLine().trim(); words.add(s); } } // shuffle Collections.shuffle(words); return words; } }

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• how should I design Objects around this business requirement?

  - by brainydexter

  This is the business requirement: " A Holiday Package (e.g. New York NY Holiday Package) can be offered in different ways based on the Origin city: From New Delhi to NY From Bombay to NY NY itself ( Land package ) (Bold implies default selection) a. and b. User can fly from either New Delhi or Bombay to NY. c. NY is a Land package, where a user can reach NY by himself and is a standalone holidayPackage. " Let's say I have a class that represents HolidayPackage, Destination (aka City). public class HolidayPackage{ Destination holidayCity; ArrayList<BaseHolidayPackageVariant> variants; BaseHolidayPackageVariant defaultVariant; } public abstract class BaseHolidayPackageVariant { private Integer variantId; private HolidayPackage holidayPackage; private String holidayPackageType; } public class LandHolidayPackageVariant extends BaseHolidayPackageVariant{ } public class FlightHolidayPackageVariant extends BaseHolidayPackageVariant{ private Destination originCity; } What data structure/objects should I design to support: options a default within those options Sidenote: A HolidayPackage can also be offered in different ways based on Hotel selections. I'd like to follow a design which I can leverage to support that use case in the future. This is the backend design I have in mind.

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• Setting up ASP.NET structure for code

  - by user1175327

  I've always coded in C# MVC3 when developing web applications. But now i wanted to learn a bit more about developing web sites with just ASP.NET. But now i'm wondering what a good setup for my code would be. For me, an MVC like pattern seems to be a good way to go. But obviously ASP.NET doesn't have any router and controller classes. So i guess people have a different way of setting up their code when they do ASP.NET. So i'm looking for more information on how to get started with this. So not really the basics of ASP.NET, but something that focuses on a good code setup. Any good tutorials/information about this/?

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• Inheritance vs containment while extending a large legacy project

  - by Flot2011

  I have got a legacy Java project with a lot of code. The code uses MVC pattern and is well structured and well written. It also has a lot of unit tests and it is still actively maintained (bug fixing, minor features adding). Therefore I want to preserve the original structure and code style as much as possible. The new feature I am going to add is a conceptual one, so I have to make my changes all over the code. In order to minimize changes I decided not to extend existing classes but to use containment: class ExistingClass { // .... existing code // my code adding new functionality private ExistingClassExtension extension = new ExistingClassExtension(); public ExistingClassExtension getExtension() {return extension;} } ... // somewhere in code ExistingClass instance = new ExistingClass(); ... // when I need a new functionality instance.getExtension().newMethod1(); All functionality that I am adding is inside a new ExistingClassExtension class. Actually I am adding only these 2 lines to each class that needs to be extended. By doing so I also do not need to instantiate new, extended classes all over the code and I may use existing tests to make sure there is no regression. However my colleagues argue that in this situation doing so isn't a proper OOP approach, and I need to inherit from ExistingClass in order to add a new functionality. What do you think? I am aware of numerous inheritance/containment questions here, but I think my question is different.

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• Paradigms fit for UI programming

  - by Inca

  This is a more specific question (or actually two, but they are related) coming from the comments of OOP technology death where someone stated that OOP is not the right paradigm for GUI programming. Reading the comments there and here I still have the feeling there are things to learn: which programming paradigms are considered good fits and why are they better than others (perhaps with examples to illustrate?) I removed the tk-example from the title and question

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• Law of Demeter confusion [duplicate]

  - by user2158382

  This question already has an answer here: Rails: Law of Demeter Confusion 4 answers I am reading a book called Rails AntiPatterns and they talk about using delegation to to avoid breaking the Law of Demeter. Here is their prime example: They believe that calling something like this in the controller is bad (and I agree) @street = @invoice.customer.address.street Their proposed solution is to do the following: class Customer has_one :address belongs_to :invoice def street address.street end end class Invoice has_one :customer def customer_street customer.street end end @street = @invoice.customer_street They are stating that since you only use one dot, you are not breaking the Law of Demeter here. I think this is incorrect, because you are still going through customer to go through address to get the invoice's street. I primarily got this idea from a blog post I read: http://www.dan-manges.com/blog/37 In the blog post the prime example is class Wallet attr_accessor :cash end class Customer has_one :wallet # attribute delegation def cash @wallet.cash end end class Paperboy def collect_money(customer, due_amount) if customer.cash < due_ammount raise InsufficientFundsError else customer.cash -= due_amount @collected_amount += due_amount end end end The blog post states that although there is only one dot customer.cash instead of customer.wallet.cash, this code still violates the Law of Demeter. Now in the Paperboy collect_money method, we don't have two dots, we just have one in "customer.cash". Has this delegation solved our problem? Not at all. If we look at the behavior, a paperboy is still reaching directly into a customer's wallet to get cash out. Can somebody help me clear the confusion. I have been searching for the past 2 days trying to let this topic sink in, but it is still confusing.

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• nagios3 Error: Could not read object configuration data!

  - by user1493730

  I have a brand new install of nagios3 on ubuntu 12.04. After I log in to the web interface and click any link I get the error: Error: Could not read object configuration data! Here are some things you should check in order to resolve this error: Verify configuration options using the -v command-line option to check for errors. Check the Nagios log file for messages relating to startup or status data errors. I ran it with the -v option and it reported no errors: Total Warnings: 0 Total Errors: 0 Things look okay - No serious problems were detected during the pre-flight check The nagios log and apache error log and debug log all have nothing regarding this. Does anyone know how to turn on logging that will give me some kind of useful error? Or if anyone knows how to fix this specific problem without additional logging, I guess that's okay too. Thanks!

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• Should I limit my type name suffix vocabulary when using OOP?

  - by Den

  My co-workers tend to think that it is better to limit non-domain type suffixes to a small fixed set of OOP-pattern inspired words, e.g.: *Service *Repository *Factory *Manager *Provider I believe there is no reason to not extend that set with more names, e.g. (some "translation" to the previous vocabulary is given in brackets): *Distributor (= *DistributionManager or *SendingService) *Generator *Browser (= *ReadonlyRepositoryService) *Processor *Manipulator (= *StateMachineManager) *Enricher (= *EnrichmentService) (*) denotes some domain word, e.g. "Order", "Student", "Item" etc. The domain is probably not complex enough to use specialized approaches such as DDD which could drive the naming.

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• How to improve programming skills?

  - by Mike

  I'm very new to programming. I started learning PHP about half a year ago, so I do know something. I can write small functions, I can export and import information from a database and I can make a website. I don't know OOP principles and I don't know about objects and classes. Should I move to OOP principles and learn about classes, methods and objects? If not, what should I do? Continue writing simple code? How can a programmer write his/her own API? Is OOP necessary to do this? So how can i improve my skills? I love programming. I spend my 24/7 on it, so any help will be appreciated.

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• How to verify the Liskov substitution principle in an inheritance hierarchy?

  - by Songo

  Inspired by this answer: Liskov Substitution Principle requires that Preconditions cannot be strengthened in a subtype. Postconditions cannot be weakened in a subtype. Invariants of the supertype must be preserved in a subtype. History constraint (the "history rule"). Objects are regarded as being modifiable only through their methods (encapsulation). Since subtypes may introduce methods that are not present in the supertype, the introduction of these methods may allow state changes in the subtype that are not permissible in the supertype. The history constraint prohibits this. I was hoping if someone would post a class hierarchy that violates these 4 points and how to solve them accordingly. I'm looking for an elaborate explanation for educational purposes on how to identify each of the 4 points in the hierarchy and the best way to fix it. Note: I was hoping to post a code sample for people to work on, but the question itself is about how to identify the faulty hierarchies :)

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