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  • Java: Interface vs Abstract Class (regarding fields)

    - by lifeR00t
    From what I have gathered, I want to force a class to use particular private fields (and methods) I need an abstract class because an interface only declares public/static/final fields and methods. Correct?? I just started my first big java project and want to make sure I'm not going to hurt myself later :)

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  • Abstract classes and Pod::Coverage

    - by Ken Williams
    I've recently started to try to use Dist::Zilla for maintaining Path::Class. I added the [PodCoverageTests] plugin, and it's reporting some failures in the Path::Class::Entity class, which is the abstract base class for Path::Class::File and Path::Class::Dir. What I'd like is some way to tell the testing code that Entity doesn't need docs, but its two derived classes do - even though the methods are only defined in the parent class. Anyone know some way to do that?

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  • Base class with abstract subclasses in C# ?

    - by Nick Brooks
    public abstract class Request { public class Parameters { //Threre are no members here //But there should be in inherited classes } public Request() { parameters = new Parameters(); } public Parameters parameters; } Two questions: How do I make it so I can add stuff to the constructor but the original constructor will still be executed? How do I make it so the subclasses can add members to the Parameters class?

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  • Rails 3 Abstract Class vs Inherited Class

    - by R. Yanchuleff
    In my rails 3 model, I have two classes: Product, Service. I want both to be of type InventoryItem because I have another model called Store and Store has_many :InventoryItems This is what I'm trying to get to, but I'm not sure how to model this in my InventoryItem model and my Product and Service models. Should InventoryItem just be a parent class that Product and Service inherit from, or should InventoryItem be modeled as a class abstract of which Product and Service extend from. Thanks in advance for the advice!

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  • can I have an abstract base class with the key attribute being generic

    - by Greg
    Hi, I want to create a re-usable library. I was going to use extension methods however I run into some issues in some cases for the client to have to specify in the calling method the types. QUESTION - If I use an abstract base class as the basis, can I specify an attribute/property in the class to be generic (e.g. the key property might be an 'int' in one case, or a 'string' in another)?

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  • Using java abstract class

    - by user969131
    In my UI project, I have few screens that share the same header style only the text is specific to the screens. What will be a good way to implement this? Have the super class create all the header component and open the components to the sub class, the sub class will access to component's setText method to update the text? or Have abstract method in super class to create the components, sub class will implement these methods to create the component. Hope it make sense..

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  • Why abstract classes necessary?

    - by bala3569
    1.What is the point of creating a class that can't be instantiated? Most commonly to serve as a base-class or interface (some languages have a separate interface construct, some don't) - it doesn't know the implementation (that is to be provided by the subclasses / implementing classes) 2.Why would anybody want such a class? For abstraction and re-use 3.What is the situation in which abstract classes become NECESSARY?can anyone brief it with an example?

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  • Help with abstract class in Java with private variable of type List<E>

    - by Nazgulled
    Hi, It's been two years since I last coded something in Java so my coding skills are bit rusty. I need to save data (an user profile) in different data structures, ArrayList and LinkedList, and they both come from List. I want to avoid code duplication where I can and I also want to follow good Java practices. For that, I'm trying to create an abstract class where the private variables will be of type List<E> and then create 2 sub-classes depending on the type of variable. Thing is, I don't know if I'm doing this correctly, you can take a look at my code: Class: DBList import java.util.List; public abstract class DBList { private List<UserProfile> listName; private List<UserProfile> listSSN; public List<UserProfile> getListName() { return this.listName; } public List<UserProfile> getListSSN() { return this.listSSN; } public void setListName(List<UserProfile> listName) { this.listName = listName; } public void setListSSN(List<UserProfile> listSSN) { this.listSSN = listSSN; } } Class: DBListArray import java.util.ArrayList; public class DBListArray extends DBList { public DBListArray() { super.setListName(new ArrayList<UserProfile>()); super.setListSSN(new ArrayList<UserProfile>()); } public DBListArray(ArrayList<UserProfile> listName, ArrayList<UserProfile> listSSN) { super.setListName(listName); super.setListSSN(listSSN); } public DBListArray(DBListArray dbListArray) { super.setListName(dbListArray.getListName()); super.setListSSN(dbListArray.getListSSN()); } } Class: DBListLinked import java.util.LinkedList; public class DBListLinked extends DBList { public DBListLinked() { super.setListName(new LinkedList<UserProfile>()); super.setListSSN(new LinkedList<UserProfile>()); } public DBListLinked(LinkedList<UserProfile> listName, LinkedList<UserProfile> listSSN) { super.setListName(listName); super.setListSSN(listSSN); } public DBListLinked(DBListLinked dbListLinked) { super.setListName(dbListLinked.getListName()); super.setListSSN(dbListLinked.getListSSN()); } } 1) Does any of this make any sense? What am I doing wrong? Do you have any recommendations? 2) It would make more sense for me to have the constructors in DBList and calling them (with super()) in the subclasses but I can't do that because I can't initialize a variable with new List<E>(). 3) I was thought to do deep copies whenever possible and for that I always override the clone() method of my classes and code it accordingly. But those classes never had any lists, sets or maps on them, they only had strings, ints, floats. How do I do deep copies in this situation?

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  • How to persist a very abstract data type between sessions: PHP

    - by Greelmo
    I have an abstract data type that behaves much like stack. It represents a history of "graph objects" made by a particular user. Each "graph object" holds one or more "lines", a date range, keys, and a title. Each "line" holds a sql generator configured for a particular subset of data in my db. I would like for these "histories" to be available to users between their sessions. It will be in the form of a tab that reads something like "most recent graphs". What do you believe to be the best way to persist this type of data between sessions. This application could get rather large, so efficiency is a concern. Thanks in advance.

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  • Iphone -- init method of an abstract class

    - by William Jockusch
    I want to create classes Car, Vehicle, and Airplane with the following properties: Car and Airplane are both subclasses of Vehicle. Car and Airplane both have an initWithString method. The acceptable input strings for Car's and Airplane's initWithString methods do not overlap. Vehicle is "almost abstract", in the sense that any initialized instance should be either a Car or an Airplane. It is possible to pass a string into Vehicle and get back an instance of Car, an instance of Airplane, or nil, depending on the input string. Any particular design pattern I should prefer? In particular for Vehicle's initWithString and/or newVehicleWithString methods.

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  • EmguCV: Can't find ColorType abstract class

    - by roverred
    EmguCV ColorType wiki I'm trying to create a ColorType abstract class variable but it says the type or namespace does not exist. However I have access to the classes that extend it. I also tried adding all Emgu.CV libraries and have all the references and .dll files in the bin folder. using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; using System.Drawing; using Emgu.CV; using Emgu.CV.Util; using Emgu.CV.GPU; using Emgu.CV.ML; using Emgu.CV.OCR; using Emgu.CV.OpenCL; using Emgu.CV.Stitching; using Emgu.CV.VideoStab; using Emgu.CV.Structure; using Emgu.CV.UI; using Emgu.CV.CvEnum; namespace mySpace { class foo { private ColorType the color; //invalid can't find ColorType private ColorType myColor = new Gray(); //invalid } } Any ideas? Thanks for any help.

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  • Cannot create instance of abstract class

    - by SmartestVEGA
    I am trying to compile the following code and i am getting the error: Cannot create instance of abstract class . Please help m_objExcel = new Excel.Application(); m_objBooks = (Excel.Workbooks)m_objExcel.Workbooks; m_objBook = (Excel._Workbook)(m_objBooks.Add(m_objOpt)); m_objSheets = (Excel.Sheets)m_objBook.Worksheets; m_objSheet = (Excel._Worksheet)(m_objSheets.get_Item(1)); // Create an array for the headers and add it to cells A1:C1. object[] objHeaders = {"Order ID", "Amount", "Tax"}; m_objRange = m_objSheet.get_Range("A1", "C1"); m_objRange.Value = objHeaders; m_objFont = m_objRange.Font; m_objFont.Bold=true; // Create an array with 3 columns and 100 rows and add it to // the worksheet starting at cell A2. object[,] objData = new Object[100,3]; Random rdm = new Random((int)DateTime.Now.Ticks); double nOrderAmt, nTax; for(int r=0;r<100;r++) { objData[r,0] = "ORD" + r.ToString("0000"); nOrderAmt = rdm.Next(1000); objData[r,1] = nOrderAmt.ToString("c"); nTax = nOrderAmt*0.07; objData[r,2] = nTax.ToString("c"); } m_objRange = m_objSheet.get_Range("A2", m_objOpt); m_objRange = m_objRange.get_Resize(100,3); m_objRange.Value = objData; // Save the Workbook and quit Excel. m_objBook.SaveAs(m_strSampleFolder + "Book2.xls", m_objOpt, m_objOpt, m_objOpt, m_objOpt, m_objOpt, Excel.XlSaveAsAccessMode.xlNoChange, m_objOpt, m_objOpt, m_objOpt, m_objOpt); m_objBook.Close(false, m_objOpt, m_objOpt); m_objExcel.Quit();

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  • variables in abstract classes C++

    - by wyatt
    I have an abstract class CommandPath, and a number of derived classes as below: class CommandPath { public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { int stage; public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; All of the derived classes have the member variable 'stage'. I want to build a function into all of them which manipulates 'stage' in the same way, so rather than defining it many times I thought I'd build it into the parent class. I moved 'stage' from the private sections of all of the derived classes into the protected section of CommandPath, and added the function as follows: class CommandPath { protected: int stage; public: virtual CommandResponse handleCommand(std::string) = 0; virtual CommandResponse execute() = 0; std::string confirmCommand(std::string, int, int, std::string, std::string); virtual ~CommandPath() {} }; class GetTimeCommandPath : public CommandPath { public: GetTimeCommandPath() : stage(0) {} CommandResponse handleCommand(std::string); CommandResponse execute(); }; Now my compiler tells me for the constructor lines that none of the derived classes have a member 'stage'. I was under the impression that protected members are visible to derived classes? The constructor is the same in all classes, so I suppose I could move it to the parent class, but I'm more concerned about finding out why the derived classes aren't able to access the variable. Also, since previously I've only used the parent class for pure virtual functions, I wanted to confirm that this is the way to go about adding a function to be inherited by all derived classes.

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  • Liskov substitution principle with abstract parent class

    - by Songo
    Does Liskov substitution principle apply to inheritance hierarchies where the parent is an abstract class the same way if the parent is a concrete class? The Wikipedia page list several conditions that have to be met before a hierarchy is deemed to be correct. However, I have read in a blog post that one way to make things easier to conform to LSP is to use abstract parent instead of a concrete class. How does the choice of the parent type (abstract vs concrete) impacts the LSP? Is it better to have an abstract base class whenever possible?

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  • Why does PHP 5.2 disallow abstract static class methods?

    - by Artem Russakovskii
    After enabling strict warnings in PHP 5.2, I saw a load of strict standards warnings from a project that was originally written without strict warnings: Strict Standards: Static function Program::getSelectSQL() should not be abstract in Program.class.inc The function in question belongs to an abstract parent class Program and is declared abstract static because it should be implemented in its child classes, such as TVProgram. I did find references to this change here: Dropped abstract static class functions. Due to an oversight, PHP 5.0.x and 5.1.x allowed abstract static functions in classes. As of PHP 5.2.x, only interfaces can have them. My question is: can someone explain in a clear way why there shouldn't be an abstract static function in PHP?

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  • protected abstract override Foo(); &ndash; er... what?

    - by Muljadi Budiman
    A couple of weeks back, a co-worker was pondering a situation he was facing.  He was looking at the following class hierarchy: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { } class FirstConcrete : SecondaryBase { } class SecondConcrete : SecondaryBase { } Basically, the first 2 classes are abstract classes, but the OriginalBase class has Test implemented as a virtual method.  What he needed was to force concrete class implementations to provide a proper body for the Test method, but he can’t do mark the method as abstract since it is already implemented in the OriginalBase class. One way to solve this is to hide the original implementation and then force further derived classes to properly implemented another method that will replace it.  The code will look like the following: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { protected sealed override void Test() { Test2(); } protected abstract void Test2(); } class FirstConcrete : SecondaryBase { // Have to override Test2 here } class SecondConcrete : SecondaryBase { // Have to override Test2 here } With the above code, SecondaryBase class will seal the Test method so it can no longer be overridden.  Then it also made an abstract method Test2 available, which will force the concrete classes to override and provide the proper implementation.  Calling Test will properly call the proper Test2 implementation in each respective concrete classes. I was wondering if there’s a way to tell the compiler to treat the Test method in SecondaryBase as abstract, and apparently you can, by combining the abstract and override keywords.  The code looks like the following: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { protected abstract override void Test(); } class FirstConcrete : SecondaryBase { // Have to override Test here } class SecondConcrete : SecondaryBase { // Have to override Test here } The method signature makes it look a bit funky, because most people will treat the override keyword to mean you then need to provide the implementation as well, but the effect is exactly as we desired.  The concepts are still valid: you’re overriding the Test method from its original implementation in the OriginalBase class, but you don’t want to implement it, rather you want to classes that derive from SecondaryBase to provide the proper implementation, so you also make it as an abstract method. I don’t think I’ve ever seen this before in the wild, so it was pretty neat to find that the compiler does support this case.

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  • Ruby Abstract Class Design

    - by MattDiPasquale
    I'm creating a video game. It has Characters & Items. Since I want Characters & Items to each have a name, should I make another class called NamedObjects with just a name field and have Characters & Items extend that? Or is that going overboard?

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  • Abstract Factory Using Generics: Is Explicitly Converting a Specified Type to Generic a Bad Practice

    - by Merritt
    The question's title says it all. I like how it fits into the rest of my code, but does it smell? public interface IFoo<T> { T Bar { get; set; } } public class StringFoo : IFoo<string> { public string Bar { get; set; } } public static class FooFactory { public static IFoo<T> CreateFoo<T>() { if (typeof(T) == typeof(string)) { return new StringFoo() as IFoo<T>; } throw new NotImplementedException(); } } UPDATE: this is sort of a duplicate of Is the StaticFactory in codecampserver a well known pattern?

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  • Abstract base class puzzle

    - by 0x80
    In my class design I ran into the following problem: class MyData { int foo; }; class AbstraktA { public: virtual void A() = 0; }; class AbstraktB : public AbstraktA { public: virtual void B() = 0; }; template<class T> class ImplA : public AbstraktA { public: void A(){ cout << "ImplA A()"; } }; class ImplB : public ImplA<MyData>, public AbstraktB { public: void B(){ cout << "ImplB B()"; } }; void TestAbstrakt() { AbstraktB *b = (AbstraktB *) new ImplB; b->A(); b->B(); }; The problem with the code above is that the compiler will complain that AbstraktA::A() is not defined. Interface A is shared by multiple objects. But the implementation of A is dependent on the template argument. Interface B is the seen by the outside world, and needs to be abstrakt. The reason I would like this is that it would allow me to define object C like this: Define the interface C inheriting from abstrakt A. Define the implementation of C using a different datatype for template A. I hope I'm clear. Is there any way to do this, or do I need to rethink my design?

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  • My abstract class implements an interface but doesn't implement some of its methods. How do I make i

    - by Stefan Monov
    interface ICanvasTool { void Motion(Point newLocation); void Tick(); } abstract class CanvasTool_BaseDraw : ICanvasTool { protected abstract void PaintAt(Point location); public override void Motion(Point newLocation) { // implementation } } class CanvasTool_Spray : CanvasTool_BaseDraw { protected abstract void PaintAt(Point location) { // implementation } public override void Tick() { // implementation } } This doesn't compile. I could add an abstract method "Tick_Implementation" to CanvasTool_BaseDraw, then implement ICanvasTool.Tick in CanvasTool_BaseDraw with a one-liner that just calls Tick_Implementation. Is this the recommended workaround?

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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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