Questions tagged [interfaces]

Questions about interface related design considerations, such as programming to the interface.

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Should i implement same interface in derived class?

Is there a difference between public class B implements C public class A extends B implements C and public class B implements C public class A extends B Is it just redundant implementation? ...
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Is it considered good practice to declare base interfaces without mutators, supplying mutatators in a sub-interface

I asked a question on StackOverflow on how to properly implement an ImmutableMap that abides by the SOLID principles. Due to Java's Map interface containing put and putAll, it violates the interface ...
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Why use arg type `class Object` instead of `Comparable[]`?

In the code below, I believe it would look more appropriate to make the method argument be of type Comparable[] instead of Object[]. The first reason it would be more appropriate is that one can be ...
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Should I make package private my DAO interfaces?

I have several DAO classes that implement an interface. In the other hand, I have Service classes that use those DAO implementations. So far all the DAO interfaces are public and I was thinking if ...
4
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1answer
98 views

Converting Interfaces to Sub types. Is this bad SE?

In the company I work for, I keep seeing IManager interfaces being converted into their real types and lots of "instanceof / TypeOf" if statement checks. For example: IManager manager // passed to ...
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1answer
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Inheritance from children to parents?

Seeing this UML class diagram : FileHandler, Uploader and Deleter are abstract classes. The four bottom classes are implementations. They extend on FileHandlerInterface which requires a handle method ...
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2answers
834 views

Is Dependency Inversion a valid alternative to the pImpl idiom?

If I want to present to the user of my code an interface, that is unlikely to change, I can write only the public part of the classes in public headers and have a single private pointer to another ...
4
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1answer
3k views

Interface with multiple default methods OR Interface + Class

In a code base I am "starting from" there are a handful of interfaces with many default methods. They look something like this: public interface HasXY { double getX(); double getY(); ...
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Design strategy for wrapping exceptions

I'm implementing a type of Repository for a framework/library that has (roughly) the following: public interface FooRepository { boolean contains(String id); Foo fetch(String id); void ...
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784 views

Clarification on the Dependency Inversion Principle

I'm reading the book "Agile Software Development, Principles, Patterns, and Practices" by Robert C. Martin. When he talks about the Dependency Inversion Principle he gives the following example of a ...
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Is it acceptable to make changes to an interface during implementation?

When writing a library/API for the first time I'll usually start by sketching some ideas on a white-board or loose-leaf while thinking about how different parts of the system interact. This usually ...
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Library IO: Use Interface classes or Callbacks?

I'm building a smallish library (few kLOC) which processes stream data in C++. From the streamed data (comes in packets) the library compiles a database piece by piece and naturally has to convey that ...
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Is Design by Contract the same as using Interfaces to create a “contract”?

Does an OOP design that uses a Design by Contract mean the designer is using interfaces to create a "contract." The term "contract" is used quite often when discussing OOP interfaces, so I didn't ...
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525 views

The inheritance argument of zope.interface (providedby vs isinstance)

What limitations does inheritance of an interface through an abstract base class present that are addressed by zope.interface? In the following talk given in 2010 by Jeff Rush about interfaces, at 11:...
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How to manage memory in C interface for C++ implementation considering c++11?

I have a library implemented in C++ which has a C interface. This C interface is, for all intents and purposes, the only way to use this library. C++11 seems to discourage the use of raw pointers but ...
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1answer
177 views

C programming multiple storage backends

I am starting a side project in C which requires multiple storage backends to be driven by a particular piece of logic. These storage backends would each be linked with the decision of which one to ...
4
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1answer
359 views

Discoverable default implementation of an interface

I have a couple of simple classes that implement the Null Object pattern. To illustrate the hierarchy, let's define a Config interface with two classes implementing it ConfigItem and MissingConfig, ...
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108 views

Message publishing interface when deferring until transaction is committed

Suppose I have the following interface used for publishing messages onto a message queue: interface IMessageProducer { void Publish<TMessage>(TMessage message); } Normally, an implementer ...
4
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2answers
433 views

Design interface for WebService to access several MySQL databases

I am currently trying to design an interface for a WebService that can access several MySQL databases. There will be 4 operations available, Add(), Read(), Update() and Delete(). The WebService just ...
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1answer
321 views

Is this Hybrid of Interface / Composition kosher?

I'm working on a project in which I'm considering using a hybrid of interfaces and composition as a single thing. What I mean by this is having a contain*ee* class be used as a front for ...
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Why 'List<E>' is an 'interface' but not 'abstract class'?

Amidst defining the hierarchy, firstly, one can think to embed the abstract method(behavior) in abstract class only because the derive concrete class possess that behavior as core behavior with it's ...
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7answers
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Architectural patterns for interaction beyond MVC? [closed]

We all know the venerable Model-View-Controller pattern used to design interaction [mostly] with human users. It is the de-facto standard in OOP environment. What are some other architectural ...
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6answers
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Design Patterns - Why the need for interfaces?

OK. I am learning design patterns. Every time I see someone code an example of a design pattern they use interfaces. Here is an example: http://visualstudiomagazine.com/Articles/2013/06/18/the-facade-...
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How to “program to an interface”

I've read these questions: Understanding "programming to an interface" What is the point of an interface? Does it always make sense to "program to an interface" in Java? I don't ...
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Design: Lisp (or other scripting language) as an interactive interface for C++?

I'm working on a medium size C++ project (will probably end up around 50k lines) and I have to provide an interactive terminal interface. The program produces scientific data as an output and the ...
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7answers
673 views

What problems will I face if I remove the concept of interfaces from my code?

I have been programming for many years but I am still not comfortable with the concept of "Interfaces". I try to use interfaces but many times I don't see a mandatory use for it. I think this is ...
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287 views

When and why would you put a new method into an interface instead of an abstract base class?

I have been asked the following question in an interview: "What is the need of an interface when you can have an abstract method within an abstract class?" Which I did not know the answer to. Could ...
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Do “avoid primitive obsession” and “use most abstract type as possible” contradict each other?

According to Is "avoid the yo-yo problem" a valid reason to allow the "primitive obsession"?, I should define "price" like this: public class Main{ private Price price; } ...
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Implicit optimization versus explicit optimization

To explain what I mean, let me start with an example. Consider a deque that supports O(logn) concatenation with another deque and O(n) addition of n elements at one end. This dequeimplements a ...
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Is it a good practice if using Object when a method can accept more than one type of object?

public class TaskA implements Runnable { .... } public class TaskB implements Runnable { .... } I have two runnable class as TaskA, TaskB. I want to have a TaskManager to run these two tasks and have ...
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when using dependency injection, should I always pass an interface

When using depending injection, you generally pass everything around as an interface (perhaps with the exception of primitives and strings). That allows you to easily chance the behavior, without ...
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190 views

What is the motivation or usage to create a interface use once only just for breaking circular dependency?

I understand if 2 classes have circular dependency, eg: public class MyWindow{ public MyWindow(){ new MyDialog(this); } public onDialogResponse(int option){ } } public class ...
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How should I write an interface that takes a list of items?

I'm writing a library function that takes a list (or "bunch") of items (let's say Student) and does something with them. What's the best way to write the function signature in the interface? std::...
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5answers
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User stories about one and the same functionality for two different roles

My team is building a solution where a mobile app communicates with a backend. I need to describe functionality where the communication between the app and the backend is optimized according to some ...
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573 views

Is it bad practice to create an interface only to combine two other interfaces?

I'm working on an infrastructure for inter process communication. I have created two interfaces, one to send data and another one to listen to data being sent: public interface ISender<T> : ...
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3answers
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Implementing the Interface Segregation Principle

Does this IConvertible interface satisfy the Interface Segregation Principle (ie. the "I" in SOLID)? Here is the definition: public interface IConvertible { TypeCode GetTypeCode(); bool ...
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201 views

Circular Interface references

I've heard circular references are generally an issue, however I was wondering if this was true for interfaces that reference other interfaces, for example: IQuestion{ IAnswer getCorrectAnswer(); ...
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3answers
661 views

How to remove dependencies on internal classes in the interface

I have a software component that is a part of a bigger software product. The software component lives in its namespace Component. Also the component has an interface (some part of it is below) that ...
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3answers
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Is it good practice to create interfaces that limit usage?

So I'm coding a way to send events to multiple clients, and then having the clients decide how they want to handle it. I'll exclude the bits that don't lend themselves to explaining the situation. ...
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Switch interface implementation using configuration [closed]

We want to allow the same core service to be either fully implemented or, as other option, to be a proxy toward a client legacy system (via a WSDL for example). In that way, we have both ...
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3answers
562 views

How to decide, should I put methods to abstract class or to interface?

I'm writing an app it needs to have generic registration step item. It needs to be able to do some specific things (I use interface for that) and it needs to be a visual element (of Xamarin. It doesn'...
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870 views

If Class is to define attributes and methods, and Interface is to define (a set of) methods, then how to think of interface needing new attributes?

I thought a class is supposed to define, or give a blueprint, of attributes and methods for an object. And then, an interface is to provide a set of methods, as a contract for its clients. (and so a ...
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2answers
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Where should I use abstract classes vs interfaces for a REST API client?

I'm trying to write a REST API client for practice and I'm having trouble figuring out how lay out the project. The approach I'm taking right now has Actions, DomainObjects, Requests, and a class ...
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1answer
380 views

When adding a property to an interface in C#, is that consider major, minor, or patch using semantic versioning?

My team and I are trying to follow semantic versioning 2.0.0 to keep tabs on our library versions. We primarily use C# for our development and are currently in a situation where we are going to add a ...
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“One of some”-type

Say that you have some different classes that does not really have any functionality in common, but somewhere in your program, you need one of them (which one is not necessarily important) because ...
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2answers
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How do you maintain protocol of function return value in dynamic language?

In dynamic programming language like Python, Javascript, it's very easy to make a function return an object: def make_vector2(a, b): return {"x": a, "y": b} The 'signature' of the returned ...
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2answers
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Is it a good programming practice to have a class with several .h files?

I suppose the class have several different interfaces. Some it shows to some class, some it shows to other classes. Are there any good reason for that? One thing I can think of is with one .h per ...
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As a tooling/automation developer, can I be making better use of OOP?

My time as a developer (~8 yrs) has been spent creating tooling/automation of one sort or another. The tools I develop usually interface with one or more API's. These API's could be win32, WMI, VMWare,...
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Fruit obj=new Orange(); and Orange obj=new Orange(); if both works identically in my code, which is the less coupling one?

Suppose I have 2 classes (which don't show methods to look simpler): public interface Fruit{ } public class Orange implements Fruit{ } , and assume I can use 2 ways to initialize Orange without ...
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1answer
114 views

How should equality be defined for classes that implement same interface?

Suppose I have two classes that implement the same interface, as in the example in C# below: public interface ICommonInterface { string Text { get; } int Count { get; } } public class ...

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