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

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2
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2answers
1k views

Class design for calling “the same method” on different classes from one place

Let me introduce my situation: I have Java EE application and in one package, I want to have classes which will act primarily as cache for some data from database, for example: class that will hold ...
55
votes
4answers
31k views

Why should I prefer composition over inheritance?

I always read that composition is to be preferred over inheritance. A blog post on unlike minds, for example, advocates using composition over inheritance, but I can't see how polymorphism is achieved....
123
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15answers
40k views

Do I need to use an interface when only one class will ever implement it?

Isn't the whole point of an interface to for multiple classes to adhere to a set of rules and implementations?
1
vote
2answers
187 views

Better application design - where to place interfaces

Where to place interfaces in a typical multi-layered app with DataAccess, BusinessLogic and an Endpoint modules? I propose 2 options In both cases there's only dependency from abstractions, but in ...
2
votes
3answers
402 views

Manual Dependency Injection Examples Still Tightly Coupled

I've been using AutoFac for some time now to take care of the dependency injection we're using in a web project. All is well, but I now want to demonstrate DI outside of an AutoFac context for reasons ...
0
votes
1answer
43 views

How do I use type assertions in Go when returning an interface type?

A struct I'm working on called fieldDefinition holds metadata about a field used by an object in my web app. One of the fields on fieldDefinition (it does get a bit confusing) looks something like ...
7
votes
2answers
205 views

Optional features: default method or separated interface

Dedicated interfaces seems to be a good way to expose the optional features in a domain-specific type hierarchy. However, they impede the use of decorator and composite patterns, which is also common ...
4
votes
4answers
372 views

Should an application configuration interface be broken into multiple interfaces to reduce feature creep?

My windows service is neatly separated into 5 components - each with their own interface and pulled together by a bootstrapper. One of my requirements is to provide configuration options in my app....
0
votes
1answer
81 views

Should I separate the interface or use single one [closed]

I'm developing a game, I will generate objects. I have create an interface called IObject which has the following properties: String tag // Tag for the object Vector3 position // Where the element is ...
123
votes
19answers
91k views

Why are interfaces useful?

I have been studying and coding in C# for some time now. But still, I can't figure the usefulness of Interfaces. They bring too little to the table. Other than providing the signatures of function, ...
1
vote
4answers
346 views

How can I avoid the use of strings?

I'm implementing a program where the user can 'create a musical scale' from a variety of notes (identified by their names), and the program will generate music from this scale. I want to implement a ...
9
votes
5answers
448 views

Separate interface for mutation methods

I've been working on refactoring some code, and I think I may have taken the first step down the rabbit hole. I'm writing the example in Java, but I suppose it could be agnostic. I have an interface ...
2
votes
2answers
159 views

Correct approach for creating api contract

I am trying to design an API. For creating contracts below are the two approaches: Approach 1: public class MyController { public void MyAction1(Dictionary<string, dynamic> input) { //...
38
votes
4answers
31k views

Why were default and static methods added to interfaces in Java 8 when we already had abstract classes?

In Java 8, interfaces can contain implemented methods, static methods, and the so-called "default" methods (which the implementing classes do not need to override). In my (probably naive) view, there ...
3
votes
4answers
341 views

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 ...
1
vote
2answers
178 views

Could changing the return type from void to string introduce breaking changes?

This SDK have an interface like this: public interface Contract { void update(..); void action(..); void delete(..); } Now, we need to change it to something like this: public ...
3
votes
4answers
216 views

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 ...
1
vote
1answer
169 views

Inefficient use of interfaces in OOP (C#)

In my code, I've got two interfaces, let's say IOpenable and IExaminable. IOpenable allows the user to Open or Close the object, and IExaminable allows the user to Examine the object. Now, we have ...
2
votes
1answer
142 views

Define an object with the interface as a type instead of class name [duplicate]

I try to practice with the design patterns and explore one of the possible implementations of the Observer Design Pattern in Java. I paid attention, that in this example the object is defined with the ...
11
votes
3answers
1k views

Is an interface considered 'empty' if it inherits from other interfaces?

Empty interfaces are generally consider bad practice, as far as I can tell - especially where things like attributes are supported by the language. However, is an interface considered 'empty' if it ...
1
vote
2answers
45 views

Declaring 'chained' interface inheritance

I assume this is largely language-agnostic, but I'm working in C# if it's not Let's say interface I3 inherits from I2, which in turn inherits from I1. I could write this: interface I1 { ... } ...
25
votes
4answers
18k views

Model-View-Presenter implementation thoughts

I'm trying to get a good grasp of how to implement good decoupling between a UI and the model, but I'm having trouble figuring out exactly where to divide the lines. I've been looking at Model-View-...
0
votes
1answer
72 views

What should this interface contain?

I am creating a schema for Doctrine but first I'm creating interfaces, abstract classes (models) which will be extended by the entities. I have a PresentationInterface which contain getter and ...
3
votes
1answer
139 views

Interfaces, abstraction, coding to an interface

Original question here I am learning OOP and SOLID. I have a 'main' class that performs some actions after reading variables from a config file. This 'main' class is not the focus of this question ...
1
vote
2answers
242 views

Convert this abstract class to an interface

I have a security method I would like to be able to sprinkle into other classes throughout my program. It is currently an abstract class but I feel it would be more appropriate as an interface. Can ...
12
votes
2answers
552 views

UnsupportedOperationException in java collections framework interfaces

Looking through the Java Collections Framework, I've noticed quite a few of the interfaces have the comment (optional operation). These methods allow implementing classes to through an ...
0
votes
3answers
450 views

Why List<E> interface is additionally introduced in collection hierarchy? [duplicate]

Below is the diagram, where, if we just consider the implementations of List, AbstractList maintains the core behavior of list. To introduce the new implementation class MyList(say) one can ...
5
votes
1answer
17k views

Difference between spring setter and interface injection?

I know how constructor and setter injection works in spring. Normally I use interfaces instead of classes to inject beans using setter and I consider it as interface injection, but in case of ...
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votes
2answers
162 views

Advantages of these recommendations in ooprogramming using Java

Below are the recommendation from section 5.1 of this essay. While Java is not a pure object-oriented language, it is possible to program in a pure object-oriented style by obeying the following ...
3
votes
1answer
349 views

Creating an interface just to decouple from third party libraries

I'm currently developing the Authorization module on a framework of mine. I have the following class so far: public interface IAuthorizationManager<C> where C : ...
0
votes
1answer
80 views

What would this interface be called? [closed]

At work we have a java backend that talks to python on some mobile devices. The mobile devices have no GUI, it's just pure string manipulation. All contact is initiated by the python; the java is just ...
2
votes
1answer
91 views

How valuable is decoupling in proprietary software?

When developing with Symfony2 PHP framework I often see reccomendations to decouple code but most of the time that is accompanied by a 'if you want to release as a third party bundle'. Which begs the ...
1
vote
1answer
401 views

Static methods vs Interface implementation

Here is my problem: I stared to create an e-commerce web site info collector. So I created a parser for each site. The parser class is stateless. I have got methods like: getItemPrice(WebElement ...
1
vote
3answers
100 views

Programming to an Interface and Interface Segregation in the Context of a User Class [duplicate]

I try to program to an interface whenever possible, but its not clear to me how I could apply it to a model as broad as a user. Which can hold many disparate fields (name, age, phone number, ssn, etc.)...
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votes
1answer
74 views

Programming to an Interface and Keep Testability in Unique Classes [duplicate]

I try to program to an interface whenever possible, but when I have a class that fulfills a very specific and unique purpose, one that can't be abstracted. Is it correct for me to say that I've ...
1
vote
1answer
49 views

Do my “dal” and “fileHandler” interfaces overlap?

I want my program to: read some input lines from CSV file write the output lines to plain string file read some input from the same file in (2) and compare it to some calculated data I want to ...
12
votes
1answer
776 views

Is it good practice to implement two Java 8 default methods in terms of each other?

I'm designing an interface with two related methods, similar to this: public interface ThingComputer { default Thing computeFirstThing() { return computeAllThings().get(0); } ...
2
votes
1answer
78 views

Repeating Interface inheritance declarations

Take the following example: public interface ISerialRVD { RouteValueDictionary ToRVD(); } public interface IViewModel : ISerialRVD // Here? { Int32 Page { get; set; } String Action { get;...
7
votes
5answers
414 views

Should private functions be held to the same standards as public functions?

If I'm building private utility functions, should they be held to the same rigorous standards in terms of handling invalid data as public functions? Example:If I'm writing code to calculate the ...
1
vote
3answers
169 views

When is a event listener invoked during program execution?

I am using the Obervable-Observer Pattern. MyClass extends Observable{ invokeListeners(){ doSomething; setChanged(); notifyListeners();//This invokes onUpdate() in "implements ...
0
votes
1answer
92 views

Provide part of context to class using interface

Currently I have class Context which I inject in some places in my code, like: protected override object GenerateSomething (object input, Context ctx) Depending on Context, Generate method gives ...
2
votes
4answers
3k views

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 ...
3
votes
4answers
2k views

How to force “program to an interface” without using a java Interface in java 1.6

In java 1.8 they have wonderful new "default interface methods". In 1.6 how close can we come? The goal: use code to keep clients from being able to tell that a class is not a java interface. If we ...
9
votes
5answers
705 views

Does it always make sense to “program to an interface” in Java?

I've seen the discussion at this question regarding how a class that implements from an interface would be instantiated. In my case, I'm writing a very small program in Java that uses an instance of ...
2
votes
2answers
278 views

Lesser of two evils regarding return types

I'm implementing a system in PHP where values are represented with objects that implement an Amount interface. I'm building two different implementations of this interface, one using a simple integer ...
21
votes
8answers
8k views

Interfaces on an abstract class

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 ...
2
votes
1answer
204 views

Application plugin system - interfaces - adding new features

Imagine I have an application, which have plugin system. public class MyPlugin : Plugin { public override ExecuteImpl (Context ctx) { // do something... } ...
28
votes
4answers
4k views

Why is .compareTo() in an interface while .equals() is in a class in Java?

I want to know why the .compareTo() is in the Comparable interface while a method like .equals is in the Object class. To me, it seems arbitrary why a method like .compareTo() is not in the Object ...
1
vote
0answers
251 views

Class Interfaces with Multiple Classes and Dependency Injection

NOTE ON QUESTION TITLE: I did not really even know how to phrase the title so if someone can edit and make it more articulate I would really appreciate it. QUESTION: Basically, what I'm trying to do ...
4
votes
2answers
179 views

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 ...