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

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25
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3answers
4k views

If I implement an Interface, is it called an Inheritance?

If my class implements an interface then can I say that I'm following inheritance? I know that when a class extends another class then it's inheritance.
1
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2answers
157 views

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? ...
0
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1answer
90 views

How to make interfaces usable for special classes only?

Is there a way to make Java interfaces only implementable by classes of a special type? So for instance, I have a class Foo and an interface Bar. Only subclasses of Foo should be able to implement ...
1
vote
1answer
129 views

What's the benefit of generics in an in interface e.g. IEnumerable<HttpPostedFileBase>

I've come across a method that requires a parameter that implements IEnumerable and is of a certain type like this: public myMethod (IEnumerable<HttpPostedFileBase> myParameter) { ...
1
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0answers
37 views

Should I use RFC 2119 in interface documentation?

RFC 2119 defines several terms, including MUST, SHOULD, and MAY, for use in standards documents, particularly those relating to networking protocols such as IP and HTTP. These terms are widely used ...
0
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1answer
66 views

Passing a Serial Port Instance

Background I am thinking about designing a (GoF/behavioral) command-pattern interface. I may decide to call this thing ICommand. I am thinking that I would have some sort of a queue containing a ...
16
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2answers
1k views

Principle of least astonishment (POLA) and interfaces

A good quarter of a century ago when I was learning C++, I was taught that interfaces should be forgiving and as far as possible not care about the order that methods were called since the consumer ...
4
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2answers
130 views

Understanding polymorphism and interface in Java

I'm reading though some notes. And I'm not understanding the following two statements. Polymorphism means that it is always the class of the actual object at run time that determines which method ...
2
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2answers
119 views

Why would an interface override methods of the interface(s) it extends in Java 7?

I was looking at Map and SortedMap documentation from Java 7 and I have realized that SortedMap, which extends Map overrides entrySet(), keySet() and values(). AFAIK, interfaces cannot implement a ...
4
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3answers
124 views

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? ...
2
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1answer
54 views

Should an interface covariant on T ever implement an interface invariant on it?

I was reading through the Hacklang docs on Collections, and came across this curious definition [paraphrased slightly]: interface KeyedIterable<Tk, Tv> ... interface ConstVector<+Tv> ...
0
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0answers
24 views

Usage of “Passive View” for winforms application

I'm currently working on a winforms project which will have a rather complex structure with about 300/400 controls which I will have to access during the program is running. I am contemplating the ...
3
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1answer
64 views

Within an interface specified by a core component, should it request IReadOnlyCollection or IEnumerable?

In thinking about the principle of "be conservative in what you send and liberal in what you accept", I generally try to make my methods receive IEnumerable parameters, but emit a IReadOnlyCollection ...
0
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3answers
191 views

What to do if I need more than one base class in C#? [closed]

Let's say I have a grid with square fields. For the fields I have an abstract Field class. This class has several subclasses, for example EmptyField or RoadField. Some of these fields can be connected ...
2
votes
1answer
123 views

Lower class count vs explicitness

To help with an application that manipulates and works from an XML structure to produce other information, I've created a class structure that closely follows the XML structure. So, the XML is: ...
1
vote
1answer
53 views

Package Interfaces - Coupling & Re-Usability

Intent Packages should be designed to perform a single function well. Ideally this means that they should be highly modular and different packages should be able to be 'plugged-in' simply by ...
3
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1answer
213 views

Why covariance is forbidden for abstract class in C#

I've been digging in covariance and contravariance in C# and there is one thing I could not manage to understand. C# (AFAIK, as of 4 version) allows one to declare the covariant or contravariant ...
2
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3answers
167 views

When and why would you extract an abstract method from an abstract class to an interface?

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 ...
1
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1answer
82 views

Use the chance to return booleans after method calls for an optional layer of exception handling? [duplicate]

I would like to ask a follow-up to a question I just asked: Better to have 2 methods with clear meaning, or just 1 dual use method? I now understand why it is best to separate charge(float c); and ...
26
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6answers
3k views

Better to have 2 methods with clear meaning, or just 1 dual use method?

To simplify the interface, is it better to just not have the getBalance() method? Passing 0 to the charge(float c); will give the same result: public class Client { private float bal; float ...
2
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1answer
236 views

Open / Closed Principle

I found this code example explaining Open / Closed principle. Code before application of principle: public class Logger { public void Log(string message, LogType logType) { switch ...
0
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0answers
53 views

Software Architecture: CQRS and port modeling

I have a PersonComponent, which an internal implementation is based on CQRS pattern. So which one is better way to model ports (and their interfaces): I'm not totally sure that how high or low ...
0
votes
1answer
123 views

Neat way on passing interface parameter to a constructor

Having lots of Interface that needs to pass in a constructor looks messy, is there any neat way of doing it? Code snippet: public class Foo { private readonly IRepository1 _repository1; ...
-2
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1answer
144 views

Why are interfaces necessary in MVP design pattern?

I am trying to understands MVP using Winforms. I found this example. Why do UserModel and UserView need to implement the IUserModel and IUserView interfaces ?
1
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2answers
110 views

Does an interface including several methods that return instances of Object make sense?

I am in the process of writing my first true API. In the process, I am defining an interface for mapping complex data structures onto other complex data structures. At the moment, the interface ...
1
vote
2answers
84 views

Where to inject dependency required by all implementors of an interface?

I have an interface whose job is to communicate with repository (that implements some interface). It doesn't seem to make sense to implement this interface without receiving a repository,so I'd like ...
0
votes
1answer
111 views

Can I enforce the overriding of GetHashCode() and Equals() methods for users of a generic container class?

I have a container class similar to the one below (with much of the logic omitted): class Container<T> { Dictionary<T, TWrapped> contains = new Dictionary<T, TWrapper>(); ...
1
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3answers
301 views

How can I sell DRY? [closed]

Where I work we have around 10 VS projects in a solution which are identical in functionality (with some different different rules in a few methods) and share many exact methods. They share the same ...
2
votes
1answer
133 views

Structuring projects in a solution for interfaces

I had this idea that I would achieve some good automation and separation of concerns as follows: Define an interface, IDataProvider, in a class in a DataMuncher project that needs to both consume ...
2
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2answers
73 views

Where to put configuration constants?

Considering a small embedded C project, how to decide if certain constants belong to a global configuration file the header of the "module == compilation unit" on top of the the actual C file or ...
9
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2answers
471 views

Interface Segregation Principle: What to do if interfaces have significant overlap?

From Agile Software Development, Principles, Patterns, and Practices: Pearson New International Edition: Sometimes, the methods invoked by different groups of clients will overlap. If the overlap ...
9
votes
2answers
198 views

Programming to Data Oriented Interfaces

There is a portion of our codebase written in the following style: // IScheduledTask.cs public interface IScheduledTask { string TaskName { get; set; } int TaskPriority { get; set; } ...
3
votes
6answers
169 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 ...
4
votes
2answers
347 views

How and when did it happen that, a type is an interface?

I came from a highly functional and procedural background in programming, and never knew that a type is the same as an interface. As in the Design Patterns book by GoF, it says: A type is a name ...
21
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5answers
1k views

Implementing an interface when you don't need one of the properties

Pretty straight-forward. I'm implementing an interface, but there's one property that is unnecessary for this class and, in fact, shouldn't be used. My initial idea was to just do something like: int ...
1
vote
1answer
151 views

When should interface be owned by client?

In Agile Software Development: Principles, Patterns, and Practices, Uncle Bob talks about client owning the service interface. My questions are : Should client always own the interface or only ...
2
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3answers
169 views

What is the purpose of a wrapper class that does nothing but delegate to the object it wraps?

The specific example I have in mind is javax.servlet.ServletResponseWrapper: public class ServletResponseWrapper implements ServletResponse { private ServletResponse response; /** * The ...
3
votes
3answers
223 views

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 ...
0
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4answers
380 views

In C#, what is the benefit of assigning a class variable to an interface variable before calling any methods?

Where I work we develop in C# .NET and I was looking a code that they have made (my job is to optimize it) but I saw something in particular: Assuming that InterfaceDHO is an interface and ClassDHO ...
0
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2answers
114 views

Best practice for encapsulating a parameter that requires multiple interfaces to be implemented

I encounter this issue multiple times, but I'm never sure how best to deal with it. Basically, some methods I write require the implementing object to support multiple interfaces. The example I have ...
3
votes
3answers
523 views

Generics vs common interface?

I don't remember when I wrote generic class last time. Every time I think I need it after some thinking I make a conclusion I don't. The second answer to this question made me to ask for ...
3
votes
3answers
144 views

Communicating to an Object from another without coupling in java?

So I have a Person object, and a GumballMachine object. The behavior I'm searching for is, in the intent to avoid unnecessary coupling, have the method insertCoin() called from within the Person ...
4
votes
3answers
360 views

Composition over inheritance but

I'm trying to teach myself software engineering and coming up against some conflicting information which is confusing me. I've been learning OOP and what abstract classes / Interfaces are and how to ...
3
votes
2answers
425 views

Should the main method be separate in a separate class? [closed]

In Java main methods often do little more than parsing the command line arguments and initializing an object that then takes over, for example: public class FooServer { // ... public static ...
4
votes
1answer
177 views

UML: Should an asynchronous request-response message exchange be modelled as two ports/interfaces or one

I want to model an asynchronous request-response message exchange in UML. The request is sent from a client to a server. The server responses asynchronously. This can be modelled in a component ...
0
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0answers
25 views

Text based command/interface design

When using inter-process communication (pipes, memory streams, ...), I typically have a byte stream to communicate, also with http (unless using some heavy-weight web framework), the body comes as a ...
1
vote
2answers
208 views

To god (class) or not to god? [duplicate]

I'm working on a project that requires several different users in the system, all of which have overlapping responsibilities; we've isolated two possible ways of tackling this problem, but we're ...
0
votes
1answer
86 views

When designing input interfaces for a library, when to use data class rather than data interface?

Let's say library A, B and C are all custom math libraries. They may or may not use the same data types. The libraries have methods that accept data type inputs like ProcessAsync(DataTypeA) or ...
1
vote
1answer
138 views

Interface Design: Specific vs General parameter (A Minimal design vs anticipated use variation)

Code public interface IVehicle { string VehicleMake { get; } int MonthsSincePurchase { get; } bool IsApprovedUsed { get; } ... } public class WarrantyPopUpHandler { virtual bool ...
-3
votes
1answer
133 views

Why can't I return an implementation of an interface for a method that requests the interface? [closed]

I am implementing an interface I on a class A. Class A implements I. I have an Iterator T that is supposed to return an object which implements I everytime I call next. My iterator goes as follows ...