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• Switch interface implementation using configuration

  - by Marcos

  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 implementation (proxy & full) and we switch which one to use in the configuration of the app. So in a nutshell, Some desired features: Two different implementation (proxy, full) instead of one implementation with a switch inside Switch implementation using configuration: dependency injection? reflection? Nice-to-have: the packaged delivered to the client doesn’t have to change depending on the choice between proxy or full Nice-to-have: Client can develop their custom implementation of the Core Interface and configure the applciation to use that one With this background, the question is: What alternatives we have to choose one implementation or other of an interface just changing configuration? Thanks

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• Developing JSON API for a Carpool Engine

  - by Siddharth

  I am developing a new set of API methods for carpooling/cab booking, so if a developer needs to develop an app or webportal for carpooling, he can call my JSON API. Basically making it easy for developers. My API current has: AddVehicle AddJourney SearchJourney SubscribeToThisJourney(journey) SubscriberList(journey) to get list of people who have subscribed for this journey AcceptSubscription(subscriber) AcceptedSubcriberList SubscriberList to get list of providers I have subscribed to I need help with replacing subscriber with something else. It's difficult to remember, and confusing when you see 3 methods that mean very different things: SubscriberList, SubscribedToThisJourneyList and AcceptedSubscriberList. Confusing to remember. One is a list of who I have subscribed to Who has subscribed to me Whose subscription I have accepted How can I name these methods to make them easier to understand and remember?

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• How to create contracts in python

  - by recluze

  I am just moving to python from Java and have a question about the way the two do things. My question relates to contracts. An example: an application defines an interface that all plugins must implement and then the main application can call it. In Java: public interface IPlugin { public Image modify(Image img); } public class MainApp { public main_app_logic() { String pluginName = "com.example.myplugin"; IPlugin x = (IPlugin) Class.forName(pluginName); x.modify(someimg); } } The plugin implements the interface and we use reflection in main app to call it. That way, there's a contract between the main app and the plugin that both can refer to. How does one go about doing something similar in Python? And also, which approach is better? p.s. I'm not posting this on SO because I'm much more concerned with the philosophy behind the two approaches.

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• Java - Interfaces

  - by Paul

  Why interfaces cannot be declared as static ?

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• UML Class Diagram: Abstract or Interface?

  - by J Smith

  I am modeling a class diagram and have spotted an opportunity to simplify it slightly. What I want to know is, would this it be better to implement an abstract class or an interface? The scenario is this, I have the classes: Artist Genre Album Song All of which share the methods getName, setName, and getCount (playcount that is). Would it be best to create an abstract 'Music' class with the aforementioned abstract methods, or should I create an interface, since the classes that implement the interface have to include all of the interface's methods (I think, correct me if I'm wrong). I hope I've given enough detail, please ask questions if I haven't. Thanks!

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• Why does Java allow to implement different interfaces, each containing a method with the same signature?

  - by Software Engeneering Learner

  I've recently found that I can have two interfaces containing method with the same signature as a method in the other interface. And then I can have an interface or class that implements both of that interfaces. So the descendant class/interface has implicitly implements two different methods as a one method. Why is this allowed in Java? I can see a numerous problems that arises from that. Even eclipse only can find out about implementations for only one interface method, but for the second one it doesn't show any implementations at all. Also I believe there would be problems with automatic refactoring, like when you would like to change the signature of the method in one of the interfaces and IDE won't be able to correctly change that signature in all implementations, as they implement two different interfaces and how will IDE know what interface method it implementation descends. Why don't just make a compiler error like 'interfaces method names clashes' or something like that?

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• What resources are there for facial recognition

  - by Zintinio

  I'm interested in learning the theory behind facial recognition software so that I can hopefully implement it in the future. Not just face tracking, but being able to recognize individuals. What papers, books, libraries, or source is available so that I can learn more about the subject? I have found libface which seems to use eigenfaces for recognition. If there are any practitioners out there, please share any information that you can.

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• What are good reasons to use explicit interface implementation for the sole purpose of hiding members?

  - by Nathanus

  During one of my studies into the intricacies of C#, I came across an interesting passage concerning explicit interface implementation. While this syntax is quite helpful when you need to resolve name clashes, you can use explicit interface implementation simply to hide more "advanced" members from the object level. The difference between allowing the use of object.method() or requiring the casting of ((Interface)object).method() seems like mean-spirited obfuscation to my inexperienced eyes. The text noted that this will hide the method from Intellisense at the object level, but why would you want to do that if it was not necessary to avoid name conflicts?

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• Design for an interface implementation that provides additional functionality

  - by Limbo Exile

  There is a design problem that I came upon while implementing an interface: Let's say there is a Device interface that promises to provide functionalities PerformA() and GetB(). This interface will be implemented for multiple models of a device. What happens if one model has an additional functionality CheckC() which doesn't have equivalents in other implementations? I came up with different solutions, none of which seems to comply with interface design guidelines: To add CheckC() method to the interface and leave one of its implementations empty: interface ISomeDevice { void PerformA(); int GetB(); bool CheckC(); } class DeviceModel1 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } public bool CheckC() { bool res; // assign res a value based on some validation return res; } } class DeviceModel2 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } public bool CheckC() { return true; // without checking anything } } This solution seems incorrect as a class implements an interface without truly implementing all the demanded methods. To leave out CheckC() method from the interface and to use explicit cast in order to call it: interface ISomeDevice { void PerformA(); int GetB(); } class DeviceModel1 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } public bool CheckC() { bool res; // assign res a value based on some validation return res; } } class DeviceModel2 : ISomeDevice { public void PerformA() { // do stuff } public int GetB() { return 1; } } class DeviceManager { private ISomeDevice myDevice; public void ManageDevice(bool newDeviceModel) { myDevice = (newDeviceModel) ? new DeviceModel1() : new DeviceModel2(); myDevice.PerformA(); int b = myDevice.GetB(); if (newDeviceModel) { DeviceModel1 newDevice = myDevice as DeviceModel1; bool c = newDevice.CheckC(); } } } This solution seems to make the interface inconsistent. For the device that supports CheckC(): to add the logic of CheckC() into the logic of another method that is present in the interface. This solution is not always possible. So, what is the correct design to be used in such cases? Maybe creating an interface should be abandoned altogether in favor of another design?

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• Should I use an interface when methods are only similar?

  - by Joshua Harris

  I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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• Prepared statement alternatives for this middle-man program?

  - by user2813274

  I have an program that is using a prepared statement to connect and write to a database working nicely, and now need to create a middle-man program to insert between this program and the database. This middle-man program will actually write to multiple databases and handle any errors and connection issues. I would like advice as to how to replicate the prepared statements such as to create minimal impact to the existing program, however I am not sure where to start. I have thought about creating a "SQL statement class" that mimics the prepared statement, only that seems silly. The existing program is in Java, although it's going to be networked anyways so I would be open to writing it in just about anything that would make sense. The databases are currently MySQL, although I would like to be open to changing the database type in the future. My main question is what should the interface for this program look like, and does doing this even make sense? A distributed DB would be the ideal solution, but they seem overly complex and expensive for my needs. I am hoping to replicate the main functionality of a distributed DB via this middle-man. I am not too familiar with sql-based servers distributing data (or database in general...) - perhaps I am fighting an uphill battle by trying to solve it via programming, but I would like to make an attempt at least.

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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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• Declaring interface in the same file as the base class, is it a good practice?

  - by Louis Rhys

  To be interchangable and testable, normally services with logic needs to have interface, e.g. public class FooService: IFooService { ... } Design-wise, I agree with this, but one of the things that bothers me with this approach is that for one service you will need to declare two things (the class and the interface), and in our team, normally two files (one for the class and one for the interface). Another discomfort is the difficulty in navigation because using "Go to definition" in IDE (VS2010) will point to the interface (since other classes refer to the interface), not the actual class. I was thinking that writing IFooService in the same file as FooService will reduce the above weirdness. After all, IFooService and FooService are very related. Is this a good practice? Is there a good reason that IFooService must be located in its own file?

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• Java - What methods to put in an interface and what to keep out

  - by lewicki

  I'm designing a file handler interface: public interface FileHandler { public void openFileHandler(String fileName); public void closeFileHandler(); public String readLine(); public String [] parseLine(String line); public String [] checkLine(String line[]); public void incrementLineCount(); public void incrementLineSuccessCount(); public void incrementLineErrorCount(); public int getLineCount(); public int getLineSuccessCount(); public int getLineErrorCount(); } It is soon apparent to me that these methods can't be made private. I don't want incrementLineCount to be public. What is proper way to design an interface like this?

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• Interface extension

  - by user877329

  Suppose that I have an input stream interface, which defines a method for reading data. I also have a seekable interface which defines a method for seeking. A natural way of defining a input file is then to implement both input stream and seekable. I want to construct a data decoder from the input stream interface so I can read data from a file or from another stream. The problem is that I also want to implement seek functionality to the data decoder, since I want to be able to step individual records not raw bytes. This is not possible if I only provide an input stream, which does not have the bytewise seek method. Should I skip the seekable interface and add the seek method to input stream instead and force all streams to at least leave it as a nop.

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• Is excessive indirection and/or redundant encapsulation a recognized concept?

  - by Omega

  I'm curious if there's a series of tendencies or anti-patterns when programming whereby a developer will always locally re-wrap external dependencies when consuming them. A slightly less vague example might be say when consuming an implementation of an interface or abstract, and mapping every touch-point locally before interacting with them. Like an overcomplicated take on composition. Given my example, would the interface not be reliable enough and any change to it never be surmountable any any level of indirection? Is this a good or a bad practice? Can it ever go too far? Does it have a proper name?

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• Function that requires many parameters

  - by user877329

  I have a problem related to this: Are there guidelines on how many parameters a function should accept? In my case, I have a function that describes a rounded rectangle. The caller specifies An integer which determines how the rectangle should be merged into previously created shapes An Anchor, which is a point that is used for alignment (right, left, top, bottom etc). (0,-1) means that position (next parameter) describes the top, middle point of the rectangle. The position of the rectangle Width and height Corner radius Should I use Parameter Object pattern in this case? It is hard to see how these parameters are related

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• Use of keyword "Using" in C# interface

  - by Onno

  When I'm using C# to write some code and I define an interface using Visual Studio 2010, it always includes a number of "using" statements (as shown in the example) using System; using System.Collections.Generic; using System.Linq; using System.Text; namespace TestEngine.TestNameSpace { interface ITest1 { bool testMethod(int xyz); } } I wonder what these are for and if they are really necessary. Can I leave these out? Are they only necessary when I'm using those parts in my interface description?

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• Class design for calling "the same method" on different classes from one place

  - by betatester07

  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 all articles for our website class that will hold all categories etc. Every class should have some update() method, which will update data for that class from database and also some other methods for data manipulation specific for that data type. Now, I would like to call update() method for all class instances (there will be exactly one class instance for every class) from one place. What is the best design?

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• Java best practice Interface - subclasses and constants

  - by Taiko

  In the case where a couple of classes implements an interface, and those classes have a couple of constants in common (but no functions), were should I put this constant ? I've had this problem a couple of times. I have this interface : DataFromSensors that I use to hide the implementations of several sub classes like DataFromHeartRateMonitor DataFromGps etc... For some reason, those classes uses the same constants. And there's nowere else in the code were it is used. My question is, were should I put those constants ? Not in the interface, because it has nothing to do with my API Not in a static Constants class, because I'm trying to avoid those Not in a common abstract class, that would stand between the interface and the subclasses, because I have no functions in common, only a couple of constants (TIMEOUT_DURATION, UUID, those kind of things) I've read best practice for constants and interface to define constants but they don't really answer my question. Thanks !

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• How do I use the Microsoft VSTO interfaces?

  - by user557554

  hi, I would like to create an addin for microsoft outlook, and am using the visual studio tools to do so. However I am really struggling to get my head around the use of interfaces within the VSTO environment - the resources on MSDN show many useful looking interfaces, but I am unsure how to use these interfaces to access data. For example I am trying to add a new folder into an IMAP account but am finding it very difficult to work out how to get outlook to do so. Can anyone recommend any good resources for learning how to use VSTO (I have VSTO for dummies, but it doesn't cover the level of detail I need, I have been using MSDN, but I have found it doesnt offer much information on how to use the interfaces etc.) thanks.

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• yes another question about Interfaces?

  - by sam

  Hi Guys, I started commercial programming lately, I am used to functions, then now I always questions about interfaces.. Do you provide me with some links and book names, that can explain deeply why using interfaces? is interfaces required for small projects?? I am using C#. thanks

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• Need some advice on CLI design, I need to provide simple but powerful command line options

  - by howtechstuffworks

  I am writing a utility that runs on RHEL5 command line. I need my command line options to be simple but powerful. I looked at the various UNIX utilities to get an idea of how simple command line utilities have to be. Do you guys suggest any documents/links that talk about command line etiquette? I am modelling my utility on top of LVM (that's all the info I can give for now). I know it's a software engineering question, but I thought it would be appropriate to post here. Please advise.... PS: I am not asking for details about getopt or command line utility parsers.....

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• Should I implement an interface directly or have the superclass do it?

  - by c_maker

  Is there a difference between public class A extends AbstractB implements C {...} versus... public class A extends AbstractB {...} AbstractB implements C {...} I understand that in both cases, class A will end up conforming to the interface. In the second case, AbstractB can provide implementation for interface methods in C. Is that the only difference? If I do NOT want to provide an implementation for any of the interface methods in AbstractB, which style should I be using? Does using one or the other have some hidden 'documentation' purpose?

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• Should interface only be used for behavior and not to show logical data grouped together?

  - by jags

  Should an interface only be used to specify certain behavior? Would it be wrong to use interface to group logically related data? To me it looks like we should not use interface to group logically related data as structure seems a better fit. A class may be used but class name should indicate something like DTO so that user gets the impression that class does not have any behavior. Please let me know if my assumption is correct. Also, are there any exceptions where interface can be used to group logically related data?

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