A design pattern is a general reusable solution to a commonly occurring problem in software design.

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How could I avoid singletons in this case? [duplicate]

Using Dart in the client part of a web app where I have an application manager that contains a List of application instances and references to services that are used by each application as in the ...
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235 views

What design pattern for changing interface?

Sorry guys, I should have clarified the fact that the modified method is abstract in Father. Then if the method signature changes, all its implementations in SonX shall also change(at least the ...
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253 views

How to design a scriptable communication emulator?

Requirement: We need a tool that simulates a hardware device that communicates via RS232 or TCP/IP to allow us to test our main application which will communicate with the device. Current flow: ...
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How should I represent composeable, associative computations to be repeatedly applied to units of data?

Spoiler My question is the following: Are there any design patterns for representing chainable functions that are for the problem described below? High-Level Decription of the Process I'm ...
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207 views

Template pattern with varying input type in overridden method

I am trying to use template pattern to define a generic algorithm in java. But the method that needs to be overridden, takes an object as input. This object will vary depending on the concrete ...
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436 views

State Pattern - should a state know about its context?

I am referring to the state pattern as described in this link. In the example class diagram, a context has numerous states. However, it does not show how does a state communicates with a context ...
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How to improve upon Bloch's Builder Pattern, to make it more appropriate for use in highly-extendable classes

I have been greatly influenced by Joshua Bloch's Effective Java book (2nd edition), probably more so than with any programming book I've read. In particular, his Builder Pattern (item 2) has had the ...
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1answer
169 views

Why use a enum to create the singleton pattern [duplicate]

Why would you use an enum to create a singleton pattern? To what purpose would it serve over a conventional singleton pattern? I have seen the above used. The code uses an enum to create this pattern ...
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123 views

Applying initialization-on-demand holder idiom at variable level rather than class

I was looking for the idiomatic way to implement thread-safe lazy initialization for a configuration collection retrieved from the DB inside a Spring bean. I decided to adapt the ...
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What is the point of using DTO (Data Transfer Objects)?

What is the point of using DTO and is it an out dated concept? I use POJOs in the view layer to transfer and persist data. Can these POJOs be considered as an alternative to DTOs?
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162 views

Is this a pattern? If so, which one? (Contexts, Requests and Responses) [closed]

In most of my code nowadays, I adapted to an approach which I think I read in the context of "Clean Code". It was some years ago and I cannot find the source again, so I would like to know what the ...
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279 views

Client vs Creator in Factory Method and Abstract Factory patterns

This page descibes one important difference between Factory Method and Abstract Factory: http://architects.dzone.com/articles/factory-method-vs-abstract The difference, according to this page, is ...
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Is it misleading to label code as a particular design pattern if it only loosely fits the definition?

Background: I have a rough, but working understanding of ~15 design patterns. It's been my experience using design patterns in my own projects that the resulting implementations usually end up as some ...
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100 views

Should make concrete factories in the same count of families of objects or according to stages in my problem?

I am programming a game. In this game I have 3 stages. In the first stage, there is a static goal and a static shooter in the game. In the second stage, the goal will move. And in the third one both ...
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2answers
161 views

Design pattern for composition workflows

Please bear with me as I find this tricky to articulate exactly what I am after (probably not a good sign..). I have several services set up which can be combined in a particular order to create ...
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434 views

Trying to identify IClass, Class, ClassImpl pattern

I've been seeing a lot of code recently that looks like this: public interface IFoo { int Bar(); } public static class Foo { public static IFoo Create() { return new FooImpl(); } private ...
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711 views

Design Patterns for Coordinating Change Event Listeners

I've been working with the Observer pattern in JavaScript using various popular libraries for a number of years (YUI & jQuery). It's often that I need to observe a set of property value changes ...
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99 views

Can JUnit be used to test this project?

I currently have an interesting situation occurring with my code, and after hacking away at what turned out to be a dead end for the last two weeks, I'm here asking those smarter than I to educate me ...
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1answer
123 views

Is Singleton enough for a EMailUtil or there is any better implementation? [duplicate]

I am developing an application, where I have to send lots of emails for user account creations, validation, invites etc. I have implemented a static class EMailUtil which has different methods like ...
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135 views

Simple and Composite transactional services: Question about separation of concerns and transactions

I believe I know the answer to this but I'm looking for any holes or anything I may be missing. This is focused on Spring and Java but could really apply to any programming stack. Anyway, we have a ...
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Is it bad to use DI to inject constructor parameters at runtime?

These are two classes, the first one I inject an instance of type IEngine while the second one I inject owner's name, tickets and engine. Version 1: public class Car { public Car(IEngine ...
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1answer
75 views

How to organize conversion logic for strategy pattern?

I have a Color class. It has a property model which is a class that implements ColorModel interface, this property could be a RGB, Hex or HSL classes which implementing ColorModel interface. // ...
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141 views

Various methods manipulating same member variable versus each takes inputs and provides output [closed]

As software design paradigm which is better? to let various methods manipulate a member variable, or define each method or function to take some inputs and provide some outputs? For example class ...
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189 views

Design Pattern Question

I'm relatively new to the world of OOP, and having read through some design patterns, I'm struggling with that 'aha' moment. I have the following objects Event (Single event, with start time and end ...
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Return magic value, throw exception or return false on failure?

I sometimes end up having to write a method or property for a class library for which it is not exceptional to have no real answer, but a failure. Something cannot be determined, is not available, not ...
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Which design pattern restricts limits class creation to certain classes

I have a fairly simple application that is divided into two classes. The first class is the Manager class and the second class is the employee class. These are simple classes and do not inherit from ...
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Front-end or Back-end Implementation of API? [closed]

Lets say I want to implement an API from an external website, for example like Dribbble or Last.fm. I'm fairly new to this new generation of front-end MVC's (angular, etc), and most example's I've ...
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How to unit test a function that is refactored to strategy pattern?

If I have a function in my code that goes like: class Employee{ public string calculateTax(string name, int salary) { switch (name) { case "Chris": ...
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115 views

Should Form Object be considered a DTO?

I got this from one of online video tutorials. Author binds form data not to Value Object directly, but first to validable DTO, and THEN to Value Object, using service. Example: package ...
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108 views

In a Table Data Gateway, where do I put queries that use joins

The book Pattern of Enterprise Application Architecture has the following description over the Table Data Gateway pattern: “A Table Data Gateway holds all the SQL for accessing a single table or ...
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What preconditions should be checked while adding/removing a listener?

Imagine the following interface: interface Service { addListener(Listener l) removeListener(Listener l) } Should I check for null values while add/remove? Is it a good idea on remove to ...
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231 views

architecture of database heavy application

A program I'm currently designing is extremely database heavy, almost anything the user does will alter the database, or read from it. Now I have one interface which defines all these operations, and ...
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1answer
161 views

Build a map with city blocks and road

Is there a design pattern or well known algorithm to build a simple map with roads and city blocks? To have an idea of what's my target i describe some of the constraints and the context: a matrix ...
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234 views

How to ensure objects unique by equality?

I frequently have this problem but didn't find it as an established programming pattern. I have some Class C whose equality is determined by some key k and I want to prevent time-consuming ...
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149 views

How to deal with product owner who refuses to follow UI design rules

We develop Android application. We base on old version of similar application developed in our company. This old application was designed by some noobs which didn't follow UI Android design rules. ...
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Web Developer interview questions

I read an article today that listed some basic questions about web development: Describe how POST data was submitted to a server by a browser. Explain a number of HTTP status codes (except maybe 404 ...
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Proper Model-View-_____ design

I've been reading up about Model View Controller, Model View Presenter, Model View ViewModel, and so on, and generally, the underlying concept seems pretty simple to understand: keep the pretty ...
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1answer
246 views

What is this pattern called? Run finally?

Is there a name for this pattern? I've written this kind of thing a few times in JavaScript and recently found myself writing it in C#. Thing is, I expect this has already been implemented in a ...
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Name/Fix for Production Code Whose Sole Purpose is to Facilitate Testing? [duplicate]

The linked "duplicate" question is an iffy match at best, because it's asking is pattern X OK (YES/NO) and I'm clearly already in the NO camp, and subsequently asking what is pattern X called ...
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160 views

The ViewController design in iOS vs MVC in tradiational web apps design

As I came from the background of webapps and move to iOS programming, I am wondering why we can't just apply the MVC design approach to native apps, i.e. in iOS, the view and controller are tightly ...
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102 views

Patterns for subclass constructors that vary the parent class constructor slightly

So, my problem is in the context of an MVC-style approach. The code here is PHP, but I'm hoping this is a design issue independent of it. abstract class Controller { private $domain; private ...
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6answers
806 views

What should an object be called that contains only setters and getters? [closed]

Suppose there's an object that contains only setters and getters: class Config { public void setName(String name) { this.name = name; } public String getName() { ...
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Communicating between unrelated components/objects

Imagine that I have a game, with Monsters, Missions, Vehicles, and of course their controllers and such, so a Monster class, Mission Controller class, Vehicle Controller class and so on. Suppose that ...
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120 views

Using entityManager/repository Class/session factory directly in controller

I wonder what is your approach on following subject: let's say we have MVC structure with entities, repositories, controllers and service layer. My approach to use above was pretty clear for me: ...
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Need to refactor file downloader and post processing utility [duplicate]

Not sure whether this is the right forum to ask this but here goes. Using this solution - http://stackoverflow.com/questions/26571351/replacing-if-else-logic-with-state-strategy-pattern I was able to ...
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6answers
4k views

What is the simplest human readable configuration file format? [closed]

Current configuration file is as follows: mainwindow.title = 'test' mainwindow.position.x = 100 mainwindow.position.y = 200 mainwindow.button.label = 'apply' mainwindow.button.size.x = 100 ...
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2answers
316 views

Does this Decorator implementation violate the Liskov Substitution Principle?

Please consider the following implementation of the Decorator design pattern: WordBank objects store strings and return them to the client through the method getWords(). The decorator class, ...
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207 views

Should we use data object (or the data transfer object) for sharing data between these three classes?

I found an article by Martin Fowler that has made me doubt my design choices, particularly about data objects. Martin Fowler has written an article about what he thinks is a code smell. In this ...
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Null Object Pattern and Input validation - copy real implementation or silently accept everything?

I have a WifiComponent in my Camera in my client application. It's responsible for handling the Wifi-related functionality of the Camera. The Camera represents a real world camera. This WifiComponent ...
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55 views

Control (avoid) changing fields with side-effects

I have been thinking about a design problem and possible solutions in my own. I am pretty sure I am not the first one to have noticed it, but I cannot google for it since I do not know the standard ...