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  • What is the difference between all-static-methods and applying a singleton pattern?

    - by shahensha
    I am making a database to store information about the users of my website (I am using stuts2 and hence Java EE technology). For the database I'll be making a DBManager. Should I apply singleton pattern here or rather make all it's methods static? I will be using this DBManager for basic things like adding, deleting and updating User profiles. Along with it, I'll use for all other querying purposes, for instance to find out whether a username already exists and to get all users for administrative purposes and stuff like that. My questions What is the benefit of singleton pattern? Which thing is most apt here? All static methods or a singleton pattern? Please compare both of them. P.S. The database is bigger than this. Here I am talking only about the tables which I'll be using for storing User Information.

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  • Does anyone have a specific example of using the Flyweight Pattern?

    - by Jeremy E
    I have been studying design patterns and came accross the fly weight pattern. I have been trying to see opportunities to use the pattern in my applications but I am having trouble seeing how to use it. Also, what are some signs that a fly weight pattern is being used when I read other peoples code? According to the definition it says: Use sharing to support large numbers of fine-grained objects efficiently. If I read it right Dictionaries and Hashtables could be instances of fly weights is this correct? Thanks in advance.

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  • Singleton design pattern vs Singleton beans in Spring container

    - by Peeyush
    As we all know we have beans as singleton by default in Spring container and if we have a web application based on Spring framework then in that case do we really need to implement Singleton design pattern to hold global data rather than just creating a bean through spring. Please bear with me if I'm not able to explain what I actually meant to ask.

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  • Java Singleton Pattern

    - by Spencer
    I'm used the Singleton Design Pattern public class Singleton { private static final Singleton INSTANCE = new Singleton(); // Private constructor prevents instantiation from other classes private Singleton() {} public static Singleton getInstance() { return INSTANCE; } } My question is how do I create an object of class Singleton in another class? I've tried: Singleton singleton = new Singleton(); // error - constructor is private Singleton singleton = Singleton.getInstance(); // error - non-static method cannot be referenced from a static context What is the correct code? Thanks, Spencer

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  • how to load wpf usercontrol in MVVM pattern

    - by Anish
    Hi, I'm creating a wpf user control which is in mvvm pattern. So we have : view(with no code in codebehind file), viewmodel,model,dataaccess files. I have MainWindow.xaml as a view file, which I need to bind with MainWindowModel.cs. Usually, in a a wpf application we can do this with onStartUp event in App.xaml file. But in user control, as we do not have App.xaml...How do I achieve it ? Please help :(...Thanks in Advance !!!

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  • Pattern for verifying authenticity of a request to WCF service

    - by fung
    I have a client app that makes calls to a WCF service. This app is on a public computer that's easily accessible and anyone can easily copy the .EXE and .CONFIG of my app into another machine and start using it. Is there a pattern where I can check if the request is coming only from an app on a computer I installed it on and not on one it has been copied to? Thanks in advance.

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  • Validating XML using XSD with regex pattern

    - by Steel Plume
    Hello, I am parsing a XML file against a XSD containing some regex patterns used for checking input data, but only this regex generates an error, even if it passes into the Eclipse XSD plugin: InvalidRegex: Pattern value '(((com|it|org)\.)+(\b[a-z]+[.]{1}\b)+)?[A-Z]{1}[A-Za-z]+' is not a valid regular expression. The reported error was: 'This expression is not supported in the current option setting.'. So, with SAX validator where can I find the fatal "current option setting"?

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  • Pattern Recognition for image comparision in .net

    - by vinod R
    hi Can anybody share code or algorithm(using pattern recognition) for image comparision in .net . I need to compare 2 images of different resolution and textures and the find the difference . Now i have code to find the difference between 2 images using C# // Load the images. Bitmap bm1 = (Bitmap) (Image.FromFile(txtFile1.Text)); Bitmap bm2 = (Bitmap) (Image.FromFile(txtFile2.Text)); // Make a difference image. int wid = Math.Min(bm1.Width, bm2.Width); int hgt = Math.Min(bm1.Height, bm2.Height); Bitmap bm3 = new Bitmap(wid, hgt); // Create the difference image. bool are_identical = true; int r1; int g1; int b1; int r2; int g2; int b2; int r3; int g3; int b3; Color eq_color = Color.Transparent; Color ne_color = Color.Transparent; for (int x = 0; x <= wid - 1; x++) { for (int y = 0; y <= hgt - 1; y++) { if (bm1.GetPixel(x, y).Equals(bm2.GetPixel(x, y))) { bm3.SetPixel(x, y, eq_color); } else { bm1.SetPixel(x, y, ne_color); are_identical = false; } } } // Display the result. picResult.Image = bm1; Bitmap Logo = new Bitmap(picResult.Image); Logo.MakeTransparent(Logo.GetPixel(1, 1)); picResult.Image = (Image)Logo; //this.Cursor = Cursors.Default; if ((bm1.Width != bm2.Width) || (bm1.Height != bm2.Height)) { are_identical = false; } if (are_identical) { MessageBox.Show("The images are identical"); } else { MessageBox.Show("The images are different"); } //bm1.Dispose() // bm2.Dispose() BUT this compare if the 2 images are of same resolution and size.if some shadow is there on one image(but the 2 images are same) it shows the difference between the image..so i am trying to compare using pattern recognition. Thanks in advance

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  • Data access pattern

    - by andlju
    I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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  • Android Dashboard Pattern

    - by Rpond
    In Tim Bray's latest Android blog post he mentions the "dashboard" ui pattern (what is used for the Twitter app, Facebook app, etc. Is this layout as simple as a GridView with Buttons or is it something else?

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  • Simple string pattern matching

    - by Joonas Trussmann
    What's the easiest way of doing simple pattern matching a la .something.com something.com/ something.com/somefolder/*.jpg in the iPhone SDK? At this point it looks like I'm going to have to use a regular expression library of some sort, which is really overkill when all I need is simple wildcard matching. None of the standard NSString methods seem to be available on the iPhone.

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  • Unit of Work Pattern in .Net

    - by Jazza
    Does anyone have any concrete examples of a simple Unit of Work pattern in C# or Visual Basic that would handle the following scenario? I'm writing a WinForms application in which a customer can have multiple addresses associated with it. The user can add, edit and delete addresses belonging to the customer before the customer is saved back to the database. Therefore, at the time of saving, all the original addresses need to be deleted from the database and the new addresses added in a single transaction.

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  • Using ViewModel Pattern with MVC 2 Strongly Typed HTML Helpers

    - by Brettski
    I am working with ASP.NET MVC2 RC and can't figure out how to get the HTML helper, TextBoxfor to work with a ViewModel pattern. When used on an edit page the data is not saved when UpdateModel() is called in the controller. I have taken the following code examples from the NerdDinner application. Edit.aspx <%@ Language="C#" Inherits="System.Web.Mvc.ViewUserControl<NerdDinner.Models.DinnerFormViewModel>" %> ... <p> // This works when saving in controller (MVC 1) <label for="Title">Dinner Title:</label> <%= Html.TextBox("Title", Model.Dinner.Title) %> <%= Html.ValidationMessage("Title", "*") %> </p> <p> // This does not work when saving in the controller (MVC 2) <label for="Title">Dinner Title:</label> <%= Html.TextBoxFor(model => model.Dinner.Title) %> <%= Html.ValidationMessageFor(model=> model.Dinner.Title) %> </p> DinnerController // POST: /Dinners/Edit/5 [HttpPost, Authorize] public ActionResult Edit(int id, FormCollection collection) { Dinner dinner = dinnerRepository.GetDinner(id); if (!dinner.IsHostedBy(User.Identity.Name)) return View("InvalidOwner"); try { UpdateModel(dinner); dinnerRepository.Save(); return RedirectToAction("Details", new { id=dinner.DinnerID }); } catch { ModelState.AddModelErrors(dinner.GetRuleViolations()); return View(new DinnerFormViewModel(dinner)); } } When the original helper style is used (Http.TextBox) the UpdateModel(dinner) call works as expected and the new values are saved. When the new (MVC2) helper style is used (Http.TextBoxFor) the UpdateModel(dinner) call does not update the values. Yes, the current values are loaded into the edit page on load. Is there something else which I need to add to the controller code for it to work? The new helper works fine if I am just using a model and not a ViewModel pattern. Thank you.

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  • Data access pattern, combining push and pull?

    - by andlju
    I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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  • Specification Pattern vs Spec in BDD

    - by cadmium
    I'm trying to explore Behavior Driven Design and Domain Driven Design. I'm getting that written specifications drive the tests in BDD, but also that business logic can be encapsulated using the specification pattern for re-use in domain objects and repositories, etc. Are these basically the same concept just used in different ways, used in conjunction together, or am I completely confusing the concepts? Please shed some light, if possible.

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  • Unit of Work pattern and persistence

    - by Mosh
    Hello, I have been reading about Unit of Work pattern but I am confused about how the UoW actually persists data. When we commit the changes, UoW should iterate through the list of Added, Updated and Deleted objects and somehow find a class responsible to Add, Update, Delete objects of a certain type. I couldn't find an example showing this technique. Any advice on this would be greatly appreciated. Mosh

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  • Decorator pattern in C++

    - by AlgoMan
    Can someone give me an example of Decorator pattern in C++ ? I have come across the Java version of it. But C++ i have found it difficult to understand the examples that are given.

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  • Is this a dangerous locking pattern?

    - by Martin
    I have an enumerator written in C#, which looks something like this: try { ReadWriteLock.EnterReadLock(); yield foo; yield bar; yield bash; } finally { ReadWriteLock.ExitReadLock(); } I believe this may be a dangerous locking pattern, as the ReadWriteLock will only be released if the enumeration is complete, otherwise the lock is left hanging and is never released, am I correct? If so, what's the best way to combat this?

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  • decorator pattern

    - by vbNewbie
    I have a program that converts currency using a specific design pattern. I now need to take my converted result and using the decorator pattern allow the result to be converted to 3 different formats: 1 - exponential notation, rounded to 2 decimal points. using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Text; using System.Windows.Forms; namespace Converter { public partial class Form1 : Form { // Setup Chain of Responsibility Handler h1 = new USDHandler(); Handler h2 = new CADHandler(); Handler h3 = new AUDHandler(); public string reqCurName; public int reqAmt; public string results; public string requestID; public Form1() { InitializeComponent(); h1.SetSuccessor(h2); h2.SetSuccessor(h3); } // "Handler" private void button1_Click_1(object sender, EventArgs e) { reqCurName = txtInput.Text; reqAmt = Convert.ToInt32(txtAmt.Text.ToString()); results = h1.HandleRequest(reqCurName, reqAmt); if (results != "") { lblResult.Text = results; lblResult.Visible = true; } } abstract class Handler { protected Handler successor; public string retrn; public void SetSuccessor(Handler successor) { this.successor = successor; } public abstract string HandleRequest(string requestID, int reqAmt); } // "USD Handler" class USDHandler : Handler { public override string HandleRequest(string requestID, int reqAmt) { if (requestID == "USD") { retrn = "Request handled by " + this.GetType().Name + " \nConversion from Euro to USD is " + reqAmt/0.630479; return (retrn); } else if (successor != null) { retrn = successor.HandleRequest(requestID, reqAmt); } return (retrn); } } // "CAD Handler" class CADHandler : Handler { public override string HandleRequest(string requestID, int reqAmt) { if (requestID == "CAD") { retrn = "Request handled by " + this.GetType().Name + " \nConversion from Euro to CAD is " + reqAmt /0.617971; return (retrn); } else if (successor != null) { retrn = successor.HandleRequest(requestID, reqAmt); } return (retrn); } } // "AUD Handler" class AUDHandler : Handler { public override string HandleRequest(string requestID, int reqAmt) { if (requestID == "AUD") { requestID = "Request handled by " + this.GetType().Name + " \nConversion from Euro to AUD is " + reqAmt / 0.585386; return (requestID); } else if (successor != null) { retrn = successor.HandleRequest(requestID, reqAmt); } return (requestID); } } } }

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  • preg_replace Pattern

    - by codeworxx
    Hey Guys, i'm not very firm with preg_replace - in other Words i do not really understand - so i hope you can help me. I have a string in a Text like this one: [demo category=1] and want to replace with the Content of Category (id=1) e.g. "This is the Content of my first Category" This is my startpoint Pattern - that's all i have: '/[demo\s*.*?]/i'; Hope you can help? Thanks, Sascha

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