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• State pattern: Why doesn't the context class implement or inherit the State abstract interface/class

  - by Ricket

  I'm reading about the State pattern. I have only just begun, so of course I begin by reading the entire Wikipedia article on it. I noticed that both of the examples in the article have some base abstract class or Java interface for a generic State's methods/functions. Then there are some states which inherit from the base and implement those methods/functions in different ways. Then there's a Context class which has a private member of type State and which, at any time, can be equal to an instance of one of the implementations. That context class also implements the same methods, and passes them onto the current state instance, and then has an additional method to change the state (or depending on design I understand the change of state could be a reaction to one of the implemented methods). Why doesn't this context class specifically "extend" or "implement" the generic State base class/interface?

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• Which method should I use ?

  - by Ivan

  I want to do this exercise but I don't know exactly which method should I use for an exercise like this and what data will I use to test the algorithm. The driving distance between Perth and Adelaide is 1996 miles. On the average, the fuel consumption of a 2.0 litre 4 cylinder car is 8 litres per 100 kilometres. The fuel tank capacity of such a car is 60 litres. Design and implement a JAVA program that prompts for the fuel consumption and fuel tank capacity of the aforementioned car. The program then displays the minimum number of times the car’s fuel tank has to be filled up to drive from Perth to Adelaide. Note that 62 miles is equal to 100 kilometres. What data will you use to test that your algorithm works correctly?

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• Javascript Rich Display Component/Methodology

  - by Laramie

  quick back story-- I am working on ASP.Net based template editor that lets authors create text templates using Javascript inserted placeholder tags that will be filled in with dynamic text when the templates are used to display the final results. For example the author might create a template like The word [%12#add] was generated dynamically. The application would eventually replace the tag with a dynamic word down the road (though it's not specifically relevant to this post) The word foo was generated dynmamically. Depending on the circumstances, the template may be created in a text input, textarea or a modified version of the Ajax Control Toolkit HTML Editor. There might be 40 or more of these editable elements on the page, so using lots of stripped down or modified HTML editors would probably bog the page down too much. The problem is that the tags such as [%12#add] are displayed inline with the user text and the result is confusing and aesthetically gross. The goal is parse the contens of the source element and when a tags such as [%12#add] are encountered, display something prettier and less cryptic to the user such as a stylable element or image wherever tags such as [%12#add] occur. The application still needs the template text with the tags on postback. So the user might see The word tag placeholder was generated dynamically. but the original template would still be the value of the text input box The word [%12#add] was generated dynamically. It seems HTML editors like the ACT version and FckEditor accomplish this by rendering their output in an IFrame, but rather than kill myself trying to roll a lighter specialized version myself, I thought I'd ask if anyone knows of an existing free component or approach that has already tackled this. With good reason, I don't think S.O. allows HTML formatting, but the bold "tag placeholder" above would ideally be something like tag placeholder.

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• Ordering the calling of asynchronous methods in c#

  - by Peter Kelly

  Hi, Say I have 4 classes ControllerClass MethodClass1 MethodClass2 MethodClass3 and each MethodClass has an asynchronous method DoStuff() and each has a CompletedEvent. The ControllerClass is responsible for invoking the 3 asynchronous methods on the 3 MethodClasses in a particular order. So ControllerClass invokes MethodClass1.DoStuff() and subscribes to MethodClass1.CompletedEvent. When that event is fired, ControllerClass invokes MethodClass2.DoStuff() and subscribes to MethodClass2.CompletedEvent. When that event is fired, the ControllerClass invokes MethodClass3.DoStuff() Is there a best practice for a situation like this? Is this bad design? I believe it is because I am finding it hard to unit test (a sure sign) It is not easy to change the order I have an uneasy, code-smell feeling about it What are the alternatives in a situation like this?

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• Why does Excel expose an 'Evaluate' method at all?

  - by jtolle

  A few questions have come up recently involving the Application.Evaluate method callable from Excel VBA. The old XLM macro language also exposes an EVALUATE() function. Both can be quite useful. Does anyone know why the general expression evaluator is exposed, though? My own hunch is that Excel needed to give people a way to get ranges from string addresses, and to get the value of named formulas, and just opening a portal to the expression evaluator was the easiest way. But of course you don't need the ability to evaluate arbitrary expressions just to do that. Application.Evaluate seems kind of...unfinished. It isn't very well documented, and there are quite a few quirks and limitations (as described by Charles Williams here: http://www.decisionmodels.com/calcsecretsh.htm) with what is exposed. I suppose the answer could be simply "why not expose it?", but I'd be interested to know what design decisions led to this feature. Failing that, I'd be interested to hear other hunches.

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• Mock Assertions on objects inside Parallel ForEach's???

  - by jacko

  Any idea how we can assert a mock object was called when it is being accessed inside Parallel.ForEach via a closure? I assume that because each invocation is on a different thread that Rhino Mocks loses track of the object? Pseudocode: var someStub = MockRepository.GenerateStub() Parallel.Foreach(collectionOfInts, anInt => someStub.DoSomething(anInt)) someStub.AssertWasCalled(s => s.DoSomething, Repeat.Five.Times) This test will return an expectation violation, expecting the stub to be called 5 times but being actually called 0 times. Any ideas how we can tell the lambdas to keep track of the thread-local stub object?

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• Should functions of a C library always expect a string's length?

  - by Benjamin Kloster

  I'm currently working on a library written in C. Many functions of this library expect a string as char* or const char* in their arguments. I started out with those functions always expecting the string's length as a size_t so that null-termination wasn't required. However, when writing tests, this resulted in frequent use of strlen(), like so: const char* string = "Ugh, strlen is tedious"; libFunction(string, strlen(string)); Trusting the user to pass properly terminated strings would lead to less safe, but more concise and (in my opinion) readable code: libFunction("I hope there's a null-terminator there!"); So, what's the sensible practice here? Make the API more complicated to use, but force the user to think of their input, or document the requirement for a null-terminated string and trust the caller?

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• EnterpriseLibrary.Logging directory ..

  - by MüllerDK

  Hi, I'm using MS EnterpriseLibrary.Logging and that works perfectly. But the logfile(s) are placed in where the program file are located. How do I get it to place my logfiles in individual users applicationData folder?? The folder I'm talking about is the one you get by calling "Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)". Any help appreciated :-) Best Regards Søren

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• Maven - Include dependent libs in jar without unpacking dependencies?

  - by Marcus

  We're trying to build a client jar that includes unpacked depenedent jar's. And the manifest should have class-path entries to the dependent jars. The snippet below works but the jars are unpacked - how can we stop the jars from being unpacked? <plugin> <artifactId>maven-assembly-plugin</artifactId> <configuration> <descriptorRefs> <descriptorRef>jar-with-dependencies</descriptorRef> </descriptorRefs> <archive> <manifest> <addClasspath>true</addClasspath> </manifest> </archive> </configuration> <executions> <execution> <id>make-assembly</id> <phase>package</phase> <goals> <goal>single</goal> </goals> </execution> </executions> </plugin>

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• Display contents of a file

  - by Hulk

  there is a file as data.html.How to display the contents of this file using javascript or jquery Thanks..

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• Javascript Rich Display WYSIWYG Component/Methodology

  - by Laramie

  quick back story-- I am working on ASP.Net based template editor that lets authors create text templates using Javascript inserted placeholder tags that will be filled in with dynamic text when the templates are used to display the final results. For example the author might create a template like The word [%12#add] was generated dynamically. The application would eventually replace the tag with a dynamic word down the road (though it's not specifically relevant to this post) The word foo was generated dynmamically. Depending on the circumstances, the template may be created in a text input, textarea or a modified version of the Ajax Control Toolkit HTML Editor. There might be 40 or more of these editable elements on the page, so using lots of stripped down or modified HTML editors would probably bog the page down too much. The problem is that the tags such as [%12#add] are displayed inline with the user text and the result is confusing and aesthetically gross. The goal is parse the contens of the source element and when a tags such as [%12#add] are encountered, display something prettier and less cryptic to the user such as a stylable element or image wherever tags such as [%12#add] occur. The application still needs the template text with the tags on postback. So the user might see The word tag placeholder was generated dynamically. but the original template would still be the value of the text input box The word [%12#add] was generated dynamically. It seems HTML editors like the ACT version and FckEditor accomplish this by rendering their output in an IFrame, but rather than kill myself trying to roll a lighter specialized version myself, I thought I'd ask if anyone knows of an existing free component or approach that has already tackled this. With good reason, I don't think S.O. allows HTML formatting, but the bold "tag placeholder" above would ideally be something like tag placeholder.

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• Resources to learn about engineering aspects of data analytics (OLAP, warehousing, ETL, etc.)

  - by JT

  I'm a math/stats guy, interested in learning more about the engineering aspects of "data analytics" (this may be an overly broad term, this is a case of "I don't know what I don't know", so I'm not sure how to be more specific). I'm fine with manipulating and analyzing the data once it's already stored somewhere and I can access it, and I'm fine with writing scripts and SQL queries (and have a general knowledge of things like normalization). What I don't know is the whole engineering process of capturing and storing the data. For example, terms I've heard thrown about that I only vaguely understand the meaning of include: - OLAP, OLTP - Data warehousing - ETL - ??? What's a good book (or any other resource) to learn about these kinds of things? What are things I should know about database design (normalization seems kinda "obvious" to me, something I would have done even before I knew the term -- is there anything else?)? In other words, for jobs falling under the umbrella term of "analytics engineer", what kinds of things should I know?

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• What is the difference between MVC model 1 and model 2?

  - by Alex Ciminian

  I've recently discovered that MVC is supposed to have two different flavors, model one and model two. I'm supposed to give a presentation on MVC1 and I was instructed that "it's not the web based version, that is refered to as MVC2". As the presentations are about design patterns in general, I doubt that this separation is related to Java (I found some info on Sun's site, but it seemed far off) or ASP. I have a pretty good understanding of what MVC is and I've used several (web) frameworks that enforce it, but this terminology is new to me. How is the web-based version different from other MVC (I'm guessing GUI) implementations? Does it have something to do with the stateless nature of HTTP? Thanks, Alex

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• Is testability alone justification for dependency injection?

  - by fearofawhackplanet

  The advantages of DI, as far as I am aware, are: Reduced Dependencies More Reusable Code More Testable Code More Readable Code Say I have a repository, OrderRepository, which acts as a repository for an Order object generated through a Linq to Sql dbml. I can't make my orders repository generic as it performs mapping between the Linq Order entity and my own Order POCO domain class. Since the OrderRepository by necessity is dependent on a specific Linq to Sql DataContext, parameter passing of the DataContext can't really be said to make the code reuseable or reduce dependencies in any meaningful way. It also makes the code harder to read, as to instantiate the repository I now need to write new OrdersRepository(new MyLinqDataContext()) which additionally is contrary to the main purpose of the repository, that being to abstract/hide the existence of the DataContext from consuming code. So in general I think this would be a pretty horrible design, but it would give the benefit of facilitating unit testing. Is this enough justification? Or is there a third way? I'd be very interested in hearing opinions.

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• Surrogate key for date dimension?

  - by Navin

  There are 2 school of thoughts : Use surrogate key preferbly in the format of YYYYMMDD as this will always be sequential. Eliminate Date dimension surrogate key and use actual date instead. My Questions to experts on dimension modeling are : 1> Which design would you prefer and why ? 2> How should we handle unknown values in each of the cases, Can we simply place NULL in Fact table for unknown dates as Foreign Key can be NULL (if no why)? 3> If we need to partition fact table on date column ,how would we achieve that in case 1. I am inclined towards using actual date and using NULL to represent UNKNOWN dates in fact table , as date related validation on fact can be done without need to look in to dimension table.

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• Collision detections and how efficient they are

  - by Shadow

  How exactly do you implement collision detection? What are the costs involved? Do different platforms(c/c++, java, cocoa/iphone, flash, directX) have different optimizations for calculating collisions. And lastly are there libraries available to do this for me, or some that I can just interpret for my platform of choice? As I understand it you would need to loop through the collision map and find the area in question and then compair the input thing(e.g. a sprite) to the type of pixel that is in the questioned area. I understand the very basic idea, but I don't understand the underlying implementation or even a higher level one for that matter. It would seem that this type of detection, or any for that matter, is very costly. Tile map? Bit array? How are these created from an image(I would guess looping and doing stuff)? The reason I ask this question is to get a better understanding of the efficiency behind the scenes and to understand exactly what is going on. Links, references, or examples would be very helpful. I know this question is a bit longwinded so any help or references would be very welcome. Thanks SO!

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• creational pattern for instances depending on multiple subclass instances

  - by markusw

  I have a problem, for that I was not able to identify a suitable design pattern. I want to create instances depending on a given type that has been passed to a factory method. What I am doing until now is the following: T create(SuperType x) { if (x instanceof SubType1) { // do some stuff and return a new SubType extends T } else if (x instanceof SubType2) { // do some stuff and return a new SubType extends T } else if ... } else { throw new UnSupportedOperationException("nothing defined for " + x); } } It seems not to be best pratice for me. Has anybody an idea how to solve this in a better way?

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• Data Quality Check - SQL Server

  - by user319384

  I am trying to find a good mechanism where I can check whether the data being entered by a group of people is grammatically correct, has correct spellings, etc, etc. I also would like to compute words per minute and accuracy. Is there any process to do this so that I do not have to re-invent the wheel? Thanks in advance.

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• Custom Validator and specifying type of message

  - by user102533

  I have a custom validation in the enterprise validation block. The DoValidate method is as shown below. protected override void DoValidate(Double objectToValidate, object currentTarget, string key, ValidationResults validationResults) { if (!IsSalMoreThanMinWage(objectToValidate)) { //Here I need to mark this message as a "Warning" LogValidationResult(validationResults, "Salary is too low for this state", currentTarget, key); } } I'd need to mark this validation failure as a "warning" message. In the front end, when I iterate through the ValidationResults collection and grab a ValidationResult object, I would need to identify and group different types of messages and render them differently. My question is - how do I mark a failure as a warning?

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• How to use OpenCV in Python?

  - by Roman

  I have just installed OpenCV on my Windows 7 machine. As a result I get a new directory: C:\OpenCV2.2\Python2.7\Lib\site-packages In this directory I have two files: cv.lib and cv.pyd. Then I try to use the opencv from Python. I do the following: import sys sys.path.append('C:\OpenCV2.2\Python2.7\Lib\site-packages') import cv As a result I get the following error message: File "<stdin>", line 1, in <module> ImportError: DLL load failed: The specified module could not be found. What am I doing wrong? ADDED As it was recommended here, I have copied content of C:\OpenCV2.0\Python2.6\Lib\site-packages to the C:\Python26\Lib\site-packages. It did not help.

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• Database layout tagging system

  - by Kurresmack

  I am creating a web site for a customer and they want to be able to create articles. My idea is to tag them so I am going to implement the system. What is the best design, both from an architectural and a perfomance perspective: 1. To have table with all tags and then have a one to many relationship table that links a tag like this: articles table with ID tags table with ID one to many table with columns Article.ID and Tags.ID 2. To have one table with articles and one with tags for articles like this: articles table with ID tags table with Article.ID and tag text Thanks in advance!

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• Problem setting up Direct X for C++

  - by Josh

  I've downloaded Direct X SDK from the microsoft website but when I try to compile my code i'm getting this error: Error 1 error LNK2019: unresolved external symbol _Direct3DCreate9@4 referenced in function "void __cdecl initD3D(struct HWND__ *)" (?initD3D@@YAXPAUHWND__@@@Z) C:\Users\Josh\Desktop\Tutorial\Tutorial\Tutorial.obj Tutorial I have added Direct X to my C++ build directories like that: $(DXSDK_DIR)include $(DXSDK_DIR)Lib\x64 I've googled it and found out that most of the time people were forgetting this line: #pragma comment (lib, "d3dx9.lib") But it's there for me here are my includes and lib: #include <windows.h> #include <windowsx.h> #include <d3d9.h> #include <d3dx9.h> #pragma comment (lib, "d3d9.lib") #pragma comment (lib, "d3dx9.lib") Can anyone help me with this? I'm using Visual studio 2010 Professional on win7 x64

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• One executable with cmd-line params or just many satellite executables?

  - by Nikos Baxevanis

  I design an application back-end. For now, it is a .NET process (a Console Application) which hosts various communication frameworks such as Agatha and NServiceBus. I need to periodically update my datastore with values (coming from the application while it's running). I found three possible ways: Accept command line arguments, so I can call my console app with -update. On start up a background thread will periodically invoke the update method. Create an updater.exe app which will do the updates, but I will have code duplication since in some way it will need to query the data from the source in order to save it to the datastore. Which one is better?

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• Lackadaisical One-to-One between Char and Byte Streams

  - by Vaibhav Bajpai

  I expected to have a one-to-one correspondence between the character streams and byte streams in terms of how the classes are organized in their hierarchy. FilterReader and FilterWriter (character streams) correspond back to FilterInputStream and FilterOutputStream (byte stream) classes. However I noticed few changes as - BufferedInputStream extends FilterInputStream, but BufferedReader does NOT extend FilterReader. BufferedOutputStream and PrintStream both extend FilterOutputStream, but BufferedWriter and PrintWriter does NOT extend FilterWriter. FilterInputStream and FilterOutputStream are not abstract classes, but FilterReader and FilterWriter are. I am not sure if I am being too paranoid to point out such differences, but was just curious to know if there was design reasoning behind such decision.

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• Is there a standard practice for storing default application data?

  - by Rox Wen

  Our application includes a default set of data. The default data includes coefficients and other factors that are unlikely to ever change but still need to be update-able by the user. Currently, the original default data is stored as a populated class within the application. Data updates are stored to an external XML file. This design allows us to include a "reset" feature to restore the original default data. Our rationale for not storing defaults externally [e.g. XML file] was to minimize the risk of being altered. The overall volume of data doesn't warrant a database. Is there a standard practice for storing "default" application data?

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