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• Java 'Prototype' pattern - new vs clone vs class.newInstance

  - by Guillaume

  In my project there are some 'Prototype' factories that create instances by cloning a final private instance. The author of those factories says that this pattern provides better performance than calling 'new' operator. Using google to get some clues about that, I've found nothing really relevant about that. Here is a small excerpt found in a javdoc from an unknown project javdoc from an unknown project Sadly, clone() is rather slower than calling new. However it is a lot faster than calling java.lang.Class.newInstance(), and somewhat faster than rolling our own "cloner" method. For me it's looking like an old best practice of the java 1.1 time. Does someone know more about this ? Is this a good practice to use that with 'modern' jvm ?

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• Pattern Matching in Scheme

  - by kunjaan

  How do I accept the following input? (list of 0 or more charcters and ends with 3) or (list of 1 or more characters 4 and 0 or more characters after 4) something like (match ( list 3)) -> #t (match ( list 1 2 3)) -> #t (match (list 1 2 3 4)) -> #t (match (list 1 2 3 4 5)) -> #t (match (list 4)) -> #f EDIT: THIS IS NOT MY HOMEWORK. I trying to write something like ELIZA from PAIP but I know only how to write a pattern that begins with a word.

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• How to show that the double-checked-lock pattern with Dictionary's TryGetValue is not threadsafe in

  - by Amir

  Recently I've seen some C# projects that use a double-checked-lock pattern on a Dictionary. Something like this: private static readonly object _lock = new object(); private static volatile IDictionary<string, object> _cache = new Dictionary<string, object>(); public static object Create(string key) { object val; if (!_cache.TryGetValue(key, out val)) { lock (_lock) { if (!_cache.TryGetValue(key, out val)) { val = new object(); // factory construction based on key here. _cache.Add(key, val); } } } return val; } This code is incorrect, since the Dictionary can be "growing" the collection in _cache.Add() while _cache.TryGetValue (outside the lock) is iterating over the collection. It might be extremely unlikely in many situations, but is still wrong. Is there a simple program to demonstrate that this code fails? Does it make sense to incorporate this into a unit test? And if so, how?

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• Which design pattern to manage windows?

  - by Lu Lu

  Hello, I am using .NET 2.0 & C# to develop a WinForm Mdi application. It will have a Main Window and a lot of mdi windows. I am thinking I should use which design pattern to manage mdi windows. Because I want only one instance for each window, if window is existed, I will show it on top, & otherwise I will create and show it. Note: a mdi window is opened from Menus of Main Window or open from another mdi window. An example is very good. Update: Menu's status is depended on mdi window's status. Ex: If Window 'A' is openned - menu 'A' - disabled. When window 'A' is closed - I update menu 'A' status to Enabled. Thanks.

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• Exception in JEE application Email Notification Pattern

  - by Build Monkey

  We have spring 3.0.x based application, we use SimpleMappingExceptionResolver which sends emails on an exception, when the exception happens within the DispatcherServlet. This gives us following flexibility: Subject can include who the logged in user is, so that we can send personalized email to the user Subject also includes the server on which the error occurred The request params, request url, and headers -- helped us find some problems when search engine indexing the site. However, lately we have been finding the exceptions have been occurring in the filters, and since this is not going through the Resolver, we dont get any emails. We dont like the log4j email appender solution, and not writing another filter to send emails seems right. Is there an accepted pattern to resolve this issue

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• Regexing it up with IIS re-write module

  - by Michael Jasper

  I am developing a profile-based web application where each user is assigned there own url through their username & iis rewrite mod's magic. A typical user's profile url would be http://www.mymark.com/mike Each user is also created a blog in a multi-user wordpress installation. The wordpress url would look like this: http://www.mymark.com/blog/mike I am trying to use the rewrite module to create more canonical urls for the user (http://www.mymark.com/mike/blog), and have tried several regex variations that I have created through RegExr(a regex generation tool) and come up with this as the pattern to match (www.|)mymark.com/([^/]+)/blog but haven't had any success so far. What am I doing wrong here? Here is a screen shot of my re-write rule:

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• problem in basic implementation of MVVM pattern - Services

  - by netmajor

  I watch some video and read articles about MVVM pattern and start thinking how should I implement it in my Silverlight app. So at first I create Silverlight application. I think that for clear view I create 3 folders: View - for each user control page in my app, ViewModel - for c# class which will querying date and Model- Entity Data Model of my SQL Server or Oracle Database. And now I am confused, cause I want to implement *WCF/RIA Services/Web services* in my project. In which folder should I put in class of services? I see in examples that Services take date and filtering it and then output data was binding in View - so It looks as ViewModel. But I was sure that someone use Services in Model and that I want to do. But how? Can someone explain me implementing Services as Model? Is my point of view at MVVM is correctly?

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• Which design pattern should I be using?

  - by Gabriel

  Here's briefly what I'm trying to do. The user supplies me with a link to a photo from one of several photo-sharing websites (such as Flickr, Zooomr, et. al). I then do some processing on the photo using their respective APIs. Right now, I'm only implementing one service, but I will most likely add more in the near future. I don't want to have a bunch of if/else or switch statements to define the logic for the different websites (but maybe that's necessary?) I'd rather just call GetImage(url) and have it get me the image from whatever service the url's domain is from. I'm confused how the GetImage function and classes should be designed. Maybe I need the strategy pattern? I'm still reading and trying to understand the various design patterns and how I could make one fit in this case. I'm doing this in C#, but this question is language-agnostic.

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• Generalized plugable caching pattern?

  - by BCS

  Given that it's one of the hard things in computer science, does anyone know of a way to set up a plugable caching strategy? What I'm thinking of would allow me to write a program with minimal thought as to what needs to be cached (e.i. use some sort of boiler-plate, low/no cost pattern that compiles away to nothing anywhere I might want caching) and then when things are further along and I know where I need caching I can add it in without making invasive code changes. As an idea to the kind of solution I'm looking for; I'm working with the D programing language (but halfway sane C++ would be fine) and I like template.

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• WCF competitive consumer pattern

  - by Simon Thompson

  Is it possible to create a WCF service (web service) that only accepts a single connection at any one time with all other calls either queued or rejected. Need to implement the competitive consumer pattern where there are a number of clients which could deal with task at hand but when a client askes for more work a task must go to only one of them. Usual done as part of an enterprise service bus but can not find one that I'm happy to start using so looking to get this behaviour through a WCF service. Any ideas people ?

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• Pattern filters in Laravel 4

  - by ali A

  I want to make a pattern route, to redirect users to login page when they are not logged in. I searched but couldn't find a solution. as always Laravel's Documentation is useless! I have this in my filter.php Route::filter('auth', function() { if (Auth::guest()) return Redirect::guest('login'); }); Route::filter('auth.basic', function() { return Auth::basic(); }); And this route in my routes.php Route::when('/*', 'auth' ); but It's not working. How can I do that?

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• Design Pattern for Server Emulator

  - by adisembiring

  I wanna build server socket emulator, but I want implement some design pattern there. I will described my case study that I have simplified like these: My Server Socket will always listen client socket. While some request message come from the client socket, the server emulator will response the client through the socket. the response is response code. '00' will describe request message processed successfully, and another response code expect '00' will describe there are some error while processing the message request. IN the server there are some UI, this UI contain check response parameter such as. response code timeout interval While the server want to response the client message, the response code taken from input parameter response form UI check the timeout interval, it will create sleep thread and the interval taken from timeout interval input from UI. I have implement the function, but I create it in one class. I feel it so sucks. Can you suggest me what class / interface that I must create to refactor my code.

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• Server Emulator Design Pattern

  - by adisembiring

  I wanna build server socket emulator, but I want implement some design pattern there. I will described my case study that I have simplified like these: My Server Socket will always listen client socket. While some request message come from the client socket, the server emulator will response the client through the socket. the response is response code. '00' will describe request message processed successfully, and another response code expect '00' will describe there are some error while processing the message request. IN the server there are some UI, this UI contain check response parameter such as. response code timeout interval While the server want to response the client message, the response code taken from input parameter response form UI check the timeout interval, it will create sleep thread and the interval taken from timeout interval input from UI. I have implement the function, but I create it in one class. I feel it so sucks. Can you suggest me what class / interface that I must create to refactor my code.

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• some confusions to singleton pattern in PHP

  - by SpawnCxy

  Hi all, In my team I've been told to write resource class like this style: class MemcacheService { private static $instance = null; private function __construct() { } public static function getInstance($fortest = false) { if (self::$instance == null) { self::$instance = new Memcached(); if ($fortest) { self::$instance->addServer(MEMTEST_HOST, MEMTEST_PORT); } else { self::$instance->addServer(MEM_HOST, MEM_PORT); } } return self::$instance; } } But I think in PHP resource handles will be released and initialized again every time after a request over. That means MemcacheService::getInstance() is totally equal new Memcached() which cannot be called singleton pattern at all. Please correct me if I'm wrong. Regards

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• Search for a pattern in a list of strings - Python

  - by Holtz

  I have a list of strings containing filenames such as, file_names = ['filei.txt','filej.txt','filek.txt','file2i.txt','file2j.txt','file2k.txt','file3i.txt','file3j.txt','file3k.txt'] I then remove the .txt extension using: extension = os.path.commonprefix([n[::-1] for n in file_names])[::-1] file_names_strip = [n[:-len(extension)] for n in file_names] And then return the last character of each string in the list file_names_strip: h = [n[-1:] for n in file_names_strip] Which gives h = ['i', 'j', 'k', 'i', 'j', 'k', 'i', 'j', 'k'] How can i test for a pattern of strings in h? So if i,j,k occur sequentially it would return True and False if not. I need to know this because not all file names are formatted like they are in file_names. So: test_ijk_pattern(h) = True no_pattern = ['1','2','3','1','2','3','1','2','3'] test_ijk_pattern(no_pattern) = False

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• db2 sql pattern matching

  - by Jitesh

  I have a table in db2 which has the following fields int xyz; string myId; string myName; Example dataset xyz | myid | myname -------------------------------- 1 | ABC.123.456 | ABC 2 | PRQS.12.34 | PQRS 3 | ZZZ.3.2.2 | blah I want to extract the rows where myName matches the character upto "." in the myId field. So from the above 3 rows, I want the firs 2 rows since myName is present in myId before "." How can I do this in the query, can I do some kind of pattern matching inside the query?

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• Need help understanding the MVC design pattern

  - by Doron Sinai

  Hi, I am trying to find a ood example of MVC design pattern in java. This is what i understood from reading about it, please correct me if I am wrong: I have the Model part which is the logic behind the program, let's say if we have a phonebook, so adding and removing contact from the Array will be the model. The Gui is the view and it contains buttons that upon clicking them, the model is changing. What I am trying to undersand what is the controller part, is it the ActionListeners? how to you seperate those modules in practice. thank you

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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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• Self-Configuring Classes W/ Command Line Args: Pattern or Anti-Pattern?

  - by dsimcha

  I've got a program where a lot of classes have really complicated configuration requirements. I've adopted the pattern of decentralizing the configuration and allowing each class to take and parse the command line/configuration file arguments in its c'tor and do whatever it needs with them. (These are very coarse-grained classes that are only instantiated a few times, so there is absolutely no performance issue here.) This avoids having to do shotgun surgery to plumb new options I add through all the levels they need to be passed through. It also avoids having to specify each configuration option in multiple places (where it's parsed and where it's used). What are some advantages/disadvantages of this style of programming? It seems to reduce separation of concerns in that every class is now doing configuration stuff, and to make programs less self-documenting because what parameters a class takes becomes less explicit. OTOH, it seems to increase encapsulation in that it makes each class more self-contained because no other part of the program needs to know exactly what configuration parameters a class might need.

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• What software design pattern is best for the following scenario (C#)

  - by askjdh

  I have a gps device that records data e.g. datetime, latitude, longitude I have an sdk that reads the data from the device. The way the data is read: A command packet (basically a combination of int values in a struct) is sent to the device. The device responds with the data in fixed size chunks e.g. 64bytes Depending on the command issued I will get back differect data structs e.g. sending command 1 to the device returns a struct like struct x { id int, name char[20] } command 2 returns a collection of the following structs (basically it boils down to an array of the structs - y[12]) struct y { date datetime, lat decimal, lon decimal } I would then want to convert the struct to a class and save the data to a database. What would be the best way to encapsulate the entire process, preferably using some established design pattern? Many thanks M

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• Dashboard pattern: HorizontalScrollView with pagination or ScrollView?

  - by Macarse

  I am starting a new application and I am willing to use the Dashboard pattern. For example: The Google IO app uses it: My issue is that the amount of buttons will be more than six. I'm not sure if I should use vertical or horizontal scrolling. Vertical scrolling could be done with a ScrollView or a GridView but I am not sure which would be the easier way to implement the horizontal version. I was thinking of using an HorizontalScrollView but it doesn't have pagination. It should feel similar to the tweetdeck app. How would you implement it?

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• regex pattern to match only strings that don't contain spaces PHP

  - by Jamex

  Hi, I want to match the word/pattern that is contained in the variable, but only match against the words that don't have white spaces. Please give suggestions. $var = 'look'; $array = ('look', 'greatlook', 'lookgreat', 'look great', 'badlook', 'look bad', 'look ', ' look'); matches words: look, greatlook, lookgreat, badlook non matches: look great, bad look, look (trailing space(s)), (space(s)) look. The syntax of the below functions are OK, but it matches everything $match = preg_grep ("/$var/", $array); $match = preg_grep ("/^$var/", $array); (match words with 'look' at the start) but when I include the [^\s], it gives an error $match = preg_grep ("/$var[^\s]/", $array); Parse error: syntax error, unexpected '^', expecting T_STRING or T_VARIABLE TIA

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• Design pattern for extending Android's activities?

  - by Carl

  While programming on Android, I end up writing a parent activity which is extended by several others. A bit like ListActivity. My parent activity extends Activity. if I intend to use a Map or a List, I can't use my parent activity as superclass - the child activity can only extend one activity obviously. As such I end up writing my parent activities with the same logic for Activity, ListActivity, MapActivity and so forth. What am I looking for is some sort of trait functionality/design pattern which would help in this case. Any suggestions?

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• Xcode iphone sdk - Searching in UITableView, different pattern matching

  - by Lorenzo

  Hi everyone, I'm coding a UITableView with a UISearchBar to search between a list of cities (loaded in the uitableview) Here is my code for searhing: - (void) searchTableView { NSString *searchText = searchBar.text; NSMutableArray *searchArray = [[NSMutableArray alloc] init]; for (NSDictionary *dictionary in listOfItems) { NSArray *array = [dictionary objectForKey:@"Cities"]; [searchArray addObjectsFromArray:array]; } for (NSString *sTemp in searchArray) { NSRange titleResultsRange = [sTemp rangeOfString:searchText options:NSCaseInsensitiveSearch]; if (titleResultsRange.length > 0) [copyListOfItems addObject:sTemp]; } [searchArray release]; searchArray = nil;} And with this everything works fine, but i need to do something a bit different. I need to search only between items that match pattern Word* and not * Word *. For example if I search "roma", this need to match just with "Roma" or "Romania" and not with "Castelli di Roma". Is that possible with this searchbar? How can i modify this? Thanks

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• ClearCase UCM Mainline Configuration Management Pattern Question

  - by cogmios

  A configuration management pattern question (using Rational ClearCase UCM) When I use the mainline approach I create new releases by: - create release 1 from mainline - on a certain moment baseline release 1, deliver release 1 to mainline - create release 2 from mainline - on a certain moment baseline release 2, deliver release 2 to mainline - create release 3 from mainline - etc... Works very nice because the pathname is /main/release 3/latest instead of /main/release 1/release 2/release 3/latest etc... However... when in release 1 are new elements that have to be propagated to later releases I can not use the mainline since the mainline is already on e.g. release 4. The only thing I can do is deliver/merge from release 1 directly to release 2. The bad thing is that the pathname then becomes /main/release 1/release 2/latest for that files (and possibly later releases). That is I think not in line with the mainline approach. What am I doing wrong?

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