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• Why people are so afraid of using clone() (on collection and JDK classes) ?

  - by Bozho

  A number of times I've argued that using clone() isn't such a bad practice. Yes, I know the arguments. Bloch said it's bad. He indeed did, but he said that implementing clone() is bad. Using clone on the other hand, especially if it is implemented correctly by a trusted library, such as the JDK, is OK. Just yesterday I had a discussion about an answer of mine that merely suggests that using clone() for ArrayList is OK (and got no upvotes for that reason, I guess). If we look at the @author of ArrayList, we can see a familiar name - Josh Bloch. So clone() on ArrayList (and other collections) is perfectly fine. (Just look at the implementation). Same goes for Calendar and perhaps most of the java.lang and java.util classes. So, give me a reason why not to use clone() with JDK classes?

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• How to store images efficiently (memory-wise) while still being able to process them

  - by Sheeo

  I'm working on a silverlight project where users get to create their own Collages. The problem When loading images into memory, I'm using BitmapImage so that they can be displayed directly with the Image control--but they're locked in afterwards. So I've tried storing them seperately aswell, but that just sucks up huge amounts of RAM. So in short, is there a class that'll let me store JPEG images, be able to show them with the image control, and still be able to export it afterwards? All this needs to be efficient--i.e. I'd rather not want any copying to ARGB arrays or use the WriteableBitmap to copy them over. I require to work with large collections of images, up to 300 at most. Any help apreciated!

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• How to sort an array or ArrayList<Point> ASC first by x and then by y?

  - by newba

  Hi everyone, I just want to use Collections.sort or Arrays.sort to sort a list of points (class Point) by x first and then by y. I have a class Ponto that implements Comparable like this: public int compareTo(Ponto obj) { Ponto tmp = obj; if (this.x < tmp.x) { return -1; } else if (this.x > tmp.x) { return 1; } return 0; } but now I want to sort by y too after x. How can I do that by modifying the above code? Or is that a better and "clean" way to do this? I also use to pass this code to C++, in which I've created a structure called Point with a equivalent comparable method.

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• In C#, What is <T> After a Method Declaration?

  - by Drew

  I'm a VB.Net guy. (because I have to be, because the person who signs my check says so. :P) I grew up in Java and I don't generally struggle to read or write in C# when I get the chance. I came across some syntax today that I have never seen, and that I can't seem to figure out. In the following method declaration, what does < T represent? static void Foo < T (params T[] x) I have seen used in conjunction with declaring generic collections and things, but I can't for the life of me figure out what it does for this method. In case it matters, I came across it when thinking about some C# brain teasers. The sixth teaser contains the entire code snippet.

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• How to prevent UI from freezing during lengthy process?

  - by OverTheRainbow

  Hello, I need to write a VB.Net 2008 applet to go through all the fixed-drives looking for some files. If I put the code in ButtonClick(), the UI freezes until the code is done: Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click 'TODO Find way to avoid freezing UI while scanning fixed drives Dim drive As DriveInfo Dim filelist As Collections.ObjectModel.ReadOnlyCollection(Of String) Dim filepath As String For Each drive In DriveInfo.GetDrives() If drive.DriveType = DriveType.Fixed Then filelist = My.Computer.FileSystem.GetFiles(drive.ToString, FileIO.SearchOption.SearchAllSubDirectories, "MyFiles.*") For Each filepath In filelist 'Do stuff Next filepath End If Next drive End Sub Google returned information on a BackGroundWorker control: Is this the right/way to solve this issue? If not, what solution would you recommend, possibly with a really simple example? FWIW, I read that Application.DoEvents() is a left-over from VBClassic and should be avoided. Thank you.

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• Forcing GWT to assume List is implemented as ArrayList

  - by joecks

  For some reason I'm stucked with model classes using List as Collection Type and I would like to use the model on the client side. However GWT of course fails serializing java.util.List. However all implementations of List in this model are based on ArrayList. So is it possible to tell GWT to assume List is ArrayList? Edit GWT fails on compile time, since a possible candidate for List is also java.util.Collections.SingeltonList - which can not be compiled. I'm using GWT 2.1 and Java 1.6 .

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• Is this physical collection class that contains only static methods an Anti-Pattern?

  - by Tj Kellie

  I'm trying to figure out if I should continue on with a current pattern in an application I'm working in, or refactor this into something else. I have a set of collection classes off a generic base of List. These classes have public constructors but contain only static methods that return collections. They look like this: public class UserObjCollection : BaseCollection<UserObj> { public static UserObjCollection GetAllUserObj() { UserObjCollection obj = new UserObjCollection(); obj.MapObjects(new UserObjDataService().GetAllUserObj()); return obj; } } Is this a Pattern or Anti-Pattern and what are the merits of this over a straight factory pattern?

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• VPS goes slow at more than 20 users online at the same time

  - by hachiari

  I have 512 MB VPS (brustable to 1GB) Somehow, the site goes slow when there are about 10 users, and becomes impossible to load at 20 users online at the same time. I wonder what could be the problem for this. The bandwidth connection of the VPS is 1Gbps. Here is some settings in my VPS: KeepAlive Off <IfModule prefork.c> StartServers 7 MinSpareServers 7 MaxSpareServers 10 ServerLimit 64 MaxClients 64 MaxRequestsPerChild 0 </IfModule> my.cnf settings - calculated Max Memory 300MB Output from UNIXBENCH INDEX VALUES TEST BASELINE RESULT INDEX Dhrystone 2 using register variables 376783.7 13429727.4 356.4 Double-Precision Whetstone 83.1 1137.5 136.9 Execl Throughput 188.3 1637.4 87.0 File Copy 1024 bufsize 2000 maxblocks 2672.0 148868.0 557.1 File Copy 256 bufsize 500 maxblocks 1077.0 79430.0 737.5 File Read 4096 bufsize 8000 maxblocks 15382.0 1410009.0 916.7 Pipe Throughput 111814.6 4419722.0 395.3 Pipe-based Context Switching 15448.6 561505.1 363.5 Process Creation 569.3 10272.7 180.4 Shell Scripts (8 concurrent) 44.8 514.3 114.8 System Call Overhead 114433.5 3537373.8 309.1 ========= FINAL SCORE 295.0 I am afraid that the VPS company limit the number of connection to the VPS... is it possible? The server is in Japan, but the site has global traffic (some of the traffic are from countries with low speed connection). Could this be the problem? This is a serious problem :( my site just cant grow if this keeps on happening... please tell me if you have any idea. Thank You, Bryant

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• LINQ-to-SQL: Searching against a CSV

  - by Peter Bridger

  I'm using LINQtoSQL and I want to return a list of matching records for a CSV contains a list of IDs to match. The following code is my starting point, having turned a CSV string in a string array, then into a generic list (which I thought LINQ would like) - but it doesn't: Error Error 22 Operator '==' cannot be applied to operands of type 'int' and 'System.Collections.Generic.List<int>' C:\Documents and Settings\....\Search.cs 41 42 C:\...\ Code DataContext db = new DataContext(); List<int> geographyList = new List<int>( Convert.ToInt32(geography.Split(',')) ); var geographyMatches = from cg in db.ContactGeographies where cg.GeographyId == geographyList select new { cg.ContactId }; Where do I go from here?

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• Understanding ulimit -u

  - by tripleee

  I'd like to understand what's going on here. linvx$ ( ulimit -u 123; /bin/echo nst ) nst linvx$ ( ulimit -u 122; /bin/echo nst ) -bash: fork: Resource temporarily unavailable Terminated linvx$ ( ulimit -u 123; /bin/echo one; /bin/echo two; /bin/echo three ) one two three linvx$ ( ulimit -u 123; /bin/echo one & /bin/echo two & /bin/echo three ) -bash: fork: Resource temporarily unavailable Terminated one I speculate that the first 122 processes are consumed by Bash itself, and that the remaining ulimit governs how many concurrent processes I am allowed to have. The documentation is not very clear on this. Am I missing something? More importantly, for a real-world deployment, how can I know what sort of ulimit is realistic? It's a long-running daemon which spawns worker threads on demand, and reaps them when the load decreases. I've had it spin the server to its death a few times. The most important limit is probably memory, which I have now limited to 200M per process, but I'd like to figure out how I can enforce a limit on the number of children (the program does allow me to configure a maximum, but how do I know there are no bugs in that part of the code?)

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• Serializing Request.Form to a Dictionary or something

  - by André Alçada Padez

  Hi i need to pass my Request.Form as a parameter, but first i have to add some key/value pairs to it. I get the exception that the Collection is readonly. I've tried: System.Collections.Specialized.NameValueCollection myform = Request.Form; and i get the same error. and i've tried: foreach(KeyValuePair<string, string> pair in Request.Form) { Response.Write(Convert.ToString(pair.Key) + " - " + Convert.ToString(pair.Value) + "<br />"); } to test if i can pass it one by one to another dictionary, but i get: System.InvalidCastException: Specified cast is not valid. some help, anyone? Thanx

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• Howto check if a object is connected to another in hibernate

  - by codevourer

  Imagine two domain object classes, A and B. A has a bidirectional one-to-many relationship to B. A is related to thousands of B. The relations must be unique, it's not possible to have a duplicate. To check if an instance of B is already connected to a given instance of A, we could perform an easy INNER JOIN but this will only ensure the already persisted relations. What about the current transient relations? class A { @OneToMany private List<B> listOfB; } If we access the listOfB and perform a check of contains() this will fetch all the connected instances of B lazy from the datasource. I only want to validate them by their primary-key. Is there an easy solution where I can do things like "Does this instance of A is connected with this instance of B?" Without loading all these data into memory and perform a based on collections?

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• Deep Copy using Reflection in an Extension Method for Silverlight?

  - by didibus

  So I'm trying to find a generic extension method that creates a deep copy of an object using reflection, that would work in Silverlight. Deep copy using serialization is not so great in Silverlight, since it runs in partial trust and the BinaryFormatter does not exist. I also know that reflection would be faster then serialization for cloning. It would be nice to have a method that works to copy public, private and protected fields, and is recursive so that it can copy objects in objects, and that would also be able to handle collections, arrays, etc. I have searched online, and can only find shallow copy implementations using reflection. I don't understand why, since you can just use MemberwiseClone, so to me, those implementations are useless. Thank You.

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• Enumerable.Range in and Expression and Entity Framework

  - by eka808

  I'm currently developping an expression method (used in linq to entity queries) who has to give me a daycount for a given period (start date and end date) decrementing this daycount if specials days are in the period. My idea was the following : Generate an enumerable with all the dates (and with Enumerable.Range) Make a .Where on this enumerable to remove the specials dates Like a MyEnumerable.Where(a = a != "20120101") After that, return a MyEnumerable.Count() I come with this code : return (p) => Enumerable .Range(1, 4) .Where(a => a != 20120101) .AsQueryable() .Count() I tried to cast as a list, as a queryable, both (like the example) and no way ! it doesn't work ! I always get this error : LINQ to Entities does not recognize the method 'System.Collections.Generic.IEnumerable`1[System.Int32] Range(Int32, Int32)' method, and this method cannot be translated into a store expression. Have you got an idea about that ? Using an enumerable is of course not mandatory, any working solutions is good ^^ Thank's by advance !

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• How would you write this C# code succinctly in Ruby?

  - by Valentin Vasilyev

  Here is the code: using System; using System.Collections.Generic; using System.Linq; namespace cs2 { class Program { static void Main(string[] args) { var i=Fibs().TakeWhile(x=>x < 1000).Where(x=>x % 2==0).Sum(); } static IEnumerable<long> Fibs() { long a = 0, b = 1; while (true) { yield return b; b += a; a = b - a; } } } } If it is possible, please give an example.

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• ASP.NET MVC Using Multiple user controls on a single .aspx(view)

  - by Pinu

  I am getting this following error , when i am tring to having two user controls in one page. The model item passed into the dictionary is of type 'System.Linq.EnumerableQuery1[Data.EventLog]' but this dictionary requires a model item of type 'System.Collections.Generic.IEnumerable1[Data.Notes]'. <%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage" %> <asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server"> Test </asp:Content> <asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server"> <h2>Test</h2> <% Html.RenderPartial("~/Views/Shared/UserControl/Tracking.ascx"); %> <% Html.RenderPartial("~/Views/Shared/UserControl/Notes.ascx"); %> </asp:Content>

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• In .NET which loop runs faster for or foreach

  - by Binoj Antony

  In c#/VB.NET/.NET which loop runs faster for or foreach? Ever since I read that for loop works faster than foreach a long time ago I assumed it stood true for all collections, generic collection all arrays etc. I scoured google and found few articles but most of them are inconclusive (read comments on the articles) and open ended. What would be ideal is to have each scenarios listed and the best solution for the same e.g: (just example of how it should be) for iterating an array of 1000+ strings - for is better than foreach for iterating over IList (non generic) strings - foreach is better than for Few references found on the web for the same: Original grand old article by Emmanuel Schanzer CodeProject FOREACH Vs. FOR Blog - To foreach or not to foreach that is the question asp.net forum - NET 1.1 C# for vs foreach [Edit] Apart from the readability aspect of it I am really interested in facts and figures, there are applications where the last mile of performance optimization squeezed do matter.

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• What is so great about STL?

  - by Zygrob

  Hello StackOverflow. I am a Java developer trying to learn C++. I have many times read over the web (including StackOverflow) that STL is the best collections library that you can get in *any* language. (Sorry, I do not have any citations atm) However after studying some STL, I am really failing to see what makes STL so special. Would you please shed some light on what sets STL apart from the collection libraries of other languages and make it the _best_ collection library? Thanks in advance, Zygr??b.

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• Is there a way to combine streaming data retrieval with hibernate?

  - by Steve B.

  For the purposes of handling very large collections (and by very large I just mean "likely to throw OutOfMemory exception"), it seems problematic to use Hibernate because normally collection retrieval is done in a block, i.e. List values=session.createQuery("from X").list(), where you monolithically grab all N-million values and then process them. What I'd prefer to do is to retrieve the values as an iterator so that I grab 1000 or so (or whatever's a reasonable page size) at a time. Apart from writing my own iteration (which seems like it's likely to be re-inventing the wheel) is there a hibernate-native way to handle this?

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• NHibernateUtil.Initialize and Table where clause (Soft Delete)

  - by Pascal

  We are using NHibernate but sometimes manually load proxies using the NHibernateUtil.Initialize call. We also employ soft delete and have a "where" condition on all our mapping to tables. SQL generated by NHibernate successfully adds the where condition (i.e. DELETED IS NULL) however we notice that NHibernateUtil.Initialize does not observe the constraints of the mapping files. i.e. None of the SQL generated by NHibernateUtil.Initialize observes our DELETED IS NULL condition. Is there something we're missing as we would really like to employ manual loading of some entity collections when the situation demands it. We are using FluentNhibernate for our mapping.

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• Servers - Buying New vs Buying Second-hand

  - by Django Reinhardt

  We're currently in the process of adding additional servers to our website. We have a pretty simple topology planned: A Firewall/Router Server infront of a Web Application Server and Database Server. Here's a simple (and technically incorrect) diagram that I used in a previous question to illustrate what I mean: We're now wondering about the specs of our two new machines (the Web App and Firewall servers) and whether we can get away with buying a couple of old servers. (Note: Both machines will be running Windows Server 2008 R2.) We're not too concerned about our Firewall/Router server as we're pretty sure it won't be taxed too heavily, but we are interested in our Web App server. I realise that answering this type of question is really difficult without a ton of specifics on users, bandwidth, concurrent sessions, etc, etc., so I just want to focus on the general wisdom on buying old versus new. I had originally specced a new Dell PowerEdge R300 (1U Rack) for our company. In short, because we're going to be caching as much data as possible, I focussed on Processor Speed and Memory: Quad-Core Intel Xeon X3323 2.5Ghz (2x3M Cache) 1333Mhz FSB 16GB DDR2 667Mhz But when I was looking for a cheap second-hand machine for our Firewall/Router, I came across several machines that made our engineer ask a very reasonable question: If we stuck a boat load of RAM in this thing, wouldn't it do for the Web App Server and save us a ton of money in the process? For example, what about a second-hand machine with the following specs: 2x Dual-Core AMD Opteron 2218 2.6Ghz (2MB Cache) 1000Mhz HT 16GB DDR2 667Mhz Would it really be comparable with the more expensive (new) server above? Our engineer postulated that the reason companies upgrade their servers to newer processors is often because they want to reduce their power costs, and that a 2.6Ghz processor was still a 2.6Ghz processor, no matter when it was made. Benchmarks on various sites don't really support this theory, but I was wondering what server admin thought. Thanks for any advice.

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• Many clients on a wireless AP for UDP broadcast packets

  - by distorteddisco

  I asked this question on StackOverflow and was directed over here, so I'd appreciate any advice. I'm deploying a smartphone application as part of a live music performance that depends on receiving UDP broadcast packets from a wireless access point. I'm guessing that between 20 and 50 clients will be connected at any one time. I'm aware that a maximum of 20 clients per access point is advised, but as the UDP broadcast packets are ground through the LAN, how would I be able to link multiple APs together? I'm looking for recommendations on a suitable AP for this. The actual data transmission rates are very low - only a few kB/s - as I'm just sending small messages to the smartphone apps, and there will be no WAN internet connection. I tried it with a few connected peers on an adhoc wireless connection without any problems, but ran into dropped packet issues on an old WRT54G running ddwrt, though it's in pretty rough shape. What's the best way to do this? I suppose I could limit concurrent wireless connections to 20 clients... but more would be nice. EDIT: I should also say that it's purely one-way communication; the smartphone application is only receiving broadcast packets, not sending anything.

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• Threading errors with Application.LoadComponent (key already exists)

  - by Kellls

  MSDN says that public static members of System.Windows.Application are thread safe. But when I try to run my app with multiple threads I get the following exception: ArgumentException: An entry with the same key already exists. at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) at System.Collections.Generic.SortedList`2.Add(TKey key, TValue value) at System.IO.Packaging.Package.AddIfNoPrefixCollisionDetected(ValidatedPartUri partUri, PackagePart part) at System.IO.Packaging.Package.GetPartHelper(Uri partUri) at System.IO.Packaging.Package.GetPart(Uri partUri) at System.Windows.Application.GetResourceOrContentPart(Uri uri) at System.Windows.Application.LoadComponent(Uri resourceLocator, Boolean bSkipJournaledProperties) at System.Windows.Application.LoadComponent(Uri resourceLocator) The application works fine on a single thread and even on two or three. When I get up past 5 then I get the error every time. Am I doing something wrong? What can I do to fix this?

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• How do I configure NetBeans to only step through Java code that I've written.

  - by blissapp

  Am I missing something? I'm delighted that all that code is there showing how the generic collections work etc. However when I want to simply walk my code I'm forever finding myself going deeper into Java's own library code than I care to. Is it possible to simply disable that when stepping code - I want to treat all of that stuff as a Black Box, code stepping is just for stuff I've written. And you know what, now I've got that capability, is it possible to wrap up my own code that way too so that I can step just the bits I'm most interested in? And if i can't easily in netbeans, is it possible in eclipse? thanks

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• Apache https is slow

  - by raucous12

  Hey, I've set apache up to use SSL with a self signed certificate. With https (KeepAlive on), I can get over 3000 requests per second. However, with https (KeepAlive off), I can only get 13 requests per second. I know there is supposed to be a bit of an overhead, but this seems abnormal. Can anyone suggest how I might go about debugging this. Here is the ab log for https: Server Software: Apache/2.2.3 Server Hostname: 127.0.0.1 Server Port: 443 SSL/TLS Protocol: TLSv1/SSLv3,DHE-RSA-AES256-SHA,4096,256 Document Path: /hello.html Document Length: 29 bytes Concurrency Level: 5 Time taken for tests: 30.49425 seconds Complete requests: 411 Failed requests: 0 Write errors: 0 Total transferred: 119601 bytes HTML transferred: 11919 bytes Requests per second: 13.68 [#/sec] (mean) Time per request: 365.565 [ms] (mean) Time per request: 73.113 [ms] (mean, across all concurrent requests) Transfer rate: 3.86 [Kbytes/sec] received Connection Times (ms) min mean[+/-sd] median max Connect: 190 347 74.3 333 716 Processing: 0 14 24.0 1 166 Waiting: 0 11 21.6 0 165 Total: 191 361 80.8 345 716 Percentage of the requests served within a certain time (ms) 50% 345 66% 377 75% 408 80% 421 90% 468 95% 521 98% 578 99% 596 100% 716 (longest request)

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