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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 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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• Get unique artist names from MPMediaQuery

  - by Akash Malhotra

  I am using MPMediaQuery to get all artists from library. Its returning unique names I guess but the problem is I have artists in my library like "Alice In Chains" and "Alice In Chains ". The second "Alice In Chains" has some white spaces at the end, so it returns both. I dont want that. Heres the code... MPMediaQuery *query=[MPMediaQuery artistsQuery]; NSArray *artists=[query collections]; artistNames=[[NSMutableArray alloc]init]; for(MPMediaItemCollection *collection in artists) { MPMediaItem *item=[collection representativeItem]; [artistNames addObject:[item valueForProperty:MPMediaItemPropertyArtist]]; } uniqueNames=[[NSMutableArray alloc]init]; for(id object in artistNames) { if(![uniqueNames containsObject:object]) { [uniqueNames addObject:object]; } } Any ideas?

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• Setting tabindex in dynamic table vertically then horizontally

  - by Wil

  I have a page that is currently generating dynamically created textboxes in a table format. The users are requesting that the tab order be changed from horizontal-vertical to vertical-horizontal. I know that you can use the tabindex attribute to control the tab ordering, but I can't for the life of me figure out the right way to get the sequential number properly for the textboxes. I guess this is more of a math question than anything else! FYI, the textboxes are made while looping two different collections. First collection looped to make the rows, for each row, second collection (which is a property of the first collection objects) is looped to create the columns. Any help would be greatly appreciated. Thanks!

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• One liner for getting a sublist from a Set

  - by yegor256

  Is there a one-liner (maybe from Guava or Apache Collections) that gets a sublist from a set. Internally it should do something like this: public <T> List<T> sublist(Set<T> set, int count) { Iterator<T> iterator = set.iterator(); List<T> sublist = new LinkedList<T>(); int pos = 0; while (iterator.hasNext() && pos++ < count) { sublist.add(iterator.next()); } return sublist; } Obviously, if there are not enough elements it has to return as many as possible.

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• Add String to adapter

  - by Waggoner_Keith

  I have an adapter and i want to add a string to it but when i run this code it only add the last string in the songstoadd variable ... That is a custom adapter which adds dividers in where neccessary but in the Array Adapter i want to a all of the strings that have the same first letter in their name .... SeparatedListAdapter adapter = new SeparatedListAdapter(this); ArrayList<String> songstoadd = new ArrayList<String>(); Collections.sort(songtitle); int m = 0; while( m <songtitle.size()-1){ if(songtitle.get(m).substring(0, 1) == songtitle.get(m+1).substring(0, 1)){ m++; }else{ songstoadd.clear(); songstoadd.add(songtitle.get(m)); adapter.addSection(songtitle.get(m).substring(0, 1), new ArrayAdapter<String>(getApplicationContext(),R.layout.song, songstoadd)); m++; } } setListAdapter(adapter); }

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• java best way to transfer images

  - by d.raev

  I have a application that reads a PDF, transform the content to collection of TIF files, and send them to Glass Fish Server for saving. Usually there are 1-5 pages and it works nice, but when I got a input file with 100+ pages... it throws error on the transfer. Java heap space at java.util.Arrays.copyOf(Arrays.java:2786) at java.io.ByteArrayOutputStream.write(ByteArrayOutputStream.java:94) Putting more resources is not a good option in my case, so I m looking for a way to optimize it somehow. I store the data in: HashMap<TifProfile, List<byte[]> Is there a better way to store or send them ? EDIT I did some tests and the final collections for PDF with 80 pages has size over 280mb (240 tiffs with different settings inside)

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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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• 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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• 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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• 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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• 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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• 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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• 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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• Can I serialize a BitArray to XML?

  - by SimonNet

  Hello I have a business class which I need to serialize to xml. It has a BitArray property. I have decorated it with [XmlAttribute] but the serialization is failing with To be XML serializable, types which inherit from ICollection must have an implementation of Add(System.Boolean) at all levels of their inheritance hierarchy. System.Collections.BitArray does not implement Add(System.Boolean). I am not sure whether its possible to serialize to xml? If not what would be an efficient means of serializing the BitArray Thanks for looking

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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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• How to see what objects lie in which generation in YourKit?

  - by prams

  I am using YourKit (11.0) to try to profile my j2ee app. The app uses java 6 and running on 64-bit linux (centos). I was told that YourKit possibly tells us which objects exist in which generation (eden, old, etc) at any given point of time. On a side note, I am trying to chase a problem where memory usage keeps increasing until a major collection happens (every 4 hrs) and I am suspicious about few particular objects, so I am interested to know where those objects lie at different times. Fortunately I know lot of memory is being consumed in one particular area of code (so other objects are possibly directly being put into the old gen), but don't exactly know how much of that memory is being put into eden space, how much is being collected by the minor collections, etc. Thanks.

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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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• 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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• When is @uncheckedVariance needed in Scala, and why is it used in GenericTraversableTemplate?

  - by retronym

  @uncheckedVariance can be used to bridge the gap between Scala's declaration site variance annotations and Java's invariant generics. scala import java.util.Comparator import java.util.Comparator scala trait Foo[T] extends Comparator[T] defined trait Foo scala trait Foo[-T] extends Comparator[T] :5: error: contravariant type T occurs in invariant position in type [-T]java.lang.Object with java.util.Comparator[T] of trait Foo trait Foo[-T] extends Comparator[T] ^ scala import annotation.unchecked._ import annotation.unchecked._ scala trait Foo[-T] extends Comparator[T @uncheckedVariance] defined trait Foo This says that java.util.Comparator is naturally contra-variant, that is the type parameter T appears in parameters and never in a return type. Which begs the question, why is it also used in the Scala collections library: trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] What are the valid uses for this annotation?

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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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• C# ToDictionary can valueSelector give null?

  - by Trimack

  Hi, I want to make a dictionary out of list in a way, that the list becomes keys and values would be empty. I have following code Dictionary<XmlTest, int?> testBattery = new XmlTests().GetRandomTestBattery(id). ToDictionary(k => k, v => null); But I am getting the error "Cannot convert lambda expression to type System.Collections.Generic.IEqualityComparer' because it is not a delegate type" Any ideas how could I fix it? (I know I could iterate through and fill the dict one element at a time, but I simply want to use something more elegant)

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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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• multi-dimensional ArrayList

  - by wishi

  Hi! Just a very small question... I seem to run into too much complexity here: I have to realize an index-structure like {42, someString}. I tried: Object entry[][] = new Object[1][1]; ArrayList<Object> my_list = new ArrayList<Object>(); However that looks really strange. Isn't there a better much simpler solution to just store some Integer and a String? I need to perfrom search for the Strings and return the Integer... so I thought Collections and ArrayLists are good friends in the Java API.

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• python dictionary with constant value-type

  - by s.kap

  hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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