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• Periodically iterating over a collection that's constantly changing

  - by rwmnau

  I have a collection of objects that's constantly changing, and I want to display some information about objects (my application is multi-threaded, and differently threads are constantly submitting requests to modify an object in the collection, so it's unpredictable), and I want to display some information about what's currently in the collection. If I lock the collection, I can iterate over it and get my information without any problems - however, this causes problems with the other threads, since they could have submitted multiple requests to modify the collection in the meantime, and will be stalled. I've thought of a couple ways around this, and I'm looking for any advice. Make a copy of the collection and iterate over it, allowing the original to continue updating in the background. The collection can get large, so this isn't ideal, but it's safe. Iterate over it using a For...Next loop, and catch an IndexOutOfBounds exception if an item is removed from the collection while we're iterating. This may occasionally cause duplicates to appear in my snapshot, so it's not ideal either. Any other ideas? I'm only concerned about a moment-in-time snapshot, so I'm not concerned about reflecting changes in my application - my main concern is that the collection be able to be updated with minimal latency, and that updates never be lost.

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• How to pop items from a collection in Java?

  - by Tom Brito

  Is there a method in JDK or apache commons to "pop" a list of elements from a java.util.List? I mean, remove the list of elements and return it, like this method: public Collection pop(Collection elementsToPop, Collection elements) { Collection popped = new ArrayList(); for (Object object : elementsToPop) { if (elements.contains(object)) { elements.remove(object); popped.add(object); } } return popped; }

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• Can I have a set containing identical elements?

  - by Roman

  It is convenient for me to use a set. I like how I can "add" ("remove") an element to (from) the set. It is also convenient to check if a given element is in the set. The only problem, I found out that I cannot add a new element to a set if the set has already such an element. Is it possible to have "sets" which can contain several identical elements.

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• Scala version of Rubys' each_slice?

  - by Brian Heylin

  Does Scala have a version of Rubys' each_slice from the Array class?

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• Difference between a Deprecated and Legacy API?

  - by Vaibhav Bajpai

  I was studying the legacy API's in the Java's Collection Framework and I learnt that classes such as Vector and HashTable have been superseded by ArrayList and HashMap. However still they are NOT deprecated, and deemed as legacy when essentially, deprecation is applied to software features that are superseded and should be avoided, so, I am not sure when is a API deemed legacy and when it is deprecated.

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• Why do methods contains(), indexOf() in a Java Collection use o.equals(e) and not e.equals(o)?

  - by Fernando

  anyone know the reasons of that??

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• Backbone.js "model" query

  - by Novice coder

  I'm a learning coder trying to understand this code from a sample MVC framework. The below code is from a "model" file. I've done research on Backbone.js, but I'm still confused as to exactly how this code pull information from the app's database. For example, how are base_url, Model.prototype, and Collection.prototype being used to retrieve information from the backend? Any help would be greatly appreciated. exports.definition = { config : { "defaults": { "title": "-", "description": "-" }, "adapter": { "type": "rest", "collection_name": "schools", "base_url" : "/schools/", } }, extendModel: function(Model) { _.extend(Model.prototype, { // Extend, override or implement Backbone.Model urlRoot: '/school/', name:'school', parse: function(response, options) { response.id = response._id; return response; }, }); return Model; }, extendCollection: function(Collection) { _.extend(Collection.prototype, { // Extend, override or implement Backbone.Collection urlRoot: '/schools/', name: 'schools', }); return Collection; } }

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• How can I display a list of three different Models sortable by the same :attribute in rails?

  - by Angela

  I have a Campaign model which has_many Calls, Emails, and Letters. For now, these are each a separate Model with different controllers and actions (although I would like to start to think of ways to collapse them once the models and actions stabilize). They do share two attributes at least: :days and :title I would like a way to represent all the Calls, Emails, and Letters that belong_to a specific Campaign as a sortable collection (sortable by :days), in a way that outputs the model name and the path_to() for each. For example (I know the below is not correct, but it represents the kind of output/format I've been trying to do: @campaign_events.each do |campaign_event| <%= campaign_event.model_name %> <%= link_to campaign_event.title, #{model_name}_path(campaign_event) %> end Thanks so much. BTW, if this matters, I would then want to make the :days attribute editable_in_place.

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• scala implicit or explicit conversion from iterator to iterable

  - by landon9720

  Does Scala provide a built-in class, utility, syntax, or other mechanism for converting (by wrapping) an Iterator with an Iterable? For example, I have an Iterator[Foo] and I need an Iterable[Foo], so currently I am: val foo1: Iterator[Foo] = .... val foo2: Iterable[Foo] = new Iterable[Foo] { def elements = foo1 } This seems ugly and unnecessary. What's a better way?

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• Inheriting from List<T> in .NET (vb or C#)

  - by Tony

  I have been delved in C++ world for a while, but now I'm in .NET world again, VB and C# and I wondered if you have a class that represents a collection of something, and you want the ability to use this in a foreach loop, etc... is it better to implement IEnumerable and IEnumerator yourself or should you inherit from the List<T> where T is the object type in it's singular form? I know in C++ for example, inheriting from a container is considered a bad idea. But what about .NET.

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• Retrieve KEYWORDS from META tag in a HTML WebPage using JAVA.

  - by kooldave98

  Hello all, I want to retrieve all the content words from a HTML WebPage and all the keywords contained in the META TAG of the same HTML webpage using Java. For example, consider this html source code: <html> <head> <meta name = "keywords" content = "deception, intricacy, treachery"> </head> <body> My very short html document. <br> It has just 2 'lines'. </body> </html> The CONTENT WORDS here are: my, very, short, html, document, it, has, just, lines Note: The punctuation and the number '2' are ruled out. The KEYWORDS here are: deception, intricacy, treachery I have created a class for this purpose called WebDoc, this is as far as I have been able to get. import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; import java.net.URL; import java.util.Set; import java.util.TreeSet; public class WebDoc { protected URL _url; protected Set<String> _contentWords; protected Set<String> _keyWords public WebDoc(URL paramURL) { _url = paramURL; } public Set<String> getContents() throws IOException { //URL url = new URL(url); Set<String> contentWords = new TreeSet<String>(); BufferedReader in = new BufferedReader(new InputStreamReader(_url.openStream())); String inputLine; while ((inputLine = in.readLine()) != null) { // Process each line. contentWords.add(RemoveTag(inputLine)); //System.out.println(RemoveTag(inputLine)); } in.close(); System.out.println(contentWords); _contentWords = contentWords; return contentWords; } public String RemoveTag(String html) { html = html.replaceAll("\\<.*?>",""); html = html.replaceAll("&",""); return html; } public Set<String> getKeywords() { //NO IDEA ! return null; } public URL getURL() { return _url; } @Override public String toString() { return null; } }

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• Whats the best to way convert a set of Java objects to another set of objects?

  - by HDave

  Basic Java question here from a real newbie. I have a set of Java objects (of class "MyClass") that implement a certain interface (Interface "MyIfc"). I have a set of these objects stored in a private variable in my class that is declared as follows: protected Set<MyClass> stuff = new HashSet<MyClass>(); I need to provide a public method that returns this set as a collection of objects of type "MyIfc". public Collection<MyIfc> getMyStuff() {...} How do I do the conversion? The following line gives me an error that it can't do the conversion. I would have guessed the compiler knew that objects of class MyClass implemented MyIfc and therefore would have handled it. Collection<MyIfc> newstuff = stuff; Any enlightenment is appreciated.

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• Entity Framework: a proxy collection for displaying a subset of data

  - by Jefim

  Imagine I have an entity called Product and a repository for it: public class Product { public int Id { get; set; } public bool IsHidden { get; set; } } public class ProductRepository { public ObservableCollection<Product> AllProducts { get; set; } public ObservableCollection<Product> HiddenProducts { get; set; } } All products contains every single Product in the database, while HiddenProducts must only contain those, whose IsHidden == true. I wrote the type as ObservableCollection<Product>, but it does not have to be that. The goal is to have HiddenProducts collection be like a proxy to AllProducts with filtering capabilities and for it to refresh every time when IsHidden attribute of a Product is changed. Is there a normal way to do this? Or maybe my logic is wrong and this could be done is a better way?

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• Is it okay to violate the principle that collection properties should be readonly for performance?

  - by uriDium

  I used FxCop to analyze some code I had written. I had exposed a collection via a setter. I understand why this is not good. Changing the backing store when I don't expect it is a very bad idea. Here is my problem though. I retrieve a list of business objects from a Data Access Object. I then need to add that collection to another business class and I was doing it with the setter method. The reason I did this was that it is going to be faster to make an assignment than to insert hundreds of thousands of objects one at a time to the collection again via another addElement method. Is it okay to have a getter for a collection in some scenarios? I though of rather having a constructor which takes a collection? I thought maybe I could pass the object in to the Dao and let the Dao populate it directly? Are there any other better ideas?

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• IList<T> and IReadOnlyList<T>

  - by Safak Gür

  My problem is that I have a method that can take a collection as parameter that, Has a Count property Has an integer indexer (get-only) And I don't know what type should this parameter be. I would choose IList<T> before .NET 4.5 since there is no other indexable collection interface for this and arrays implement it, which is a big plus. But .NET 4.5 introduces the new IReadOnlyList<T> interface and I want my method to support that, too. How can I write this method to support both IList<T> and IReadOnlyList<T> without violating the basic principles like DRY? Can I convert IList<T> to IReadOnlyList<T> somehow in an overload? What is the way to go here? Edit: Daniel's answer gave me some pretty ideas, I guess I'll go with this: public void Do<T>(IList<T> collection) { DoInternal(collection, collection.Count, i => collection[i]); } public void Do<T>(IReadOnlyList<T> collection) { DoInternal(collection, collection.Count, i => collection[i]); } private void DoInternal<T>(IEnumerable<T> collection, int count, Func<int, T> indexer) { // Stuff } Or I could just accept a ReadOnlyList<T> and provide an helper like this: public static class CollectionEx { public static IReadOnlyList<T> AsReadOnly<T>(this IList<T> collection) { if (collection == null) throw new ArgumentNullException("collection"); return new ReadOnlyWrapper<T>(collection); } private sealed class ReadOnlyWrapper<T> : IReadOnlyList<T> { private readonly IList<T> _Source; public int Count { get { return _Source.Count; } } public T this[int index] { get { return _Source[index]; } } public ReadOnlyWrapper(IList<T> source) { _Source = source; } public IEnumerator<T> GetEnumerator() { return _Source.GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } } } Then I could call Do(array.AsReadOnly())

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• Sort collection of objects in hashmap based on the object's variable in java

  - by chandra wibowo

  hi everyone, i have a collection of book object in a hashmap, the book has book_title, book_author, book_year_published, etc. i want to sort them based on the book_title which is a String, in both ascending and descending order, and display them on the screen. i wish someone can help me, i have been doing this for hours and still havent come up with a solution. thanks in advance

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• Sorting an ArrayList of Contacts

  - by Sameera0

  Ok so I have a been making an addressbook application and have pretty much finished all the key features but I am looking to implement a sort feature in the program. I want to sort an Arraylist which is of a type called Contact (contactArray) which is a separate class which contains four fields; name, home number, mobile number and address. So I was looking into using the collection sort yet am not sure how i'd implement this. Is this the right sort I should be using / is it possible to use or should I look into making a custom sort?

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• Why de methods contains(), indexOf() in a Java Collection use o.equals(e) and not e.equals(0)?

  - by Fernando

  anyone know the reasons of that??

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• WPF How to bind to a specific element in the Collection

  - by PaN1C_Showt1Me

  Hi, I want to make a binding to a specific element in the Collection. But I cannot figure out how to write the Binding. This is the code: public class MySource { .. public string SomeProp; public ICollection<T> MyCollection; .. } this.DataContext = new MySource(); <TextBox Text={Binding SomeProp} /> <TextBox Text={Binding FIRST_ELEMENT_OF_THE_MyCollection} /> <TextBox Text={Binding SECOND_ELEMENT_OF_THE_MyCollection} /> <!--Ignore other elements--> Try to replace those binding strings, please Thank you

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• What's the best way to return something like a collection of `std::auto_ptr`s in C++03?

  - by Billy ONeal

  std::auto_ptr is not allowed to be stored in an STL container, such as std::vector. However, occasionally there are cases where I need to return a collection of polymorphic objects, and therefore I can't return a vector of objects (due to the slicing problem). I can use std::tr1::shared_ptr and stick those in the vector, but then I have to pay a high price of maintaining separate reference counts, and object that owns the actual memory (the container) no longer logically "owns" the objects because they can be copied out of it without regard to ownership. C++0x offers a perfect solution to this problem in the form of std::vector<std::unique_ptr<t>>, but I don't have access to C++0x. Some other notes: I don't have access to C++0x, but I do have TR1 available. I would like to avoid use of Boost (though it is available if there is no other option) I am aware of boost::ptr_container containers (i.e. boost::ptr_vector), but I would like to avoid this because it breaks the debugger (innards are stored in void *s which means it's difficult to view the object actually stored inside the container in the debugger)

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• Java queue and multi-dimension array

  - by javaLearner.java

  First of all, this is my code (just started learning java): Queue<String> qe = new LinkedList<String>(); qe.add("b"); qe.add("a"); qe.add("c"); qe.add("d"); qe.add("e"); My question: Is it possible to add element to the queue with two values, like: qe.add("a","1"); // where 1 is integer So, that I know element "a" have value 1. If I want to add a number let say "2" to element a, I will have like a = 3. If this cant be done, what else in java classes that can handle this? I tried to use multi-dimention array, but its kinda hard to do the queue, like pop, push etc. (Maybe I am wrong) How to call specific element in the queue? Like, call element a, to check its value. [Note] Please don't give me links that ask me to read java docs. I was reading, and I still dont get it. The reason why I ask here is because, I know I can find the answer faster and easier.

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• How to bind WPF TreeView to a List<Drink> programmatically?

  - by Joan Venge

  So I am very new to WPF and trying to bind or assign a list of Drink values to a wpf treeview, but don't know how to do that, and find it really hard to find anything online that just shows stuff without using xaml. struct Drink { public string Name { get; private set; } public int Popularity { get; private set; } public Drink ( string name, int popularity ) : this ( ) { this.Name = name; this.Popularity = popularity; } } List<Drink> coldDrinks = new List<Drink> ( ){ new Drink ( "Water", 1 ), new Drink ( "Fanta", 2 ), new Drink ( "Sprite", 3 ), new Drink ( "Coke", 4 ), new Drink ( "Milk", 5 ) }; } } How can I do this in code? For example: treeview1.DataItems = coldDrinks; and everything shows up in the treeview.

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• Merge object from list by comparing one value

  - by Bala

  I have two List of Objects (one is master list and other is error list) and if there is a match of one value when compared two lists then merge all other error list values into mast list value (only one object). Other than iterating is there any other way to compare a value and then merge that object. Object is a Value object with some setters and getters. Appreciate your help. List<OrderVO> masterList; List<OrderVO> errorList; If errorList.OrderVO.getOrderID = masterList.OrderVO.getOrderID then masterList.OrderVO.merge(errorList.OrderVO) or copy all values of masterList.OrderVO.copy(errorList.OrderVO). Hoper this is clear

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• Java LinkedList iterator being exhausted prematurely

  - by Sujeet

  I am using LinkedList and retrieving an Iterator object by using list.iterator(). After that, I am checking it.hasNext(), real issue is while checking it.hasNext(), sometimes it returns false. I need help why this is happening, though I have elements in the list. Some code: public synchronized void check(Object obj) throws Exception { Iterator itr = list.iterator(); while(itr.hasNext()) { //This Line I get false.. though i have list size is 1 Item p = (Item)itr.next(); if(p.getId() == null) {continue;} if(p.getId().getElemntId() == obj.getId() || obj.getId() == 0 ) { p.setResponse(obj); notifyAll(); return; } } Log.Error("validate failed obj.getId="+obj.getId()+" **list.size="+list.size()*This shows 1*); throw new Exception("InvalidData"); }

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• WPF Databinding With A Collection Object

  - by Randster

  Argh, although I've been googling, I really would appreciate it if someone could break my problem down as all the code examples online are confusing me more than assisting (perhaps it's just late)... I have a simple class as defined below: public class Person { int _id; string _name; public Person() { } public int ID { get { return _id; } set { _id = value; } } public string Name { get { return _name; } set { _name = value; } } } that is stored in a database, and thru a bit more code I put it into an ObservableCollection object to attempt to databind in WPF later on: public class People : ObservableCollection<Person> { public People() : base() { } public void Add(List<Person> pListOfPeople) { foreach (Person p in pListOfPeople) this.Add(p); } } In XAML, I have myself a ListView that I would like to populate a ListViewItem (consisting of a textblock) for each item in the "People" object as it gets updated from the database. I would also like that textblock to bind to the "Name" property of the Person object. I thought at first that I could do this: lstPeople.DataContext = objPeople; where lstPeople is my ListView control in my XAML, but that of course does nothing. I've found TONS of examples online where people through XAML create an object and then bind to it through their XAML; but not one where we bind to an instantiated object and re-draw accordingly. Could someone please give me a few pointers on: A) How to bind a ListView control to my instantiated "People" collection object? B) How might I apply a template to my ListView to format it for the objects in the collection? Even links to a decent example (not one operating on an object declared in XAML please) would be appreciated. Thanks for your time.

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