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  • How can the generic method called know the type of the generic return?

    - by Paulo Guedes
    I couldn't find a duplicate for this question for Java, although there are a lot of them for C#. I have this method: public <T> T getSomething() { // } According to the type of T, I will have a different return. For example: String a = getSomething(); int b = getSomething(); For a, my method will return a specific String. For b, it will return a specific int. And so on. It seems that this can be done with typeof() in C#. How can I achieve it in Java?

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  • What would happen to GC if I run process with priority = RealTime?

    - by Bobb
    I have a C# app which runs with priority RealTime. It was all fine until I made few hectic changes in past 2 days. Now it runs out of memory in few hours. I am trying to find whether it is a memory leak I created of this is because I consume lot more objects than before and GC simply cant collect them because it runs with same priority. My question is - what could happen to GC when it tries to collect objects in application with RealTime priority (there is also at least one thread running with Highest thread priority)? (P.S. by realtime priority I mean Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.RealTime) Sorry forgot to tell. GC is in Server mode

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  • Generic applet style system for publishing mathematics demonstrations?

    - by Alex
    Anyone who's tried to study mathematics using online resources will have come across these Java applets that demonstrate a particular mathematical idea. Examples: http://www.math.ucla.edu/~tao/java/Mobius.html http://www.mathcs.org/java/programs/FFT/index.html I love the idea of this interactive approach because I believe it is very helpful in conveying mathematical principles. I'd like to create a system for visually designing and publishing these 'mathlets' such that they can be created by teachers with little programming experience. So in order to create this app, i'll need a GUI and a 'math engine'. I'll probably be working with .NET because thats what I know best and i'd like to start experimenting with F#. Silverlight appeals to me as a presentation framework for this project (im not worried about interoperability right now). So my questions are: does anything like this exist already in full form? are there any GUI frameworks for displaying mathematical objects such as graphs & equations? are there decent open source libraries that exposes a mathematical framework (Math.NET looks good, just wondering if there is anything else out there) is there any existing work on taking mathematical models/demos built with maple/matlab/octave/mathematica etc and publishing them to the web?

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  • How to create a reference tables for collection classes using fluent nhibernate

    - by Akk
    How can i create a 3 table schema from the following model classes. public class Product { public int Id {get; set;} public string Name {get; set;} public IList<Photo> Photos {get; set;} } public class Photo { public int Id {get; set;} public string Path {get; set;} } I want to create the following table structure in the database: Product ------- Id Name ProductPhotos ------------- ProductId (FK Products.Id) PhotoId (FK Photos.Id) Photos ------ Id Path How i can express the above Database Schema using Fluent NHibernate? I could only manage the following the Mapping but this does not get me the 3rd Photo ref table. public class ProductMap : ClassMap<Product> { public CityMap() { Id(x => x.Id); Map(x => x.Name); Table("Products"); HasMany(x => x.Photos).Table("ProductPhotos").KeyColumn("ProductId"); } }

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  • C# type safe and developer friendly list/collection technique

    - by Agile Noob
    I am populating a "Dictionary" with the results of an sp call. The key is the field name and the value is whatever value the sp returns for the field. This is all well and good but I'd like developers to have a predefined list of keys to access this list, for safety and documentation reasons. What I'd like to do is have something like an enum as a key for the dictionary so developers can safely access the list, but still have the ability to access the dictionary with a string key value. I am hoping to have a list of string values that I can access with an enum key AND a string key. Please make sure any suggestions are simple to implement, this is not the kind of thing I'm willing to build a lot of overhead to implement.

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  • hibernate empty collection in component

    - by Jurgen H
    I have a component mapped using Hibernate. If all fields in the component in the database are null, the component itself is set to null by hibernate. This is the expected behavior and also what I need. The problem I have, is that when I add a bag to that component, the bag is initialized to an empty list. This means the component has a non null value... resulting in the component being created. Any idea how to fix this? <class name="foo.bar.Entity" table="Entity"> <id name="id" column="id"> <generator class="native" /> </id> <property name="departure" column="departure_time" /> <property name="arrival" column="arrival_time" /> <component name="statistics"> <bag name="linkStatistics" lazy="false" cascade="all" > <key column="entity_id" not-null="true" /> <one-to-many class="foo.bar.LinkStatistics" /> </bag> <property name="loggedTime" column="logged_time" /> ... </component> A criteria with Restirctions.isNull("statistics") does return the expected values.

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  • Multiple levels of 'collection.defaultdict' in Python

    - by Morlock
    Thanks to some great folks on SO, I discovered the possibilities offered by collections.defaultdict, notably in readability and speed. I have put them to use with success. Now I would like to implement three levels of dictionaries, the two top ones being defaultdict and the lowest one being int. I don't find the appropriate way to do this. Here is my attempt: from collections import defaultdict d = defaultdict(defaultdict) a = [("key1", {"a1":22, "a2":33}), ("key2", {"a1":32, "a2":55}), ("key3", {"a1":43, "a2":44})] for i in a: d[i[0]] = i[1] Now this works, but the following, which is the desired behavior, doesn't: d["key4"]["a1"] + 1 I suspect that I should have declared somewhere that the second level defaultdict is of type int, but I didn't find where or how to do so. The reason I am using defaultdict in the first place is to avoid having to initialize the dictionary for each new key. Any more elegant suggestion? Thanks pythoneers!

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  • Which type of data can be garbage collected when app is in background?

    - by Neoh
    Let's say I start from activity A - activity B. While in activity B I press home to exit. After a long time, gc may be called because other apps take higher priority. My question is, which of the following type of data will be garbage collected (I'm pretty sure static fields can be garbage collected any time but I'm not sure about these): i) fields that are declared final or static final ii) intent and its data that I passed from activity A to activity B iii) onSavedInstanceState when orientation is changed during the app running I ask this because I want to ensure that my app won't crash when I restore activity B from background after a long period.

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  • .NET object creation and generations

    - by nimoraca
    Is there a way to tell the .NET to allocate a new object in generation 2 heap. I have a problem where I need to allocate approximately 200 MB of objects, do something with them, and throw them away. What happens here is that all the data gets copied two times (from gen0 to gen1 and then from gen1 to gen2).

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  • [VB.Net] Typecasting generic parameters.

    - by CFP
    Hello world! Using the following code: Function GetSetting(Of T)(ByVal SettingName As String, ByRef DefaultVal As T) As T Return If(Configuration.ContainsKey(SettingName), CType(Configuration(SettingName), T), DefaultVal) End Function Yields the following error: Value of type 'String' cannot be converted to 'T'. Any way I could specify that in all cases, the conversion will indeed be possible (I'm basically getting integers, booleans, doubles and strings). Thanks!

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  • C# What would happen to GC if I run process with priority = RealTime?

    - by Bobb
    I have a C# app which runs with priority RealTime. It was all fine until I made few hectic changes in past 2 days. Now it runs out of memory in few hours. I am trying to find whether it is a memory leak I created of this is because I consume lot more objects than before and GC simply cant collect them because it runs with same priority. My question is - what could happen to GC when it tries to collect objects in application with RealTime priority (there is also at least one thread running with Highest thread priority)? (P.S. by realtime priority I mean Process.GetCurrentProcess().PriorityClass = ProcessPriorityClass.RealTime)

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  • Java GC: top object classes promoted (by size)?

    - by Java Geek
    Hello! Please let me know what is the best way to determine composition of young generation memory promoted to old generation, after each young GC event? Ideally I would like to know class names which are responsible say, for 80% of heap in each "young gen - old gen" promotion chunk; Example: I have 600M young gen, each tenure promotes 6M; I want to know which objects compose this 6M. Thank you.

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  • Best practice to avoid InvalidOperationException: Collection was modified?

    - by Roflcoptr
    Very often I need something like that: foreach (Line line in lines) { if (line.FullfilsCertainConditions()) { lines.Remove(line) } } This does not work, because I always get a InvalidOperationException because the Enumerator was changed during the loop. So I changed all my loops of this kind to the following: List<Line> remove = new List<Line>(); foreach (Line line in lines) { if (line.FullfilsCertainConditions()) { remove.Add(line) } } foreach (Line line in remove) { { lines.Remove(line); } I'm not sure if this is really the best way since in the worst case I have to iterate 2 times over the original list and so it needs time 2n instead of n. Is there a better way to do this?

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  • content_tag_for a collection in Rails?

    - by Nick
    I have a Post model. Posts have many Comments. I want to generate a <ul> element for post.comments using content_tag_for. Ideally, it'd produce <ul id="comments_post_7" class="comments"> ... </ul> where 7 is the ID of the Post. The closest I can get uses <% content-tag-for :ul post, :comments do %> which produces <ul id="comments_post_7" class="post"> ... </ul> which is pretty close, except for the class="post". Using :class => :comments in the content_tag_for yields class="post comments", but I just want class="comments". It seems logical that I'd be able to use something like <% content_tag_for :ul post.comments do %> but, sadly, that yields <ul id="array_2181653100" class="array"> ... </ul> I've searched far and wide. I feel like I'm missing some elegant way to do this. Am I? Because, seriously, <ul id="comments_post_<%= post.id %>" class="comments"> is painful.

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  • What is root reference ?

    - by DotNetGuy
    class GCTest { static Object r1; static void Main() { r1 = new Object(); Object r2 = new Object(); Object r3 = new Object(); System.GC.Collect(); // what can be reclaimed here ? r1 = null; r3.ToString(); System.GC.Collect(); // what can be reclaimed here ? } } // code from - DonBox's Essential .Net

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  • Binding a select box to a Collection (with Spring)

    - by WiPU
    i have the following problem. I have a form bean and in this bean is a list with objects. List<SomeObjectForm> toDisplay; Now i want map a html select to this list. Something like that: <form:select id="inputGroupFields" path="templateKey" multiple="true"... <form:select id="inputGroupFields" path="templateKey.id" multiple="true"... And this dosnt work of course. Now i have tryed to add different custom Converter like: myConv implements Converter<SomeObjectForm, String> myConv extends StringToObject And this also not work. I'm not sure if this is the right approach or there is a easier way to do that. Some addional Infos: --i'm using spring 3.0.5 --all this happens during a web flow regards and thanks, WiPu

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  • C++ creating generic template function specialisations

    - by Fire Lancer
    I know how to specialise a template function, however what I want to do here is specialise a function for all types which have a given method, eg: template<typename T> void foo(){...} template<typename T, if_exists(T::bar)>void foo(){...}//always use this one if the method T::bar exists T::bar in my classes is static and has different return types. I tried doing this by having an empty base class ("class HasBar{};") for my classes to derive from and using boost::enable_if with boost::is_base_of on my "specialised" version. However the problem then is that for classes that do have bar, the compiler cant resolve which one to use :(. template<typename T> typename boost::enable_if<boost::is_base_of(HasBar, T>, void>::type f() {...} I know that I could use boost::disable_if on the "normal" version, however I do not control the normal version (its provided by a third party library and its expected for specialisations to be made, I just don't really want to make explicit specialisations for my 20 or so classes), nor do I have that much control over the code using these functions, just the classes implementing T::bar and the function that uses it. Is there some way to tell the compiler to "always use this version if possible no matter what" without altering the other versions?

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  • WPF Converter to look up in generic list

    - by user310046
    I have a list of data where I keep e.g. countries with code, name and some other data. List<Country> countries = <deserialized objects from file> which consist of objects like this: public class Country { public string Code { get; set;} public string Name { get; set;} } The object which use as a DataContext may look like this: public class Address { public string StreetName{ get; set;} public string CountryCode { get; set;} } Then in my XAML I want to do something like this to show the name of the country <TextBlock Text="{Binding Path=CountryCode, Converter={StaticResource CountryNameLookupConverter}}"/> But how can I make the CountryNameLookupConverter use the countries list I read from the xml file?

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  • Rspec and Rails 3 - Problem Validating Nested Attribute Collection Size

    - by MunkiPhD
    When I create my Rspec tests, I keep getting a validation of false as opposed to true for the following tests. I've tried everything and the following is the measly code that I have now - so if it's waaaaay wrong, that's why. class Master < ActiveRecord::Base attr_accessible :name, :specific_size # Associations ---------------------- has_many :line_items accepts_nested_attributes_for :line_items, :allow_destroy => true, :reject_if => lambda { |a| a[:item_id].blank? } # Validations ----------------------- validates :name, :presence => true, :length => {:minimum => 3, :maximum => 30} validates :specific_size, :presence => true, :length => {:minimum => 4, :maximum => 30} validate :verify_items_count def verify_items_count if self.line_items.size < 2 errors.add(:base, "Not enough items to create a master") end end end And here it the items model: class LineItem < ActiveRecord::Base attr_accessible :specific_size, :other_item_type_id # Validations -------------------- validates :other_item_type_id, :presence => true validates :master_id, :presence => true validates :specific_size, :presence => true # Associations --------------------- belongs_to :other_item_type belongs_to :master end The RSpec Tests: before(:each) do @master_lines = [] @master_lines << LineItem.new(:other_item_type_id => 1, :master_id => 2, :specific_size => 1) @master_lines << LineItem.new(:other_item_type_id => 2, :master_id => 2, :specific_size => 1) @attr = {:name => "Some Master", :specific_size => "1 giga"} end it "should create a new instance given a valid name and specific size" do @master = Master.create(@attr) line_item_one = @master.line_items.build(:other_item_type_id => 1, :specific_size => 1) line_item_two = @master.line_items.build(:other_item_type_id => 2, :specific_size => 2) @master.line_items.size === 2 @master.should be_valid end it "should have at least two items to be valid" do master = Master.new(:name => "test name", :specific_size => "1 mega") master_item_one = LineItem.new(:other_item_type_id => 1, :specific_size => 2) master_item_two = LineItem.new(:other_item_type_id => 2, :specific_size => 1) master.line_items << master_item_one master.should_not be_valid master.line_items << master_item_two master.line_items.size.should === 2 master.should be_valid end I'm very new to Rspec and Rails - and I've been failing at this for the past couple of hours. Thanks for any help in advance.

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  • Logic: Best way to sample & count bytes of a 100MB+ file

    - by Jami
    Let's say I have this 170mb file (roughly 180 million bytes). What I need to do is to create a table that lists: all 4096 byte combinations found [column 'bytes'], and the number of times each byte combination appeared in it [column 'occurrences'] Assume two things: I can save data very fast, but I can update my saved data very slow. How should I sample the file and save the needed information? Here're some suggestions that are (extremely) slow: Go through each 4096 byte combinations in the file, save each data, but search the table first for existing combinations and update it's values. this is unbelievably slow Go through each 4096 byte combinations in the file, save until 1 million rows of data in a temporary table. Go through that table and fix the entries (combine repeating byte combinations), then copy to the big table. Repeat going through another 1 million rows of data and repeat the process. this is faster by a bit, but still unbelievably slow This is kind of like taking the statistics of the file. NOTE: I know that sampling the file can generate tons of data (around 22Gb from experience), and I know that any solution posted would take a bit of time to finish. I need the most efficient saving process

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  • Accessing child collection in query

    - by Gokul
    I am populating a list using List<Country> countries = new List<Country> { new Country() { CountryID = "US", City = new List<City> { new City() { CountryID = "US", CityName="dfdsf", sqkm = 2803 } } }; and so on How to access sqkm in the following query? var countryQuery = countries .Select(c => new { Id = c.CountryId, Area = c.City.sqkm???}); c.city.sqkm gives compilation error...how to modify query

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  • C++ Generic List Assignment

    - by S73417H
    I've clearly been stuck in Java land for too long... Is it possible to do the C++ equivalent of the following Java code: // Method List<Bar> getBars() { return new LinkedList<Bar>(); } // Assignment statement. List<Foo> stuff = getBars(); Where Foo is a sub-class of Bar. So in C++.... std::list<Bar> & getBars() { std::list<Bar> bars; return bars; } std::list<Foo> stuff = getBars(); Hope that makes sense....

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