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  • Why does instanceof seem to work in a static generic function sometimes?

    - by michael
    Greetings. This is my first post in this site. I thought that because of type erasure, one could not expect the following code to compile, and indeed, it did not compile on an earlier version of Eclipse. My understanding was that instanceof was a run-time operator and could not know about the generic type which would be, by run-time, compiled away: public static <E extends Comparable<? super E>> void SampleForQuestion(E e) { if ( !(e instanceof String) ) System.out.println("I am not a String"); else System.out.println("I am a String"); } However, I was surprised to see that one of your threads actually included some code like this in an answer, and my latest Eclipse (Galileo on Windows with JVM 1.6 rev 20) is perfectly happy with it -- and it works, too. (I did notice that someone said it worked on Eclipse but not in another IDE/JDK in that thread, but don't remember the specifics.) Can someone explain why it works, and more importantly, because I have to guide my students, whether it should be expected to work in the future. Thank you. (I hope the code formatting comes through correctly - it looks indented correctly from my perspective and there are no tabs.)

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  • Weak reference and Strong reference

    - by theband
    package uk.co.bigroom.utils { import flash.utils.Dictionary; /** * Class to create a weak reference to an object. A weak reference * is a reference that does not prevent the object from being * garbage collected. If the object has been garbage collected * then the get method will return null. */ public class WeakRef { private var dic:Dictionary; /** * The constructor - creates a weak reference. * * @param obj the object to create a weak reference to */ public function WeakRef( obj:* ) { dic = new Dictionary( true ); dic[obj] = 1; } /** * To get a strong reference to the object. * * @return a strong reference to the object or null if the * object has been garbage collected */ public function get():* { for ( var item:* in dic ) { return item; } return null; } } } In this Class, how they denote one as Weak Reference and one as Strong reference.

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  • JPA DAO integration test not throwing exception when duplicate object saved?

    - by HDave
    I am in the process of unit testing a DAO built with Spring/JPA and Hibernate as the provider. Prior to running the test, DBUnit inserted a User record with username "poweruser" -- username is the primary key in the users table. Here is the integration test method: @Test @ExpectedException(EntityExistsException.class) public void save_UserTestDataSaveUserWithPreExistingId_EntityExistsException() { User newUser = new UserImpl("poweruser"); newUser.setEmail("[email protected]"); newUser.setFirstName("New"); newUser.setLastName("User"); newUser.setPassword("secret"); dao.persist(newUser); } I have verified that the record is in the database at the start of this method. Not sure if this is relevant, but if I do a dao.flush() at the end of this method I get the following exception: javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update

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  • Is there a way to transfrom a list of key/value pairs into a data transfer object

    - by weevie
    ...apart from the obvious looping through the list and a dirty great case statement! I've turned over a few Linq queries in my head but nothing seems to get anywhere close. Here's the an example DTO if it helps: class ClientCompany { public string Title { get; private set; } public string Forenames { get; private set; } public string Surname { get; private set; } public string EmailAddress { get; private set; } public string TelephoneNumber { get; private set; } public string AlternativeTelephoneNumber { get; private set; } public string Address1 { get; private set; } public string Address2 { get; private set; } public string TownOrDistrict { get; private set; } public string CountyOrState { get; private set; } public string PostCode { get; private set; } } We have no control over the fact that we're getting the data in as KV pairs, I'm afraid.

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  • How to encapsulate a third party complex object structure?

    - by tangens
    Motivation Currently I'm using the java parser japa to create an abstract syntax tree (AST) of a java file. With this AST I'm doing some code generation (e.g.: if there's an annotation on a method, create some other source files, ...) Problem When my code generation becomes more complex, I've to dive deeper into the structure of the AST (e.g. I have to use visitors to extract some type information of method parameters). But I'm not sure if I want to stay with japa or if I will change the parser library later. Because my code generator uses freemarker (which isn't good at automatic refactoring) I want the interface that it uses to access the AST information to be stable, even if I decide to change the java parser. Question What's the best way to encapsulate complex datastructures of third party libraries? I could create my own datatypes and copy the parts of the AST that I need into these. I could create lots of specialized access methods that work with the AST and create exactly the infos I need (e.g. the fully qualified return type of a method as one string, or the first template parameter of a class). I could create wrapper classes for the japa datastructures I currently need and embed the japa types inside, so that I can delegate requests to the japa types and transform the resulting japa types to my wrapper classes again. Which solution should I take? Are there other (better) solutions to this problem?

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  • What is the naming convention in Python for variable and function names?

    - by Ray Vega
    Coming from a C# background the naming convention for variables and method names are usually either CamelCase or Pascal Case: // C# example string thisIsMyVariable = "a" public void ThisIsMyMethod() In Python, I have seen the above but I have also seen underscores being used: # python example this_is_my_variable = 'a' def this_is_my_function(): Is there a more preferable, definitive coding style for Python?

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  • How to skip integers in C++ taken from a fstream txt file?

    - by Elaina
    I need to create a function that uses a loop. This function will open a text file and then must be able to skip a variable number of leading random integers. The program must be able to handle any number of leading random integers. Example if the opened file reads this on its first line: 100 120 92 82 38 49 102 and the SKIP_NUMBER variable is assigned 3 the number the function would grab is 82. The function must continue to grab the integers every SKIP_NUMBER until it reaches the end of the file. These integers taken from the txt file are then placed into another text file. Please help I'm really lost on how to create this loop! :D Here is my function so far... //Function skips variables and returns needed integer int skipVariable (int SKIP_NUMBER) { return 0; //temporary return } These are my program variables: // initialize function/variables ifstream fin; string IN_FILE_NAME, OUT_FILE_NAME; int SKIP_NUMBER;

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  • Google App Engine JDO error could be caused by Serializable object ?

    - by Frank
    I got the following error mesage : java.lang.UnsupportedOperationException org.datanucleus.store.appengine.EntityUtils.getPropertyName(EntityUtils.java:62) org.datanucleus.store.appengine.DatastoreFieldManager.storeObjectField(DatastoreFieldManager.java:839) org.datanucleus.state.AbstractStateManager.providedObjectField(AbstractStateManager.java:1037) PayPal_Monitor.Contact_Info_Entry.jdoProvideField(Contact_Info_Entry.java) PayPal_Monitor.Contact_Info_Entry.jdoProvideFields(Contact_Info_Entry.java) org.datanucleus.state.JDOStateManagerImpl.provideFields(JDOStateManagerImpl.java:2715) Could it be caused by my Contact_Info_Entry.java ? It looks like this : @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) Long Id; public static final long serialVersionUID=26362862L; @Persistent String Contact_Id=""; ... }

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  • More elegant way to make a C++ member function change different member variables based on template p

    - by Eric Moyer
    Today, I wrote some code that needed to add elements to different container variables depending on the type of a template parameter. I solved it by writing a friend helper class specialized on its own template parameter which had a member variable of the original class. It saved me a few hundred lines of repeating myself without adding much complexity. However, it seemed kludgey. I would like to know if there is a better, more elegant way. The code below is a greatly simplified example illustrating the problem and my solution. It compiles in g++. #include <vector> #include <algorithm> #include <iostream> namespace myNS{ template<class Elt> struct Container{ std::vector<Elt> contents; template<class Iter> void set(Iter begin, Iter end){ contents.erase(contents.begin(), contents.end()); std::copy(begin, end, back_inserter(contents)); } }; struct User; namespace WkNS{ template<class Elt> struct Worker{ User& u; Worker(User& u):u(u){} template<class Iter> void set(Iter begin, Iter end); }; }; struct F{ int x; explicit F(int x):x(x){} }; struct G{ double x; explicit G(double x):x(x){} }; struct User{ Container<F> a; Container<G> b; template<class Elt> void doIt(Elt x, Elt y){ std::vector<Elt> v; v.push_back(x); v.push_back(y); Worker<Elt>(*this).set(v.begin(), v.end()); } }; namespace WkNS{ template<class Elt> template<class Iter> void Worker<Elt>::set(Iter begin, Iter end){ std::cout << "Set a." << std::endl; u.a.set(begin, end); } template<> template<class Iter> void Worker<G>::set(Iter begin, Iter end){ std::cout << "Set b." << std::endl; u.b.set(begin, end); } }; }; int main(){ using myNS::F; using myNS::G; myNS::User u; u.doIt(F(1),F(2)); u.doIt(G(3),G(4)); } User is the class I was writing. Worker is my helper class. I have it in its own namespace because I don't want it causing trouble outside myNS. Container is a container class whose definition I don't want to modify, but is used by User in its instance variables. doIt<F> should modify a. doIt<G> should modify b. F and G are open to limited modification if that would produce a more elegant solution. (As an example of one such modification, in the real application F's constructor takes a dummy parameter to make it look like G's constructor and save me from repeating myself.) In the real code, Worker is a friend of User and member variables are private. To make the example simpler to write, I made everything public. However, a solution that requires things to be public really doesn't answer my question. Given all these caveats, is there a better way to write User::doIt?

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  • Objective-C Basic class related question, retaining the value of a specific object using a class fil

    - by von steiner
    Members, scholars, code gurus. My background is far from any computer programming thus my question may seems basic and somewhat trivial to you. Nevertheless it seems that I can't put my head around it. I have googled and searched for the answer, just to get myself confused even more. With that, I would kindly ask for a simple explanation suitable for a non technical person such as myself and for other alike arriving to this thread. I have left a comment with the text "Here is the issue" below, referring to my question. // character.h #import <Foundation/Foundation.h> @interface character : NSObject { NSString *name; int hitPoints; int armorClass; } @property (nonatomic,retain) NSString *name; @property int hitPoints,armorClass; -(void)giveCharacterInfo; @end // character.m #import "character.h" @implementation character @synthesize name,hitPoints,armorClass; -(void)giveCharacterInfo{ NSLog(@"name:%@ HP:%i AC:%i",name,hitPoints,armorClass); } @end // ClassAtLastViewController.h #import <UIKit/UIKit.h> @interface ClassAtLastViewController : UIViewController { } -(void)callAgain; @end // ClassAtLastViewController.m #import "ClassAtLastViewController.h" #import "character.h" @implementation ClassAtLastViewController - (void)viewDidLoad { //[super viewDidLoad]; character *player = [[character alloc]init]; player.name = @"Minsc"; player.hitPoints = 140; player.armorClass = 10; [player giveCharacterInfo]; [player release]; // Up until here, All peachy! [self performSelector:@selector(callAgain) withObject:nil afterDelay:2.0]; } -(void)callAgain{ // Here is the issue, I assume that since I init the player again I loss everything // Q1. I loss all the data I set above, where is it than? // Q2. What is the proper way to implement this character *player = [[character alloc]init]; [player giveCharacterInfo]; } Many thanks in advance, Kindly remember that my background is more related to Salmons breeding than to computer code, try and lower your answer to my level if it's all the same to you.

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  • a class function with if(this==NULL) test got compiled?

    - by James
    I saw this code snippet during our lab and it actually compiles in MSVC2008 and G++. void LinkList< class T ::Insert(T n) { if (this == NULL) // some code here } As far as I know the this must not be null since you cannot call a class functions in c++ if it wasn't instantiated. Is this a valid code? if so what's the reason behind and where it can be useful?

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  • How do you return a pointer to a base class with a virtual function?

    - by Nick Sweet
    I have a base class called Element, a derived class called Vector, and I'm trying to redefine two virtual functions from Element in Vector. //element.h template <class T> class Element { public: Element(); virtual Element& plus(const Element&); virtual Element& minus(const Element&); }; and in another file //Vector.h #include "Element.h" template <class T> class Vector: public Element<T> { T x, y, z; public: //constructors Vector(); Vector(const T& x, const T& y = 0, const T& z =0); Vector(const Vector& u); ... //operations Element<T>& plus(const Element<T>& v) const; Element<T>& minus(const Element<T>& v) const; ... }; //sum template <class T> Element<T>& Vector<T>::plus(const Element<T>& v) const { Element<T>* ret = new Vector((x + v.x), (y + v.y), (z + v.z)); return *ret; } //difference template <class T> Element<T>& Vector<T>::minus(const Element<T>& v) const { Vector<T>* ret = new Vector((x - v.x), (y - v.y), (z - v.z)); return *ret; } but I always get error: 'const class Element' has no member named 'getx' So, can I define my virtual functions to take Vector& as an argument instead, or is there a way for me to access the data members of Vector through a pointer to Element? I'm still fairly new to inheritance polymorphism, fyi.

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  • jQuery programming style?

    - by Sam Dufel
    I was recently asked to fix something on a site which I haven't worked on before. I haven't really worked with jQuery that much, but I figured I'd take a look and see if I could fix it. I've managed to mostly clear up the problem, but I'm still horrified at the way they chose to build this site. On document load, they replace the click() method of every anchor tag and form element with the same massive function. When clicked, that function then checks if the tag has one of a few different attributes (non-standard attributes, even), and does a variety of different tasks depending on what attributes exist and what their values are. Some hyperlinks have an attribute on them called 'ajaxrel', which makes the click() function look for another (hidden) hyperlink with an ID specified by the ajaxrel attribute, and then calls the click() function for that other hyperlink (which was also modified by this same click() function). On the server side, all the php files are quite long and have absolutely no indentation. This whole site has been a nightmare to debug. Is this standard jQuery practice? This navigation scheme seems terrible. Does anyone else actually use jQuery this way? I'd like to start incorporating it into my projects, but looking at this site is giving me a serious headache. Here's the click() function for hyperlinks: function ajaxBoxA(theElement, urltosend, ajaxbox, dialogbox) { if ($(theElement).attr("href") != undefined) var urltosend = $(theElement).attr("href"); if ($(theElement).attr('toajaxbox') != undefined) var ajaxbox = $(theElement).attr('toajaxbox'); // check to see if dialog box is called for. if ($(theElement).attr('dialogbox') != undefined) var dialogbox = $(theElement).attr('dialogbox'); var dodialog = 0; if (dialogbox != undefined) { // if dialogbox doesn't exist, then flag to create dialog box. var isDiaOpen = $('[ajaxbox="' + ajaxbox + '"]').parent().parent().is(".ui-dialog-container"); dodialog = 1; if (isDiaOpen) { dodialog = 0; } dialogbox = parseUri(dialogbox); dialogoptions = { close: function () { // $("[id^=hierarchy]",this).NestedSortableDestroy(); $(this).dialog('destroy').remove() } }; for ( var keyVar in dialogbox['queryKey'] ) eval( "dialogoptions." + keyVar + " = dialogbox['queryKey'][keyVar]"); }; $("body").append("<div id='TB_load'><img src='"+imgLoader.src+"' /></div>"); $('#TB_load').show(); if (urltosend.search(/\?/) > 0) { urltosend = urltosend + "&-ajax=1"; } else { urltosend = urltosend + "?-ajax=1"; } if ($('[ajaxbox="' + ajaxbox + '"]').length) { $('[ajaxbox="' + ajaxbox + '"]').each( function () { $(this).empty(); }); }; $.ajax({ type: "GET", url: urltosend, data: "", async: false, dataType: "html", success: function (html) { var re = /^<toajaxbox>(.*?)<\/toajaxbox>+(.*)/; if (re.test(html)) { var match = re.exec(html); ajaxbox = match[1]; html = Right(html, String(html).length - String(match[1]).length); } var re = /^<header>(.*?)<\/header>+(.*)/; if (re.test(html)) { var match = re.exec(html); window.location = match[1]; return false; } if (html.length > 0) { var newHtml = $(html); if ($('[ajaxbox="' + ajaxbox + '"]').length) { $('[ajaxbox="' + ajaxbox + '"]').each( function () { $(this).replaceWith(newHtml).ready( function () { ajaxBoxInit(newHtml) if (window.ajaxboxsuccess) ajaxboxsuccess(newHtml); }); }); if ($('[ajaxdialog="' + ajaxbox + '"]').length = 0) { if (dodialog) $(newHtml).wrap("<div class='flora ui-dialog-content' ajaxdialog='" + ajaxbox + "' style='overflow:auto;'></div>").parent().dialog(dialogoptions); } } else { $("body").append(newHtml).ready( function () { ajaxBoxInit(newHtml); if (window.ajaxboxsuccess) ajaxboxsuccess(newHtml); }); if (dodialog) $(newHtml).wrap("<div class='flora ui-dialog-content' ajaxdialog='" + ajaxbox + "' style='overflow:auto;'></div>").parent().dialog(dialogoptions); } } var rel = $(theElement).attr('ajaxtriggerrel'); if (rel != undefined) $('a[ajaxrel="' + rel + '"]').click(); tb_remove(); return false; }, complete: function () { $("#TB_load").remove(); } }); return false; }

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  • How do you determine when an object is drawn on-screen in OpenGL?

    - by Harry
    I'm extremely new to OpenGL. I'm writing a program that displays flying text on screen. I need to know when certain text string appears (drawn) onto the screen and are visible to the user. The program needs to identify which text strings are displayed. At first, I started to think that I could use OpenGL's picking mechanism, but so far I've only seen examples where the selection area is focused on some sort of user interaction. I want to know what objects are displayed on the entire window area. This leads me to think I'm on the wrong track... Am I missing something? Any suggestions are welcome.

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  • Strange client's address returned throug accept(..) function.

    - by Negai
    Hi everyone, I'm a socket programming newbie. Here's a snippet: struct sockaddr_storage client_addr; ... client_addr_size = sizeof(client_addr); client_socket = accept( server_socket, (struct sockaddr *)&client_addr, &client_addr_size ); ... result = inet_ntop( AF_INET, &((struct sockaddr_in *)&client_addr)->sin_addr, client_addr_str, sizeof(client_addr_str) ); Whenever the client connects the address I get is 0.0.0.0 regardless from the host. Can anybody explain, what I'm doing wrong? Thanks.

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  • Run javascript function after Server-Side validation is complete.

    - by Ed Woodcock
    Ok, I've got a lightbox with a small form (2 fields) in it, inside an UpdatePanel, and I want to close this lightbox (must be done via javascript) when the 'Save' button is pressed. However, there is a need to have a server-side CustomValidator on the page, and I only want to close the lightbox if this returns as valid. Does anyone know a way to trigger javascript (or jQuery) code from a server-side validator?

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  • Pass Types as arguments to a function in Haskell?

    - by Charles Peng
    The following two functions are extremely similar. They read from a [String] n elements, either [Int] or [Float]. How can I factor the common code out? I don't know of any mechanism in Haskell that supports passing types as arguments. readInts n stream = foldl next ([], stream) [1..n] where next (lst, x:xs) _ = (lst ++ [v], xs) where v = read x :: Int readFloats n stream = foldl next ([], stream) [1..n] where next (lst, x:xs) _ = (lst ++ [v], xs) where v = read x :: Float I am at a beginner level of Haskell, so any comments on my code are welcome.

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  • In flex how do I pass data retrieved from a remote object service to a modules interface?

    - by Dan G
    I found at this Adobe tutorial a nice "RemoteService" class that creates a RemoteObject and contains the functions for handling the result and fault events. If I wanted to use this approach, how could I pass the data from the result handler to interfaces that modules from the main application could use? I could put the RemoteService/RemoteObject in the modules, but (in my opinion- and I could be wrong) the best design seems to be using the remote calls in the main app and passing the data along to the modules.

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  • How can I add a field with an array value to my Perl object?

    - by superstar
    What's the difference between these two constructors in perl? 1) sub new { my $class = shift; my $self = {}; $self->{firstName} = undef; $self->{lastName} = undef; $self->{PEERS} = []; bless ($self, $class); return $self; } 2) sub new { my $class = shift; my $self = { _firstName => shift, _lastName => shift, _ssn => shift, }; bless $self, $class; return $self; } I am using the second one so far, but I need to implement the PEERS array in the second one? How do I do it with the second constructor and how can we use get and set methods on those array variables?

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  • jQuery Looking for a function to equalize heights of divs based on tallest image in a table.

    - by Jamie
    I am doing a site that will have a table with a bunch of images in them. They are user added images so I have no control over aspect ratio, what I do have control over is I can the force a max height/width and the image will not exceed this in either direction, but the height can (and will) fluctuate. <table class="pl_upload"> <tr class="row1"> <td class="col1"> <div> <div class="img-container"> <a href="#"><img src="img.jpg" width="182" alt="X" /></a> </div> </div> </td> ....... What I need ideally is to get the height of the tallest image and then make the all of the children divs the same height based on the height of the tallest one. I hope that makes sense, been a long day. I made a jsfiddle page for it here: http://jsfiddle.net/Evolution/27EJB/

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