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Search found 1449 results on 58 pages for 'oop'.

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  • Why is there no parameter contra-variance for overriding?

    - by Oak
    C++ and Java support return-type covariance when overriding methods. Neither, however, support contra-variance in parameter types - instead, it translates to overloading (Java) or hiding (C++). Why is that? It seems to me that there is no harm in allowing that. I can find one reason for it in Java - since it has the "choose-the-most-specific-version" mechanism for overloading anyway - but can't think of any reason for C++. Example (Java): class A { public void f(String s) {...} } class B extends A { public void f(Object o) {...} // Why doesn't this override A.f? }

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  • Is this class + constructor definition pattern overly redundant?

    - by Protector one
    I often come across a pattern similar to this: class Person { public string firstName, lastName; public Person(string firstName, string lastName) { this.firstName = firstName; this.lastName = lastName; } } This feels overly redundant (I imagine typing "firstName" once, instead of thrice could be enough…), but I can't think of a proper alternative. Any ideas? Maybe I just don't know about a certain design pattern I should be using here? Edit - I think I need to elaborate a little. I'm not asking how to make the example code "better", but rather, "shorter". In its current state, all member names appear 3 times (declaration, initialization, constructor arguments), and it feels rather redundant. So I'm wondering if there is a pattern (or semantic sugar) to get (roughly) the same behavior, but with less bloat. I apologize for being unclear initially.

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  • Java - how to tell class of an object?

    - by lkm
    Given a method that accepts as a parameter a certain supertype. Is there any way, within that method, to determine the actual class of the object that was passed to it? I.e. if a subtype of the allowable parameter was actually passed, is there a way to find out which type it is? If this isn't possible can someone explain why not (from a language design perspective)? Thanks Update: just to make sure I was clear void doSomething(MyType myType) { //determine if myType is MyType OR one of its subclasses } Since the method signature specifies the parameter as being MyType, then how can one tell if the object is actually a subtype of MyType (and which one).

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  • How to maintain a pool of names ?

    - by Jacques René Mesrine
    I need to maintain a list of userids (proxy accounts) which will be dished out to multithreaded clients. Basically the clients will use the userids to perform actions; but for this question, it is not important what these actions are. When a client gets hold of a userid, it is not available to other clients until the action is completed. I'm trying to think of a concurrent data structure to maintain this pool of userids. Any ideas ? Would a ConcurrentQueue do the job ? Clients will dequeue a userid, and add back the userid when they are finished with it.

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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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  • Example of forum in Object Oriented PHP

    - by Martin Trigaux
    Hello, I'm trying to learn to use PHP with an object oriented scheme. I think I understand the concept but I need real example, a forum exactly (the closest to what I want to do). I know PhpBB but it's maybe too complicated to fully understand it so I'm looking for something simpler but still in object oriented. Do you know any ? Thank you

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  • Singletons and other design issues

    - by Ahmed Saleh
    I have worked using different languages like C++/Java and currently AS3. Most applications were computer vision, and small 2D computer games. Most companies that I have worked for, they use Singletons in a language like AS3, to retrieve elements or classes in an easy way. Their problem is basically they needs some variables or to call other functions from other classes. In a language like AS3, there is no private constructor, and they write a hacky code to prevent new instances. In Java and C++ I also faced the situation that I need to use other classe's members or to call their functions in different classes. The question is, is there a better or another design, to let other classes interact with each others without using singletons? I feel that composition is the answer, but I need more detailed solutions or design suggestions.

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  • Is there anything bad in declaring static inner class inside interface in java?

    - by Roman
    I have an interface ProductService with method findByCriteria. This method had a long list of nullable parameters, like productName, maxCost, minCost, producer and so on. I refactored this method by introducing Parameter Object. I created class SearchCriteria and now method signature looks like this: findByCriteria (SearchCriteria criteria) I thought that instances of SearchCriteria are only created by method callers and are only used inside findByCriteria method, i.e.: void processRequest() { SearchCriteria criteria = new SearchCriteria () .withMaxCost (maxCost) ....... .withProducer (producer); List<Product> products = productService.findByCriteria (criteria); .... } and List<Product> findByCriteria(SearchCriteria criteria) { return doSmthAndReturnResult(criteria.getMaxCost(), criteria.getProducer()); } So I did not want to create separate public class for SearchCriteria and put it inside ProductServiceInterface: public interface ProductService { List<Product> findByCriteria (SearchCriteria criteria); static class SearchCriteria { ... } } Is there anything bad in this interface? Where whould you place SearchCriteria class?

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  • PHP Classes: Call method in instance of a class by instance's name

    - by Ursus Russus
    Hi, i have a class of this kind Class Car { private $color; public function __construct($color){ $this->color=$color; } public function get_color(){ return $this->$color; } } Then i create some instances of it: $blue_car = new car('blue'); $green_car = new car('green'); etc. Now i need to call method get_color() on the fly, according to instance's name $instance_name='green_car'; Is there any way to do it?

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  • 2 Classes need each other declared C++

    - by Prodigga
    I have a "Game" class which holds all the games settings and manages the game. I have a "Grid" class which is the grid the game is played on. The "Game" class initializes a "Grid" object as one of its members (passing itself ("this") as one of the parameters for "Grid"s constructor).. The "Grid" object therefor needs to deal with a "Game*" pointer. To do this it needs to know what "Game" is; i need to declare it before "Grid". But "Game" uses "Grid"...so it also needs "Grid" declared before it. so confused on how to include headers/etc correctly here..

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  • Transferring object from parent to child

    - by waiwai933
    I'm currently developing an Custom Application using the IP.Board framework, which is in PHP, which by default, creates a IPSMember object for the logged-in user. However, I'm developing an additional class, basically class SpecialUser extends IPSMember Is there a way to get the parent object, which is IPSMember to change to SpecialUser?

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  • How to prevent inheritance for some methods?!

    - by Dr TJ
    Hi How can I prevent inheritance of some methods or properties in derived classes?! public class BaseClass : Collection { //Some operations... //Should not let derived classes inherit 'Add' method. } public class DerivedClass : BaseClass { public void DoSomething(int Item) { this.Add(Item); // Error: No such method should exist... } }

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  • Is there any short way to load data to the properties of a class, for each column name matching the properties of the class?

    - by Ugur Gümüshan
    I want to load data to an instance of an object using its constructor and I write $this->property=$row["colname"] each time for each property. the mysql_fetch_object function fetches the data as an object but I am not sure if the instance of an object can be assigned to some object from inside. othwerwise I would use __construct($object) { $this=$object; } //doesn't give any syntax error Maybe I should look into iteration of properties and use foreach($object as $key => $value) $value=$object[$key]; or can I assign like $this=$object; within the constructor?

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  • Abstract attributes in Python

    - by deamon
    What is the shortest / most elegant way to implement the following Scala code with an abstract attribute in Python? abstract class Controller { val path: String } A subclass of Controller is enforced to define "path" by the Scala compiler. A subclass would look like this: class MyController extends Controller { override val path = "/home" }

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  • How to work with PHP abstract?

    - by YumYumYum
    Why would you use such abstract? Does it speed up work or what exactly its for? // file1.php abstract class Search_Adapter_Abstract { private $ch = null; abstract private function __construct() { } abstract public funciton __destruct() { curl_close($this->ch); } abstract public function search($searchString,$offset,$count); } // file2.php include("file1.php"); class abc extends Search_Adapter_Abstract { // Will the curl_close now automatically be closed? } What is the reason of extending abstract here? Makes me confused. What can i get from it now?

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  • Python and classes

    - by Artyom
    Hello, i have 2 classes. How i call first.TQ in Second ? Without creating object First in Second. class First: def __init__(self): self.str = "" def TQ(self): pass def main(self): T = Second(self.str) # Called here class Second(): def __init__(self): list = {u"RANDINT":first.TQ} # List of funcs maybe called in first ..... ..... return data

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  • Actionscript 2.0 Functions problem and somewhat "global" variable

    - by Joshua
    I have two problems. The first problem is with the following functions; when I call the function in (enterFrame), it doesn't work: onClipEvent (load) { function failwhale(levelNum) { _root.gotoAndStop("fail"); failFrom = levelNum; } function guardSightCollision(guardName, guardSightName) { if (_root.guardName.guardSightName.hitTest(_x, _y+radius, true)) { failwhale(1); } if (_root.guardName.guardSightName.hitTest(_x, _y-radius, true)) { failwhale(1); } if (_root.guardName.guardSightName.hitTest(_x-radius, _y, true)) { failwhale(1); } if (_root.guardName.guardSightName.hitTest(_x+radius, _y, true)) { failwhale(1); } } } onClipEvent (enterFrame) { guardSightCollision(guard1, guard1Sight); } Why doesn't it work?... The second problem lies in the failFrom variable: function failwhale(levelNum) { _root.gotoAndStop("fail"); failFrom = levelNum; } How do I make failFrom a "global" variable in that it can be accessed anywhere (from actionscript in frames and even movieclips)...Right now, when I try to trace failFrom in a different frame, it is "undefined".

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  • Actionscript 2.0 Functions problem

    - by Joshua
    I have two problems. The first problem is with the following functions; when I call the function in (enterFrame), it doesn't work: onClipEvent (load) { function failwhale(levelNum) { _root.gotoAndStop("fail"); failFrom = levelNum; } function guardSightCollision(guardName, guardSightName) { if (_root.guardName.guardSightName.hitTest(_x, _y+radius, true)) { failwhale(1); } if (_root.guardName.guardSightName.hitTest(_x, _y-radius, true)) { failwhale(1); } if (_root.guardName.guardSightName.hitTest(_x-radius, _y, true)) { failwhale(1); } if (_root.guardName.guardSightName.hitTest(_x+radius, _y, true)) { failwhale(1); } } } onClipEvent (enterFrame) { guardSightCollision(guard1, guard1Sight); } Why doesn't it work?... The second problem lies in the failFrom variable: function failwhale(levelNum) { _root.gotoAndStop("fail"); failFrom = levelNum; } How do I make failFrom a "global" variable in that it can be accessed anywhere (from actionscript in frames and even movieclips)...Right now, when I try to trace failFrom in a different frame, it is "undefined".

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  • Method return values and exceptions

    - by dnagirl
    I have an interface called iIncident which defines a single method when(). when() should return a DateTime object. I'm trying to decide what to do if $object->when() has no DateTime to return as might be the case just after an object is instantiated and before all its properties are set. My choices are: return false throw some kind of Exception return some default DateTime like '9999-01-01' My inclination is to go with an Exception since $object really can't act as an incident until it knows when it occurred. I don't want to return a default DateTime because it complicates comparisons and it's not true. And I don't really want to return false because then I have to check for it every time I call the method- but if that is the preferred method, I guess I will. Is throwing an exception the best way? And is there a predefined exception type I should use (none of the SPL ones struck me as particularly appropriate- but that might just indicate my lack of experience)?

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  • PHP Session Class and $_SESSION Array

    - by Gianluca Bargelli
    Hello, i've implemented this custom PHP Session Class for storing sessions into a MySQL database: class Session { private $_session; public $maxTime; private $database; public function __construct(mysqli $database) { $this->database=$database; $this->maxTime['access'] = time(); $this->maxTime['gc'] = get_cfg_var('session.gc_maxlifetime'); session_set_save_handler(array($this,'_open'), array($this,'_close'), array($this,'_read'), array($this,'_write'), array($this,'_destroy'), array($this,'_clean') ); register_shutdown_function('session_write_close'); session_start();//SESSION START } public function _open() { return true; } public function _close() { $this->_clean($this->maxTime['gc']); } public function _read($id) { $getData= $this->database->prepare("SELECT data FROM Sessions AS Session WHERE Session.id = ?"); $getData->bind_param('s',$id); $getData->execute(); $allData= $getData->fetch(); $totalData = count($allData); $hasData=(bool) $totalData >=1; return $hasData ? $allData['data'] : ''; } public function _write($id, $data) { $getData = $this->database->prepare("REPLACE INTO Sessions VALUES (?, ?, ?)"); $getData->bind_param('sss', $id, $this->maxTime['access'], $data); return $getData->execute(); } public function _destroy($id) { $getData=$this->database->prepare("DELETE FROM Sessions WHERE id = ?"); $getData->bind_param('S', $id); return $getData->execute(); } public function _clean($max) { $old=($this->maxTime['access'] - $max); $getData = $this->database->prepare("DELETE FROM Sessions WHERE access < ?"); $getData->bind_param('s', $old); return $getData->execute(); } } It works well but i don't really know how to properly access the $_SESSION array: For example: $db=new DBClass();//This is a custom database class $session=new Session($db->getConnection()); if (isset($_SESSION['user'])) { echo($_SESSION['user']);//THIS IS NEVER EXECUTED! } else { $_SESSION['user']="test"; Echo("Session created!"); } At every page refresh it seems that $_SESSION['user'] is somehow "resetted", what methods can i apply to prevent such behaviour?

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  • Why is my class method not visible when I implement an interface in my class?

    - by Phsika
    i can not see MyLoad.TreeLoader(.... but why i can not see? i implemented iloader to TreeViewLoad. i should see TreeLoader why? namespace Rekursive { public partial class Form1 : Form { public Form1() { InitializeComponent(); } private void Form1_Load(object sender, EventArgs e) { //treeView1.Nodes.Add("Test"); iloader MyLoad = new TreeViewLoad(); MyLoad.loader("test", treeView1, 1); // i can not see MyLoad.TreeLoader(.... but why i can not see? // i implemented iloader to TreeViewLoad. i should see TreeLoader why? //TreeViewLoad myloader = new TreeViewLoad(); } } interface iloader { void loader(string nodeName, TreeView myTre, int id); } class TreeViewLoad : iloader { public void TreeLoader(TreeView tre) { // i will call loader... } public void loader(string nodeName, TreeView myTre, int id) { myTre.Nodes.Add(nodeName + id.ToString()); if (id

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  • Am I trying to Implement Multiple Inheritance. How can I do this.

    - by Shantanu Gupta
    I have created a class say A which has some functions defined as protected. Now Class B inherits A and class C inherits B. Class A has private default constructor and protected parameterized constructor. I want Class B to be able to access all the protected functions defined in Class A but class C can have access on some of the functions only not all the functions and class C is inheriting class B. How can I restrict access to some of the functions of Class A from Class C ? EDIT: namespace Db { public Class A { private A(){} protected A(string con){assign this value} protected DataTable getTable(){return Table;} protected Sqlparameters setParameters(){return parameter;} } } namespace Data { public Class B:A { protected B():base("constring"){} protected DataTable output(){return getTable();} protected sqlparameter values(param IDataParameter[] parameter){} } } namespace Bsns { public Class C:B { protected C():base(){} protected DataTable show() {return values(setparameter());} } } EDIT I think what I am trying to do here is Multiple inheritance. Please check. Class A { //suppose 10 functions are declared } Class B:A { //5 functions declared which are using A's function in internal body } Class C:B { //using all functions of B but require only 4 functions of A to be accessible by C. }

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