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  • real time scenario between interface/abstract class ?

    - by JavaUser
    Hi , Please give me a real time simple example for the below questions : Where to use interface rather abstract class Where to use abstract class rather interface I need code snippet for both . Which takes low memory and which performs well . Do I need to consider the design aspect also? What is the conceptual difference not the syntactical difference .

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  • How do I create a class repository in Java and do I really need it?

    - by Roman
    I have a large number of objects which are identified by names (strings). So, I would like to have a kind of mapping from object name to the class instances. I was told that in this situation I can use a "repository" class which works like that: Server myServer = ServerRepository.getServer("NameOfServer"); So, if there is already an object (sever) with the "NameOfServer" it will be returned by the "getServer". If such an object does not exist yet, it will be created and returned by the "getServer". So, my question is how to program such a "repository" class? In this class I have to be able to check if there is an instance of a given class such that it has a given value of a given field. How can I do it? I need to have a kind of loop over all existing object of a given class? Another part of my question is why I cannot use associative arrays (associative container, map, mapping, dictionary, finite map)? (I am not sure how do you call it in Java) In more details, I have an "array" which maps names of objects to objects. So, whenever I create a new object, I add a new element to the array: myArray["NameOfServer"] = new Server("NameOfServer").

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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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  • How to determine which inheriting class is using an abstract class's methods.

    - by Kin
    In my console application have an abstract Factory class "Listener" which contains code for listening and accepting connections, and spawning client classes. This class is inherited by two more classes (WorldListener, and MasterListener) that contain more protocol specific overrides and functions. I also have a helper class (ConsoleWrapper) which encapsulates and extends System.Console, containing methods for writing to console info on what is happening to instances of the WorldListener and MasterListener. I need a way to determine in the abstract ListenerClass which Inheriting class is calling its methods. Any help with this problem would be greatly appreciated! I am stumped :X Simplified example of what I am trying to do. abstract class Listener { public void DoSomething() { if(inheriting class == WorldListener) ConsoleWrapper.WorldWrite("Did something!"); if(inheriting class == MasterListener) ConsoleWrapper.MasterWrite("Did something!"); } } public static ConsoleWrapper { public void WorldWrite(string input) { System.Console.WriteLine("[World] {0}", input); } } public class WorldListener : Listener { public void DoSomethingSpecific() { ConsoleWrapper.WorldWrite("I did something specific!"); } } public void Main() { new WorldListener(); new MasterListener(); } Expected output [World] Did something! [World] I did something specific! [Master] Did something! [World] I did something specific!

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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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  • PHP - Concatenating objects and casting to string - bad idea?

    - by franko75
    Is it bad practice to concatenate objects when used in this context: $this->template->head .= new View('custom_javascript') This is the way i normally add extra css/js stuff to specific pages. I use an MVC structure where my basic html template has a $head variable which I set in my main Website_controller. I have used this approach for a while as it means I can just add bits and pieces of css/js stuff from whichever page/controller needs it. But having come across a problem in PHP 5.1.6 where the above code results in "Object ID #24", the result of toString() not being called i think, I am rethinking whether i should just fix this to work in PHP 5.1.6 or if i should rethink this approach in general. Any pointers appreciated!

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • C# Design a class with interface?

    - by Haroon
    I am having a bit of trouble understanding how I will design a class. My class will have 3 methods ICollection<Field> GetFields(); //perform validation internally - return back the object T UpdateFields(ICollection<Field> fields); //pass in model object with values on it, set up fields, then pass back all fields ICollection<Field> GetFieldsWithValues(T object); What is the best way to construct/design such a class keeping in mind: 1. The model object I pass in will be one of 3 or 4 tables, however when I call GetFIelds - internally for each object I know what fields will be there i.e. list.add(new Field{name = "id", value = "5"}); list.add(new Field{name = "nameofcompany", value = "super guys"});

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  • Method Overloading for NULL parameter

    - by Phani
    I have added three methods with parameters: public static void doSomething(Object obj) { System.out.println("Object called"); } public static void doSomething(char[] obj) { System.out.println("Array called"); } public static void doSomething(Integer obj) { System.out.println("Array called"); } When I am calling doSomething(null) , then compiler throws error as ambiguous methods. So Is the issue because Integer and char[] methods or Integer and Object methods?

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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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  • 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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  • accessing private variable from member function in PHP

    - by Carson Myers
    I have derived a class from Exception, basically like so: class MyException extends Exception { private $_type; public function type() { return $this->_type; //line 74 } public function __toString() { include "sometemplate.php"; return ""; } } Then, I derived from MyException like so: class SpecialException extends MyException { private $_type = "superspecial"; } If I throw new SpecialException("bla") from a function, catch it, and go echo $e, then the __toString function should load a template, display that, and then not actually return anything to echo. This is basically what's in the template file <div class="<?php echo $this->type(); ?>class"> <p> <?php echo $this->message; ?> </p> </div> in my mind, this should definitely work. However, I get the following error when an exception is thrown and I try to display it: Fatal error: Cannot access private property SpecialException::$_type in C:\path\to\exceptions.php on line 74 Can anyone explain why I am breaking the rules here? Am I doing something horribly witty with this code? Is there a much more idiomatic way to handle this situation? The point of the $_type variable is (as shown) that I want a different div class to be used depending on the type of exception caught.

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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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  • 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 do I change the URL Alias for Security/login in SilverStripe to user/login

    - by pthurmond
    I am working on a new website being built in SilverStripe. Currently I am having a ton of trouble trying to get the system to let me change the URL alias (or create a second one) for the Security controller's login (and eventually logout) function. I have tried playing around with the routes.yml file and I tried creating the paths in my own UserController and loading directly from the Security controller with "return Security::login()". But that gives me errors about the use of the static functions. Unfortunately I don't come from a ton of object oriented experience and this is the first CMS I have used that actually uses a bunch of true object orientation. The current version of SilverStripe we are using is 3.0 (but we will be upgrading to 3.1.1 in a few days). Does anyone know much about the routing in SilverStripe?

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  • Calling overridden method from within overriding method in OO PHP

    - by paddymcc
    Working in a symfony model, I want to override a function and call the overridden function from within the overriding one, along the lines of class MyClass extends BaseMyClass { function setMyProperty($p) { parent::setMyProperty($p); //do some other stuff } } This is resulting in a segmentation fault. I don't want to alter the parent class - it's been generated by symfony, and may feasibly be overwritten in the future if the model is rebuilt. This seems like something that should be straightforward, but I'm struggling to find the solution. Thanks for any advice

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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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