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• How to manage member variable in C++

  - by rhapsodyn

  In brief, my question is about member variables as pointers in unmanaged C++. In java or c#, we have "advanced pointer". In fact, we can't aware the "pointer" in them. We usually initialize the member of a class like this: member = new Member(); or member = null; But in c++, it becomes more confusing. I have seen many styles: using new, or leave the member variable in stack. In my point of view, using boost::shared_ptr seems friendly, but in boost itself source code there are news everywhere. It's the matter of efficiency,isn't it? Is there a guildline like "try your best to avoid new" or something?

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• Is fetching data from database a get-method thing?

  - by theva

  I have a small class that I call Viewer. This class is supposed to view the proper layout of each page or something like that... I have a method called getFirstPage, when called the user of this method will get a setting value for which page is currently set as the first page. I have some code here, I think it works but I am not really shure that I have done it the right way: class Viewer { private $db; private $user; private $firstPage; function __construct($db, $user) { $this->db = $db; if(isset($user)) { $this->user = $user; } else { $this->user = 'default'; } } function getFistPage() { $std = $db->prepare("SELECT firstPage FROM settings WHERE user = ':user'"); $std->execute(array(':user' => $user)); $result = $std->fetch(); $this->firstPage = $result['firstPage']; return $this->firstPage; } } My get method is fetching the setting from databse (so far so good?). The problem is that then I have to use this get method to set the private variable firstPage. It seems like I should have a set method to do this, but I cannot really have a set method that just fetch some setting from database, right? Because the user of this object should be able to assume that there already is a setting defined in the object... How should I do that?

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• Abstract Design Pattern implementation

  - by Pathachiever11

  I started learning design patterns a while ago (only covered facade and abstract so far, but am enjoying it). I'm looking to apply the Abstract pattern to a problem I have. The problem is: Supporting various Database systems using one abstract class and a set of methods and properties, which then the underlying concrete classes (inheriting from abstract class) would be implementing. I have created a DatabaseWrapper abstract class and have create SqlClientData and MSAccessData concrete class that inherit from the DatabaseWrapper. However, I'm still a bit confused about how the pattern goes as far as implementing these classes on the Client. Would I do the following?: DatabaseWrapper sqlClient = new SqlClientData(connectionString); This is what I saw in an example, but that is not what I'm looking for because I want to encapsulate the concrete classes; I only want the Client to use the abstract class. This is so I can support for more database systems in the future with minimal changes to the Client, and creating a new concrete class for the implementations. I'm still learning, so there might be a lot of things wrong here. Please tell me how I can encapsulate all the concrete classes, and if there is anything wrong with my approach. Many Thanks! PS: I'm very excited to get into software architecture, but still am a beginner, so take it easy on me. :)

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• Objective C - creating concrete class instances from base class depending upon type

  - by indiantroy

  Just to give a real world example, say the base class is Vehicle and concrete classes are TwoWheeler and FourWheeler. Now the type of the vehicle - TwoWheeler or FourWheeler, is decided by the base class Vehicle. When I create an instance of TwoWheeler/FourWheeler using alloc-init method, it calls the super implementation like below to set the value of common properties defined in the Vehicle class and out of these properties one of them is type that actually decides if the type is TwoWheeler or FourWheeler. if (self = [super initWithDictionary:dict]){ [self setOtherAttributes:dict]; return self; } Now when I get a collection of vehicles some of them could be TwoWheeler and others will be FourWheeler. Hence I cannot directly create an instance of TwoWheeler or FourWheeler like this Vehicle *v = [[TwoWheeler alloc] initWithDictionary:dict]; Is there any way I can create an instance of base class and once I know the type, create an instance of child class depending upon type and return it. With the current implementation, it would result in infinite loop because I call super implementation from concrete class. What would be the perfect design to handle this scenario when I don't know which concrete class should be instantiated beforehand?

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• Three customer addresses in one table or in separate tables?

  - by DR

  In my application I have a Customer class and an Address class. The Customer class has three instances of the Address class: customerAddress, deliveryAddress, invoiceAddress. Whats the best way to reflect this structure in a database? The straightforward way would be a customer table and a separate address table. A more denormalized way would be just a customer table with columns for every address (Example for "street": customer_street, delivery_street, invoice_street) What are your experiences with that? Are there any advantages and disadvantages of these approaches?

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• Javascript plugin creation

  - by Aneesh

  I want to create a plugin called 'myPlugin'. Which method should I use and what is the difference between these two methods? Please tell me the advantages too. I am from designing background and not much programming knowledge. var myPlugin = { myId:"testId", create:function(){}, destroy:function(){} } OR function myPlugin() { this.myId = "testId"; this.create = function(){}; this.destroy = function(){}; }

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• PHP class extends not working why and is this how to correctly extend a class?

  - by Matthew

  Hi so I'm trying to understand how inherteince works in PHP using object oriented programming. The main class is Computer, the class that is inheriting is Mouse. I'm extedning the Computer class with the mouse class. I use __construct in each class, when I istinate the class I use the pc type first and if it has mouse after. For some reason computer returns null? why is this? class Computer { protected $type = 'null'; public function __construct($type) { $this->type = $type; } public function computertype() { $this->type = strtoupper($this->type); return $this->type; } } class Mouse extends Computer { protected $hasmouse = 'null'; public function __construct($hasmouse){ $this->hasmouse = $hasmouse; } public function computermouse() { if($this->hasmouse == 'Y') { return 'This Computer has a mouse'; } } } $pc = new Computer('PC', 'Y'); echo $pc->computertype; echo $pc->computermouse;

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• javascript : make a new safe class constructor

  - by guilin ??

  sometimes we loss the new keyword when define new object, obj = new Clazz(); //correct obj = Clazz(); //wrong, but no syntax error, hard to debug. I want to write a function to help me create Class and make it new safe. var Class = function(constructor){ //when constructor // if not call by new return new constructor(); // else constructor(); } var MyClazz = Class(function(name){ this.name = name }, SuperClazz1, SuperClass2 ) MyClazz.extend({ show: function(){console.log(this.name)} }) obj1 = new MyClazz(); obj2 = MyClazz(); // obj1 should same as obj2 Is it possible, any exists module?

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• Can a problem have a relation of aggregation and composition both between two classes at same point

  - by learner

  Can a problem have a relation of aggregation and composition both between two classes at same point of time? Like any real time scenario where there can be aggregation corresponding to one method and composition related to other method. I m unable to figure out any scenario where both composition and aggregation occurs simultaneously between two classes. Any help will be appreciable.

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• How to access constant defined in child class from parent class functions?

  - by kavoir.com

  I saw this example from php.net: <?php class MyClass { const MY_CONST = "yonder"; public function __construct() { $c = get_class( $this ); echo $c::MY_CONST; } } class ChildClass extends MyClass { const MY_CONST = "bar"; } $x = new ChildClass(); // prints 'bar' $y = new MyClass(); // prints 'yonder' ?> But $c::MY_CONST is only recognized in version 5.3.0 or later. The class I'm writing may be distributed a lot. Basically, I have defined a constant in ChildClass and one of the functions in MyClass (father class) needs to use the constant. Any idea?

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• Creating instance of interface in C#

  - by Max

  I'm working with MS Excel interop in C# and I don't understand how this particular line of code works: var excel = new Microsoft.Office.Interop.Excel.Application(); where Microsoft.Office.Interop.Excel.Application is an INTERFACE defined as: [Guid("000208D5-0000-0000-C000-000000000046")] [CoClass(typeof(ApplicationClass))] public interface Application : _Application, AppEvents_Event { } I'm thinking that some magic happens when the interface is decorated with a CoClass attribute, but still how is it possible that we can create an instance of an interface with a new keyword? Shouldn't it generate a compile time error?

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• is "Object();" a predefined function in javascript?

  - by Qlidnaque

  I come across code such as "personObj=new Object();" where a new object called personObj is being defined. What I'm trying to find out is whether Object() is a prefined function in javascript, because I understand by using the mentioned code, a instance of a class is being formed but in the example code where I'm studying from, the class Object() is not being defined anywhere, so I was wondering if Object() was a predefined function in javascript and whether I can be directed to some online resources, as all that shows up in google when I try to find Object() are articles in general javascript object oriented programming.

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• Why is the clone() method protected in java.lang.Object?

  - by Alex N.

  What is the specific reason that clone() is defined as protected in java.lang.Object?

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• Is it possible for an abstract class to force it's children to have a constructor in PHP?

  - by Logan Serman

  I would like to do something like this: abstract class Foo { public function __construct() { echo 'This is the parent constructor'; } abstract function __construct(); } class Bar extends Foo { // constructor is required as this class extends Foo public function __construct() { //call parent::__construct() if necessary echo 'This is the child constructor'; } } But I get a fatal error when doing this: Fatal error: Cannot redeclare Foo::__construct() in Foo.php on line 8 Is there another way to ensure child classes have a constructor?

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• Catch requests to non-existent classes (not autoload)

  - by Spot

  Is there a manner in which to catch requests to a class which does not exist. I'm looking for something exactly like __call() and __static(), but for classes as opposed to methods in a class. I am not talking about autoloading. I need to be able to interrupt the request and reroute it. Ideas?

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• C#: Specify that a function arg must inhert from one class, and implement an interface?

  - by Rosarch

  I'm making a game where each Actor is represented by a GameObjectController. Game Objects that can partake in combat implement ICombatant. How can I specify that arguments to a combat function must inherit from GameObjectController and implement ICombatant? Or does this indicate that my code is structured poorly? public void ComputeAttackUpdate(ICombatant attacker, AttackType attackType, ICombatant victim) In the above code, I want attacker and victim to inherit from GameObjectController and implement ICombatant. Is this syntactically possible?

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• Is Multiple Inheritance allowed at class level in PHP?

  - by Parth

  Is Multiple Inheritance allowed at class level in PHP?

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• What is the fragile base class problem?

  - by SunilRai86

  What is the fragile base class problem in java?

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• interface abstract in php real world scenario

  - by jason

  The goal is to learn whether to use abstract or interface or both... I'm designing a program which allows a user to de-duplicate all images but in the process rather then I just build classes I'd like to build a set of libraries that will allow me to re-use the code for other possible future purposes. In doing so I would like to learn interface vs abstract and was hoping someone could give me input into using either. Here is what the current program will do: recursive scan directory for all files determine file type is image type compare md5 checksum against all other files found and only keep the ones which are not duplicates Store total duplicates found at the end and display size taken up Copy files that are not duplicates into folder by date example Year, Month folder with filename is file creation date. While I could just create a bunch of classes I'd like to start learning more on interfaces and abstraction in php. So if I take the scan directory class as the first example I have several methods... ScanForFiles($path) FindMD5Checksum() FindAllImageTypes() getFileList() The scanForFiles could be public to allow anyone to access it and it stores in an object the entire directory list of files found and many details about them. example extension, size, filename, path, etc... The FindMD5Checksum runs against the fileList object created from scanForFiles and adds the md5 if needed. The FindAllImageTypes runs against the fileList object as well and adds if they are image types. The findmd5checksum and findallimagetypes are optionally run methods because the user might not intend to run these all the time or at all. The getFileList returns the fileList object itself. While I have a working copy I've revamped it a few times trying to figure out whether I need to go with an interface or abstract or both. I'd like to know how an expert OO developer would design it and why?

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• Running a loop (such as one for a mock webserver) within a thread

  - by bob c

  I'm trying to run a mock webserver within a thread within a class. I've tried passing the class' @server property to the thread block but as soon as I try to do server.accept the thread stops. Is there some way to make this work? I want to basically be able to run a webserver off of this script while still taking user input via stdin.gets. Is this possible? class Server def initialize() @server = TCPServer.new(8080) end def run() @thread = Thread.new(@server) { |server| while true newsock = server.accept puts "some stuff after accept!" next if !newsock # some other stuff end } end end def processCommand() # some user commands here end test = Server.new while true do processCommand(STDIN.gets) end In the above sample, the thread dies on server.accept

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• A self-creator: What pattern is this? php

  - by user151841

  I have several classes that are basically interfaces to database rows. Since the class assumes that a row already exists ( __construct expects a field value ), there is a public static function that allows creation of the row and returns an instance of the class. Here's a pseudo-code example : class fruit { public $id; public function __construct( $id ) { $this->id = $id; $sql = "SELECT * FROM Fruits WHERE id = $id"; ... $this->arrFieldValues[$field] = $row[$value]; } public function __get( $var ) { return $this->arrFieldValues[$var]; } public function __set( $var, $val ) { $sql = "UPDATE fruits SET $var = $val WHERE id = $this->id"; } public static function create( $id ) { $sql = "INSERT INTO Fruits ( fruit_name ) VALUE ( '$fruit' )"; $id = mysql_insert_id(); $fruit = & new fruit($id); return $fruit; } } $obj1 = fruit::create( "apple" ); $obj2 = & new fruit( 12 ); What is this pattern called? Edit: I changed the example to one that has more database-interface functionality. For most of the time, this kind of class would be instantiated normally, through __construct(). But sometimes when you need to create a new row first, you would call create().

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• When to Use Properties & When to Use Methods?

  - by DaveDev

  Hi Guys I was looking at the following line of code foreach (PropertyInfo prop in t.GetProperties()) and I noticed that tprovides a method to return the type's properties instead of a property like t.Properties This makes me wonder why sometimes people use properties to make a type's data avilable and other times there's a method provided? Is there some logic behind the decision? Thanks Dave

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• Patterns to deal with with functions that can have different kinds of results.

  - by KaptajnKold

  Suppose you have an method on an object that given the some input alters the objects state if the input validates according to some complex logic. Now suppose that when the input doesn't validate, it can be due to several different things, each of which we would like to be able to deal with in different ways. I'm sure many of you are thinking: That's what exceptions are for! I've thought of this also. But my reservation against using exceptions is that in some cases there is nothing exceptional about the input not validating and I really would like to avoid using exceptions to control what is really just in the expected flow of the program. If there were only one interpretation possible, I could simply choose to return a boolean value indicating whether or not the operation resulted in a state change or not and the respond appropriately when it did not. There is of course also the option to return a status code which the client can then choose to interpret or not. I don't like this much either because there is nothing semantic about status codes. The solution I have so far is to always check for each possible situation which I am able to handle before I call the method which then returns a boolean to inform the client if the object changed state. This leaves me the flexibility to handle as few or as many as the possible situations as I wish depending on the context I am in. It also has the benefit of making the method I am calling simpler to write. The drawback is that there is quite a lot of duplication in the client code wherever I call the method. Which of these solutions do you prefer and why? What other patterns do people use for providing meaningful feedback from functions? I know that some languages support multiple return values, and I if I had that option I would surely prefer it.

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• Upcasting in C#: Making a Fruit a Pear

  - by Adam Kane

  Why can't I upcast (?) a Fruit to a Pear? public static class PearGenerator { public static Pear CreatePear () { // Make a new generic fruit. Fruit genericFruit = new Fruit(); // Upcast it to a pear. (Throws exception: Can't cast a Fruit to a Pear.) Pear pear = (Pear)genericFruit; // Return freshly grown pear. return ( pear ); } } public class Fruit { // some code } public class Pear : Fruit { public void PutInPie () { // some code } } Thanks!

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• Why does this program stop running?

  - by designloper

  Hi everyone....I am developing a card making system...nothing fancy. Right got this far but program now stops running with no error when running after the first card sample i.e. " Enter 'OK' if this card is OK, otherwise enter an alternative border character: + ". Any suggestions Java Masters? //Ask user for input //makes use of print line method System.out.println("Enter name: "); //took the variables //called the object of the scanner 'cardOrder' //and use the Scanner objects method '.nextLine' //to read the next line of the input firstName = cardOrder.nextLine(); mInitial = cardOrder.nextLine(); lastName = cardOrder.nextLine(); //Print out the "Here is a sample card" + the first name, middle initial and last name System.out.println("Here is a sample card: \n\n" + firstName + mInitial + lastName + "**************" + "**************" + firstName + mInitial + lastName + "\n* *" + "\n*" + " " + firstName + mInitial + lastName + " *" + "\n* *\n" + firstName + mInitial + lastName +"**************" + "**************" + firstName + mInitial + lastName + "\n"); //Ask user is the card is OK to proceed to order query or if they want an alternative border character: + System.out.println("Enter 'OK' if this card is OK, otherwise enter an alternative border character: + "); //Check if user entered "OK" and store it in var optionA optionA = cardOrder.nextLine(); //test if (a == optionA){ System.out.println("\nHow many cards would you like? "); cardsOrdered = cardOrder.nextInt(); equals = (int) (cardPriceA * cardsOrdered); System.out.println("The price of " + cardsOrdered + " cards"+ " is £" + equals + ".\n"); System.out.println("No Discount given."); } else if(b == optionA) { //Print out the "Here is a sample card" + the first name, middle initial and last name System.out.println("Here is a sample card: \n\n" + firstName + mInitial + lastName + "++++++++++++++" + "++++++++++++++" + firstName + mInitial + lastName + "\n+ +" + "\n+" + " " + firstName + mInitial + lastName + " +" + "\n+ +\n" + firstName + mInitial + lastName +"++++++++++++++" + "++++++++++++++" + firstName + mInitial + lastName + "\n"); //Ask user is the card is OK to proceed to order query or if they want an alternative border character: + System.out.println("Enter 'OK' if this card is OK, otherwise enter an alternative border character: OK "); //Check if user entered "OK" and store it in var optionA optionA = cardOrder.nextLine(); if (a == optionA){ System.out.println("\nHow many cards would you like? "); cardsOrdered = cardOrder.nextInt(); equals = (int) (cardPriceA * cardsOrdered); System.out.println("The price of " + cardsOrdered + " cards"+ " is £" + equals + ".\n"); System.out.println("No Discount given."); } } else if (c == optionA) {//Print out the "Here is a sample card" + the first name, middle initial and last name System.out.println("Here is a sample card: \n\n" + firstName + mInitial + lastName + "**************" + "**************" + firstName + mInitial + lastName + "\n* *" + "\n*" + " " + firstName + mInitial + lastName + " *" + "\n* *\n" + firstName + mInitial + lastName +"**************" + "**************" + firstName + mInitial + lastName + "\n"); //Ask user is the card is OK to proceed to order query or if they want an alternative border character: + System.out.println("Enter 'OK' if this card is OK, otherwise enter an alternative border character: + "); //Check if user entered "OK" and store it in var optionA optionA = cardOrder.nextLine(); if (a == optionA){ System.out.println("\nHow many cards would you like? "); cardsOrdered = cardOrder.nextInt(); equals = (int) (cardPriceA * cardsOrdered); System.out.println("The price of " + cardsOrdered + " cards"+ " is £" + equals + ".\n"); System.out.println("No Discount given."); } }

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