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• How to write Composition and Aggregation in java

  - by Mifas

  I want to know how to identify composition and aggregation code in java. I have C++ Code, But I don't understand how to write in java. Composition class A {}; class B { A composited_A; }; Aggregation via Pointer class A {}; class B { A* pointer_to_A; B(A anA){ pointer_to_A = &anA; } Can anyone please tell me how both are working in JAVA. (I know what is meant by Composition and aggregation ) };

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• use of assertions for type checking in php?

  - by user151841

  I do some checking of arguments in my classes in php using exception-throwing functions. I have functions that do a basic check ( ===, in_array etc ) and throw an exception on false. So I can do assertNumeric($argument, "\$argument is not numeric."); instead of if ( ! is_numeric($argument) ) { throw new Exception("\$argument is not numeric."); } Saves some typing I was reading in the comments of the php manual page on assert() that As noted on Wikipedia - "assertions are primarily a development tool, they are often disabled when a program is released to the public." and "Assertions should be used to document logically impossible situations and discover programming errors— if the 'impossible' occurs, then something fundamental is clearly wrong. This is distinct from error handling: most error conditions are possible, although some may be extremely unlikely to occur in practice. Using assertions as a general-purpose error handling mechanism is usually unwise: assertions do not allow for graceful recovery from errors, and an assertion failure will often halt the program's execution abruptly. Assertions also do not display a user-friendly error message." This means that the advice given by "gk at proliberty dot com" to force assertions to be enabled, even when they have been disabled manually, goes against best practices of only using them as a development tool So, am I 'doing it wrong'? What other/better ways of doing this are there?

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• Keyword 'this'(Me) is not available calling the base constructor

  - by serhio

  In the inherited class I use the base constructor, but can't use class's members calling this base constructor. In this example I have a PicturedLabel that knows it's own color and has a image. A TypedLabel : PictureLabel knows it's type but uses the base color. The (base)image that uses TypedLabel should be colored with the (base)color, however, I can't obtain this color: Error: Keyword 'this' is not available in the current context A workaround? /// base class public class PicturedLabel : Label { PictureBox pb = new PictureBox(); public Color LabelColor; public PicturedLabel() { // initialised here in a specific way LabelColor = Color.Red; } public PicturedLabel(Image img) : base() { pb.Image = img; this.Controls.Add(pb); } } public enum LabelType { A, B } /// derived class public class TypedLabel : PicturedLabel { public TypedLabel(LabelType type) : base(GetImageFromType(type, this.LabelColor)) //Error: Keyword 'this' is not available in the current context { } public static Image GetImageFromType(LabelType type, Color c) { Image result = new Bitmap(10, 10); Rectangle rec = new Rectangle(0, 0, 10, 10); Pen pen = new Pen(c); Graphics g = Graphics.FromImage(result); switch (type) { case LabelType.A: g.DrawRectangle(pen, rec); break; case LabelType.B: g.DrawEllipse(pen, rec); break; } return result; } }

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• Polymorphic call

  - by harigm

  I am new to java, I have seen in the code at many places where my seniors have declared as List myList = new ArrayList(); (option1) Instead of ArrayList myList = new ArrayList(); (option2) Can you please tell me why people use Option1, is there any advantages? If we use option2, do we miss out any advantages or features?

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• MVC pattern and State Machine

  - by topright

  I think of a game as a state machine. Game States separate I/O processing, game logic and rendering into different classes: while (game_loop) { game->state->io_events(this); game->state->logic(this); game->state->rendering(); } You can easily change a game state in this approach. MVC separation works in more complex way: while (game_loop) { game->cotroller->io_events(this); game->model->logic(this); game->view->rendering(); } So changing Game States becomes error prone task (switch 3 MVC objects, not 1). What are practical ways of combining these 2 concepts?

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• PHP: How to cast object to inherited class?

  - by andreyvlru

  I'd like to inherit PDOStatement class and use it in my website scripts. But I am frustrated how to get required object. PDO::query returns only direct PDOStatement object and looks like there are no other method to create PDOStatement object or inherited class. Initially i thought to move PDOStatement object to constructor of inherit class Something like that: $stmt = PDO -> query("select * from messages"); $messageCollection = new Messaging_Collection($stmt); But how to make instance of PDOStatement to inherited object (Messaging_Collection). It is a big question for me. class Messaging_Collection extends PDOStatement { public function __construct(PDOStatement $stmt) { //there i should to transform $stmt to $this // direct $this = $stmt is not possible // is there other right way? }

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• DDD and MVC: Difference between 'Model' and 'Entity'

  - by Nathan Loding

  I'm seriously confused about the concept of the 'Model' in MVC. Most frameworks that exist today put the Model between the Controller and the database, and the Model almost acts like a database abstraction layer. The concept of 'Fat Model Skinny Controller' is lost as the Controller starts doing more and more logic. In DDD, there is also the concept of a Domain Entity, which has a unique identity to it. As I understand it, a user is a good example of an Entity (unique userid, for instance). The Entity has a life-cycle -- it's values can change throughout the course of the action -- and then it's saved or discarded. The Entity I describe above is what I thought Model was supposed to be in MVC? How off-base am I? To clutter things more, you throw in other patterns, such as the Repository pattern (maybe putting a Service in there). It's pretty clear how the Repository would interact with an Entity -- how does it with a Model? Controllers can have multiple Models, which makes it seem like a Model is less a "database table" than it is a unique Entity. So, in very rough terms, which is better? No "Model" really ... class MyController { public function index() { $repo = new PostRepository(); $posts = $repo->findAllByDateRange('within 30 days'); foreach($posts as $post) { echo $post->Author; } } } Or this, which has a Model as the DAO? class MyController { public function index() { $model = new PostModel(); // maybe this returns a PostRepository? $posts = $model->findAllByDateRange('within 30 days'); while($posts->getNext()) { echo $posts->Post->Author; } } } Both those examples didn't even do what I was describing above. I'm clearly lost. Any input?

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• Create a Python User() class that both creates new users and modifies existing users

  - by ensnare

  I'm trying to figure out the best way to create a class that can modify and create new users all in one. This is what I'm thinking: class User(object): def __init__(self,user_id): if user_id == -1 self.new_user = True else: self.new_user = False #fetch all records from db about user_id self._populateUser() def commit(self): if self.new_user: #Do INSERTs else: #Do UPDATEs def delete(self): if self.new_user == False: return False #Delete user code here def _populate(self): #Query self.user_id from database and #set all instance variables, e.g. #self.name = row['name'] def getFullName(self): return self.name #Create a new user >>u = User() >>u.name = 'Jason Martinez' >>u.password = 'linebreak' >>u.commit() >>print u.getFullName() >>Jason Martinez #Update existing user >>u = User(43) >>u.name = 'New Name Here' >>u.commit() >>print u.getFullName() >>New Name Here Is this a logical and clean way to do this? Is there a better way? Thanks.

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• Dizzy-like game level representation (format)

  - by topright

  How would you store game level for a Dizzy-like adventure game? How would you specify walkable areas and graphics? Is it tile-based, pixel-based or walkable surfaces can be described by vectors?

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• How can i use complextype class or multi type class is it generic collection?

  - by programmerist

  i need a complex returning type. i have 4 class returning types COMPLEXTYPE must include Company, Muayene, Radyoloji, Satis because i must return data switch case situation how can i do? Maybe i need generic collections How can i do that? public class GenoTipController { public COMPLEXTYPE Generate(DataModelType modeltype) { _Company company = null; _Muayene muayene = null; _Radyoloji radyoloji = null; _Satis satis = null; switch (modeltype) { case DataModelType.Radyoloji: radyoloji = new Radyoloji(); return radyoloji; break; case DataModelType.Satis: satis = new Satis(); return satis; break; case DataModelType.Muayene: muayene = new Muayene(); return muayene; break; case DataModelType.Company: company = new Company(); return company; break; default: break; } } } public class CompanyView { public static List GetPersonel() { GenoTipController controller = new GenoTipController(); _Company company = controller.Generate(DataModelType.Company); return company.GetPersonel(); } } public enum DataModelType { Radyoloji, Satis, Muayene, Company }

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• Generics and Constrained Polymorphism versus Subtyping

  - by Rahul G

  Hullo all. In this (Warning: PDF) presentation on Haskell Type Classes, on slide #54, there's this question: Open Question: In a language with generics and constrained polymorphism, do you need subtyping too? My questions are: How do generics and constrained polymorphism make subtyping unnecessary? If generics and constrained polymorphism make subtyping unnecessary, why does Scala have subtyping?

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• Is Method Overloading considered part of polymorphism?

  - by iTayb

  Is Method Overloading considered part of polymorphism? Thank you very much.

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• why assign null value or another default value firstly?

  - by Phsika

  i try to generate some codes. i face to face delegates. Everythings is ok.(Look below) But appearing a warning: you shold assing value why? but second code below is ok. namespace Delegates { class Program { static void Main(string[] args) { HesapMak hesapla = new HesapMak(); hesapla.Calculator = new HesapMak.Hesap(hesapla.Sum); double sonuc = hesapla.Calculator(34, 2); Console.WriteLine("Toplama Sonucu:{0}",sonuc.ToString()); Console.ReadKey(); } } class HesapMak { public double Sum(double s1, double s2) { return s1 + s2; } public double Cikarma(double s1, double s2) { return s1 - s2; } public double Multiply(double s1, double s2) { return s1 * s2; } public double Divide(double s1, double s2) { return s1 / s2; } public delegate double Hesap(double s1, double s2); public Hesap Calculator; ----&#60; they want me assingn value } } namespace Delegates { class Program { static void Main(string[] args) { HesapMak hesapla = new HesapMak(); hesapla.Calculator = new HesapMak.Hesap(hesapla.Sum); double sonuc = hesapla.Calculator(34, 2); Console.WriteLine("Toplama Sonucu:{0}",sonuc.ToString()); Console.ReadKey(); } } class HesapMak { public double Sum(double s1, double s2) { return s1 + s2; } public double Cikarma(double s1, double s2) { return s1 - s2; } public double Multiply(double s1, double s2) { return s1 * s2; } public double Divide(double s1, double s2) { return s1 / s2; } public delegate double Hesap(double s1, double s2); public Hesap Calculator=null; } }

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• Non-Linear Database Retrieval

  - by pws5068

  I'm building an article system, and each article will have one more Tags associated with it (similar to the Tags on this site). The tables are set up something like this: Article_Table Article_ID | Title | Author_ID | Content | Date_Posted | IP ... Tag_Table Tag_ID | Name ... Tag_Intersect_Table Tag_ID | Article_ID Is it possible query an article and all of its associated tags in one database call? If so, how is this done?

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• How to handle the pylint message: Warning: Method could be a function

  - by biffabacon

  Being new to Python, I decided to get some feedback on a class I'd written ASAP so I ran it against pylint. Is the message it gave "Warning: Method could be a function" telling me that it would be better to move this method out of the class because it doesn't use any instance variables? In c# I would make this a static method. What's the most pythonic thing to do here?

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• adding one time options to items

  - by rap-uvic

  Hello, I'm building an Event Registration site. For any given event, we'll have a handful of items to choose from. I have a table for these items. For each event we might have special options for users. For example, for one of the events new users get to buy an item which is not available to other users. This may not apply to all the events. For other events we might have some other restriction on items. I will obviously be checking this programmatically on application side. I would like to though, set up a column containing flag in the items table. But I don't find it feasible because this condition may only apply to one particular event. I don't want all the future items to have this column. What is a good approach to take in such a situation? Should I create a special "restrictions" table and just do a join? How would I handle this on the application side?

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• Bug in the official Android Fragments training sample?

  - by Jeff Axelrod

  It seems to me that there must be a bug in the Android Fragments demo. As background, Fragments are apparently sometimes instantiated by the Android OS and thus need a public no-arg constructor: All subclasses of Fragment must include a public empty constructor. The framework will often re-instantiate a fragment class when needed, in particular during state restore, and needs to be able to find this constructor to instantiate it. If the empty constructor is not available, a runtime exception will occur in some cases during state restore. But the NewsReader demo from the official Android training on Fragments constructs the HeadlinesFragment class and configures it with setOnHeadlineSelectedListener(this) from NewsReaderActivity.onCreate(). If the Android OS re-instantiates this fragment, the mHeadlineSelectedListener field will be null because HeadlinesFragment doesn't save or restore its state. Is this a bug or am I missing something?

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• Javascript static method intheritance

  - by Matteo Pagliazzi

  I want to create a javascript class/object that allow me to have various method: Model class Model.all() » static method Model.find() » static method Model delete() » instance method Model save() » instance method Model.create() » static that returns a new Model instance For static method I can define them using: Model.staticMethod(){ method } while for instance method is better to use: function Model(){ this.instanceMethod = function(){} } and then create a new instance or using prototype? var m = function Model(){ } m.prototype.method() = function(){ } Now let's say that I want to create a new class based on Model, how to inherit not only its prototypes but also its static methods?

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• A good design pattern for almost similar objects

  - by Sam

  Hello, I have two websites that have an almost identical database schema. the only difference is that some tables in one website have 1 or 2 extra fields that the other and vice versa. I wanted to the same Database Access layer classes to will manipulate both websites. What can be a good design pattern that can be used to handle that little difference. for example, I have a method createAccount(Account account) in my DAO class but the implementation will be slightly different between website A and website B. I know design patterns don't depend on the language but FYI i m working with Perl. Thanks

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• exclude private property from print_r or object?

  - by Hailwood

  Basically I am using Code Igniter, and the Code Igniter base class is huge, when I print_r some of my objects they have the base class embedded inside them. this makes it a pain to get the information I actually wanted (the rest of the properties). So, I am wondering if there is a way I can hide, or remove the base class object? I have tried clone $object; unset($object->ci); print_r($object); but of course the ci property is private. the actual function I am using for dumping is: /** * Outputs the given variables with formatting and location. Huge props * out to Phil Sturgeon for this one (http://philsturgeon.co.uk/blog/2010/09/power-dump-php-applications). * To use, pass in any number of variables as arguments. * Optional pass in "true" as final argument to kill script after dump * * @return void */ function dump() { list($callee) = debug_backtrace(); $arguments = func_get_args(); $total_arguments = count($arguments); if (end($arguments) === true) $total_arguments--; echo '<fieldset style="background: #fefefe !important; border:2px red solid; padding:5px">'; echo '<legend style="background:lightgrey; padding:5px;">' . $callee['file'] . ' @ line: ' . $callee['line'] . '</legend><pre>'; $i = 0; foreach ($arguments as $argument) { //if the last argument is true we don't want to display it. if ($i == ($total_arguments) && $argument === true) break; echo '<br/><strong>Debug #' . (++$i) . ' of ' . $total_arguments . '</strong>: '; if ((is_array($argument) || is_object($argument)) && count($argument)) { print_r($argument); } else { var_dump($argument); } } echo '</pre>' . PHP_EOL; echo '</fieldset>' . PHP_EOL; //if the very last argument is "true" then die if (end($arguments) === true) die('Killing Script'); }

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• What objects would get defined in a Bridge scoring app (Javascript)

  - by Alex Mcp

  I'm writing a Bridge (card game) scoring application as practice in javascript, and am looking for suggestions on how to set up my objects. I'm pretty new to OO in general, and would love a survey of how and why people would structure a program to do this (the "survey" begets the CW mark. Additionally, I'll happily close this if it's out of range of typical SO discussion). The platform is going to be a web-app for webkit on the iPhone, so local storage is an option. My basic structure is like this: var Team = { player1: , player2: , vulnerable: , //this is a flag for whether or //not you've lost a game yet, affects scoring scoreAboveLine: , scoreBelowLine: gamesWon: }; var Game = { init: ,//function to get old scores and teams from DB currentBid: , score: , //function to accept whether bid was made and apply to Teams{} save: //auto-run that is called after each game to commit to DB }; So basically I'll instantiate two teams, and then run loops of game.currentBid() and game.score. Functionally the scoring is working fine, but I'm wondering if this is how someone else would choose to break down the scoring of Bridge, and if there are any oversights I've made with regards to OO-ness and how I've abstracted the game. Thanks!

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• PHP: Recursive array function

  - by Industrial

  Hi everybody, I want to create a function that returns the full path from a set node, back to the root value. I tried to make a recursive function, but ran out of luck totally. What would be an appropriate way to do this? I assume that a recursive function is the only way? Here's the array: Array ( [0] => Array ( [id] => 1 [name] => Root category [_parent] => ) [1] => Array ( [id] => 2 [name] => Category 2 [_parent] => 1 ) [2] => Array ( [id] => 3 [name] => Category 3 [_parent] => 1 ) [3] => Array ( [id] => 4 [name] => Category 4 [_parent] => 3 ) ) The result I want my function to output when getting full path of node id#4: Array ( [0] => Array ( [id] => 1 [name] => Root category [_parent] => ) [1] => Array ( [id] => 3 [name] => Category 3 [_parent] => 1 ) [2] => Array ( [id] => 4 [name] => Category 4 [_parent] => 3 ) ) The notoriously bad example of my recursive skills: function recursive ($id, $array) { $innerarray = array(); foreach ($array as $k => $v) { if ($v['id'] === $id) { if ($v['_parent'] !== '') { $innerarray[] = $v; recursive($v['id'], $array); } } } return $innerarray; } Thanks!

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• Python: Can subclasses overload inherited methods?

  - by Rosarch

  I'm making a shopping cart app in Google App Engine. I have many classes that derive from a base handler: class BaseHandler(webapp.RequestHandler): def get(self, CSIN=None): self.body(CSIN) Does this mean that the body() method of every descendant class needs to have the same argument? This is cumbersome. Only one descendant actually uses that argument. And what about when I add new args? Do I need to go through and change every class? class Detail(BaseHandler): def body(self, CSIN): class MainPage(BaseHandler): def body(self, CSIN=None): #@UnusedVariable class Cart(BaseHandler): def body(self, CSIN): #@UnusedVariable

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• How to add event listners / signals to a simple superman class?

  - by Kabumbus

  I can and would love to use boost or std for this. Sorry - I am new to C++. So I created a really simple program like: #include <iostream> #include <string> using namespace std; class superman { public: string punch(){return cout << "superman: I hit the bad guy!" << endl;}; }; int main() { superman clark; clark.punch(); cin.get(); } I want to add an event listner that would tell me when clark punched and cout something like "superman punched!". How to add such event listner and event function to my class?

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• Magento - Show Custom Attributes in Grouped Product table.

  - by greencoconut

  I need to find a way to show the value of a custom attribute in place of the "Product Name" shown in the image below. I'm working with /app/design/frontend/default/defaultx/template/catalog/product/view/type/grouped.php The code below doesn't work(the custom attribute is yearmade): <?php if (count($_associatedProducts)): ?> <?php foreach ($_associatedProducts as $_item): ?> <tr> <td><?php echo $this->htmlEscape($_item->getYearmade()) ?></td> Any help would be appreciated. EDIT: So the answer turned out to be quite simple. You see what I failed to mention above was that there was indeed output... but that it was just a number (eg: 52). Turns out this was the ID for that custom attribute value (It was a Dropdown type of custom attribute). So in summary This works for custom attributes of type text: echo $this->htmlEscape($_item->getYearmade()) But for all other types of custom attribute (I think), the following should be used: echo $this->htmlEscape($_item->getAttributeText('yearmade')) I would not have discovered this without the most excellent answer provided by Alan Storm, below. Thank you sir.

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