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• Structuring Access Control In Hierarchical Object Graph

  - by SB2055

  I have a Folder entity that can be Moderated by users. Folders can contain other folders. So I may have a structure like this: Folder 1 Folder 2 Folder 3 Folder 4 I have to decide how to implement Moderation for this entity. I've come up with two options: Option 1 When the user is given moderation privileges to Folder 1, define a moderator relationship between Folder 1 and User 1. No other relationships are added to the db. To determine if the user can moderate Folder 3, I check and see if User 1 is the moderator of any parent folders. This seems to alleviate some of the complexity of handling updates / moved entities / additions under Folder 1 after the relationship has been defined, and reverting the relationship means I only have to deal with one entity. Option 2 When the user is given moderation privileges to Folder 1, define a new relationship between User 1 and Folder 1, and all child entities down to the grandest of grandchildren when the relationship is created, and if it's ever removed, iterate back down the graph to remove the relationship. If I add something under Folder 2 after this relationship has been made, I just copy all Moderators into the new Entity. But when I need to show only the top-level Folders that a user is Moderating, I need to query all folders that have a parent folder that the user does not moderate, as opposed to option 1, where I just query any items that the user is moderating. Thoughts I think it comes down to determining if users will be querying for all parent items more than they'll be querying child items... if so, then option 1 seems better. But I'm not sure. Is either approach better than the other? Why? Or is there another approach that's better than both? I'm using Entity Framework in case it matters.

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• Sort rectangles in a grid based on a comparison of the center point of each

  - by Mrwolfy

  If I have a grid of rectangles and I move one of the rectangles, say above and to the left of another rectangle, how would I resort the rectangles? Note the rectangles are in an array, so each rectangle has an index and a matching tag. All I really need to do is set the proper index based on the rectangles new center point position within the rectangle, as compared with the center point position of the other rectangles in the grid. Here is what I am doing now in pseudo code (works somewhat, but not accurate): -(void)sortViews:myView { int newIndex; // myView is the view that was moved. [viewsArray removeObject:myView]; [viewsArray enumerate:obj*view]{ if (myView.center.x > view.center.x) { if (myView.center.y > view.center.y) { newIndex = view.tag -1; *stop = YES; } else { newIndex = view.tag +1; *stop = YES; } } else if (myView.center.x < view.center.x) { if (myView.center.y > view.center.y) { newIndex = view.tag -1; *stop = YES; } else { newIndex = view.tag +1; *stop = YES; } } }]; if (newIndex < 0) { newIndex = 0; } else if (newIndex > 5) { newIndex = 5; } [viewsArray insertObject:myView atIndex:newIndex]; [self arrangeGrid]; }

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• Why is it good to split a program into multiple classes?

  - by user1276078

  I'm still a student in high school (entering 10th grade), and I have yet to take an actual computer course in school. Everything I've done so far is through books. Those books have taught me concepts such as inheritance, but how does splitting a program into multiple classes help? The books never told me. I'm asking this mainly because of a recent project. It's an arcade video game, sort of like a flash game as some people have said (although I have no idea what a flash game is). The thing is, it's only one class. It works perfectly fine (a little occasional lag however) with just one class. So, I'm just asking how splitting it into multiple classes would help it. This project was in JAVA and I am the only person working on it, for the record.

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• Advice on approaching a significant rearrangement/refactoring?

  - by Prog

  I'm working on an application (hobby project, solo programmer, small-medium size), and I have recently redesigned a significant part of it. The program already works in it's current state, but I decided to reimplement things to improve the OO design. I'm about to implement this new design by refactoring a big part of the application. Thing is I'm not sure where to start. Obviously, by the nature of a rearrangement, the moment you change one part of the program several other parts (at least temporarily) break. So it's a little 'scary' to rearrange something in a piece of software that already works. I'm asking for advice or some general guidelines: how should I approach a significant refactoring? When you approach rearranging large parts of your application, where do you start? Note that I'm interested only in re-arranging the high-level structure of the app. I have no intention of rewriting local algorithms.

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• How to learn to translate real world problems to code?

  - by StudioWorks

  I'm kind of a beginner to Java and OOP and I didn't quite get the whole concept of seeing a real world problem and translating it to classes and code. For example, I was reading a book on UML and at the beginning the author takes the example of a tic tac toe game and says: "In this example, it's natural to see three classes: Board, Player and Position." Then, he creates the methods in each class and explains how they relate. What I can't understand is how he thought all this. So, where should I start to learn how to see a real world problem and then "translate" it into code?

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• Why am I seeing so many instantiable classes without state?

  - by futlib

  I'm seeing a lot of instantiable classes in the C++ and Java world that don't have any state. I really can't figure out why people do that, they could just use a namespace with free functions in C++, or a class with a private constructor and only static methods in Java. The only benefit I can think of is that you don't have to change most of your code if you later decide that you want a different implementation in certain situations. But isn't that a case of premature design? It could be turned into a class later, when/if it becomes appropriate. Am I getting this wrong? Is it not OOP if I don't put everything into objects (i.e. instantiated classes)? Then why are there so many utility namespaces and classes in the standard libraries of C++ and Java? Update: I've certainly seen a lot examples of this in my previous jobs, but I'm struggling to find open source examples, so maybe it's not that common after all. Still, I'm wondering why people do it, and how common it is.

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• How to store multiple requirements with OR and AND?

  - by Cano

  Well I'm working on a personal project that needs to check if a user has met certain requirements, and they come in a form of Requirement: [c1 OR c2] AND [d1 OR d2] Requirement: [c1 AND c2] OR [d1 AND d2] Requirement: c1 AND any dn(n can be any integer) I'm just not sure how to store these sorts of requirements, I'm thinking of using another object to hold c1,c2,d1,d2....dn and OR, but that seems like a roundabout way of doing things. Is there a better method?

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• Is there an alternative to the term "calling object"?

  - by ybakos

  Let's suppose you've got a class defined (in pseudocode): class Puppy { // ... string sound = "Rawr!"; void bark() { print(sound); } } And say, given a Puppy instance, you call it's bark() method: Puppy p; p.bark(); Notice how bark() uses the member variable sound. In many contexts, I've seen folks describe sound as the member variable of the "calling object." My question is, what's a better term to use than "calling object?" To me, the object is not doing any calling. We know that member functions are in a way just functions with an implicit this or self parameter. I've come up with "receiving object," or "message recipient," which makes sense if you're down with the "messaging" paradigm. Do any of you happy hackers have a term that you like to use? I feel it should mean "the object upon which a method is called" and TOUWAMIC just doesn't cut it.

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• The Data Distribution Service for Real-Time Systems: Part 2

  Structuring and managing your data Data Distribution Service - Business - Data Distribution Service for Real-Time Systems - Databases - Data Warehousing

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• How to handle status columns in designing tables

  - by altsyset

  How to handle multiple statuses for a table entry, for example an item table may have an active, inactive, fast moving, and/or batch statuses. And I wanted to handle them in single column with VARCHAR type. Also I might set each of those attributes as a boolean with different columns. But I am not sure what consequences this might lead to. So if you have experienced such situations which one would be the best way to handle it?

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• How to insert images using labels in NetBeans IDE, Java? [migrated]

  - by Vaishnavi Kanduri

  I'm making a virtual mall using NetBeans IDE 7.3.1 I inserted images using the following steps: Drag and drop label onto frame Go to label properties Click on ellipsis of 'icon' option Import to project, select desired image Resize or reposition it accordingly. Then, I saved the project, copied the project folder into a pendrive, tried to 'Open Project' in mate's laptop, using the same Java Netbeans IDE version. When I tried to open the frames, they displayed empty labels, without images. What went wrong?

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• Do functional generics exist and what is the correct name for them if they do?

  - by voroninp

  Consider the following generic class: public class EntityChangeInfo<EntityType,TEntityKey> { ChangeTypeEnum ChangeType {get;} TEntityKeyType EntityKey {get;} } Here EntityType unambiguously defines TEntityKeyType. So it would be nice to have some kind of types' map: public class EntityChangeInfo<EntityType,TEntityKey> with map < [ EntityType : Person -> TEntityKeyType : int] [ EntityType : Car -> TEntityKeyType : CarIdType ]> { ChangeTypeEnum ChangeType {get;} TEntityKeyType EntityKey {get;} } Another one example is: public class Foo<TIn> with map < [TIn : Person -> TOut1 : string, TOut2 : int, ..., TOutN : double ] [TIn : Car -> TOut1 : int, TOut2 :int, ..., TOutN : Price ] > { TOut1 Prop1 {get;set;} TOut2 Prop2 {get;set;} ... TOutN PropN {get;set;} } The reasonable question: how can this be interpreted by the compiler? Well, for me it is just the shortcut for two structurally similar classes: public sealed class Foo<Person> { string Prop1 {get;set;} int Prop2 {get;set;} ... double PropN {get;set;} } public sealed class Foo<Car> { int Prop1 {get;set;} int Prop2 {get;set;} ... Price PropN {get;set;} } But besides this we could imaging some update of the Foo<>: public class Foo<TIn> with map < [TIn : Person -> TOut1 : string, TOut2 : int, ..., TOutN : double ] [TIn : Car -> TOut1 : int, TOut2 :int, ..., TOutN : Price ] > { TOut1 Prop1 {get;set;} TOut2 Prop2 {get;set;} ... TOutN PropN {get;set;} public override string ToString() { return string.Format("prop1={0}, prop2={1},...propN={N-1}, Prop1, Prop2,...,PropN); } } This all can seem quite superficial but the idea came when I was designing the messages for our system. The very first class. Many messages with the same structure should be discriminated by the EntityType. So the question is whether such construct exists in any programming language?

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• Should I pass an object into a constructor, or instantiate in class?

  - by Prisoner

  Consider these two examples: Passing an object to a constructor class ExampleA { private $config; public function __construct($config) { $this->config = $config; } } $config = new Config; $exampleA = new ExampleA($config); Instantiating a class class ExampleB { private $config; public function __construct() { $this->config = new Config; } } $exampleA = new ExampleA(); Which is the correct way to handle adding an object as a property? When should I use one over the other? Does unit testing affect what I should use?

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• Use constructor or setter method?

  - by user633600

  I am working on a UI code where I have an Action class, something like this - public class MyAction extends Action { public MyAction() { setText("My Action Text"); setToolTip("My Action Tool tip"); setImage("Some Image"); } } When this Action class was created it was pretty much assumed that the Action class wont be customizable (in a sense- its text, tooltip or image will be not be changed anywhere in the code). Of late, now we are in need of changing the action text at some location in code. So I suggested my co-worker to remove the hardcoded action text from the constructor and accept it as an argument, so that everybody is forced to pass the action text. Something like this code below - public class MyAction extends Action { public MyAction(String actionText) { setText(actionText); setTooltip("My Action tool tip); setImage("My Image"); } } He however thinks that since setText() method belongs to base class. It can be flexibly used to pass the action text wherever action instance is created. That way, there is no need to change the existing MyAction class. So his code would look something like this. MyAction action = new MyAction(); //this creates action instance with the hardcoded text action.setText("User required new action text"); //overwrite the exisitng text. I am not sure if that is a correct way to deal with problem. I think in above mentioned case user is anyway going to change the text, so why not force him while constructing the action. The only benefit I see with the original code is that user can create Action class without much thinking about setting text.

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• What processes would make the selling of a hard drive that previously held sensitive data justifiable? [closed]

  - by user12583188

  Possible Duplicate: Securely erasing all data from a hard drive In my personal collection are an increasing number of relatively new drives, only put on the shelf due to upgrades; in the past I have never sold hard drives with used machines for fear of having the encrypted password databases that have been stored on them compromised, but as their numbers increase I find myself more tempted to do so (due to the $$$ I know they're worth on the used market). What tools then exist to make the recovery of data from said drives difficult to the extent that selling them could be justified? Another way of saying this would be: what tools/method exist for making the attempts at recovery of any data previously stored on a certain drive impractical? I assume that it is always possible to recover data from a drive that is in working order. I assume also there are some methods for preventing recovery of data due a program called dban, and one particular feature in macOSX that deals with permanently deleting data from a disk.

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• What OO Design to use ( is there a Design Pattern )?

  - by Blundell

  I have two objects that represent a 'Bar/Club' ( a place where you drink/socialise). In one scenario I need the bar name, address, distance, slogon In another scenario I need the bar name, address, website url, logo So I've got two objects representing the same thing but with different fields. I like to use immutable objects, so all the fields are set from the constructor. One option is to have two constructors and null the other fields i.e: class Bar { private final String name; private final Distance distance; private final Url url; public Bar(String name, Distance distance){ this.name = name; this.distance = distance; this.url = null; } public Bar(String name, Url url){ this.name = name; this.distance = null; this.url = url; } // getters } I don't like this as you would have to null check when you use the getters In my real example the first scenario has 3 fields and the second scenario has about 10, so it would be a real pain having two constructors, the amount of fields I would have to declare null and then when the object are in use you wouldn't know which Bar you where using and so what fields would be null and what wouldn't. What other options do I have? Two classes called BarPreview and Bar? Some type of inheritance / interface? Something else that is awesome?

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• Is this a violation of the Liskov Substitution Principle?

  - by Paul T Davies

  Say we have a list of Task entities, and a ProjectTask sub type. Tasks can be closed at any time, except ProjectTasks which cannot be closed once they have a status of Started. The UI should ensure the option to close a started ProjectTask is never available, but some safeguards are present in the domain: public class Task { public Status Status { get; set; } public virtual void Close() { Status = Status.Closed; } } public ProjectTask : Task { public override void Close() { if (Status == Status.Started) throw new Exception("Cannot close a started Project Task"); base.Close(); } } Now when calling Close() on a Task, there is a chance the call will fail if it is a ProjectTask with the started status, when it wouldn't if it was a base Task. But this is the business requirements. It should fail. Can this be regarded as a violation?

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• Interface hierarchy design for separate domains

  - by jerzi

  There are businesses and people. People could be liked and businesses could be commented on: class Like class Comment class Person implements iLikeTarget class Business implements iCommentTarget Likes and comments are performed by a user(person) so they are authored: class Like implements iAuthored class Comment implements iAuthored People's like could also be used in their history: class history class Like implements iAuthored, iHistoryTarget Now, a smart developer comes and says each history is attached to a user so history should be authored: interface iHistoryTarget extends iAuthored so it could be removed from class Like: class Person implements iLikeTarget class Business implements iCommentTarget class Like implements iHistoryTarget class Comment implements iAuthored class history interface iHistoryTarget extends iAuthored Here, another smart guy comes with a question: How could I capture the Authored fact in Like and Comment classes? He may knows nothing about history concept in the project. By scalling these kind of functionallities, interfaces may goes to their encapsulated types which cause more type strength, on the other hand explicitness suffered and also code end users will face much pain to process. So here is the question: Should I encapsulate those dependant types to their parent types (interface hierarchies) or not or explicitly repeat each type for every single level of my type system or ...?

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• Is this JS code a good way for defining class with private methods?

  - by tigrou

  I was recently browsing a open source JavaScript project. The project is a straight port from another project in C language. It mostly use static methods, packed together in classes. Most classes are implemented using this pattern : Foo = (function () { var privateField = "bar"; var publicField = "bar";     function publicMethod() { console.log('this is public');     } function privateMethod() { console.log('this is private'); } return {   publicMethod : publicMethod, publicField : publicField }; })(); This was the first time I saw private methods implemented that way. I perfectly understand how it works, using a anonymous method. Here is my question : is this pattern a good practice ? What are the actual limitations or caveats ? Usually i declare my JavaScript classes like that : Foo = new function () { var privateField = "test"; this.publicField = "test";     this.publicMethod = function()     { console.log('this method is public'); privateMethod();     } function privateMethod() { console.log('this method is private'); } }; Other than syntax, is there any difference with the pattern show above ?

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• Designing a single look up entity

  - by altsyset

  In almost every application you have this look up entity that provides a dynamic references. This are things like type, category, etc. These entities will always have id, name, desc So at first I designed different entities for each look up. Like education_type, education_level, degree_type.... But on a second thought I decided to have on entity for each of these kinds of entities. But when I am done with the design and check the relation this entity will be referenced by almost all entities in the system and I don't believe that is appropriate. So What is your take on this? Can you give me some clear pros and cons?

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• Do functional generics exist or what is the correct name for them if they do?

  - by voroninp

  Consider the following generic class public class EntityChangeInfo<EntityType,TEntityKey> { ChangeTypeEnum ChangeType {get;} TEntityKeyType EntityKey {get;} } Here EntityType unambiguously defines TEntityKeyType. So it would be nice to have some kind of types' map public class EntityChangeInfo<EntityType,TEntityKey> with map < [ EntityType : Person -> TEntityKeyType : int] [ EntityType : Car -> TEntityKeyType : CarIdType ]> { ChangeTypeEnum ChangeType {get;} TEntityKeyType EntityKey {get;} } Another one example is: public class Foo<TIn> with map < [TIn : Person -> TOut1 : string, TOut2 : int, ..., TOutN : double ] [TIn : Car -> TOut1 : int, TOut2 :int, ..., TOutN : Price ] > { TOut1 Prop1 {get;set;} TOut2 Prop2 {get;set;} ... TOutN PropN {get;set;} } The reasonable question how this can be interpreted by the compiler? Well, for me it is just the sortcut for two structurally similar classes: public sealed class Foo<Person> { string Prop1 {get;set;} int Prop2 {get;set;} ... double PropN {get;set;} } public sealed class Foo<Car> { int Prop1 {get;set;} int Prop2 {get;set;} ... Price PropN {get;set;} } But besides this we could imaging some update of the Foo<: public class Foo<TIn> with map < [TIn : Person -> TOut1 : string, TOut2 : int, ..., TOutN : double ] [TIn : Car -> TOut1 : int, TOut2 :int, ..., TOutN : Price ] > { TOut1 Prop1 {get;set;} TOut2 Prop2 {get;set;} ... TOutN PropN {get;set;} public override string ToString() { return string.Format("prop1={0}, prop2={1},...propN={N-1}, Prop1, Prop2,...,PropN); } } This all can seem quite superficial but the idea came when I was designing the messages for our system. The very first class. Many messages with the same structrue should be discriminated by the EntityType. So the question is whether such construct exist in any programming language?

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• How to access functions in extended classes efficiently?

  - by nischayn22

  In PHP I have classes as below class Animal { //some vars public function printname(){ echo $this->name; } } class AnimalMySql extends Animal { static public function getTableFields(){ return array(); } } class AnimalPostgreSql extends Animal { static public function getTableFields(){ return array(); } } Now I have an object $lion = new Animal(); and I want to do if($store == mysql) //getTableFields from class AnimalMySql else //getTableFields form class AnimalPostgreSql I am new to OOP and not sure what is the best way to call the method from the specific class P.S. Please leave a note with the answer to explain the efficiency of the approach

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• "Default approach" when creating a class from scratch: getters for everything, or limited access?

  - by Prog

  Until recently I always had getters (and sometimes setters but not always) for all the fields in my class. It was my 'default': very automatic and I never doubted it. However recently some discussions on this site made me realize maybe it's not the best approach. When you create a class, you often don't know exactly how it's going to be used in the future by other classes. So in that sense, it's good to have getters and setter for all of the fields in the class. So other classes could use it in the future any way they want. Allowing this flexibility doesn't require you to over engineer anything, only to provide getters. However some would say it's better to limit the access to a class, and only allow access to certain fields, while other fields stay completely private. What is your 'default' approach when building a class from scratch? Do you make getters for all the fields? Or do you always choose selectively which fields to expose through a getter and which to keep completely private?

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• Sharing object between 2 classes

  - by Justin

  I am struggling to wrap my head around being able to share an object between two classes. I want to be able to create only one instance of the object, commonlib in my main class and then have the classes, foo1 and foo2, to be able to mutually share the properties of the commonlib. commonlib is a 3rd party class which has a property Queries that will be added to in each child class of bar. This is why it is vital that only one instance is created. I create two separate queries in foo1 and foo2. This is my setup: abstract class bar{ //common methods } class foo1 extends bar{ //add query to commonlib } class foo2 extends bar{ //add query to commonlib } class main { public $commonlib = new commonlib(); public function start(){ //goal is to share one instance of $this->commonlib between foo1 and foo2 //so that they can both add to the properites of $this->commonlib (global //between the two) //now execute all of the queries after foo1 and foo2 add their query $this->commonlib->RunQueries(); } }

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• using static methods and classes

  - by vedant1811

  I know that static methods/variables are associated with the class and not the objects of the class and are useful in situations when we need to keep count of, say the number of objects of the class that were created. Non-static members on the other hand may need to work on the specific object (i.e. to use the variables initialized by the constructor) My question what should we do when we need neither of the functionalities? Say I just need a utility function that accepts value(s) and returns a value besed solely on the values passed. I want to know whether such methods should be static or not. How is programming efficiency affected and which is a better coding practice/convention and why. PS: I don't want to spark off a debate, I just want a subjective answer and/or references.

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