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• software architecture (OO design) refresher course

  - by PeterT

  I am lead developer and team lead in a small RAD team. Deadlines are tight and we have to release often, which we do, and this is what keep the business happy. While we (the development team) are trying to maintain the quality of the code (clean and short methods), I can't help but notice that the overall quality of the OO design&architecture is getting worse over the time - the library we are working on is gradually reducing itself to a "bag of functions". Well, we try to use the design patterns, but since we don't really have much time for a design as such we are mostly using the creational ones. I have read Code Complete / Design Patterns (GOF & enterprise) / Progmatic Programmer / and many books from Effective XXX series. Should I re-read them again as I have read them a long time ago and forgotten quite a lot, or there are other / better OO design / software architeture books been published since then which I should definitely read? Any ideas, recommendations on how can I get the situation under control and start improving the architecture. The way I see it - I will start improving the architectural / design quality of software components I am working on and then will start helping other team members once I find what is working for me.

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• OpenGL and gluUnProject, 3d object following mouse

  - by Robert

  i have a 3d object and i want him to "follow" my mouse position, so i use gluUnProject function to convert screen coordinates to 3d world coordinates and i translate this object with the new coordinates. Its working but i have a problem, my object can follow my mouse but he is moving extremely fast, when i move my mouse a little bit(something like 2 pixels), its moving extremly fast in the 3d world. I want something like that : http://www.youtube.com/watch?v=90zS8SVUAIY (red circle following mouse). Thanks for your help.

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• what is message passing in OO?

  - by Tom

  I've been studying OO programming, primarily in C++, C# and Java. I thought I had a good grasp on it with my understanding of encapsulation, inheritance and polymorphism (as well as reading a lot of questions on this site). One thing that seems to popup up here and there is the concept of "message passing". Apparently, this is something that is not used whilst OO programming in today's mainstream languages, but is supported by Smalltalk. My questions are: What is message passing? (Can someone give a practical example?) Is there any support for this "message passing" in C++, C# or Java?

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• Rotating an object about a point (2D) using box2d

  - by noob

  i just started developing using box2d on flixel and i realise the pivot point of the rotation of an object in box2d is set to the center of an object. i had read on forums and i found out that SetAsBox can change the pivot point of the object, however, i cannot seem to get it work to rotate about a point. what i would like to achieve is to rotate an object about a point like earth revolving around the sun. any one can help me with it? really thanks a lot and sorry for the bad english

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• Examples of Liskov Substitution

  - by james lewis

  I'm facilitating a session next week on the Liskov Substitution Principle and I was wondering if anyone had any examples of violations 'from the trenches'? I'm looking for something other than uncle Bob's rectangle - square problem and the persistent set problem he talks about in A-PPP (although that is a great example). So far I'm using the example of a (very simple) List and an IndexedList as the 'correct' use of inheritance. And the addition of a Set to this hierarchy as a violation (as a Set is distinct; strengthening the pre condition of the Add method). I've also taken this great example and it's solution from this question Both those examples are great but I'm looking for something more subtle and harder to spot. So far I've come up with nothing so if you've got a great, subtle example post it up. Also, any metaphors you've come across that helped you understand LSP would be really useful too.

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• Why is my class worse than the hierarchy of classes in the book (beginner OOP)?

  - by aditya menon

  I am reading this book. The author is trying to model a lesson in a college. The goal is to output the Lesson Type (Lecture or Seminar), and the Charges for the lesson depending on whether it is a hourly or fixed price lesson. So the output should be: lesson charge 20. Charge type: hourly rate. lesson type seminar. lesson charge 30. Charge type: fixed rate. lesson type lecture. When the input is as follows: $lessons[] = new Lesson('hourly rate', 4, 'seminar'); $lessons[] = new Lesson('fixed rate', null, 'lecture'); I wrote this: class Lesson { private $chargeType; private $duration; private $lessonType; public function __construct($chargeType, $duration, $lessonType) { $this->chargeType = $chargeType; $this->duration = $duration; $this->lessonType = $lessonType; } public function getChargeType() { return $this->getChargeType; } public function getLessonType() { return $this->getLessonType; } public function cost() { if($this->chargeType == 'fixed rate') { return "30"; } else { return $this->duration * 5; } } } $lessons[] = new Lesson('hourly rate', 4, 'seminar'); $lessons[] = new Lesson('fixed rate', null, 'lecture'); foreach($lessons as $lesson) { print "lesson charge {$lesson->cost()}."; print " Charge type: {$lesson->getChargeType()}."; print " lesson type {$lesson->getLessonType()}."; print "<br />"; } But according to the book, I am wrong (I am pretty sure I am, too). The author gave a large hierarchy of classes as the solution instead. In a previous chapter, the author stated the following 'four signposts' as the time when I should consider changing my class structure: Code Duplication The Class Who Knew Too Much About His Context The Jack of All Trades - Classes that try to do many things Conditional Statements The only problem I can see is Conditional Statements, and that too in a vague manner - so why refactor this? What problems do you think might arise in the future that I have not foreseen?

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• Configuration Data in a Custom Timer job in Sharepoint 2010 : The Hierarchical Object Store

  - by Gino Abraham

  I was planning for a custom timer job for which i wanted to store some configuration data. Was looking for some best practices, found a useful links on The Hierarchical Object store Store http://www.chaholl.com/archive/2011/01/30/the-skinny-on-sppersistedobject-and-the-hierarchical-object-store-in.aspxInitially was planning for a custom list, but this would make us run a cross site query and the list name and the url should again be kept in some configuration which is an headache to maintain. Hierarchical object store was zeroed in and thanks to google for the same :)

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• OOP - Composition, Components and Composites Example?

  - by coder3

  I've been reading a bit about OOP in relation to Composition, Components and Composites. I believe I understand the fundamental principle (not sure). Can some one please provide a code example of a person or car (both have many properties) using Composition, Components and Composites. I think seeing it in code would clear up the confusion I have regarding this pattern. Preferably in Java or PHP - many thanks!

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• how do you read from system.out in Java [closed]

  - by Dan

  I'm trying to create a word scramble game and so far I have taken a vector of randomly assorted strings that contains both words and hints and split them into two vectors. I have randomly scrambled the word and set this all up in text boxes. Right now I'm stuck because I have a text box that takes input but I'm not sure how to read that in? I want the user to type the unscrambled word into the text box and have it calculate as correct and move on to the next word immediately. I also don't know how to get the keys working. I want the "?" character to be the hint button that shows the hint. At the moment the hint box works if I type the question mark in using the System.in but it doesn't work if I type it directly in to the text box. The characters are showing up in the text box but nothing is working after that.

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• Translating an Object to a certain Vector 3 in OpenGL and Java LWJGL

  - by aliasmk

  So after almost two hours, I got the hang of using glTranslated() (with Java and LWJGL). If I am correct, applying glTranslated on an object moves that object with the x,y,z relative to the previously moved object. I believe the correct term for this is local vs global, global being the one I want. I was wondering if there was a way to translate an object to a specific XYZ position, or relative to the origin. Thanks! (Code or other details can be supplied if it helps, just let me know. Also sorry if this is a noob comment, Im very new to OpenGL.)

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• C# vector class - Interpolation design decision

  - by Benjamin

  Currently I'm working on a vector class in C# and now I'm coming to the point, where I've to figure out, how i want to implement the functions for interpolation between two vectors. At first I came up with implementing the functions directly into the vector class... public class Vector3D { public static Vector3D LinearInterpolate(Vector3D vector1, Vector3D vector2, double factor) { ... } public Vector3D LinearInterpolate(Vector3D other, double factor { ... } } (I always offer both: a static method with two vectors as parameters and one non-static, with only one vector as parameter) ...but then I got the idea to use extension methods (defined in a seperate class called "Interpolation" for example), since interpolation isn't really a thing only available for vectors. So this could be another solution: public class Vector3D { ... } public static class Interpolation { public static Vector3D LinearInterpolate(this Vector3D vector, Vector3D other, double factor) { ... } } So here an example how you'd use the different possibilities: { var vec1 = new Vector3D(5, 3, 1); var vec2 = new Vector3D(4, 2, 0); Vector3D vec3; vec3 = vec1.LinearInterpolate(vec2, 0.5); //1 vec3 = Vector3D.LinearInterpolate(vec1, vec2, 0.5); //2 //or with extension-methods vec3 = vec1.LinearInterpolate(vec2, 0.5); //3 (same as 1) vec3 = Interpolation.LinearInterpolation(vec1, vec2, 0.5); //4 } So I really don't know which design is better. Also I don't know if there's an ultimate rule for things like this or if it's just about what someone personally prefers. But I really would like to hear your opinions, what's better (and if possible why ).

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• Basis of definitions

  - by Yttrill

  Let us suppose we have a set of functions which characterise something: in the OO world methods characterising a type. In mathematics these are propositions and we have two kinds: axioms and lemmas. Axioms are assumptions, lemmas are easily derived from them. In C++ axioms are pure virtual functions. Here's the problem: there's more than one way to axiomatise a system. Given a set of propositions or methods, a subset of the propositions which is necessary and sufficient to derive all the others is called a basis. So too, for methods or functions, we have a desired set which must be defined, and typically every one has one or more definitions in terms of the others, and we require the programmer to provide instance definitions which are sufficient to allow all the others to be defined, and, if there is an overspecification, then it is consistent. Let me give an example (in Felix, Haskell code would be similar): class Eq[t] { virtual fun ==(x:t,y:t):bool => eq(x,y); virtual fun eq(x:t, y:t)=> x == y; virtual fun != (x:t,y:t):bool => not (x == y); axiom reflex(x:t): x == x; axiom sym(x:t, y:t): (x == y) == (y == x); axiom trans(x:t, y:t, z:t): implies(x == y and y == z, x == z); } Here it is clear: the programmer must define either == or eq or both. If both are defined, the definitions must be equivalent. Failing to define one doesn't cause a compiler error, it causes an infinite loop at run time. Defining both inequivalently doesn't cause an error either, it is just inconsistent. Note the axioms specified constrain the semantics of any definition. Given a definition of == either directly or via a definition of eq, then != is defined automatically, although the programmer might replace the default with something more efficient, clearly such an overspecification has to be consistent. Please note, == could also be defined in terms of !=, but we didn't do that. A characterisation of a partial or total order is more complex. It is much more demanding since there is a combinatorial explosion of possible bases. There is an reason to desire overspecification: performance. There also another reason: choice and convenience. So here, there are several questions: one is how to check semantics are obeyed and I am not looking for an answer here (way too hard!). The other question is: How can we specify, and check, that an instance provides at least a basis? And a much harder question: how can we provide several default definitions which depend on the basis chosen?

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• Should a Parent with Children have a DefaultChild, or should a Child have a Default property?

  - by Stijn

  Which of the following two models makes more sense? I'm leaning towards the first one because there can only be one default child. The examples are in C# but I think it can apply to other languages too. Here DefaultChild holds one of the items in Children. class Parent { int ID { get; set; } Child DefaultChild { get; set; } IEnumerable<Child> Children { get; set; } } class Child { int ID { get; set; } } Here one of the items in Children has Default set to true while the others have it set to false. class Parent { int ID { get; set; } IEnumerable<Child> Children { get; set; } } class Child { int ID { get; set; } bool Default { get; set; } } A concrete situation: a User in our system has one or more Customers attached. When logging in, if said User has a default Customer, they are immediately working under this Customer. If they don't, they have to select a Customer to work under. While logged in, they can switch between Customers.

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• How to show or direct a business analyst to a data modelling subject?

  - by AaronLS

  Our business analysts pushed hard to collect data through a spreadsheet. I am the programmer responsible for importing that data. Usually when they push hard for something like this, I never know how well it will work out until a few weeks later when I have time assigned to work on the task of programming the import of the data. I have tried to do as much as possible along the way, named ranges, data validations, etc. But I usually don't have time to take a detailed look at all the data and compare to the destination in the database to determine how well it matches up. A lot of times there will be maybe a little table of items that somehow I have to relate to something else in the database, but there are not natural or business keys present that would allow me to do so. Make the best of this, trying to write something that can compare strings and make a best guess at it and then go through the effort of creating interfaces for a user to match the imported data to the destination. I feel like if the business analyst was actually creating a data model, they would be forced to think about these relationships, and have an appreciation for the need of natural or business keys to be part of the spreadsheet for the purposes of smoothly importing the data. The closest they come to business analysis is a big flat list of fields, and that would be fine if it were like any other data dictionary and include data types+relationships, but it isn't. They are just a bunch of names. No indication of what type of data they might hold, and it is up to me to guess. When I have pushed for more detail, they say that it is just busy work. How can I explain the importance of data modelling? How can I tell them what it is and how to do it? It feels impossible, because they don't have an appreciation for its importance. They do however, usually have an interest in helping out in whatever way they can, it's just this in particular has never gotten a motivated response.

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• What is the difference between Java 6 and PHP 5.4? [closed]

  - by Mashael

  First of all, let me explain the matter. I'm in a class where we learn Java 6 OOP fundamentals. However, my goal is to learn PHP (the last version) next. So, my question: Is there a big difference between PHP and Java 6 in OOP concepts? Meaning that after I finish the OOP class in Java will I find a lot of things that need to be learned in PHP regarding OOP? Update: *My goal of learning PHP next is to build dynamic sites* (I'm not sure of other options) and to follow OOP.

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• How do we keep dependent data structures up to date?

  - by Geo

  Suppose you have a parse tree, an abstract syntax tree, and a control flow graph, each one logically derived from the one before. In principle it is easy to construct each graph given the parse tree, but how can we manage the complexity of updating the graphs when the parse tree is modified? We know exactly how the tree has been modified, but how can the change be propagated to the other trees in a way that doesn't become difficult to manage? Naturally the dependent graph can be updated by simply reconstructing it from scratch every time the first graph changes, but then there would be no way of knowing the details of the changes in the dependent graph. I currently have four ways to attempt to solve this problem, but each one has difficulties. Nodes of the dependent tree each observe the relevant nodes of the original tree, updating themselves and the observer lists of original tree nodes as necessary. The conceptual complexity of this can become daunting. Each node of the original tree has a list of the dependent tree nodes that specifically depend upon it, and when the node changes it sets a flag on the dependent nodes to mark them as dirty, including the parents of the dependent nodes all the way down to the root. After each change we run an algorithm that is much like the algorithm for constructing the dependent graph from scratch, but it skips over any clean node and reconstructs each dirty node, keeping track of whether the reconstructed node is actually different from the dirty node. This can also get tricky. We can represent the logical connection between the original graph and the dependent graph as a data structure, like a list of constraints, perhaps designed using a declarative language. When the original graph changes we need only scan the list to discover which constraints are violated and how the dependent tree needs to change to correct the violation, all encoded as data. We can reconstruct the dependent graph from scratch as though there were no existing dependent graph, and then compare the existing graph and the new graph to discover how it has changed. I'm sure this is the easiest way because I know there are algorithms available for detecting differences, but they are all quite computationally expensive and in principle it seems unnecessary so I'm deliberately avoiding this option. What is the right way to deal with these sorts of problems? Surely there must be a design pattern that makes this whole thing almost easy. It would be nice to have a good solution for every problem of this general description. Does this class of problem have a name?

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• Functional programming readability

  - by Jimmy Hoffa

  I'm curious about this because I recall before learning any functional languages, I thought them all horribly, awfully, terribly unreadable. Now that I know Haskell and f#, I find it takes a little longer to read less code, but that little code does far more than an equivalent amount would in an imperative language, so it feels like a net gain and I'm not extremely practiced in functional. Here's my question, I constantly hear from OOP folks that functional style is terribly unreadable. I'm curious if this is the case and I'm deluding myself, or if they took the time to learn a functional language, the whole style would no longer be more unreadable than OOP? Has anybody seen any evidence or got any anecdotes where they saw this go one way or another with frequency enough to possibly say? If writing functionally really is of lower readability than I don't want to keep using it, but I really don't know if that's the case or not..

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• Liskov principle: violation by type-hinting

  - by Elias Van Ootegem

  According to the Liskov principle, a construction like the one below is invalid, as it strengthens a pre-condition. I know the example is pointless/nonsense, but when I last asked a question like this, and used a more elaborate code sample, it seemed to distract people too much from the actual question. //Data models abstract class Argument { protected $value = null; public function getValue() { return $this->value; } abstract public function setValue($val); } class Numeric extends Argument { public function setValue($val) { $this->value = $val + 0;//coerce to number return $this; } } //used here: abstract class Output { public function printValue(Argument $arg) { echo $this->format($arg); return $this; } abstract public function format(Argument $arg); } class OutputNumeric extends Output { public function format(Numeric $arg)//<-- VIOLATION! { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } My question is this: Why would this kind of "violation" be considered harmful? So much so that some languages, like the one I used in this example (PHP), don't even allow this? I'm not allowed to strengthen the type-hint of an abstract method but, by overriding the printValue method, I am allowed to write: class OutputNumeric extends Output { final public function printValue(Numeric $arg) { echo $this->format($arg); } public function format(Argument $arg) { $format = is_float($arg->getValue()) ? '%.3f' : '%d'; return sprintf($format, $arg->getValue()); } } But this would imply repeating myself for each and every child of Output, and makes my objects harder to reuse. I understand why the Liskov principle exists, don't get me wrong, but I find it somewhat difficult to fathom why the signature of an abstract method in an abstract class has to be adhered to so much stricter than a non-abstract method. Could someone explain to me why I'm not allowed to hind at a child class, in a child class? The way I see it, the child class OutputNumeric is a specific use-case of Output, and thus might need a specific instance of Argument, namely Numeric. Is it really so wrong of me to write code like this?

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• Nested Classes: A useful tool or an encapsulation violation?

  - by Bryan Harrington

  So I'm still on the fence as to whether or not I should be using these or not. I feel its an extreme violation of encapsulation, however I find that I am able to achieve some degree of encapsulation while gaining more flexibility in my code. Previous Java/Swing projects I had used nested classes to some degree, However now I have moved into other projects in C# and I am avoid their use. How do you feel about nested classes?

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• Code Smell: Inheritance Abuse

  - by dsimcha

  It's been generally accepted in the OO community that one should "favor composition over inheritance". On the other hand, inheritance does provide both polymorphism and a straightforward, terse way of delegating everything to a base class unless explicitly overridden and is therefore extremely convenient and useful. Delegation can often (though not always) be verbose and brittle. The most obvious and IMHO surest sign of inheritance abuse is violation of the Liskov Substitution Principle. What are some other signs that inheritance is The Wrong Tool for the Job even if it seems convenient?

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• Relationships in a Chen ERD

  - by Nibroc A Rehpotsirhc

  I am working on a Chen ERD to model our organizations merchandise. Our central entity is a Style. We have supplemental entities of Color and Season. I am defining our assortment as the relationship between these three entities, and this relationship itself will have attributes and is defined by the three entities which participate in the mandatory relationship. The rules are; Many Styles can be offered in a Season, and a Style can be offered in many Seasons. Within a Season, a Style can be offered in Many Colors. I then have 2 other entities, one of which I believe is a weak entity, Climate, and the other may be weak, but I am not sure, this being Transaction Channel. I am thinking of these as relationships off of a relationship? Meaning, for a given Style/Color combination offered in a Season, it can be available through 1 or more Transaction Channels. Additionally, within a season, a given Style/Color combination can be intended for 1 or more Climates. Is it valid to have relationships off of relationships? Or does this requirement dictate that I should think of this Style/Color/Season relationship as an entity itself, and define the relationships to Climate and Transaction Channel off of this entity?

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• How do I start correctly in building database classes in c#?

  - by e4rthdog

  I am new in C# programming and in OOP. I need to dive into web applications for my company, and I need to do it fast and correct. So even that I know ASP.NET MVC is the way to go, I want to start with some simple applications with ASP.NET Webforms and then advance to MVC logic. Also regarding my db classes: I plan to create common database classes in order to be able to use them either from WinForms or ASP.NET applications. I also know that the way to go is to learn about ORM and EF. BUT I also want to start from where I am feeling comfortable and that is the traditional ADO.NET way. So about my Data Access Layer classes: Should I return my results in datasets or arraylists/lists? Should my methods do their own connect/disconnect from the db, or have separate methods and let the application maintain the connection?

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• What is considered third party code?

  - by Songo

  Inspired by this question Using third-party libraries - always use a wrapper? I wanted to know what people actually consider as third-party libraries. Example from PHP: If I'm building an application using Zend framework, should I treat Zend framework libraries as third party code? Example from C#: If I'm building a desktop application, should I treat all .Net classes as third party code? Example from Java: Should I treat all libraries in the JDK as third party libraries? Some people say that if a library is stable and won't change often then one doesn't need to wrap it. However I fail to see how one would test a class that depends on a third party code without wrapping it.

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• Is ORM an Anti-Pattern?

  - by derphil

  I had a very stimulating and interessting discussion with a colleague about ORM and it's Pros and Cons. In my opinion, an ORM is useful only in the rarest cases. At least in my experience. But I don't want to list my own arguments at this time. So I ask you, what do you think about ORM? What are the Pros and the Cons? P.S. I've posted this "question" yesterday on Stackoverflow, but some of the user think, that this should better posted here.

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• Design pattern and best practices

  - by insane-36

  I am an iphone developer. I am quite confident on developing iphone application with some minimal feature. I would consider myself as a fair application developer but the code I write is not so much structured. I make vey little use of MVC because I dont seem to find places to impose MVC. Most of the time, I create application with viewcontrollers and very few models only. How could I improve the skill for making my code more reusable, standard, easy and maintainable. I have seen few books on design patterns and tried few chapters myself but I dont seem to skip my habit. I know few of them but I am not being able to apply those patterns into my app. What is the best way to learn the design patterns and coding habit. Any kind of suggestion is warmly welcomed.

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