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• Why avoid Java Inheritance "Extends"

  - by newbie

  Good day! Jame Gosling said “You should avoid implementation inheritance whenever possible.” and instead, use interface inheritance. But why? How can we avoid inheriting the structure of an object using the keyword "extends", and at the same time make our code Object Oriented? Could someone please give an Object Oriented example illustrating this concept in a scenario like "ordering a book in a bookstore?" Thank you in advance.

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• When is a glue or management class doing too much?

  - by jprete

  I'm prone to building centralized classes that manage the other classes in my designs. It doesn't store everything itself, but most data requests would go to the "manager" first. While looking at an answer to this question I noticed the term "God Object". Wikipedia lists it as an antipattern, understandably. Where is the line between a legitimate glue class, or module, that passes data and messages from place to place, and a class that is doing too much?

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• Where ORMs blur the lines between code and data, how do you decide what logic should be a stored procedure, and what should be coded?

  - by PhonicUK

  Take the following pseudocode: CreateInvoiceAndCalculate(ItemsAndQuantities, DispatchAddress, User); And say CreateInvoice does the following: Create a new entry in an Invoices table belonging to the specified User to be sent to the given DispatchAddress. Create a new entry in an InvoiceItems table for each of the items in ItemsAndQuantities, storing the Item, the Quantity, and the cost of the item as of now (by looking it up from an Items table) Calculate the total amount of the invoice (ex shipping and taxes) and store it in the new Invoice row. At a glace you wouldn't be able to tell if this was a method in my applications code, or a stored procedure in the database that is being exposed as a function by the ORM. And to some extent it doesn't really matter. Now technically none of this is business logic. You're not making any decisions - just performing a calculation and creating records. However some may argue that because you are performing a calculation that affects the business (the total amount to be invoiced) that this isn't something that should be done in a stored procedure and instead should be in code. So for this specific example - why would it be more appropriate to do one or the other? And where do you draw the line? Or does it even particular matter as long as it's sufficiently well documented?

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• Visitor-pattern vs inheritance for rendering

  - by akaltar

  I have a game engine that currently uses inheritance to provide a generic interface to do rendering: class renderable { public: void render(); }; Each class calls the gl_* functions itself, this makes the code hard to optimize and hard to implement something like setting the quality of rendering: class sphere : public renderable { public: void render() { glDrawElements(...); } }; I was thinking about implementing a system where I would create a Renderer class that would render my objects: class sphere { void render( renderer* r ) { r->renderme( *this ); } }; class renderer { renderme( sphere& sphere ) { // magically get render resources here // magically render a sphere here } }; My main problem is where should I store the VBOs and where should I Create them when using this method? Should I even use this approach or stick to the current one, perhaps something else? PS: I already asked this question on SO but got no proper answers.

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• How to layer if statements when order of logic is irrelevant?

  - by jimmyjimmy

  Basically I have a series of logic in my website that can lead to 5 total outcomes. Basically two different if tests and then a catch all else statement. For example: if cond1: if mod1: #do things elif mod2: #do things elif cond2: if mod1: #do things elif mod2 #do things else: #do things I was thinking about rewriting it like this: if cond1 and mod1: #do things elif cond1 and mod2: #do things elif cond2 and mod1: #do things elif cond2 and mod2: #do things else: #do things Is there any real difference in these two coding options/a better choice for this kind of logic testing?

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• Interfaces on an abstract class

  - by insta

  My coworker and I have different opinions on the relationship between base classes and interfaces. I'm of the belief that a class should not implement an interface unless that class can be used when an implementation of the interface is required. In other words, I like to see code like this: interface IFooWorker { void Work(); } abstract class BaseWorker { ... base class behaviors ... public abstract void Work() { } protected string CleanData(string data) { ... } } class DbWorker : BaseWorker, IFooWorker { public void Work() { Repository.AddCleanData(base.CleanData(UI.GetDirtyData())); } } The DbWorker is what gets the IFooWorker interface, because it is an instantiatable implementation of the interface. It completely fulfills the contract. My coworker prefers the nearly identical: interface IFooWorker { void Work(); } abstract class BaseWorker : IFooWorker { ... base class behaviors ... public abstract void Work() { } protected string CleanData(string data) { ... } } class DbWorker : BaseWorker { public void Work() { Repository.AddCleanData(base.CleanData(UI.GetDirtyData())); } } Where the base class gets the interface, and by virtue of this all inheritors of the base class are of that interface as well. This bugs me but I can't come up with concrete reasons why, outside of "the base class cannot stand on its own as an implementation of the interface". What are the pros & cons of his method vs. mine, and why should one be used over another?

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• Developing web sites that imitate desktop apps. How to fight that paradigm? [closed]

  - by user1598390

  Supposse there's a company where web sites/apps are designed to resemble desktop apps. They struggle to add: Splash screens Drop-down menus Tab-pages Pages that don't grow downward with content, context is inside scrollable area so page is of a fixed size, as if resembling the one-screen limitation of desktop apps. Modal windows, pop-ups, etc. Tree views Absolutely no access to content unless you login-first, even with non-sensitive content. After splash screen desapears, you are presented with a login screen. No links - just simulated buttons. Fixed page-size. Cannot open a linked in other tab Print button that prints directly ( not showing printable page so the user can't print via the browser's print command ) Progress bars for loading content even when the browser indicates it with its own animation Fonts and color amulate a desktop app made with Visual Basic, PowerBuilder etc. Every app seems almost as if were made in Visual Basic. They reject this elements: Breadcrumbs Good old underlined links Generated/dynamic navigation, usage-based suggestions Ability to open links in multiple tabs Pagination Printable pages Ability to produce a URL you can save or share that links to an item, like when you send someone the link to an especific StackExchange question. The only URL is the main one. Back button To achieve this, tons of javascript code is needed. Lots and lots of Javascript and Ajax code for things not related with the business but with the necessity to hide/show that button, refresh this listbox, grey-out that label, etc. The coplexity generated by forcing one paradigm into another means most lines of code are dedicated to maintain the illusion of a desktop app. What is the best way to change this mindset, and make them embrace the web, and start producing modern, web apps instead of desktop imitations ? EDIT: These sites are intranet sites. Users hate these apps. They constantly whine about them, but they have to use them to do their daily work. These sites are in-house solutions, the end-users have no choice but to use them. They are a "captive audience". Also, substitution will not happen because of high costs. But at least if that mindset is changed, new developments would be more web-like.

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• How do I decide to which class a method should belong

  - by Eleeist

  I have TopicBusiness.class and PostBusiness.class. I have no problem with deciding into which class methods such as addPostToDatabase() or getAllPostsFromDatabase() should go. But what about getAllPostsFromTopic(TopicEntity topic) or getNumberOfPostsInTopic(TopicEntity topic)? Should the parameter be the deciding factor? So when the method takes TopicEntity as parameter it should belong to TopicBusiness.class? I am quite puzzled by this. EDIT: Some more info as requested. TopicBusiness.class and PostBusiness.class are classes holding all the business logic of the application concerning topics and posts respectively - that is fetching the data from database and/or performing some operations on them. TopicEntity is data (in this case representing single topic) fetched from database. getAllPostFromTopic(TopicEntity topic) gets all posts from database that belong to particular topic, while getNumberOfPostsInTopic(TopicEntity topic) performs database query and returns the number of posts that topic passed as parameter consists of.

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• Should interface only be used for behavior and not to show logical data grouped together?

  - by jags

  Should an interface only be used to specify certain behavior? Would it be wrong to use interface to group logically related data? To me it looks like we should not use interface to group logically related data as structure seems a better fit. A class may be used but class name should indicate something like DTO so that user gets the impression that class does not have any behavior. Please let me know if my assumption is correct. Also, are there any exceptions where interface can be used to group logically related data?

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• Create Levels using blender

  - by notrodash

  I am creating a game and I have a custom level format for levels in my game. I wanted to know if it is possible to create levels for that kinda format in Blender. My format is XML based and just declares the positions of certain objects. Online I have seen many people use Blender to create levels in their own custom format that blender can understand. How do i get blender to understand my format and use blender to create levels for my game?

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• How to decide to which class does a method belong

  - by Eleeist

  I have TopicBusiness.class and PostBusiness.class. I have no problem with deciding into which class methods such as addPostToDatabase() or getAllPostsFromDatabase() should go. But what about getAllPostsFromTopic(TopicEntity topic) or getNumberOfPostsInTopic(TopicEntity topic)? Should the parameter be the deciding factor? So when the method takes TopicEntity as parameter it should belong to TopicBusiness.class? I am quite puzzled by this.

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• Random generation of interesting puzzle levels?

  - by monsterfarm

  I'm making a Sokoban-like game i.e. there's a grid that has some crates on it you can push and you have to get the crates on crosses to win the level (although I'm going to add some extra elements to it). Are there any general algorithms or reading material I can look at for how I could go about generating interesting (as in, not trivial to solve) levels for this style of game? I'm aware that random level generators exist for Sokoban but I'm having trouble finding the algorithm descriptions. I'm interested in making a game where the machine can generate lots of levels for me, sorted by difficulty. I'm even willing to constrain the rules of the game to make the level generation easier (e.g. I'll probably limit the grid size to about 7x7). I suspect there are some general ways to do level generation here as I've seen e.g. Traffic Jam-like games (where you have to move blocks around the free some block) with 1000s of levels where each one has a unique solution. One idea I had was to generate a random map in its final state (i.e. where all crates are on top of their crosses) and then the computer would pull (instead of push) these crates around to create a level. The nice property here is that we know the level is solvable. However, I'd need some heuristics to ensure the level was interesting.

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• Best approach for tracking dependent state

  - by Pace

  Let's pretend I work on a project tracking application. The application is a database backed, server hosted, web application. In this application there are Projects which have many Activities which have many Tasks. A Task has two date fields an originalDueDate and a projectedDueDate. In addition, there are dynamic fields on the Activities and the Projects which indicate whether the Activity or Project is behind schedule based on the projected due dates of the child tasks and various other variables such as remaining buffer time, etc. There are a number of things that can cause the projectedDueDate to change. For example, an employee working on the project may (via a server request) enter in a shipping delay. Alternatively, a site may (via a server request) enter in an unexpected closure. When any of these things occur I need to not only update the projectedDueDate of the Task but also trigger the corresponding Project and Activity to update as well. What is the best way to do this? I've thought of the observer pattern but I don't keep a single copy of all these objects in memory. When a request comes in, I query the Task in from the database, at that point there is no associated Activity in memory that would be a listener. I could remove the ability to query for Tasks and force the application to query first by Project, then by Activity (in context of Project), then by task (in context of Activity) adding the observer relationships at each step but I'm not sure if that is the best way. I could setup a database event listening system so when a Task modified event is dispatched I have a handler which queries for the Activity at that point. I could simply setup a two-way relationship between Task and Activity so that the Task knows about the parent Activity and when the Task updates his state the Task grabs his parent and updates state. Right now I'm stuck considering all the options and am wondering if any single approach (doesn't have to be a listed approach) is jumping out at others as the best approach.

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• How should I define my Java Objects?

  - by HonorGod

  I have a data grid where I sort of show the following information - All Guests Total Adults = 22 Total Children = 27 Confirmed Total Adults = 9 Total Children = 13 Country = Germany Total Adults = 5 Total Childres = 6 Friends Adults = 2 Children = 2 Relatives Adults = 3 Children = 4 Country = USA Total Adults = 4 Total Childres = 7 Friends Adults = 2 Children = 5 Relatives Adults = 2 Children = 2 Tentative Total Adults = 13 Total Children - 14 Country = Australia Total Adults = 7 Total Childres = 8 Friends Adults = 2 Children = 3 Relatives Adults = 5 Children = 5 Country = China Total Adults = 6 Total Childres = 6 Friends Adults = 2 Children = 4 Relatives Adults = 4 Children = 2 And in the database what I have is data at the lowest level which is Friends / Relatives and the corresponding countries set as a look-up value which in indirectly connected to another look-up that can tell me if they fall under confirmed or tentative. I guess my question is how do I layout my Java Object and perform the aggregations and give it back to the client. I am not sure if I am clear with my question, but feel free to comment so I can update the question accordingly.

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• How to separate and maintain customer specific code

  - by WYSIWYG

  I am implementing customer specific code and currently following simple approach like if (cusomterId == 23) do it. I want to separate out all the customer related code in separate place. But I have following problems. In code is in 1. Stored procs 2. Plain old classes. 3. Controllers 4. Views I came up with two solutions. First is to create table CustomerFunctionlity with columns CustomerId, FunctionalityName, method/Proc, inputs/outputs With this table I can simply check if exists, execute given function. Another way is creating a factory which returns customer related object for an interface. I am writting small end to end customer specific functionalities. How can I write maintenable code. Thanks

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• Is it better to return NULL or empty values from functions/methods where the return value is not present?

  - by P B

  I am looking for a recommendation here. I am struggling with whether it is better to return NULL or an empty value from a method when the return value is not present or cannot be determined. Take the following two methods as an examples: string ReverseString(string stringToReverse) // takes a string and reverses it. Person FindPerson(int personID) // finds a Person with a matching personID. In ReverseString(), I would say return an empty string because the return type is string, so the caller is expecting that. Also, this way, the caller would not have to check to see if a NULL was returned. In FindPerson(), returning NULL seems like a better fit. Regardless of whether or not NULL or an empty Person Object (new Person()) is returned the caller is going to have to check to see if the Person Object is NULL or empty before doing anything to it (like calling UpdateName()). So why not just return NULL here and then the caller only has to check for NULL. Does anyone else struggle with this? Any help or insight is appreciated.

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• Does C++ support subtyping?

  - by the_naive

  I know it might be a silly question to ask, but I didn't quite get an a absolute clear answer on this matter, so I thought I'd put it here. Does c++ support the subtyping in the sense that it fulfills Liskov's principle fully? I understand how parametric polymorphism, inclusion polymorphism(subclassing and overriding) work in c++ but I'm not entirely sure or understand if subtyping exists in the context of C++. Could you please explain?

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• is it valid that a state machine can have more than one possible state for some transition?

  - by shankbond

  I have a requirement for a workflow which I am trying to model as a state machine, I see that there is more than one outcome of a given transition(or activity). Is it valid for a state machine to have more than one possible states, but only one state will be true at a given time? Note: This is my first attempt to model a state machine. Eg. might be: s1-t1-s2 s1-t1-s3 s1-t1-s4 where s1, s2, s3, s4 are states and t1 is transition/activity. A fictitious real world example might be: For a human, there can be two states: hungry, not hungry A basket can have only one item from: apple, orange. So, to model it we will have: hungry-pick from basket-apple found hungry-pick from basket-orange found apple found-eat-not hungry orange found-take juice out of it and then drink- not hungry

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• ScriptResource.axd Access is denied. Cross-Domain iFrame

  - by EtienneT

  We have a web page containing an iframe containing a page sharing an authentification cookie with it's parent page. For example the iframe page is on the domain foo.domain.com and the page containing the iframe is on foo2.domain.com. Both share a cookie from domain.com. Authentification works great, but the problem is with ASP.NET in IE7, we always get a javascript error: Access is denied. ScriptResource.axd We are using ASP.NET 3.5, we use Ajax Control Toolkit also (latest version 3.0.30930.0). The problem doesn't occur for IE8. No problem in Firefox and Chrome also. Anyone encountered this problem before?

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• Cross-domain jQuery using YQL gives robots.txt error

  - by Jens Roland

  On the page http://qxlapps.dk/test.htm I am trying to perform an Ajax load from another domain, qxlapp.dk. I am using James Padolsey's xdomainajax.js plugin from: http://james.padolsey.com/javascript/cross-domain-requests-with-jquery/ When I open my test page, I get no output, but FireBug shows the JSON result, including the error message: "forbidden":"robots.txt for the domain disallows crawling for url: http://qxlapp.dk/projects/dagens_kup/show.php". The robots.txt on the qxlapp.dk domain contains the following: User-agent: Yahoo Pipes 2.0 Allow: / User-agent: * Allow: / So I don't see what the problem is? Shouldn't it pull the page just fine with those settings?

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• IE History Tracking, IFRAMES, and Cross Domain error...

  - by peiklk

  So here's the deal. We have a Flash application that is running within an HTML file. For one page we call a legacy reporting system in ASP.NET that is within an IFRAME. This page then communicates back to the Flash application using cross-domain scripting (document.domain = "domain" is set in both pages. THIS ALL WORKS. Now the kicker. Flash has history tracking enabled. This loads the history.js file that created a div tag to store page changes so the back and forward buttons work in the browser. Which works for Firefox and Chrome as they create a div tag. HOWEVER In Internet Explorer, history.js creates another IFRAME (instead of a DIV) called ie_historyFrame. When the ScriptResource.axd code attempts to access this with: var frameDoc = this._historyFrame.contentWindow.document; we get an "Access is Denied" error message. ARGH! We've tried getting a handle to this IFRAME and inserting the document.domain code. FAIL. We've tried editing the historytemplate.html file that flex also uses to include document.domain... FAIL. I've tried to edit the underlying ASP.NET page to disable history tracking in the ScriptManager control. FAIL. At my wit's end on this one. We have users who need to use IE to access this site. They are big clients who we cannot tell to just use Firefox. Any suggestions would be greatly appreciated.

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• Value vs Entity objects (Domain Driven Design)

  - by StackUnderflow

  I have just started reading DDD. I am unable to completely grasp the concept of Entity vs Value objects.. Can someone please explain the problems (maintainability, performance.. etc) a system could face when a Value object is designed as a Entity object. Example would be great... Thanks

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• cannot resolve DNS server's own domain name

  - by sims

  I have a DNS server (mega.dude - 123.123.123.123) running bind 9.4. When I: dig mega.dude I get no answer section. I have nameserver 123.123.123.123 in /etc/resolv.conf Here is my zone file: $TTL 1W @ IN SOA mega.dude. names.mega.dude. ( 2009081502 ; serial 3H ; refresh 15M ; retry 1W ; expiry 1D ) ; minimum NS ns1 NS ns2 MX 10 mail.mega.dude. A 123.123.123.123 @ A 123.123.123.123 ns1 A 123.123.123.123 ns2 A 123.123.123.123 www CNAME @ mail A 123.123.123.123 It didn't used to look like this. I read that it's evil to have an mx record pointing to a CNAME. So I changed that. Then I thought maybe that was also the case for NS. So I changed those too. Still no good. The ports are open. I can't figure it out. Oh by the way, all the other zones return fine. But not the servers own domain. So I know I'm doing something stupid. Thanks for your help all!

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• help on ejb stateless datagram and message driven beans

  - by Kemmal

  i have a client thats sending a message to the ejbserver using UDP, i want the server(stateless bean) to echo back this message to the client but i cant seem to do this. or can i implement the same logic by using JMS? please help and enlighten. this is just a test, in the end i want a midp to be sending the message to the ejb using datagrams. here is my code. @Stateless public class SessionFacadeBean implements SessionFacadeRemote { public SessionFacadeBean() { } public static void main(String[] args) { DatagramSocket aSocket = null; byte[] buffer = null; try { while(true) { DatagramPacket request = new DatagramPacket(buffer, buffer.length); aSocket.receive(request); DatagramPacket reply = new DatagramPacket(request.getData(), request.getLength(), request.getAddress(), request.getPort()); aSocket.send(reply); } } catch (SocketException e) { System.out.println("Socket: " + e.getMessage()); } catch (IOException e) { System.out.println("IO: " + e.getMessage()); } finally { if(aSocket != null) aSocket.close(); } } } and the client: public static void main(String[] args) { DatagramSocket aSocket = null; try { aSocket = new DatagramSocket(); byte [] m = "Test message!".getBytes(); InetAddress aHost = InetAddress.getByName("localhost"); int serverPort = 6789; DatagramPacket request = new DatagramPacket(m, m.length, aHost, serverPort); aSocket.send(request); byte[] buffer = new byte[1000]; DatagramPacket reply = new DatagramPacket(buffer, buffer.length); aSocket.receive(reply); System.out.println("Reply: " + new String(reply.getData())); } catch (SocketException e) { System.out.println("Socket: " + e.getMessage()); } catch (IOException e) { System.out.println("IO: " + e.getMessage()); } finally { if(aSocket != null) aSocket.close(); } } please help.

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• Install and enforce a scheduled task across a Windows domain

  - by Ricket

  We have a small domain of about 70 Windows computers (XP and 7). We want to schedule a command (an update mechanism) to run on all computers periodically, and we want the task to run regardless of the computer's connection to our network (i.e. the task should run even on a laptop that isn't connected to our VPN). We have a Microsoft System Center Essentials 2010 server so that might come in handy. The options I see are these: Do it completely manually. Install the scheduled task by hand or remotely using psexec (and the at command?) for each computer in our network. Enforce that newly imaged computers should have this task installed on them before deployed to the employee, or the task should be in the image. High initial cost (having to do this for each of 70 computers) but building it into the image might work... But there is some maintenance in making sure the task is added to everything. And I fear that a year or two down the road, we will have forgotten about it or gotten sloppy or had new IT employees who miss this step and some computers won't have the task. Having one of our servers run a script that loops through all computers and psexec's the command on each computer in the network -- it would only run on running, connected computers, so this solution wouldn't work. I suspect SCE could do something like this too, but again this is not a good solution. Neither of these are ideal, and I'm certain there is a better way to do it -- right? What is the best way to accomplish this task?

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