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• Getting Started with GlassFish 4 and OEPE

  - by gstachni

  Oracle Enterprise Pack for Eclipse 12.1.1.2.2 introduces new support for GlassFish 4.0, the reference implementation of Java EE7.  Getting started with GlassFish 4.0 in Eclipse couldn't be easier. Follow these short steps to get GlassFish 4.0 setup so you can start developing, deploying, and debugging your Java EE7 applications. Prerequisites GlassFish 4.0 Oracle Enterprise Pack for Eclipse 12.1.1.2.2+ from OTN or Eclipse Marketplace Setting up the server connection In the Servers view, click to add a New > Server . Select GlassFish 4.0 from the list of supported server configurations. Pick your GlassFish installation directory (usually <glassfish 4>/glassfish) and select your domain. After you click Finish you should now be setup to launch Glassfish 4.0 in normal and debug mode within Eclipse as well as associate projects for deployment through the Add and Remove wizard. Using GlassFish tools in Eclipse GlassFish server tools provide some useful information about your running GlassFish 4.0 environment. Resources displays current resources deployed in the domain including your JDBC Connection Pool and JDBC Resource names. I find this extra bit of information useful when working with JPA. Deployed Applications shows the current active deployments in GlassFish which can be undeployed as needed from within Eclipse. Deployed Web Services provides information about SOAP-based web services deployed in this domain. Also with the running server are quick launch links to open the Administrative Console, Server Logs, and the GlassFish Community Site all within Eclipse's embedded browser.

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• Why is there no facility to overload static properties in PHP?

  - by Jon

  Intro PHP allows you to overload method calls and property accesses by declaring magic methods in classes. This enables code such as: class Foo { public function __get($name) { return 42; } } $foo = new Foo; echo $foo->missingProperty; // prints "42" Apart from overloading instance properties and methods, since PHP 5.3.0 we can also overload static methods calls by overriding the magic method __callStatic. Something missing What is conspicuously missing from the available functionality is the ability to overload static properties, for example: echo Foo::$missingProperty; // fatal error: access to undeclared static property This limitation is clearly documented: Property overloading only works in object context. These magic methods will not be triggered in static context. Therefore these methods should not be declared static. As of PHP 5.3.0, a warning is issued if one of the magic overloading methods is declared static. But why? My questions are: Is there a technical reason that this functionality is not currently supported? Or perhaps a (shudder) political reason? Have there been any aborted attempts to add this functionality in the past? Most importantly, the question is not "how can I have dynamic static properties in userland PHP?". That said, if you know of an especially cute implementation based on __callStatic that you want to share then by all means do so.

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• Should I use an interface when methods are only similar?

  - by Joshua Harris

  I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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• Go/Obj-C style interfaces with ability to extend compiled objects after initial release

  - by Skrylar

  I have a conceptual model for an object system which involves combining Go/Obj-C interfaces/protocols with being able to add virtual methods from any unit, not just the one which defines a class. The idea of this is to allow Ruby-ish open classes so you can take a minimalist approach to library development, and attach on small pieces of functionality as is actually needed by the whole program. Implementation of this involves a table of methods marked virtual in an RTTI table, which system functions are allowed to add to during module initialization. Upon typecasting an object to an interface, a Go-style lookup is done to create a vtable for that particular mapping and pass it off so you can have comparable performance to C/C++. In this case, methods may be added /afterwards/ which were not previously known and these new methods allow newer interfaces to be satisfied; while I like this idea because it seems like it would be very flexible (disregarding the potential for spaghetti code, which can happen with just about any model you use regardless). By wrapping the system calls for binding methods up in a set of clean C-compatible calls, one would also be able to integrate code with shared libraries and retain a decent amount of performance (Go does not do shared linking, and Objective-C does a dynamic lookup on each call.) Is there a valid use-case for this model that would make it worth the extra background plumbing? As much as this Dylan-style extensibility would be nice to have access to, I can't quite bring myself to a use case that would justify the overhead other than "it could make some kinds of code more extensible in future scenarios."

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• C++ and system exceptions

  - by Abyx

  Why standard C++ doesn't respect system (foreign or hardware) exceptions? E.g. when null pointer dereference occurs, stack isn't unwound, destructors aren't called, and RAII doesn't work. The common advice is "to use system API". But on certain systems, specifically Win32, this doesn't work. To enable stack unwinding for this C++ code // class Foo; // void bar(const Foo&); bar(Foo(1, 2)); one should generate something like this C code Foo tempFoo; Foo_ctor(&tempFoo); __try { bar(&tempFoo); } __finally { Foo_dtor(&tempFoo); } Foo_dtor(&tempFoo); and it's impossible to implement this as C++ library. Upd: Standard doesn't forbid handling system exceptions. But it seems that popular compilers like g++ doesn't respect system exceptions on any platforms just because standard doesn't require this. The only thing that I want - is to use RAII to make code readable and program reliable. I don't want to put hand-crafted try\finally around every call to unknown code. For example in this reusable code, AbstractA::foo is such unknown code: void func(AbstractA* a, AbstractB* b) { TempFile file; a->foo(b, file); } Maybe one will pass to func such implementation of AbstractA, which every Friday will not check if b is NULL, so access violation will happen, application will terminate and temporary file will not be deleted. How many months uses will suffer because of this issue, until either author of func or author of AbstractA will do something with it? Related: Is `catch(...) { throw; }` a bad practice?

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• Website Ethics / legal issues, image copyrights

  - by RailsN00b

  Ignoring the technical implementation of a website for a second, assume a website that is similar to twitter but with pictures. A user say something and puts a picture of whatever they said. As the nature of the internet, the images will most likely not be his/hers image. There are 2 options that I see for dealing with this: 1. The user will post a URL of the picture and the website will pull the picture from that URL everytime someone enters that page 2. The website will save the image in its own database of images and display the image to the visitors 'locally' The problem with option #1, while it saved storage, I see an issue with 'stealing' other websites bandwidth and if my website has many many visitors it could cost the image-hosting websites a lot and possible even crash it if the server can't handle the load. The problem with opion #2, while it saves the load to other websites, it practically takes pictures that could have copyright on them. Which option is better to implement in terms of legal issues and ethics? When do I need to contact another website to request permission to use the images from that site? Does anyone really care about that anymore. Where can I read about this?

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• Floating point undesireable in highly critical code?

  - by Kirt Undercoffer

  Question 11 in the Software Quality section of "IEEE Computer Society Real-World Software Engineering Problems", Naveda, Seidman, lists fp computation as undesirable because "the accuracy of the computations cannot be guaranteed". This is in the context of computing acceleration for an emergency braking system for a high speed train. This thinking seems to be invoking possible errors in small differences between measurements of a moving object but small differences at slow speeds aren't a problem (or shouldn't be), small differences between two measurements at high speed are irrelevant - can there be a problem with small roundoff errors during deceleration for an emergency braking system? This problem has been observed with airplane braking systems resulting in hydroplaning but could this actually happen in the context of a high speed train? The concern about fp errors seems to not be well-founded in this context. Any insight? The fp is used for acceleration so perhaps the concern is inching over a speed limit? But fp should be just fine if they use a double in whatever implementation language. The actual problem in the text states: During the inspection of the code for the emergency braking system of a new high speed train (a highly critical, real-time application), the review team identifies several characteristics of the code. Which of these characteristics are generally viewed as undesirable? The code contains three recursive functions (well that one is obvious). The computation of acceleration uses floating point arithmetic. All other computations use integer arithmetic. The code contains one linked list that uses dynamic memory allocation (second obvious problem). All inputs are checked to determine that they are within expected bounds before they are used.

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• How to deal with a CEO making all technical decision but with little technical knowledge ?

  - by anonymous

  Hi, Question posted anonymously for obvious reasons. I am working in a company with a dev group of 5-6 developers, and I am in a situation which I have a hard time dealing with. Every technical choice (language, framework, database, database scheme, configuration scheme, etc...) is decided by the CEO, often without much rationale. It is very hard to modify those choices, and his main argument consists in "I don't like this", even though we propose several alternative with detailed pros/cons. He will also decide to rewrite from scratch our core product without giving a reason why, and he never participates to dev meetings because he considers it makes things slower... I am already looking at alternative job opportunities, but I was wondering if there anything we (the developers) could do to improve the situation. Two examples which shocked me: he will ask us to implement something akin to configuration management, but he reject any existing framework because they are not written in the language he likes (even though the implementation language is irrelevant). He also expects us to be able to write those systems in a couple of days, "because it is very simple". he keeps rewriting from scratch on his own our core product because the current codebase is too bad (codebase whose design was his). We are at our third rewrite in one year, each rewrite worse than the previous one. Things I have tried so far is doing elaborate benchmarks on our product (he keeps complaining that our software is too slow, and justifies rewrites to make it faster), implement solutions with existing products as working proof instead of just making pros/cons charts, etc... But still 90 % of those efforts go to the trashbox (never with any kind of rationale behind he does not like it, again), and often get reprimanded because I don't do exactly as he wants (not realizing that what he wants is impossible).

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• Sitecore Item Web API and Json.Net Test Drive (Part II –Strongly Typed)

  - by jonel

  In the earlier post I did related to this topic, I have talked about using Json.Net to consume the result of Sitecore Item Web API. In that post, I have used the keyword dynamic to express my intention of consuming the returned json of the API. In this article, I will create some useful classes to write our implementation of consuming the API using strongly-typed. We will start of with the Record class which will hold the top most elements the API will present us. Pretty straight forward class. It has 2 properties to hold the statuscode and the result elements. If you intend to use a different property name in your class from the json property, you can do so by passing a string literal of the json property name to the JsonProperty attribute and name your class property differently. If you look at the earlier post, you will notice that the API returns an array of items that contains all of the Sitecore content item or items and stores them under the result->items array element. To be able to map that array of items, we have to write a collection property and decorate that with the JsonProperty attribute. The JsonItem class is a simple class which will map to the corresponding item property contained in the array. If you notice, these properties are just the basic Sitecore fields. And here’s the main portion of this post that will binds them all together. And here’s the output of this code. In closing, the same result can be achieved using the dynamic keyword or defining classes to map the json propery returned by the Sitecore Item Web API. With a little bit more of coding, you can take advantage of power of strongly-typed solution. Have a good week ahead of you.

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• The most mind-bending programming language? [closed]

  - by Xepoch

  From a reasonably common programming language, which do you find to be the most mind-bending? I have been listening to a lot of programming podcasts and taking some time to learn some new languages that are being considered upcoming, and important. I'm not necessarily talking about BrainFuck, but which language would you consider to be one that challenges the common programming paradigms? For me, I did some functional and logic (ex. Prolog) programming in the 90s, so can't say that I find anything special there. I am far from being an expert in it, but even today the most mind-bending programming language for me is Perl. Not because "Hello World" is hard to implement but rather there is so much lexical flexibility that some of the hardest solutions can be decomposed so poetically that I have to walk outside away from my terminal to clear my head. I'm not saying I'd likely sell a commercial software implementation, just that there is a distinct reason Perl is so (in)famous. Just look at the basic list of books on it. So, what is your mind-bending language that promotes your better programming and practices?

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• Ninject/DI: How to correctly pass initialisation data to injected type at runtime

  - by MrLane

  I have the following two classes: public class StoreService : IStoreService { private IEmailService _emailService; public StoreService(IEmailService emailService) { _emailService = emailService; } } public class EmailService : IEmailService { } Using Ninject I can set up bindings no problem to get it to inject a concrete implementation of IEmailService into the StoreService constructor. StoreService is actually injected into the code behind of an ASP.NET WebForm as so: [Ninject.Inject] public IStoreService StoreService { get; set; } But now I need to change EmailService to accept an object that contains SMTP related settings (that are pulled from the ApplicationSettings of the Web.config). So I changed EmailService to now look like this: public class EmailService : IEmailService { private SMTPSettings _smtpSettings; public void SetSMTPSettings(SMTPSettings smtpSettings) { _smtpSettings = smtpSettings; } } Setting SMTPSettings in this way also requires it to be passed into StoreService (via another public method). This has to be done in the Page_Load method in the WebForms code behind (I only have access to the Settings class in the UI layer). With manual/poor mans DI I could pass SMTPSettings directly into the constructor of EmailService and then inject EmailService into the StoreService constructor. With Ninject I don't have access to the instances of injected types outside of the objects they are injected to, so I have to set their data AFTER Ninject has already injected them via a separate public setter method. This to me seems wrong. How should I really be solving this scenario?

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• Can JSON be made easily and safely editable by the non-technical Excel crowd?

  - by glitch

  I'm looking for a data storage format that's very intuitive and easy to edit. It should be ideally targeted towards the same crowd as Excel. At the same time I would like the data structure to be a tree. Ideally this would be JSON, since it offers both the tree aspect and allows for more interesting constructs like arrays. That and parsing libraries for JSON are ubiquitous, so I don't have to reinvent the wheel. The problem is that, at least with a non-specialized text editor, JSON is a giant pain to edit for a non-technical user. I'm thinking along the lines of someone who might have used Excel in the past, but never a real text editor. Someone who might not be comfortable with the idea of preserving JSON syntax by hand. Are there data formats out there that would fit this profile? I'd very much prefer this to be a JSON actually, but then it would require a solid editing tool that would hide the underlying implementation from the user. Think Excel and how it abstracts CSV syntax from the user. The reason I'm looking for something like this is because the team has been working with pretty hierarchical data for a while now and we've hit the limits of how easy it is to represent in simple CSVs without having to create complex rules for how represent hierarchy semantics from each row. Any suggestions?

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• Implicit OAuth2 endpoint vs. cookies

  - by Jamie

  I currently have an app which basically runs two halves of an API - a restful API for the web app, and a synchronisation API for the native clients (all over SSL). The web app is completely javascript based and is quite similar to the native clients anyway - except it currently does not work offline. What I'm hoping to do is merge the fragmented APIs into a single restful API. The web app currently authenticates by issuing a cookie to the client whereas the native clients work using a custom HMAC access token implementation. Obviously a public/private key scenario for a javascript app is a little pointless. I think the best solution would be to create an OAuth2 endpoint on the API (like Instagram, for example http://instagram.com/developer/authentication/) which is used by both the native apps and the web app. My question is, in terms of security how does an implicit OAuth2 flow compare (storing the access token in local storage) to "secure" cookies? Presumably although SSL solves man in the middle attacks, the user could theoretically grab the access token from local storage and copy it to another machine?

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• Proper updating of GeoClipMaps

  - by thr

  I have been working on an implementation of gpu-based geo clip maps, but there is a section of the GPU Gems 2 article that i just can't seem to understand, specifically this paragraph and more precisely the bolded part: The choice of grid size n = 2k-1 has the further advantage that the finer level is never exactly centered with respect to its parent next-coarser level. In other words, it is always offset by 1 grid unit either left or right, as well as either top or bottom (see Figure 2-4), depending on the position of the viewpoint. In fact, it is necessary to allow a finer level to shift while its next-coarser level stays fixed, and therefore the finer level must sometimes be off-center with respect to the next-coarser level. An alternative choice of grid size, such as n = 2k-3, would provide the possibility for exact centering Let's take an example image from the article: My "understanding" of the way the clip maps were update was that you floor the position of the viewpoint to an int, and such get the center vertex point if this is not the same as the previous center point, you update the entire map. Now, this obviously is not the case - but what I am failing to understand is this: If you look at the image above, if the viewpoint was to move one unit to the right, then the inner ring (the one just around the view point + white center square) would end up getting a 1 unit space on both the left and right side of itself. But there is nothing in the paper that deals with this, what i mean is that it would end up looking like this (excuse my crummy cut-and-paste editing of the above image): This is obviously not a valid state of the. So, would the solution be that a clip ring (layer) can only move in increments of the ring/layer it's contained within? Wouldn't this end up being very restrictive? I feel like I am missing some crucial understanding of parts of the algorithm, but I have been over both this paper and the original paper from 2004 and I just can't see what I am not getting.

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• Configuring Team Foundation Server Basic on Home Server.

  - by Enrique Lima

  For the installation I selected only the Team Foundation Server role. Then, I opened the Team Foundation Server Administration Console (which I think is a great addition and improvement over the way TFS was configured in the past) to proceed with the configuration of the pieces. Once I selected the Configure Installed Features, the Configuration Center opened up. Now, the choices … In my implementation here I just want to take advantage of Source Control primarily.  I want to be able to store my code and projects.  So, Basic it is! So, the Basic Configuration Wizard opens up.  Now the options to configure are very limited, but we have to provide details for the SQL Server Instance. And now, to select Install SQL Server express.  If you want to take advantage of another system in your environment to host your database, well you could Use an existing SQL Server Instance. Once it has the details it needs, you get a Summary view to confirm your choices. Once, you click next or verify, it runs readiness checks on your system to make sure the installation will have a successful pass.  And we love GREEN! Now, since got the green flag, our next stop is to let the wizard do its magic, click on Configure.  And once again, we love GREEN! We click Next, and … We like a big Green Success sign … We close the Configuration Center … First results … Web Access …  Nothing to show … but we are there! And all this running from a Microsoft Home Server installation.

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• sqlplus: Running "set lines" and "set pagesize" automatially

  - by katsumii

  This is a followup to my previous entry. Using the full tty real estate with sqlplus (INOUE Katsumi @ Tokyo) 'rlwrap' is widely used for adding 'sqlplus' the history function and command line editing. Here's another but again kludgy implementation. First this is the alias. alias sqlplus="rlwrap -z ~/sqlplus.filter sqlplus" And this is the file content. #!/usr/bin/env perl use lib ($ENV{RLWRAP_FILTERDIR} or "."); use RlwrapFilter; use POSIX qw(:signal_h); use strict; my $filter = new RlwrapFilter; $filter -> prompt_handler(\&prompt); sigprocmask(SIG_UNBLOCK, POSIX::SigSet->new(28)); $SIG{WINCH} = 'winchHandler'; $filter -> run; sub winchHandler { $filter -> input_handler(\&input); sigprocmask(SIG_UNBLOCK, POSIX::SigSet->new(28)); $SIG{WINCH} = 'winchHandler'; $filter -> run; } sub input { $filter -> input_handler(undef); return `resize |sed -n "1s/COLUMNS=/set linesize /p;2s/LINES=/set pagesize /p"` . $_; } sub prompt { if ($_ =~ "SQL> ") { $filter -> input_handler(\&input); $filter -> prompt_handler(undef); } return $_; } I hope I can compare these 2 implementations after testing more and getting some feedbacks.

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• How to structure my GUI agnostic project?

  - by Nezreli

  I have a project which loads from database a XML file which defines a form for some user. XML is transformed into a collection of objects whose classes derive from single parent. Something like Control - EditControl - TextBox Control - ContainterControl - Panel Those classes are responsible for creation of GUI controls for three different enviroments: WinForms, DevExpress XtraReports and WebForms. All three frameworks share mostly the same control tree and have a common single parent (Windows.Forms.Control, XrControl and WebControl). So, how to do it? Solution a) Control class has abstract methods Control CreateWinControl(); XrControl CreateXtraControl(); WebControl CreateWebControl(); This could work but the project has to reference all three frameworks and the classes are going to be fat with methods which would support all three implementations. Solution b) Each framework implementation is done in separate projects and have the exact class tree like the Core project. All three implementations are connected using a interface to the Core class. This seems clean but I'm having a hard time wrapping my head around it. Does anyone have a simpler solution or a suggestion how should I approach this task?

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• How can Highscores be more meaningful and engaging?

  - by Anselm Eickhoff

  I'm developing a casual Android game in which the player's success can very easily be represented by a number (I'm not more specific because I'm interested in the topic in general). Although I myself am not a highscore person at all, I was thinking of implementing a highscore for that game, but I see at least 2 problems in the classical leaderboard approach: very soon the highscore will be dominated by hardcore players, leaving no chance for beginners, who are then frustrated. This is very severe especially in casual games. there is no direct reward for being a loyal player who plays the game over and over again My current idea is to "reset" the highscore every 24 hours (for example) and each day nominate the "player of the day" who then gets a "star". Then there would be some kind of meta-highscore of players with the most stars. That way even beginners might have a chance to be "player of the day" once and continued or repeated play is rewarded much more. The idea is still very rough and there are many problems in the details and the technical implementation but I have a feeling it is a step in the right direction. Do you have creative and new ideas on how to implement highscores? Which games are doing this well / what types of highscores do you find most engaging?

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• Using a permutation table for simplex noise without storing it

  - by J. C. Leitão

  Generating Simplex noise requires a permutation table for randomisation (e.g. see this question or this example). In some applications, we need to persist the state of the permutation table. This can be done by creating the table, e.g. using def permutation_table(seed): table_size = 2**10 # arbitrary for this question l = range(1, table_size + 1) random.seed(seed) # ensures the same shuffle for a given seed random.shuffle(l) return l + l # see shared link why l + l; is a detail and storing it. Can we avoid storing the full table by generating the required elements every time they are required? Specifically, currently I store the table and call it using table[i] (table is a list). Can I avoid storing it by having a function that computes the element i, e.g. get_table_element(seed, i). I'm aware that cryptography already solved this problem using block cyphers, however, I found it too complex to go deep and implement a block cypher. Does anyone knows a simple implementation of a block cypher to this problem?

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• What is logical cohesion, and why is it bad or undesirable?

  - by Matt Fenwick

  From the c2wiki page on coupling & cohesion: Cohesion (interdependency within module) strength/level names : (from worse to better, high cohesion is good) Coincidental Cohesion : (Worst) Module elements are unrelated Logical Cohesion : Elements perform similar activities as selected from outside module, i.e. by a flag that selects operation to perform (see also CommandObject). i.e. body of function is one huge if-else/switch on operation flag Temporal Cohesion : operations related only by general time performed (i.e. initialization() or FatalErrorShutdown?()) Procedural Cohesion : Elements involved in different but sequential activities, each on different data (usually could be trivially split into multiple modules along linear sequence boundaries) Communicational Cohesion : unrelated operations except need same data or input Sequential Cohesion : operations on same data in significant order; output from one function is input to next (pipeline) Informational Cohesion: a module performs a number of actions, each with its own entry point, with independent code for each action, all performed on the same data structure. Essentially an implementation of an abstract data type. i.e. define structure of sales_region_table and its operators: init_table(), update_table(), print_table() Functional Cohesion : all elements contribute to a single, well-defined task, i.e. a function that performs exactly one operation get_engine_temperature(), add_sales_tax() (emphasis mine). I don't fully understand the definition of logical cohesion. My questions are: what is logical cohesion? Why does it get such a bad rap (2nd worst kind of cohesion)?

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• Which is a better practice - helper methods as instance or static?

  - by Ilian Pinzon

  This question is subjective but I was just curious how most programmers approach this. The sample below is in pseudo-C# but this should apply to Java, C++, and other OOP languages as well. Anyway, when writing helper methods in my classes, I tend to declare them as static and just pass the fields if the helper method needs them. For example, given the code below, I prefer to use Method Call #2. class Foo { Bar _bar; public void DoSomethingWithBar() { // Method Call #1. DoSomethingWithBarImpl(); // Method Call #2. DoSomethingWithBarImpl(_bar); } private void DoSomethingWithBarImpl() { _bar.DoSomething(); } private static void DoSomethingWithBarImpl(Bar bar) { bar.DoSomething(); } } My reason for doing this is that it makes it clear (to my eyes at least) that the helper method has a possible side-effect on other objects - even without reading its implementation. I find that I can quickly grok methods that use this practice and thus help me in debugging things. Which do you prefer to do in your own code and what are your reasons for doing so?

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• Canonical representation of a class object containing a list element in XML

  - by dendini

  I see that most implementations of JAX-RS represent a class object containing a list of elements as follows (assume a class House containing a list of People) <houses> <house> <person> <name>Adam</name> </person> <person> <name>Blake</name> </person> </house> <house> </house> </houses> The result above is obtained for instance from Jersey 2 JAX-RS implementation, notice Jersey creates a wrapper class "houses" around each house, however strangely it doesn't create a wrapper class around each person! I don't feel this is a correct mapping of a list, in other words I'd feel more confortable with something like this: <houses> <house> <persons> <person> <name>Adam</name> </person> <person> <name>Blake</name> </person> </persons> </house> <house> </house> </houses> Is there any document explaining how an object should be correctly mapped apart from any opninion?

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• Is an event loop just a for/while loop with optimized polling?

  - by Alan

  I'm trying to understand what an event loop is. Often the explanation is that in the event loop, you do something until you're notified that an event occurred. You than handle the event and continue doing what you did before. To map the above definition with an example. I have a server which 'listens' in a event loop, and when a socket connection is detected, the data from it gets read and displayed, after which the server goes to the listening it did before. However, this event happening and us getting notified 'just like that' are to much for me to handle. You can say: "It's not 'just like that' you have to register an event listener". But what's an event listener but a function which for some reason isn't returning. Is it in it's own loop, waiting to be notified when an event happens? Should the event listener also register an event listener? Where does it end? Events are a nice abstraction to work with, however just an abstraction. I believe that in the end, polling is unavoidable. Perhaps we are not doing it in our code, but the lower levels (the programming language implementation or the OS) are doing it for us. It basically comes down to the following pseudo code which is running somewhere low enough so it doesn't result in busy waiting: while(True): do stuff check if event has happened (poll) do other stuff This is my understanding of the whole idea, and i would like to hear if this is correct. I am open in accepting that the whole idea is fundamentally wrong, in which case I would like the correct explanation. Best regards

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• Using runtime generic type reflection to build a smarter DAO

  - by kerry

  Have you ever wished you could get the runtime type of your generic class? I wonder why they didn’t put this in the language. It is possible, however, with reflection: Consider a data access object (DAO) (note: I had to use brackets b/c the arrows were messing with wordpress): public interface Identifiable { public Long getId(); } public interface Dao { public T findById(Long id); public void save(T obj); public void delete(T obj); } Using reflection, we can create a DAO implementation base class, HibernateDao, that will work for any object: import java.lang.reflect.Field; import java.lang.reflect.ParameterizedType; public class HibernateDao implements Dao { private final Class clazz; public HibernateDao(Session session) { // the magic ParameterizedType parameterizedType = (ParameterizedType) clazz.getGenericSuperclass(); return (Class) parameterizedType.getActualTypeArguments()[0]; } public T findById(Long id) { return session.get(clazz, id); } public void save(T obj) { session.saveOrUpdate(obj); } public void delete(T obj) { session.delete(obj); } } Then, all we have to do is extend from the class: public class BookDaoHibernateImpl extends HibernateDao { }

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• How to document requirements for an API systematically?

  - by Heinrich

  I am currently working on a project, where I have to analyze the requirements of two given IT systems, that use cloud computing, for a Cloud API. In other words, I have to analyze what requirements these systems have for a Cloud API, such that they would be able to switch it, while being able to accomplish their current goals. Let me give you an example for some informal requirements of Project A: When starting virtual machines in the cloud through the API, it must be possible to specify the memory size, CPU type, operating system and a SSH key for the root user. It must be possible to monitor the inbound and outbound network traffic per hour per virtual machine. The API must support the assignment of public IPs to a virtual machine and the retrieval of the public IPs. ... In a later stage of the project I will analyze some Cloud Computing standards that standardize cloud APIs to find out where possible shortcomings in the current standards are. A finding could and will probably be, that a certain standard does not support monitoring resource usage and thus is not currently usable. I am currently trying to find a way to systematically write down and classify my requirements. I feel that the way I currently have them written down (like the three points above) is too informal. I have read in a couple of requirements enineering and software architecture books, but they all focus too much on details and implementation. I do really only care about the functionalities provided through the API/interface and I don't think UML diagrams etc. are the right choice for me. I think currently the requirements that I collected can be described as user stories, but is that already enough for a sophisticated requirements analysis? Probably I should go "one level deeper" ... Any advice/learning resources for me?

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