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• A Basic Thread

  - by Joe Mayo

  Most of the programs written are single-threaded, meaning that they run on the main execution thread. For various reasons such as performance, scalability, and/or responsiveness additional threads can be useful. .NET has extensive threading support, from the basic threads introduced in v1.0 to the Task Parallel Library (TPL) introduced in v4.0. To get started with threads, it's helpful to begin with the basics; starting a Thread. Why Do I Care? The scenario I'll use for needing to use a thread is writing to a file.  Sometimes, writing to a file takes a while and you don't want your user interface to lock up until the file write is done. In other words, you want the application to be responsive to the user. How Would I Go About It? The solution is to launch a new thread that performs the file write, allowing the main thread to return to the user right away.  Whenever the file writing thread completes, it will let the user know.  In the meantime, the user is free to interact with the program for other tasks. The following examples demonstrate how to do this. Show Me the Code? The code we'll use to work with threads is in the System.Threading namespace, so you'll need the following using directive at the top of the file: using System.Threading; When you run code on a thread, the code is specified via a method.  Here's the code that will execute on the thread: private static void WriteFile() { Thread.Sleep(1000); Console.WriteLine("File Written."); } The call to Thread.Sleep(1000) delays thread execution. The parameter is specified in milliseconds, and 1000 means that this will cause the program to sleep for approximately 1 second.  This method happens to be static, but that's just part of this example, which you'll see is launched from the static Main method.  A thread could be instance or static.  Notice that the method does not have parameters and does not have a return type. As you know, the way to refer to a method is via a delegate.  There is a delegate named ThreadStart in System.Threading that refers to a method without parameters or return type, shown below: ThreadStart fileWriterHandlerDelegate = new ThreadStart(WriteFile); I'll show you the whole program below, but the ThreadStart instance above goes in the Main method. The thread uses the ThreadStart instance, fileWriterHandlerDelegate, to specify the method to execute on the thread: Thread fileWriter = new Thread(fileWriterHandlerDelegate); As shown above, the argument type for the Thread constructor is the ThreadStart delegate type. The fileWriterHandlerDelegate argument is an instance of the ThreadStart delegate type. This creates an instance of a thread and what code will execute, but the new thread instance, fileWriter, isn't running yet. You have to explicitly start it, like this: fileWriter.Start(); Now, the code in the WriteFile method is executing on a separate thread. Meanwhile, the main thread that started the fileWriter thread continues on it's own.  You have two threads running at the same time. Okay, I'm Starting to Get Glassy Eyed. How Does it All Fit Together? The example below is the whole program, pulling all the previous bits together. It's followed by its output and an explanation. using System; using System.Threading; namespace BasicThread { class Program { static void Main() { ThreadStart fileWriterHandlerDelegate = new ThreadStart(WriteFile); Thread fileWriter = new Thread(fileWriterHandlerDelegate); Console.WriteLine("Starting FileWriter"); fileWriter.Start(); Console.WriteLine("Called FileWriter"); Console.ReadKey(); } private static void WriteFile() { Thread.Sleep(1000); Console.WriteLine("File Written"); } } } And here's the output: Starting FileWriter Called FileWriter File Written So, Why are the Printouts Backwards? The output above corresponds to Console.Writeline statements in the program, with the second and third seemingly reversed. In a single-threaded program, "File Written" would print before "Called FileWriter". However, this is a multi-threaded (2 or more threads) program.  In multi-threading, you can't make any assumptions about when a given thread will run.  In this case, I added the Sleep statement to the WriteFile method to greatly increase the chances that the message from the main thread will print first. Without the Thread.Sleep, you could run this on a system with multiple cores and/or multiple processors and potentially get different results each time. Interesting Tangent but What Should I Get Out of All This? Going back to the main point, launching the WriteFile method on a separate thread made the program more responsive.  The file writing logic ran for a while, but the main thread returned to the user, as demonstrated by the print out of "Called FileWriter".  When the file write finished, it let the user know via another print statement. This was a very efficient use of CPU resources that made for a more pleasant user experience. Joe

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• IsNullOrEmpty generic method for Array to avoid Re-Sharper warning

  - by Michael Freidgeim

  I’ve used the following extension method in many places. public static bool IsNullOrEmpty(this Object[] myArr) { return (myArr == null || myArr.Length == 0); }Recently I’ve noticed that Resharper shows warning covariant array conversion to object[] may cause an exception for the following codeObjectsOfMyClass.IsNullOrEmpty()I’ve resolved the issue by creating generic extension method public static bool IsNullOrEmpty<T>(this T[] myArr) { return (myArr == null || myArr.Length == 0); }Related linkshttp://connect.microsoft.com/VisualStudio/feedback/details/94089/add-isnullorempty-to-array-class    public static bool IsNullOrEmpty(this System.Collections.IEnumerable source)        {            if (source == null)                return true;            else            {                return !source.GetEnumerator().MoveNext();            }        }http://stackoverflow.com/questions/8560106/isnullorempty-equivalent-for-array-c-sharp

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• "Imprinting" as a language feature?

  - by MKO

  Idea I had this idea for a language feature that I think would be useful, does anyone know of a language that implements something like this? The idea is that besides inheritance a class can also use something called "imprinting" (for lack of better term). A class can imprint one or several (non-abstract) classes. When a class imprints another class it gets all it's properties and all it's methods. It's like the class storing an instance of the imprinted class and redirecting it's methods/properties to it. A class that imprints another class therefore by definition also implements all it's interfaces and it's abstract class. So what's the point? Well, inheritance and polymorphism is hard to get right. Often composition gives far more flexibility. Multiple inheritance offers a slew of different problems without much benefits (IMO). I often write adapter classes (in C#) by implementing some interface and passing along the actual methods/properties to an encapsulated object. The downside to that approach is that if the interface changes the class breaks. You also you have to put in a lot of code that does nothing but pass things along to the encapsulated object. A classic example is that you have some class that implements IEnumerable or IList and contains an internal class it uses. With this technique things would be much easier Example (c#) [imprint List<Person> as peopleList] public class People : PersonBase { public void SomeMethod() { DoSomething(this.Count); //Count is from List } } //Now People can be treated as an List<Person> People people = new People(); foreach(Person person in people) { ... } peopleList is an alias/variablename (of your choice)used internally to alias the instance but can be skipped if not needed. One thing that's useful is to override an imprinted method, that could be achieved with the ordinary override syntax public override void Add(Person person) { DoSomething(); personList.Add(person); } note that the above is functional equivalent (and could be rewritten by the compiler) to: public class People : PersonBase , IList<Person> { private List<Person> personList = new List<Person>(); public override void Add(object obj) { this.personList.Add(obj) } public override int IndexOf(object obj) { return personList.IndexOf(obj) } //etc etc for each signature in the interface } only if IList changes your class will break. IList won't change but an interface that you, someone in your team, or a thirdparty has designed might just change. Also this saves you writing a whole lot of code for some interfaces/abstract classes. Caveats There's a couple of gotchas. First we, syntax must be added to call the imprinted classes's constructors from the imprinting class constructor. Also, what happends if a class imprints two classes which have the same method? In that case the compiler would detect it and force the class to define an override of that method (where you could chose if you wanted to call either imprinted class or both) So what do you think, would it be useful, any caveats? It seems it would be pretty straightforward to implement something like that in the C# language but I might be missing something :) Sidenote - Why is this different from multiple inheritance Ok, so some people have asked about this. Why is this different from multiple inheritance and why not multiple inheritance. In C# methods are either virtual or not. Say that we have ClassB who inherits from ClassA. ClassA has the methods MethodA and MethodB. ClassB overrides MethodA but not MethodB. Now say that MethodB has a call to MethodA. if MethodA is virtual it will call the implementation that ClassB has, if not it will use the base class, ClassA's MethodA and you'll end up wondering why your class doesn't work as it should. By the terminology sofar you might already confused. So what happens if ClassB inherits both from ClassA and another ClassC. I bet both programmers and compilers will be scratching their heads. The benefit of this approach IMO is that the imprinting classes are totally encapsulated and need not be designed with multiple inheritance in mind. You can basically imprint anything.

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• /etc/network/interfaces doesn't always take affect

  - by user1221444

  For some reason my eth0 does not have internet on reboot sometimes. I am using a static ip. I can ping my gateway, but I am unable to ping dns servers, or anything out of my network. It seems that when my internet does work(Usually but just restarting enough times), my /etc/resolv.conf has a nameserver in it. It is empty when I have no internet access. I believe something is overwriting my interfaces settings sometimes on boot. Any help would be appreciated. I am running Ubuntu Server 12.04 64bit /etc/network/interfaces: auto lo iface lo inet loopback auto eth0 iface eth0 inet static address 173.213.192.234 netmask 255.255.255.248 network 173.213.192.232 broadcast 173.213.192.239 gateway 173.213.192.233 dns-nameservers 8.8.8.8 auto eth1 iface eth1 inet static address 10.0.0.106 netmask 255.255.255.0 gateway 10.0.0.1

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• Avoiding coupling

  - by Seralize

  It is also true that a system may become so coupled, where each class is dependent on other classes that depend on other classes, that it is no longer possible to make a change in one place without having a ripple effect and having to make subsequent changes in many places.[1] This is why using an interface or an abstract class can be valuable in any object-oriented software project. Quote from Wikipedia Starting from scratch I'm starting from scratch with a project that I recently finished because I found the code to be too tightly coupled and hard to refactor, even when using MVC. I will be using MVC on my new project aswell but want to try and avoid the pitfalls this time, hopefully with your help. Project summary My issue is that I really wish to keep the Controller as clean as possible, but it seems like I can't do this. The basic idea of the program is that the user picks wordlists which is sent to the game engine. It will pick random words from the lists until there are none left. Problem at hand My main problem is that the game will have 'modes', and need to check the input in different ways through a method called checkWord(), but exactly where to put this and how to abstract it properly is a challenge to me. I'm new to design patterns, so not sure whether there exist any might fit my problem. My own attempt at abstraction Here is what I've gotten so far after hours of 'refactoring' the design plans, and I know it's long, but it's the best I could do to try and give you an overview (Note: As this is the sketch, anything is subject to change, all help and advice is very welcome. Also note the marked coupling points): Wordlist class Wordlist { // Basic CRUD etc. here! // Other sample methods: public function wordlistCount($user_id) {} // Returns count of how many wordlists a user has public function getAll($user_id) {} // Returns all wordlists of a user } Word class Word { // Basic CRUD etc. here! // Other sample methods: public function wordCount($wordlist_id) {} // Returns count of words in a wordlist public function getAll($wordlist_id) {} // Returns all words from a wordlist public function getWordInfo($word_id) {} // Returns information about a word } Wordpicker class Wordpicker { // The class needs to know which words and wordlists to exclude protected $_used_words = array(); protected $_used_wordlists = array(); // Wordlists to pick words from protected $_wordlists = array(); /* Public Methods */ public function setWordlists($wordlists = array()) {} public function setUsedWords($used_words = array()) {} public function setUsedWordlists($used_wordlists = array()) {} public function getRandomWord() {} // COUPLING POINT! Will most likely need to communicate with both the Wordlist and Word classes /* Protected Methods */ protected function _checkAvailableWordlists() {} // COUPLING POINT! Might need to check if wordlists are deleted etc. protected function _checkAvailableWords() {} // COUPLING POINT! Method needs to get all words in a wordlist from the Word class } Game class Game { protected $_session_id; // The ID of a game session which gets stored in the database along with game details protected $_game_info = array(); // Game instantiation public function __construct($user_id) { if (! $this->_session_id = $this->_gameExists($user_id)) { // New game } else { // Resume game } } // This is the method I tried to make flexible by using abstract classes etc. // Does it even belong in this class at all? public function checkWord($answer, $native_word, $translation) {} // This method checks the answer against the native word / translation word, depending on game mode public function getGameInfo() {} // Returns information about a game session, or creates it if it does not exist public function deleteSession($session_id) {} // Deletes a game session from the database // Methods dealing with game session information protected function _gameExists($user_id) {} protected function _getProgress($session_id) {} protected function _updateProgress($game_info = array()) {} } The Game /* CONTROLLER */ /* "Guess the word" page */ // User input $game_type = $_POST['game_type']; // Chosen with radio buttons etc. $wordlists = $_POST['wordlists']; // Chosen with checkboxes etc. // Starts a new game or resumes one from the database $game = new Game($_SESSION['user_id']); $game_info = $game->getGameInfo(); // Instantiates a new Wordpicker $wordpicker = new Wordpicker(); $wordpicker->setWordlists((isset($game_info['wordlists'])) ? $game_info['wordlists'] : $wordlists); $wordpicker->setUsedWordlists((isset($game_info['used_wordlists'])) ? $game_info['used_wordlists'] : NULL); $wordpicker->setUsedWords((isset($game_info['used_words'])) ? $game_info['used_words'] : NULL); // Fetches an available word if (! $word_id = $wordpicker->getRandomWord()) { // No more words left - game over! $game->deleteSession($game_info['id']); redirect(); } else { // Presents word details to the user $word = new Word(); $word_info = $word->getWordInfo($word_id); } The Bit to Finish /* CONTROLLER */ /* "Check the answer" page */ // ?????????????????? ( http://pastebin.com/cc6MtLTR ) Make sure you toggle the 'Layout Width' to the right for a better view. Thanks in advance. Questions To which extent should objects be loosely coupled? If object A needs info from object B, how is it supposed to get this without losing too much cohesion? As suggested in the comments, models should hold all business logic. However, as objects should be independent, where to glue them together? Should the model contain some sort of "index" or "client" area which connects the dots? Edit: So basically what I should do for a start is to make a new model which I can more easily call with oneliners such as $model->doAction(); // Lots of code in here which uses classes! How about the method for checking words? Should it be it's own object? I'm not sure where I should put it as it's pretty much part of the 'game'. But on another hand, I could just leave out the 'abstraction and OOPness' and make it a method of the 'client model' which will be encapsulated from the controller anyway. Very unsure about this.

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• Tip #19 Module Private Visibility in OSGi

  - by ByronNevins

  I hate public and protected methods and classes.  It requires so much work to change them in a huge project like GlassFish.  Not to mention that you may well have to support those APIs forever.  They are highly overused in GlassFish.  In fact I'd bet that > 95% of classes are marked as public for no good reason.  It's just (bad) habit is my guess. private and default visibility (I call it package-private) is easier to maintain.  It is much much easier to change such classes and methods around.  If you have ANY public method or public class in GlassFish you'll need to grep through a tremendous amount of source code to find all callers.  But even that won't be theoretically reliable.  What if a caller is using reflection to access public methods?  You may never find such usages. If you have package private methods, it's easy.  Simply grep through all the code in that one package.  As long as that package compiles ok you're all set.  There can' be any compile errors anywhere else.  It's a waste of time to even look around or build the "outside" world.  So you may be thinking: "Aha!  I'll just make my module have one giant package with all the java files.  Then I can use the default visibility and maintenance will be much easier.  But there's a problem.  You are wasting a very nice feature of java -- organizing code into separate packages.  It also makes the code much more encapsulated.  Unfortunately to share code between the packages you have no choice but to declare public visibility. What happens in practice is that a module ends up having tons of public classes and methods that are used exclusively inside the module.  Which finally brings me to the point of this blog:  If Only There Was A Module-Private Visibility Available Well, surprise!  There is such a mechanism.  If your project is running under OSGi that is.  Like GlassFish does!  With this mechanism you can easily add another level of visibility by telling OSGi exactly which public you want to be exposed outside of the module.  You get the best of both worlds: Better encapsulation of your code so that maintenance is easier and productivity is increased. Usage of public visibility inside the module so that you can encapsulate intra-module better with packages. How I do this in GlassFish: Carefully plan out at least one package that will contain "true" publics.  This is the package that will be exported by OSGi.  I recommend just one package. Here is how to tell OSGi to use it in GlassFish -- edit osgi.bundle like so:-exportcontents:     org.glassfish.mymodule.truepublics;  version=${project.osgi.version} Now all publics declared in any other packages will be visible module-wide but not outside the module. There is one caveat: Accessing "module-private" items outside of the module is controlled at run-time, not compile-time.  The compiler has no clue that a public in a dependent module isn't really public.  it will happily compile it.  At runtime you will definitely see fireworks.  The good news is that you don't have to wait for the code path that tries to use the "module-private" items to fire.  OSGi will complain loudly when that module gets loaded.  OSGi will refuse to load it.  You will see an error like this: remote failure: Error while loading FOO: Exception while adding the new configuration : Error occurred during deployment: Exception while loading the app : org.osgi.framework.BundleException: Unresolved constraint in bundle com.oracle.glassfish.miscreant.code [115]: Unable to resolve 115.0: missing requirement [115.0] osgi.wiring.package; (osgi.wiring.package=org.glassfish.mymodule.unexported). Please see server.log for more details. That is if you accidentally change code in module B to use a public that is really a "module-private" in module A, then you will see the error immediately when you try to test whatever you were changing in module B.

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• Hosting a website from a dynamic IP

  - by nick

  I recently upgraded my internet to the point that it is much faster and more reliable than my current webhost. I would like to move my current domain to be hosted at home, but my IP address is dynamic. As far as I know, I only get a new IP when I restart my modem and or router (which is almost never) or when cable one (my ISP) pushes out a firmware update (rarely). There are a few ways I can see doing this 1) convince my ISP to give me a static IP 2) assign my router my current IP to force a static IP (which might work?) 3) set my dns record to my current IP address and update it on the rare occasions that it changes. Obviously I'm hoping that the first one works, but I don't want to pay a lot of extra money (if that's what it takes) to get a static IP address. Has anyone had any luck with something like that?

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• Euler Problem 20

  - by MarkPearl

  This was probably one of the easiest ones to complete – a quick bash got me the following… The Problem n! means n (n 1) ... 3 2 1 For example, 10! = 10 9 ... 3 2 1 = 3628800, and the sum of the digits in the number 10! is 3 + 6 + 2 + 8 + 8 + 0 + 0 = 27. Find the sum of the digits in the number 100! The Solution   private static BigInteger Factorial(int num) { if (num > 1) return (BigInteger)num * Factorial(num - 1); else return 1; } private static BigInteger SumDigits(string digits) { BigInteger result = 0; foreach (char number in digits) { result += Convert.ToInt32(number)-48; } return result; } static void Main(string[] args) { Console.WriteLine(SumDigits(Factorial(100).ToString())); Console.ReadLine(); }

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• Please help me to improve Re-Sharper

  - by TATWORTH

  Re-Sharper is an excellent aid to producing good code in either C# or VB.NET. Recently through using Resharper and StyleCop, I have found three area where ReSharper needs to be improved. Please log into the YouTrack at http://youtrack.jetbrains.net and vote for the following: RSRP-268868 Improvement to removal of redundant else and invert if optimisations for enhanced stylecop compliance. When Resharper removes a redundant else, there needs to be a blank line added. Currently there is no provision to specify this. Please vote for this! RSRP-272286 Resharper Feature Request to move initialisation to static constructor Currently ReSharper offers moving initialisation of of non-static variable to a constructor. Why not offer the same for a static constructor?  Please vote for this! RSRP-272285 Expansion of Switch Statement by Resharper Currently ReSharper will fill an empty switch statement based upon an enumeration but will not add missing enumeration values to such a switch statement.   Can't code withoutCoding assistance, smart code editing and code completion for C# and VB.NET

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• Passing class names or objects?

  - by nischayn22

  I have a switch statement switch ( $id ) { case 'abc': return 'Animal'; case 'xyz': return 'Human'; //many more } I am returning class names,and use them to call some of their static functions using call_user_func(). Instead I can also create a object of that class, return that and then call the static function from that object as $object::method($param) switch ( $id ) { case 'abc': return new Animal; case 'xyz': return new Human; //many more } Which way is efficient? To make this question broader : I have classes that have mostly all static methods right now, putting them into classes is kind of a grouping idea here (for example the DB table structure of Animal is given by class Animal and so for Human class). I need to access many functions from these classes so the switch needs to give me access to the class

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• Where should I put a method that returns a list of active entries of a table?

  - by darga33

  I have a class named GuestbookEntry that maps to the properties that are in the database table named "guestbook". Very simple! Originally, I had a static method named getActiveEntries() that retrieved an array of all GuestbookEntry objects. Each row in the guestbook table was an object that was added to that array. Then while learning how to properly design PHP classes, I learned some things: Static methods are not desirable. Separation of Concerns Single Responsibility Principle If the GuestbookEntry class should only be responsible for managing single guestbook entries then where should this getActiveEntries() method most properly go? Update: I am looking for an answer that complies with the SOLID acronym principles and allows for test-ability. That's why I want to stay away from static calls/standard functions. DAO, repository, ...? Please explain as though your explanation will be part of "Where to Locate FOR DUMMIES"... :-)

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• Naming convention: field starting with "m" or "s"

  - by Noya

  Hope this question hasn't posted yet... I saw lot of code (for example some Android source code) where fields name start with a "m" while static fields start with "s" Example (taken from Android View class source): private SparseArray<Object> mKeyedTags; private static int sNextAccessibilityViewId; I was wondering what "m" and "s" stand for... maybe is "m" mutable and "s" static? Since it seems that is a largely adopted pattern do you know if there some literature about this kind of naming convention?

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• MAC filtering after DHCP

  - by user1655161

  How to manage filtering by MAC in Ubuntu? Scenario: Ubuntu DHCP is configured and working (network 192.168.1.0) a) Laptop 1 is set in configuration on Ubuntu as static IP Laptop 1 is configured for automatic IP and when is connected to server everything works. I'm taking laptop 2 which is configured as static IP 192.168.1.10 and his configuration is not set in Ubuntu dhcpd.conf After laptop 2 is connected internet working. It is possible to do MAC filtering which disallow to connect PCs with address IP set as static but MAC address is not configured in Ubuntu (something like: intruder in network)?

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• Where would a senior PHP developer locate the method getActiveEntries()?

  - by darga33

  I have a class named GuestbookEntry that maps to the properties that are in the database table named "guestbook". Very simple! Originally, I had a static method named getActiveEntries() that retrieved an array of all GuestbookEntry objects. Each row in the guestbook table was an object that was added to that array. Then while learning how to properly design PHP classes, I learned some things: Static methods are not desirable. Separation of Concerns Single Responsibility Principle If the GuestbookEntry class should only be responsible for managing single guestbook entries then where should this getActiveEntries() method most properly go? Update: I am looking for an answer that complies with the SOLID acronym principles and allows for test-ability. That's why I want to stay away from static calls/standard functions. DAO, repository, ...? Please explain as though your explanation will be part of "Where to Locate FOR DUMMIES"... :-)

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• System.getProperty("user.dir") cannot get my project root path ,but the path which my eclipse is located

  - by facebook-100005613813158

  As the title goes , I have class named GetException.java,inside it ,I read a xml file in a static code block like(Because this document is shared): static{ ... document = db.parse(new File(System.getProperty("user.dir")+"/src/exception/ExceptionCode.xml")); ... } To test if the file path is correct, I write a main function just inside GetException.java, it proves that the path is correct ,xml file can be read successfully. My project root dir is "/home/wuchang/workspace/MongodbI". But When this Class is loaded from other class,such as I called one of its static functions , it reports the error message: /home/mrs/??/eclipse/src/exception/ExceptionCode.xml (No such file or directory) /home/mrs/??/eclipse/ is actually my eclipse installation directory.So , I wander how System.getProperty("user.dir") returned the eclipse installation directory to me ,instead of my project root directory?

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• Question about main(String[] args) [migrated]

  - by Andrew0085

  I'm new to programming, and I'm using java. Here's a program I wrote: class HelloApp { static String hi; public static void main(String[] args) { int length = args.length; if (length > 0) { hi = args[0]; sayHi(); } } static void sayHi() { if (hi == "hello") { System.out.println("Hello!"); } } } My question is: Why doesn't inputting "java HelloApp hello" make "Hello!" appear on the next line?

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• Injection with google guice does not work anymore after obfuscation with proguard

  - by sme

  Has anyone ever tried to combine the use of google guice with obfuscation (in particular proguard)? The obfuscated version of my code does not work with google guice as guice complains about missing type parameters. This information seems to be erased by the transformation step that proguard does, even when the relevant classes are excluded from the obfuscation. The stack trace looks like this: com.google.inject.CreationException: Guice creation errors: 1) Cannot inject a Provider that has no type parameter while locating com.google.inject.Provider for parameter 0 at de.repower.lvs.client.admin.user.administration.AdminUserCommonPanel.setPasswordPanelProvider(SourceFile:499) at de.repower.lvs.client.admin.user.administration.AdminUserCommonPanel.setPasswordPanelProvider(SourceFile:499) while locating de.repower.lvs.client.admin.user.administration.AdminUserCommonPanel for parameter 0 at de.repower.lvs.client.admin.user.administration.b.k.setParentPanel(SourceFile:65) at de.repower.lvs.client.admin.user.administration.b.k.setParentPanel(SourceFile:65) at de.repower.lvs.client.admin.user.administration.o.a(SourceFile:38) 2) Cannot inject a Provider that has no type parameter while locating com.google.inject.Provider for parameter 0 at de.repower.lvs.client.admin.user.administration.AdminUserCommonPanel.setWindTurbineAccessGroupProvider(SourceFile:509) at de.repower.lvs.client.admin.user.administration.AdminUserCommonPanel.setWindTurbineAccessGroupProvider(SourceFile:509) while locating de.repower.lvs.client.admin.user.administration.AdminUserCommonPanel for parameter 0 at de.repower.lvs.client.admin.user.administration.b.k.setParentPanel(SourceFile:65) at de.repower.lvs.client.admin.user.administration.b.k.setParentPanel(SourceFile:65) at de.repower.lvs.client.admin.user.administration.o.a(SourceFile:38) 2 errors at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:354) at com.google.inject.InjectorBuilder.initializeStatically(InjectorBuilder.java:152) at com.google.inject.InjectorBuilder.build(InjectorBuilder.java:105) at com.google.inject.Guice.createInjector(Guice.java:92) at com.google.inject.Guice.createInjector(Guice.java:69) at com.google.inject.Guice.createInjector(Guice.java:59) I tried to create a small example (without using guice) that seems to reproduce the problem: package de.repower.common; import java.lang.reflect.Method; import java.lang.reflect.ParameterizedType; import java.lang.reflect.Type; class SomeClass<S> { } public class ParameterizedTypeTest { public void someMethod(SomeClass<Integer> param) { System.out.println("value: " + param); System.setProperty("my.dummmy.property", "hallo"); } private static void checkParameterizedMethod(ParameterizedTypeTest testObject) { System.out.println("checking parameterized method ..."); Method[] methods = testObject.getClass().getMethods(); for (Method method : methods) { if (method.getName().equals("someMethod")) { System.out.println("Found method " + method.getName()); Type[] types = method.getGenericParameterTypes(); Type parameterType = types[0]; if (parameterType instanceof ParameterizedType) { Type parameterizedType = ((ParameterizedType) parameterType).getActualTypeArguments()[0]; System.out.println("Parameter: " + parameterizedType); System.out.println("Class: " + ((Class) parameterizedType).getName()); } else { System.out.println("Failed: type ist not instance of ParameterizedType"); } } } } public static void main(String[] args) { System.out.println("Starting ..."); try { ParameterizedTypeTest someInstance = new ParameterizedTypeTest(); checkParameterizedMethod(someInstance); } catch (SecurityException e) { e.printStackTrace(); } } } If you run this code unsbfuscated, the output looks like this: Starting ... checking parameterized method ... Found method someMethod Parameter: class java.lang.Integer Class: java.lang.Integer But running the version obfuscated with proguard yields: Starting ... checking parameterized method ... Found method someMethod Failed: type ist not instance of ParameterizedType These are the options I used for obfuscation: -injars classes_eclipse\methodTest.jar -outjars classes_eclipse\methodTestObfuscated.jar -libraryjars 'C:\Program Files\Java\jre6\lib\rt.jar' -dontskipnonpubliclibraryclasses -dontskipnonpubliclibraryclassmembers -dontshrink -printusage classes_eclipse\shrink.txt -dontoptimize -dontpreverify -verbose -keep class **.ParameterizedTypeTest.class { <fields>; <methods>; } -keep class ** { <fields>; <methods>; } # Keep - Applications. Keep all application classes, along with their 'main' # methods. -keepclasseswithmembers public class * { public static void main(java.lang.String[]); } # Also keep - Enumerations. Keep the special static methods that are required in # enumeration classes. -keepclassmembers enum * { public static **[] values(); public static ** valueOf(java.lang.String); } # Also keep - Database drivers. Keep all implementations of java.sql.Driver. -keep class * extends java.sql.Driver # Also keep - Swing UI L&F. Keep all extensions of javax.swing.plaf.ComponentUI, # along with the special 'createUI' method. -keep class * extends javax.swing.plaf.ComponentUI { public static javax.swing.plaf.ComponentUI createUI(javax.swing.JComponent); } # Keep names - Native method names. Keep all native class/method names. -keepclasseswithmembers,allowshrinking class * { native <methods>; } # Keep names - _class method names. Keep all .class method names. This may be # useful for libraries that will be obfuscated again with different obfuscators. -keepclassmembers,allowshrinking class * { java.lang.Class class$(java.lang.String); java.lang.Class class$(java.lang.String,boolean); } Does anyone have an idea of how to solve this (apart from the obvious workaround to put the relevant files into a seperate jar and not obfuscate it)? Best regards, Stefan

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• Use IIS Application Initialization for keeping ASP.NET Apps alive

  - by Rick Strahl

  I've been working quite a bit with Windows Services in the recent months, and well, it turns out that Windows Services are quite a bear to debug, deploy, update and maintain. The process of getting services set up,  debugged and updated is a major chore that has to be extensively documented and or automated specifically. On most projects when a service is built, people end up scrambling for the right 'process' to use for administration. Web app deployment and maintenance on the other hand are common and well understood today, as we are constantly dealing with Web apps. There's plenty of infrastructure and tooling built into Web Tools like Visual Studio to facilitate the process. By comparison Windows Services or anything self-hosted for that matter seems convoluted.In fact, in a recent blog post I mentioned that on a recent project I'd been using self-hosting for SignalR inside of a Windows service, because the application is in fact a 'service' that also needs to send out lots of messages via SignalR. But the reality is that it could just as well be an IIS application with a service component that runs in the background. Either way you look at it, it's either a Windows Service with a built in Web Server, or an IIS application running a Service application, neither of which follows the standard Service or Web App template.Personally I much prefer Web applications. Running inside of IIS I get all the benefits of the IIS platform including service lifetime management (crash and restart), controlled shutdowns, the whole security infrastructure including easy certificate support, hot-swapping of code and the the ability to publish directly to IIS from within Visual Studio with ease.Because of these benefits we set out to move from the self hosted service into an ASP.NET Web app instead.The Missing Link for ASP.NET as a Service: Auto-LoadingI've had moments in the past where I wanted to run a 'service like' application in ASP.NET because when you think about it, it's so much easier to control a Web application remotely. Services are locked into start/stop operations, but if you host inside of a Web app you can write your own ticket and control it from anywhere. In fact nearly 10 years ago I built a background scheduling application that ran inside of ASP.NET and it worked great and it's still running doing its job today.The tricky part for running an app as a service inside of IIS then and now, is how to get IIS and ASP.NET launched so your 'service' stays alive even after an Application Pool reset. 7 years ago I faked it by using a web monitor (my own West Wind Web Monitor app) I was running anyway to monitor my various web sites for uptime, and having the monitor ping my 'service' every 20 seconds to effectively keep ASP.NET alive or fire it back up after a reload. I used a simple scheduler class that also includes some logic for 'self-reloading'. Hacky for sure, but it worked reliably.Luckily today it's much easier and more integrated to get IIS to launch ASP.NET as soon as an Application Pool is started by using the Application Initialization Module. The Application Initialization Module basically allows you to turn on Preloading on the Application Pool and the Site/IIS App, which essentially fires a request through the IIS pipeline as soon as the Application Pool has been launched. This means that effectively your ASP.NET app becomes active immediately, Application_Start is fired making sure your app stays up and running at all times. All the other features like Application Pool recycling and auto-shutdown after idle time still work, but IIS will then always immediately re-launch the application.Getting started with Application InitializationAs of IIS 8 Application Initialization is part of the IIS feature set. For IIS 7 and 7.5 there's a separate download available via Web Platform Installer. Using IIS 8 Application Initialization is an optional install component in Windows or the Windows Server Role Manager: This is an optional component so make sure you explicitly select it.IIS Configuration for Application InitializationInitialization needs to be applied on the Application Pool as well as the IIS Application level. As of IIS 8 these settings can be made through the IIS Administration console.Start with the Application Pool:Here you need to set both the Start Automatically which is always set, and the StartMode which should be set to AlwaysRunning. Both have to be set - the Start Automatically flag is set true by default and controls the starting of the application pool itself while Always Running flag is required in order to launch the application. Without the latter flag set the site settings have no effect.Now on the Site/Application level you can specify whether the site should pre load: Set the Preload Enabled flag to true.At this point ASP.NET apps should auto-load. This is all that's needed to pre-load the site if all you want is to get your site launched automatically.If you want a little more control over the load process you can add a few more settings to your web.config file that allow you to show a static page while the App is starting up. This can be useful if startup is really slow, so rather than displaying blank screen while the user is fiddling their thumbs you can display a static HTML page instead: <system.webServer> <applicationInitialization remapManagedRequestsTo="Startup.htm" skipManagedModules="true"> <add initializationPage="ping.ashx" /> </applicationInitialization> </system.webServer>This allows you to specify a page to execute in a dry run. IIS basically fakes request and pushes it directly into the IIS pipeline without hitting the network. You specify a page and IIS will fake a request to that page in this case ping.ashx which just returns a simple OK string - ie. a fast pipeline request. This request is run immediately after Application Pool restart, and while this request is running and your app is warming up, IIS can display an alternate static page - Startup.htm above. So instead of showing users an empty loading page when clicking a link on your site you can optionally show some sort of static status page that says, "we'll be right back".  I'm not sure if that's such a brilliant idea since this can be pretty disruptive in some cases. Personally I think I prefer letting people wait, but at least get the response they were supposed to get back rather than a random page. But it's there if you need it.Note that the web.config stuff is optional. If you don't provide it IIS hits the default site link (/) and even if there's no matching request at the end of that request it'll still fire the request through the IIS pipeline. Ideally though you want to make sure that an ASP.NET endpoint is hit either with your default page, or by specify the initializationPage to ensure ASP.NET actually gets hit since it's possible for IIS fire unmanaged requests only for static pages (depending how your pipeline is configured).What about AppDomain Restarts?In addition to full Worker Process recycles at the IIS level, ASP.NET also has to deal with AppDomain shutdowns which can occur for a variety of reasons:Files are updated in the BIN folderWeb Deploy to your siteweb.config is changedHard application crashThese operations don't cause the worker process to restart, but they do cause ASP.NET to unload the current AppDomain and start up a new one. Because the features above only apply to Application Pool restarts, AppDomain restarts could also cause your 'ASP.NET service' to stop processing in the background.In order to keep the app running on AppDomain recycles, you can resort to a simple ping in the Application_End event:protected void Application_End() { var client = new WebClient(); var url = App.AdminConfiguration.MonitorHostUrl + "ping.aspx"; client.DownloadString(url); Trace.WriteLine("Application Shut Down Ping: " + url); }which fires any ASP.NET url to the current site at the very end of the pipeline shutdown which in turn ensures that the site immediately starts back up.Manual Configuration in ApplicationHost.configThe above UI corresponds to the following ApplicationHost.config settings. If you're using IIS 7, there's no UI for these flags so you'll have to manually edit them.When you install the Application Initialization component into IIS it should auto-configure the module into ApplicationHost.config. Unfortunately for me, with Mr. Murphy in his best form for me, the module registration did not occur and I had to manually add it.<globalModules> <add name="ApplicationInitializationModule" image="%windir%\System32\inetsrv\warmup.dll" /> </globalModules>Most likely you won't need ever need to add this, but if things are not working it's worth to check if the module is actually registered.Next you need to configure the ApplicationPool and the Web site. The following are the two relevant entries in ApplicationHost.config.<system.applicationHost> <applicationPools> <add name="West Wind West Wind Web Connection" autoStart="true" startMode="AlwaysRunning" managedRuntimeVersion="v4.0" managedPipelineMode="Integrated"> <processModel identityType="LocalSystem" setProfileEnvironment="true" /> </add> </applicationPools> <sites> <site name="Default Web Site" id="1"> <application path="/MPress.Workflow.WebQueueMessageManager" applicationPool="West Wind West Wind Web Connection" preloadEnabled="true"> <virtualDirectory path="/" physicalPath="C:\Clients\…" /> </application> </site> </sites> </system.applicationHost>On the Application Pool make sure to set the autoStart and startMode flags to true and AlwaysRunning respectively. On the site make sure to set the preloadEnabled flag to true.And that's all you should need. You can still set the web.config settings described above as well.ASP.NET as a Service?In the particular application I'm working on currently, we have a queue manager that runs as standalone service that polls a database queue and picks out jobs and processes them on several threads. The service can spin up any number of threads and keep these threads alive in the background while IIS is running doing its own thing. These threads are newly created threads, so they sit completely outside of the IIS thread pool. In order for this service to work all it needs is a long running reference that keeps it alive for the life time of the application.In this particular app there are two components that run in the background on their own threads: A scheduler that runs various scheduled tasks and handles things like picking up emails to send out outside of IIS's scope and the QueueManager. Here's what this looks like in global.asax:public class Global : System.Web.HttpApplication { private static ApplicationScheduler scheduler; private static ServiceLauncher launcher; protected void Application_Start(object sender, EventArgs e) { // Pings the service and ensures it stays alive scheduler = new ApplicationScheduler() { CheckFrequency = 600000 }; scheduler.Start(); launcher = new ServiceLauncher(); launcher.Start(); // register so shutdown is controlled HostingEnvironment.RegisterObject(launcher); }}By keeping these objects around as static instances that are set only once on startup, they survive the lifetime of the application. The code in these classes is essentially unchanged from the Windows Service code except that I could remove the various overrides required for the Windows Service interface (OnStart,OnStop,OnResume etc.). Otherwise the behavior and operation is very similar.In this application ASP.NET serves two purposes: It acts as the host for SignalR and provides the administration interface which allows remote management of the 'service'. I can start and stop the service remotely by shutting down the ApplicationScheduler very easily. I can also very easily feed stats from the queue out directly via a couple of Web requests or (as we do now) through the SignalR service.Registering a Background Object with ASP.NETNotice also the use of the HostingEnvironment.RegisterObject(). This function registers an object with ASP.NET to let it know that it's a background task that should be notified if the AppDomain shuts down. RegisterObject() requires an interface with a Stop() method that's fired and allows your code to respond to a shutdown request. Here's what the IRegisteredObject::Stop() method looks like on the launcher:public void Stop(bool immediate = false) { LogManager.Current.LogInfo("QueueManager Controller Stopped."); Controller.StopProcessing(); Controller.Dispose(); Thread.Sleep(1500); // give background threads some time HostingEnvironment.UnregisterObject(this); }Implementing IRegisterObject should help with reliability on AppDomain shutdowns. Thanks to Justin Van Patten for pointing this out to me on Twitter.RegisterObject() is not required but I would highly recommend implementing it on whatever object controls your background processing to all clean shutdowns when the AppDomain shuts down.Testing it outI'm still in the testing phase with this particular service to see if there are any side effects. But so far it doesn't look like it. With about 50 lines of code I was able to replace the Windows service startup to Web start up - everything else just worked as is. An honorable mention goes to SignalR 2.0's oWin hosting, because with the new oWin based hosting no code changes at all were required, merely a couple of configuration file settings and an assembly directive needed, to point at the SignalR startup class. Sweet!It also seems like SignalR is noticeably faster running inside of IIS compared to self-host. Startup feels faster because of the preload.Starting and Stopping the 'Service'Because the application is running as a Web Server, it's easy to have a Web interface for starting and stopping the services running inside of the service. For our queue manager the SignalR service and front monitoring app has a play and stop button for toggling the queue.If you want more administrative control and have it work more like a Windows Service you can also stop the application pool explicitly from the command line which would be equivalent to stopping and restarting a service.To start and stop from the command line you can use the IIS appCmd tool. To stop:> %windir%\system32\inetsrv\appcmd stop apppool /apppool.name:"Weblog"and to start> %windir%\system32\inetsrv\appcmd start apppool /apppool.name:"Weblog"Note that when you explicitly force the AppPool to stop running either in the UI (on the ApplicationPools page use Start/Stop) or via command line tools, the application pool will not auto-restart immediately. You have to manually start it back up.What's not to like?There are certainly a lot of benefits to running a background service in IIS, but… ASP.NET applications do have more overhead in terms of memory footprint and startup time is a little slower, but generally for server applications this is not a big deal. If the application is stable the service should fire up and stay running indefinitely. A lot of times this kind of service interface can simply be attached to an existing Web application, or if scalability requires be offloaded to its own Web server.Easier to work withBut the ultimate benefit here is that it's much easier to work with a Web app as opposed to a service. While developing I can simply turn off the auto-launch features and launch the service on demand through IIS simply by hitting a page on the site. If I want to shut down an IISRESET -stop will shut down the service easily enough. I can then attach a debugger anywhere I want and this works like any other ASP.NET application. Yes you end up on a background thread for debugging but Visual Studio handles that just fine and if you stay on a single thread this is no different than debugging any other code.SummaryUsing ASP.NET to run background service operations is probably not a super common scenario, but it probably should be something that is considered carefully when building services. Many applications have service like features and with the auto-start functionality of the Application Initialization module, it's easy to build this functionality into ASP.NET. Especially when combined with the notification features of SignalR it becomes very, very easy to create rich services that can also communicate their status easily to the outside world.Whether it's existing applications that need some background processing for scheduling related tasks, or whether you just create a separate site altogether just to host your service it's easy to do and you can leverage the same tool chain you're already using for other Web projects. If you have lots of service projects it's worth considering… give it some thought…© Rick Strahl, West Wind Technologies, 2005-2013Posted in ASP.NET  SignalR  IIS   Tweet !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• Authenticating Mountain Lion over Ubuntu 12 LDAP [closed]

  - by Sam Hammamy

  Possible Duplicate: Ubuntu OpenLDAP and Mac OS X Roaming Profiles I've installed slapd on Ubuntu 12 after a long long day of trial and error. I've added the apple.ldif schema, and the samba.ldif schema, plus a test user. Last week, I had installed slapd on Ubuntu 11, and was able to authenticate against it from OS X Lion after finding the following blog post: Fixing OpenLDAP Authentication on OS X Lion This suggests running the following commands to fix the authentication problem /usr/libexec/PlistBuddy -c "add ':module options:ldap:Denied SASL Methods:' string CRAM-MD5" /Library/Preferences/OpenDirectory/Configurations/LDAPv3/yourldapserver.plist /usr/libexec/PlistBuddy -c "add ':module options:ldap:Denied SASL Methods:' string NTLM" /Library/Preferences/OpenDirectory/Configurations/LDAPv3/yourldapserver.plist /usr/libexec/PlistBuddy -c "add ':module options:ldap:Denied SASL Methods:' string GSSAPI" /Library/Preferences/OpenDirectory/Configurations/LDAPv3/yourldapserver.plist However, I ran these commands on OS X Mountain Lion, and I am still unable to authenticate. I can't even use the Directory Editor app to examine the AD. I am however able to bind to the server via python-ldap's ldap.simple_bind_s('cn=admin,dc=foo,dc=net,'secret'). The error I am getting when trying to use Director Editor is Error Code (5000)

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• How to do hooking in Java? [closed]

  - by chimpaburro

  A hook is a process running to get data from another (more info), well the case was that I wanted to get the methods or functions using any application for access to a network, these methods are usually WSAConnect (), WSASendTo (), bind (), connect () and sendto () [these are the ones that need to get to the application]. I started testing, creating Runtime [Runtime.getRuntime (). exec (...)] with all possible methods [addShutdownHook (...);] and now I'm trying to ProcessBuilder [new ProcessBuilder (...);] and the famous BufferedReader [new BufferedReader (new InputStreamReader (proceso.getInputStream ()));] but I could not find the way to do it. Sorry for my bad English..

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• Problem Registering a Generic Repository with Windsor IoC

  - by Robin

  I’m fairly new to IoC and perhaps my understanding of generics and inheritance is not strong enough for what I’m trying to do. You might find this to be a mess. I have a generic Repository base class: public class Repository<TEntity> where TEntity : class, IEntity { private Table<TEntity> EntityTable; private string _connectionString; private string _userName; public string UserName { get { return _userName; } set { _userName = value; } } public Repository() {} public Repository(string connectionString) { _connectionString = connectionString; EntityTable = (new DataContext(connectionString)).GetTable<TEntity>(); } public Repository(string connectionString, string userName) { _connectionString = connectionString; _userName = userName; EntityTable = (new DataContext(connectionString)).GetTable<TEntity>(); } // Data access methods ... ... } and a SqlClientRepository that inherits Repository: public class SqlClientRepository : Repository<Client> { private Table<Client> ClientTable; private string _connectionString; private string _userName; public SqlClientRepository() {} public SqlClientRepository(string connectionString) : base(connectionString) { _connectionString = connectionString; ClientTable = (new DataContext(connectionString)).GetTable<Client>(); } public SqlClientRepository(string connectionString, string userName) : base(connectionString, userName) { _connectionString = connectionString; _userName = userName; ClientTable = (new DataContext(connectionString)).GetTable<Client>(); } // data access methods unique to Client repository ... } The Repository class provides some generics methods like Save, Delete, etc, that I want all my repository derived classes to share. The TEntity parameter is constrained to the IEntity interface: public interface IEntity { int Id { get; set; } NameValueCollection GetSaveRuleViolations(); NameValueCollection GetDeleteRuleViolations(); } This allows the Repository class to reference these methods within its Save and Delete methods. Unit tests work fine on mock SqlClientRepository instances as well as live unit tests on the real database. However, in the MVC context: public class ClientController : Controller { private SqlClientRepository _clientRepository; public ClientController(SqlClientRepository clientRepository) { this._clientRepository = clientRepository; } public ClientController() { } // ViewResult methods ... ... } ... _clientRepository is always null. I’m using Windor Castle as an IoC container. Here is the configuration: <component id="ClientRepository" service="DomainModel.Concrete.Repository`1[[DomainModel.Entities.Client, DomainModel]], DomainModel" type="DomainModel.Concrete.SqlClientRepository, DomainModel" lifestyle="PerWebRequest"> <parameters> <connectionString>#{myConnStr}</connectionString> </parameters> </component> I’ve tried many variations in the Windsor configuration file. I suspect it’s more of a design flaw in the above code. As I'm looking over my code, it occurs to me that when registering components with an IoC container, perhaps service must always be an interface. Could this be it? Does anybody have a suggestion? Thanks in advance.

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• What's my best approach on this simple hierarchy Java Problem?

  - by Nazgulled

  First, I'm sorry for the question title but I can't think of a better one to describe my problem. Feel free to change it :) Let's say I have this abstract class Box which implements a couple of constructors, methods and whatever on some private variables. Then I have a couple of sub classes like BoxA and BoxB. Both of these implement extra things. Now I have another abstract class Shape and a few sub classes like Square and Circle. For both BoxA and BoxB I need to have a list of Shape objects but I need to make sure that only Square objects go into BoxA's list and only Circle objects go into BoxB's list. For that list (on each box), I need to have a get() and set() method and also a addShape() and removeShape() methods. Another important thing to know is that for each box created, either BoxA or BoxB, each respectively Shape list is exactly the same. Let's say I create a list of Square's named ls and two BoxA objects named boxA1 and boxA2. No matter what, both boxA1 and boxA2 must have the same ls list. This is my idea: public abstract class Box { // private instance variables public Box() { // constructor stuff } // public instance methods } public class BoxA extends Box { // private instance variables private static List<Shape> list; public BoxA() { // constructor stuff } // public instance methods public static List<Square> getList() { List<Square> aux = new ArrayList<Square>(); for(Square s : list.values()) { aux.add(s.clone()); // I know what I'm doing with this clone, don't worry about it } return aux; } public static void setList(List<Square> newList) { list = new ArrayList<Square>(newList); } public static void addShape(Square s) { list.add(s); } public static void removeShape(Square s) { list.remove(list.indexOf(s)); } } As the list needs to be the same for that type of object, I declared as static and all methods that work with that list are also static. Now, for BoxB the class would be almost the same regarding the list stuff. I would only replace Square by Triangle and the problem was solved. So, for each BoxA object created, the list would be only one and the same for each BoxB object created, but a different type of list of course. So, what's my problem you ask? Well, I don't like the code... The getList(), setList(), addShape() and removeShape() methods are basically repeated for BoxA and BoxB, only the type of the objects that the list will hold is different. I can't think of way to do it in the super class Box instead. Doing it statically too, using Shape instead of Square and Triangle, wouldn't work because the list would be only one and I need it to be only one but for each sub class of Box. How could I do this differently and better? P.S: I could not describe my real example because I don't know the correct words in English for the stuff I'm doing, so I just used a box and shapes example, but it's basically the same.

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• Thread Synchronization and Synchronization Primitives

  When considering synchronization in an application, the decision truly depends on what the application and its worker threads are going to do. I would use synchronization if two or more threads could possibly manipulate the same instance of an object at the same time. An example of this in C# can be demonstrated through the use of storing data in a static object. A static object is initialized once per application and the data within the object can be accessed by all threads. I would use the synchronization primitives to prevent any data from being manipulated by multiple threads simultaneously. This would reduce any data corruption from occurring within the object. On the other hand if all the threads used non static objects and were independent of the other tasks there would be no need to use synchronization. Synchronization Primitives in C#: Basic Blocking Locking Signaling Non-Blocking Synchronization Constructs The Basic Blocking methods include Sleep, Join, and Task.Wait.  These methods force threads to wait until other threads have completed. In addition, these methods can also force a thread to wait a set amount of time before continuing to work.   The Locking primitive prevents a thread from entering a critical section of code while another thread is in the same critical section.  If another thread attempts to enter a locked code, it will wait, until the code block is released. The Signaling primitive allows a thread to temporarily pause work until receiving a notification from another thread that it is ok to continue working. The Signaling primitive removes the need for polling.The Non-Blocking Synchronization Constructs protect access to a common field by calling upon processor primitives.

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• Using RIA DomainServices with ASP.NET and MVC 2

  - by Bobby Diaz

  Recently, I started working on a new ASP.NET MVC 2 project and I wanted to reuse the data access (LINQ to SQL) and business logic methods (WCF RIA Services) that had been developed for a previous project that used Silverlight for the front-end.  I figured that I would be able to instantiate the various DomainService classes from within my controller’s action methods, because after all, the code for those services didn’t look very complicated.  WRONG!  I didn’t realize at first that some of the functionality is handled automatically by the framework when the domain services are hosted as WCF services.  After some initial searching, I came across an invaluable post by Joe McBride, which described how to get RIA Service .svc files to work in an MVC 2 Web Application, and another by Brad Abrams.  Unfortunately, Brad’s solution was for an earlier preview release of RIA Services and no longer works with the version that I am running (PDC Preview). I have not tried the RC version of WCF RIA Services, so I am not sure if any of the issues I am having have been resolved, but I wanted to come up with a way to reuse the shared libraries so I wouldn’t have to write a non-RIA version that basically did the same thing.  The classes I came up with work with the scenarios I have encountered so far, but I wanted to go ahead and post the code in case someone else is having the same trouble I had.  Hopefully this will save you a few headaches! 1. Querying When I first tried to use a DomainService class to perform a query inside one of my controller’s action methods, I got an error stating that “This DomainService has not been initialized.”  To solve this issue, I created an extension method for all DomainServices that creates the required DomainServiceContext and passes it to the service’s Initialize() method.  Here is the code for the extension method; notice that I am creating a sort of mock HttpContext for those cases when the service is running outside of IIS, such as during unit testing!     public static class ServiceExtensions     {         /// <summary>         /// Initializes the domain service by creating a new <see cref="DomainServiceContext"/>         /// and calling the base DomainService.Initialize(DomainServiceContext) method.         /// </summary>         /// <typeparam name="TService">The type of the service.</typeparam>         /// <param name="service">The service.</param>         /// <returns></returns>         public static TService Initialize<TService>(this TService service)             where TService : DomainService         {             var context = CreateDomainServiceContext();             service.Initialize(context);             return service;         }           private static DomainServiceContext CreateDomainServiceContext()         {             var provider = new ServiceProvider(new HttpContextWrapper(GetHttpContext()));             return new DomainServiceContext(provider, DomainOperationType.Query);         }           private static HttpContext GetHttpContext()         {             var context = HttpContext.Current;   #if DEBUG             // create a mock HttpContext to use during unit testing...             if ( context == null )             {                 var writer = new StringWriter();                 var request = new SimpleWorkerRequest("/", "/",                     String.Empty, String.Empty, writer);                   context = new HttpContext(request)                 {                     User = new GenericPrincipal(new GenericIdentity("debug"), null)                 };             } #endif               return context;         }     }   With that in place, I can use it almost as normally as my first attempt, except with a call to Initialize():     public ActionResult Index()     {         var service = new NorthwindService().Initialize();         var customers = service.GetCustomers();           return View(customers);     } 2. Insert / Update / Delete Once I got the records showing up, I was trying to insert new records or update existing data when I ran into the next issue.  I say issue because I wasn’t getting any kind of error, which made it a little difficult to track down.  But once I realized that that the DataContext.SubmitChanges() method gets called automatically at the end of each domain service submit operation, I could start working on a way to mimic the behavior of a hosted domain service.  What I came up with, was a base class called LinqToSqlRepository<T> that basically sits between your implementation and the default LinqToSqlDomainService<T> class.     [EnableClientAccess()]     public class NorthwindService : LinqToSqlRepository<NorthwindDataContext>     {         public IQueryable<Customer> GetCustomers()         {             return this.DataContext.Customers;         }           public void InsertCustomer(Customer customer)         {             this.DataContext.Customers.InsertOnSubmit(customer);         }           public void UpdateCustomer(Customer currentCustomer)         {             this.DataContext.Customers.TryAttach(currentCustomer,                 this.ChangeSet.GetOriginal(currentCustomer));         }           public void DeleteCustomer(Customer customer)         {             this.DataContext.Customers.TryAttach(customer);             this.DataContext.Customers.DeleteOnSubmit(customer);         }     } Notice the new base class name (just change LinqToSqlDomainService to LinqToSqlRepository).  I also added a couple of DataContext (for Table<T>) extension methods called TryAttach that will check to see if the supplied entity is already attached before attempting to attach it, which would cause an error! 3. LinqToSqlRepository<T> Below is the code for the LinqToSqlRepository class.  The comments are pretty self explanatory, but be aware of the [IgnoreOperation] attributes on the generic repository methods, which ensures that they will be ignored by the code generator and not available in the Silverlight client application.     /// <summary>     /// Provides generic repository methods on top of the standard     /// <see cref="LinqToSqlDomainService&lt;TContext&gt;"/> functionality.     /// </summary>     /// <typeparam name="TContext">The type of the context.</typeparam>     public abstract class LinqToSqlRepository<TContext> : LinqToSqlDomainService<TContext>         where TContext : System.Data.Linq.DataContext, new()     {         /// <summary>         /// Retrieves an instance of an entity using it's unique identifier.         /// </summary>         /// <typeparam name="TEntity">The type of the entity.</typeparam>         /// <param name="keyValues">The key values.</param>         /// <returns></returns>         [IgnoreOperation]         public virtual TEntity GetById<TEntity>(params object[] keyValues) where TEntity : class         {             var table = this.DataContext.GetTable<TEntity>();             var mapping = this.DataContext.Mapping.GetTable(typeof(TEntity));               var keys = mapping.RowType.IdentityMembers                 .Select((m, i) => m.Name + " = @" + i)                 .ToArray();               return table.Where(String.Join(" && ", keys), keyValues).FirstOrDefault();         }           /// <summary>         /// Creates a new query that can be executed to retrieve a collection         /// of entities from the <see cref="DataContext"/>.         /// </summary>         /// <typeparam name="TEntity">The type of the entity.</typeparam>         /// <returns></returns>         [IgnoreOperation]         public virtual IQueryable<TEntity> GetEntityQuery<TEntity>() where TEntity : class         {             return this.DataContext.GetTable<TEntity>();         }           /// <summary>         /// Inserts the specified entity.         /// </summary>         /// <typeparam name="TEntity">The type of the entity.</typeparam>         /// <param name="entity">The entity.</param>         /// <returns></returns>         [IgnoreOperation]         public virtual bool Insert<TEntity>(TEntity entity) where TEntity : class         {             //var table = this.DataContext.GetTable<TEntity>();             //table.InsertOnSubmit(entity);               return this.Submit(entity, null, DomainOperation.Insert);         }           /// <summary>         /// Updates the specified entity.         /// </summary>         /// <typeparam name="TEntity">The type of the entity.</typeparam>         /// <param name="entity">The entity.</param>         /// <returns></returns>         [IgnoreOperation]         public virtual bool Update<TEntity>(TEntity entity) where TEntity : class         {             return this.Update(entity, null);         }           /// <summary>         /// Updates the specified entity.         /// </summary>         /// <typeparam name="TEntity">The type of the entity.</typeparam>         /// <param name="entity">The entity.</param>         /// <param name="original">The original.</param>         /// <returns></returns>         [IgnoreOperation]         public virtual bool Update<TEntity>(TEntity entity, TEntity original)             where TEntity : class         {             if ( original == null )             {                 original = GetOriginal(entity);             }               var table = this.DataContext.GetTable<TEntity>();             table.TryAttach(entity, original);               return this.Submit(entity, original, DomainOperation.Update);         }           /// <summary>         /// Deletes the specified entity.         /// </summary>         /// <typeparam name="TEntity">The type of the entity.</typeparam>         /// <param name="entity">The entity.</param>         /// <returns></returns>         [IgnoreOperation]         public virtual bool Delete<TEntity>(TEntity entity) where TEntity : class         {             //var table = this.DataContext.GetTable<TEntity>();             //table.TryAttach(entity);             //table.DeleteOnSubmit(entity);               return this.Submit(entity, null, DomainOperation.Delete);         }           protected virtual bool Submit(Object entity, Object original, DomainOperation operation)         {             var entry = new ChangeSetEntry(0, entity, original, operation);             var changes = new ChangeSet(new ChangeSetEntry[] { entry });             return base.Submit(changes);         }           private TEntity GetOriginal<TEntity>(TEntity entity) where TEntity : class         {             var context = CreateDataContext();             var table = context.GetTable<TEntity>();             return table.FirstOrDefault(e => e == entity);         }     } 4. Conclusion So there you have it, a fully functional Repository implementation for your RIA Domain Services that can be consumed by your ASP.NET and MVC applications.  I have uploaded the source code along with unit tests and a sample web application that queries the Customers table from inside a Controller, as well as a Silverlight usage example. As always, I welcome any comments or suggestions on the approach I have taken.  If there is enough interest, I plan on contacting Colin Blair or maybe even the man himself, Brad Abrams, to see if this is something worthy of inclusion in the WCF RIA Services Contrib project.  What do you think? Enjoy!

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• What is Polymorphism?

  - by SAMIR BHOGAYTA

  * Polymorphism is one of the primary characteristics (concept) of object-oriented programming. * Poly means many and morph means form. Thus, polymorphism refers to being able to use many forms of a type without regard to the details. * Polymorphism is the characteristic of being able to assign a different meaning specifically, to allow an entity such as a variable, a function, or an object to have more than one form. * Polymorphism is the ability to process objects differently depending on their data types. * Polymorphism is the ability to redefine methods for derived classes. Types of Polymorphism * Compile time Polymorphism * Run time Polymorphism Compile time Polymorphism * Compile time Polymorphism also known as method overloading * Method overloading means having two or more methods with the same name but with different signatures Example of Compile time polymorphism public class Calculations { public int add(int x, int y) { return x+y; } public int add(int x, int y, int z) { return x+y+z; } } Run time Polymorphism * Run time Polymorphism also known as method overriding * Method overriding means having two or more methods with the same name , same signature but with different implementation Example of Run time Polymorphism class Circle { public int radius = 0; public double getArea() { return 3.14 * radius * radius } } class Sphere { public double getArea() { return 4 * 3.14 * radius * radius } }

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