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  • Access outer class from inner class: Why is it done this way?

    - by Vuntic
    So most of us know how to access an outer class from an inner class. Searches with those words give oodles of answered questions on that topic. But what I want to know is why the syntax is the way it is. Example: public class A { private class B { public void c() {A.this.d();} } public void d() {System.out.println("You've called d()! Go, you!");} } Why is it A.this.d()? It looks like this is a static field of class A, but... * am confused * Forgive me if this is a repeat; like I said, searches with those words give how-answers.

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  • How do I create a "global variable" in Java such that all classes can access it?

    - by Chrystle Soh
    here's my problem: I have multiple classes that are part of the same package and they need access to a certain file path String filePath = "D:/Users/Mine/School/Java/CZ2002_Assignment/src/" Rather than declaring the same Filepath in every single class, is it possible to simply have a "global" type of variable of this FilePath so that all classes can access it and I only need to declare and update it once. Thanks

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  • Can we call methods of non-static classes without an object in Java?

    - by ask
    In Java, the wrapper class Integer has the static method parseInt() which is used like this: Integer.parseInt(). I thought only methods of static classes could be called like this (ie. Class.doMethod()). All non-static classes need objects to be instantiated to use their methods. I checked the API, and apparently Integer is declared as public final Integer - not static. Someone please help me understand this.

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  • Can a problem have a relation of aggregation and composition both between two classes at same point

    - by learner
    Can a problem have a relation of aggregation and composition both between two classes at same point of time? Like any real time scenario where there can be aggregation corresponding to one method and composition related to other method. I m unable to figure out any scenario where both composition and aggregation occurs simultaneously between two classes. Any help will be appreciable.

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  • Static vs Singleton in C# (Difference between Singleton and Static)

    - by Jalpesh P. Vadgama
    Recently I have came across a question what is the difference between Static and Singleton classes. So I thought it will be a good idea to share blog post about it.Difference between Static and Singleton classes:A singleton classes allowed to create a only single instance or particular class. That instance can be treated as normal object. You can pass that object to a method as parameter or you can call the class method with that Singleton object. While static class can have only static methods and you can not pass static class as parameter.We can implement the interfaces with the Singleton class while we can not implement the interfaces with static classes.We can clone the object of Singleton classes we can not clone the object of static classes.Singleton objects stored on heap while static class stored in stack.more at my personal blog: dotnetjalps.com

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  • Should classes from the same namespace be kept in the same assembly?

    - by Dan Rasmussen
    For example, ISerializable and the Serializable Attribute are both in the System.Runtime.Serialization namespace, but not the assembly of the same name. On the other hand, DataContract attributes are in the namespace/assembly System.Runtime.Serialization. This causes confusion when a class can have using System.Runtime.Serialization but still not have reference to the System.Runtime.Serialization assembly, meaning DataContract cannot be found. Should this be avoided in practice, or is it common for namespaces to be split over multiple assemblies? What other issues should one be careful of when doing this?

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  • Is there a pattern or best practice for passing a reference type to multiple classes vs a static class?

    - by Dave
    My .NET application creates HTML files, and as such, the structure looks like variable myData BuildHomePage() variable graph = new BuildGraphPage(myData) variable table = BuildTablePage(myData) BuildGraphPage and BuildTablePage both require access data, the myData object. In the above example, I've passed the myData object to 2 constructors. This is what I'm doing now, in my current project. The myData object, and it's properties are all readonly. The problem is, the number of pages which will require this object has grown. In the real project, there are currently 4, but the new spec is to have about 20. Passing this object to the constructor of each new object and assigning it to a field is a little time consuming, but not a hardship! This poses the question whether it's better practice to continue as I have, or to refactor and create a new static class for myData which can be referenced from any where in my project. I guess my abilities to use Google are poor, because I did try and find an appropriate pattern as I am sure this type of design must be common place but my results returned nothing. Is there a pattern which is suited, or do best practices lean towards one implementation over another.

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  • UML class diagram - can aggregated object be part of two aggregated classes?

    - by user970696
    Some sources say that aggregation means that the class owns the object and shares reference. Lets assume an example where a company class holds a list of cars but departments of that company has list of cars used by them. class Department { list<Car> listOfCars; } class Company { list<Car> listOfCars; //initialization of the list } So in UML class diagram, I would do it like this. But I assume this is not allowed because it would imply that both company and department own the objects.. [COMPANY]<>------[CAR] [DEPARTMENT]<>---| //imagine this goes up to the car class

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  • When to decide to introduce interfaces (pure abstract base classes) in C++?

    - by Honza Brabec
    Assume that you are developing a functionality and are 90% sure that the implementation class will stay alone. If I was in this position in Java I would probably not use the interface right now to keep the things simple. In Java it is easy to refactor the code and extract the interface later. In C++ the refactoring is not always so easy. It may require replacing values with smart pointers (because of the introduction of polymorphism) and other non-trivial tasks. On the other hand I don't much like the idea of introducing virtual calls when I am 90% sure they won't be needed. After all speed is one of the reasons to prefer C++ over simpler languages.

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  • How do you avoid name similarities between your classes and the native ones?

    - by Oscar
    I just ran into an "interesting problem", which I would like your opinion about: I am developing a system and for many reasons (meaning: abstraction, technology independence, etc) we create our own types for exchanging information. For instance: if there is a method which is called SendEmail and is invoked by the business logic, it way have a parameter of type OurCompany.EMailMessage, which is an object which is completely technology independent and contains only "business relevant data" (for instance, no information abut head encoding). Inside the SendEmail function, we get this information from our EMailMEssage object and create a MailMessage (this one is technolgy specific) object so it can be sent over the network. As you can already notice, our class has a very similar name to the "native" language class. The problem is: this is exactly what they are, email messages, so it is hard to find another meaningful name for them. Do you have this problem often? How do you manage it? Edit: @mgkrebbs just commented about using fully qualified names. This is our current approach, but a little bit too verbose, IMHO. I would like something cleaner, if possible.

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  • Is it a bad practice to include all the enums in one file and use it in multiple classes?

    - by Bugster
    I'm an aspiring game developer, I work on occasional indie games, and for a while I've been doing something which seemed like a bad practice at first, but I really want to get an answer from some experienced programmers here. Let's say I have a file called enumList.h where I declare all the enums I want to use in my game: // enumList.h enum materials_t { WOOD, STONE, ETC }; enum entity_t { PLAYER, MONSTER }; enum map_t { 2D, 3D }; // and so on. // Tile.h #include "enumList.h" #include <vector> class tile { // stuff }; The main idea is that I declare all enums in the game in 1 file, and then import that file when I need to use a certain enum from it, rather than declaring it in the file where I need to use it. I do this because it makes things clean, I can access every enum in 1 place rather than having pages openned solely for accessing one enum. Is this a bad practice and can it affect performance in any way?

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  • Several classes need to access the same data, where should the data be declared?

    - by Juicy
    I have a basic 2D tower defense game in C++. Each map is a separate class which inherits from GameState. The map delegates the logic and drawing code to each object in the game and sets data such as the map path. In pseudo-code the logic section might look something like this: update(): for each creep in creeps: creep.update() for each tower in towers: tower.update() for each missile in missiles: missile.update() The objects (creeps, towers and missiles) are stored in vector-of-pointers. The towers must have access to the vector-of-creeps and the vector-of-missiles to create new missiles and identify targets. The question is: where do I declare the vectors? Should they be members of the Map class, and passed as arguments to the tower.update() function? Or declared globally? Or are there other solutions I'm missing entirely?

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  • Why are there so many string classes in the face of std::string?

    - by fish
    It seems to me that many bigger C++ libraries end up creating their own string type. In the client code you either have to use the one from the library (QString, CString, fbstring etc., I'm sure anyone can name a few) or keep converting between the standard type and the one the library uses (which most of the time involves at least one copy). So, is there a particular misfeature or something wrong about std::string (just like auto_ptr semantics were bad)? Has it changed in C++11?

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  • Any patent issue if I want to call my classes "signal/slot" as in Qt?

    - by user129506
    I need to code a signal-like mechanism and I was thinking of using the same "slot" and "signal" terms to indicate the signal and the function that needs to be called. Since this is a commercial application I'd like to know if there might be any issue with using these names, e.g. if Qt has some sort of patent on them (I searched around but couldn't find it). I believe this is a stupid question since patenting a class name would be moronic, to say the least.. but anyway... To add some detail: my code is ENTIRELY different and has NOTHING TO DO with Qt except the above. I don't use moc or any Qt class.

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  • Sortie de la première beta de Symfony 2.1, Composer, chargement automatique des classes et adoption des règles de codage de la communauté

    Symfony2 est un projet très communautaire, depuis le début (des centaines de bundles étaient disponibles bien avant les premières RC de la 2.0), une tendance qui se confirme : 250 contributeurs, 1 000 pull requests sur GitHub pour la première version beta de Symfony 2.1 ! Après les difficultés de migration avec symfony 1.x, l'équipe a tenté autant que possible de restreindre les changements à même de casser la rétrocompatibilité ; de même, le refactoring du module de formulaires a fait que la version finale de la 2.1 devrait sortir en août, afin de concentrer autant que possible les changements et faire que de plus en plus de code ne devra pas être modifié lors de la migration d'une version à l'autre. Ainsi, n'hésitez pas à tenter de migrer vos applications vers cette beta,...

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  • SSH not working through Double NAT

    - by d_inevitable
    I am trying to setup port forwarding for ssh through 2 NATs The first Router translates my internet IP to my outer network (10.1.7.0). In the outer network there's a second Router that does NAT to my inner network (192.168.1.0). The target server is connected to both, the outer network and the inner network. I cannot change the port forwarding options for outer router. It is currently configured to forward the SSH and HTTP port to the router for the inner network. Internet + | v +-----------------+ +------------------+ | Outer Router | | Inner Router | |-----------------| |------------------| | | SSH HTTP | | +----+ +--------------------->| | | | | | | | | | | | | +-------+---------+ +------+---------+-+ | | | | | | | | | | | | | | +------------------+ | SSH | | | | Server | | | | | |------------------| | | | +-----------> |<-------+ | | | | |HTTP (testing) | +------------------+ | | | +------v------------------+ | | Outer Workstation | +-------------------+ | |-------------------------| | Inner Workstation| | | | |-------------------| | | | | |<----------------+ +-------------------------+ | | +-------------------+ When connecting from a outer workstation to the address of the inner router, then both SSH and HTTP work fine. When connecting from the internet to my public ip with HTTP, the connection works fine as well. However SSH just times out. Most likely because the reply is not routed back properly. I suspect its either because of the SSH itself, or because the server is connected to both, the inner and outer network. Any ideas how I could resolve this issue? The routes on the server are currently: ip route show default via 10.1.7.254 dev eth0 metric 100 10.1.7.0/24 dev eth0 proto kernel scope link src 10.1.7.1 192.168.1.0/24 dev eth1 proto kernel scope link src 192.168.1.2 Do I have to change this? If so how?

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  • How to create a dynamic Linq Join extension method

    - by Royd Brayshay
    There was a library of dynamic Linq extensions methods released as a sample with VS2008. I'd like to extend it with a Join method. The code below fails with a parameter miss match exception at run time. Can anyone find the problem? public static IQueryable Join(this IQueryable outer, IEnumerable inner, string outerSelector, string innerSelector, string resultsSelector, params object[] values) { if (inner == null) throw new ArgumentNullException("inner"); if (outerSelector == null) throw new ArgumentNullException("outerSelector"); if (innerSelector == null) throw new ArgumentNullException("innerSelector"); if (resultsSelector == null) throw new ArgumentNullException("resultsSelctor"); LambdaExpression outerSelectorLambda = DynamicExpression.ParseLambda(outer.ElementType, null, outerSelector, values); LambdaExpression innerSelectorLambda = DynamicExpression.ParseLambda(inner.AsQueryable().ElementType, null, innerSelector, values); ParameterExpression[] parameters = new ParameterExpression[] { Expression.Parameter(outer.ElementType, "outer"), Expression.Parameter(inner.AsQueryable().ElementType, "inner") }; LambdaExpression resultsSelectorLambda = DynamicExpression.ParseLambda(parameters, null, resultsSelector, values); return outer.Provider.CreateQuery( Expression.Call( typeof(Queryable), "Join", new Type[] { outer.ElementType, inner.AsQueryable().ElementType, outerSelectorLambda.Body.Type, innerSelectorLambda.Body.Type, resultsSelectorLambda.Body.Type }, outer.Expression, inner.AsQueryable().Expression, Expression.Quote(outerSelectorLambda), Expression.Quote(innerSelectorLambda), Expression.Quote(resultsSelectorLambda))); } I've now fixed it myself, here's the answer. Please vote it up or add a better one.

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  • SQL Quey slow in .NET application but instantaneous in SQL Server Management Studio

    - by user203882
    Here is the SQL SELECT tal.TrustAccountValue FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = 70402 AND ta.TrustAccountID = 117249 AND tal.trustaccountlogid = ( SELECT MAX (tal.trustaccountlogid) FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = 70402 AND ta.TrustAccountID = 117249 AND tal.TrustAccountLogDate < '3/1/2010 12:00:00 AM' ) Basicaly there is a Users table a TrustAccount table and a TrustAccountLog table. Users: Contains users and their details TrustAccount: A User can have multiple TrustAccounts. TrustAccountLog: Contains an audit of all TrustAccount "movements". A TrustAccount is associated with multiple TrustAccountLog entries. Now this query executes in milliseconds inside SQL Server Management Studio, but for some strange reason it takes forever in my C# app and even timesout (120s) sometimes. Here is the code in a nutshell. It gets called multiple times in a loop and the statement gets prepared. cmd.CommandTimeout = Configuration.DBTimeout; cmd.CommandText = "SELECT tal.TrustAccountValue FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = @UserID1 AND ta.TrustAccountID = @TrustAccountID1 AND tal.trustaccountlogid = (SELECT MAX (tal.trustaccountlogid) FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = @UserID2 AND ta.TrustAccountID = @TrustAccountID2 AND tal.TrustAccountLogDate < @TrustAccountLogDate2 ))"; cmd.Parameters.Add("@TrustAccountID1", SqlDbType.Int).Value = trustAccountId; cmd.Parameters.Add("@UserID1", SqlDbType.Int).Value = userId; cmd.Parameters.Add("@TrustAccountID2", SqlDbType.Int).Value = trustAccountId; cmd.Parameters.Add("@UserID2", SqlDbType.Int).Value = userId; cmd.Parameters.Add("@TrustAccountLogDate2", SqlDbType.DateTime).Value =TrustAccountLogDate; // And then... reader = cmd.ExecuteReader(); if (reader.Read()) { double value = (double)reader.GetValue(0); if (System.Double.IsNaN(value)) return 0; else return value; } else return 0;

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  • SQL Query slow in .NET application but instantaneous in SQL Server Management Studio

    - by user203882
    Here is the SQL SELECT tal.TrustAccountValue FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = 70402 AND ta.TrustAccountID = 117249 AND tal.trustaccountlogid = ( SELECT MAX (tal.trustaccountlogid) FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = 70402 AND ta.TrustAccountID = 117249 AND tal.TrustAccountLogDate < '3/1/2010 12:00:00 AM' ) Basicaly there is a Users table a TrustAccount table and a TrustAccountLog table. Users: Contains users and their details TrustAccount: A User can have multiple TrustAccounts. TrustAccountLog: Contains an audit of all TrustAccount "movements". A TrustAccount is associated with multiple TrustAccountLog entries. Now this query executes in milliseconds inside SQL Server Management Studio, but for some strange reason it takes forever in my C# app and even timesout (120s) sometimes. Here is the code in a nutshell. It gets called multiple times in a loop and the statement gets prepared. cmd.CommandTimeout = Configuration.DBTimeout; cmd.CommandText = "SELECT tal.TrustAccountValue FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = @UserID1 AND ta.TrustAccountID = @TrustAccountID1 AND tal.trustaccountlogid = (SELECT MAX (tal.trustaccountlogid) FROM TrustAccountLog AS tal INNER JOIN TrustAccount ta ON ta.TrustAccountID = tal.TrustAccountID INNER JOIN Users usr ON usr.UserID = ta.UserID WHERE usr.UserID = @UserID2 AND ta.TrustAccountID = @TrustAccountID2 AND tal.TrustAccountLogDate < @TrustAccountLogDate2 ))"; cmd.Parameters.Add("@TrustAccountID1", SqlDbType.Int).Value = trustAccountId; cmd.Parameters.Add("@UserID1", SqlDbType.Int).Value = userId; cmd.Parameters.Add("@TrustAccountID2", SqlDbType.Int).Value = trustAccountId; cmd.Parameters.Add("@UserID2", SqlDbType.Int).Value = userId; cmd.Parameters.Add("@TrustAccountLogDate2", SqlDbType.DateTime).Value =TrustAccountLogDate; // And then... reader = cmd.ExecuteReader(); if (reader.Read()) { double value = (double)reader.GetValue(0); if (System.Double.IsNaN(value)) return 0; else return value; } else return 0;

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  • Javascript: Multiple mouseout events triggered

    - by Channel72
    I'm aware of the different event models in Javascript (the WC3 model versus the Microsoft model), as well as the difference between bubbling and capturing. However, after a few hours reading various articles about this issue, I'm still unsure how to properly code the following seemingly simple behavior: If I have an outer div and an inner div element, I want a single mouse-out event to be triggered when the mouse leaves the outer-div. When the mouse crosses from the inner-div to the outer-div, nothing should happen, and when the mouse crosses from the outer-div to the inner-div nothing should happen. The event should only fire if the mouse moves from the outer-div to the surrounding page. <div id="outer" style = "width:20em; height:20em; border:1px solid #F00" align = "center" onmouseout="alert('mouseout event!')" > <div id="inner" style = "width:18em; height:18em; border:1px solid #000"></div> </div> Now, if I place the "mouseout" event on the outer-div, two mouse-out events are fired when the mouse moves from the inner-div to the surrounding page, because the event fires once when the mouse moves from inner to outer, and then again when it moves from outer to the surrounding page. I know I can cancel the event using ev.stopPropagation(), so I tried registering an event handler with the inner-div to cancel the event propagation. However, this won't prevent the event from firing when the mouse moves from the outer-div to the inner-div. So, unless I'm overlooking something, it seems to me this behavior can't be accomplished without complex mouse-tracking functions. In the future, I plan to reimplement a lot of this code using a more advanced framework, like JQuery, but for now, I'm wondering if there is a simple way to implement the above behavior in regular Javascript.

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  • Why not lump all service classes into a Factory method (instead of injecting interfaces)?

    - by Andrew
    We are building an ASP.NET project, and encapsulating all of our business logic in service classes. Some is in the domain objects, but generally those are rather anemic (due to the ORM we are using, that won't change). To better enable unit testing, we define interfaces for each service and utilize D.I.. E.g. here are a couple of the interfaces: IEmployeeService IDepartmentService IOrderService ... All of the methods in these services are basically groups of tasks, and the classes contain no private member variables (other than references to the dependent services). Before we worried about Unit Testing, we'd just declare all these classes as static and have them call each other directly. Now we'll set up the class like this if the service depends on other services: public EmployeeService : IEmployeeService { private readonly IOrderService _orderSvc; private readonly IDepartmentService _deptSvc; private readonly IEmployeeRepository _empRep; public EmployeeService(IOrderService orderSvc , IDepartmentService deptSvc , IEmployeeRepository empRep) { _orderSvc = orderSvc; _deptSvc = deptSvc; _empRep = empRep; } //methods down here } This really isn't usually a problem, but I wonder why not set up a factory class that we pass around instead? i.e. public ServiceFactory { virtual IEmployeeService GetEmployeeService(); virtual IDepartmentService GetDepartmentService(); virtual IOrderService GetOrderService(); } Then instead of calling: _orderSvc.CalcOrderTotal(orderId) we'd call _svcFactory.GetOrderService.CalcOrderTotal(orderid) What's the downfall of this method? It's still testable, it still allows us to use D.I. (and handle external dependencies like database contexts and e-mail senders via D.I. within and outside the factory), and it eliminates a lot of D.I. setup and consolidates dependencies more. Thanks for your thoughts!

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