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  • Reference variable to an object instantiated/initialized in another class in Java

    - by Alex
    The reason I'm asking is because I'm getting NullPointerException. I now this is very easy but I'm pretty new programming and find this a bit confusing. So say I have initialized an object in a class and want to access that same object from another class. Like now for instance I'm working on a small Chess game, in my model Game class I have an instance of Board, an object. Board, in turn, has an array of Squares. Square[][]. Game has board, board has Square[][]. Now if I want to access the Square[][] through the object board (in Game) of type Board. Do I just declare a variable with the same name and type or do I have to initialize it again? Board board OR Board board = new Board(); Note, I have already initialized board in the class Game so if I do it again, won't they be two totally different Board objects?

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  • Populate JOIN into a list in one database query

    - by axio
    I am trying to get the records from the 'many' table of a one-to-many relationship and add them as a list to the relevant record from the 'one' table. I am also trying to do this in a single database request. Code derived from http://stackoverflow.com/questions/1580199/linq-to-sql-populate-join-result-into-a-list almost achieves the intended result, but makes one database request per entry in the 'one' table which is unacceptable. That failing code is here: var res = from variable in _dc.GetTable<VARIABLE>() select new { x = variable, y = variable.VARIABLE_VALUEs }; However if I do a similar query but loop through all the results, then only a single database request is made. This code achieves all goals: var res = from variable in _dc.GetTable<VARIABLE>() select variable; List<GDO.Variable> output = new List<GDO.Variable>(); foreach (var v2 in res) { List<GDO.VariableValue> values = new List<GDO.VariableValue>(); foreach (var vv in v2.VARIABLE_VALUEs) { values.Add(VariableValue.EntityToGDO(vv)); } output.Add(EntityToGDO(v2)); output[output.Count - 1].VariableValues = values; } However the latter code is ugly as hell, and it really feels like something that should be do-able in a single linq query. So, how can this be done in a single linq query that makes only a single database query? In both cases the table is set to preload using the following code: _dc = _db.CreateLinqDataContext(); var loadOptions = new DataLoadOptions(); loadOptions.LoadWith<VARIABLE>(v => v.VARIABLE_VALUEs); _dc.LoadOptions = loadOptions; I am using .NET 3.5, and the database back-end was generated using SqlMetal.

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  • Hibernate one-to-one: getId() without fetching entire object

    - by Rob
    I want to fetch the id of a one-to-one relationship without loading the entire object. I thought I could do this using lazy loading as follows: class Foo { @OneToOne(fetch = FetchType.LAZY, optional = false) private Bar bar; } Foo f = session.get(Foo.class, fooId); // Hibernate fetches Foo f.getBar(); // Hibernate fetches full Bar object f.getBar().getId(); // No further fetch, returns id I want f.getBar() to not trigger another fetch. I want hibernate to give me a proxy object that allows me to call .getId() without actually fetching the Bar object. What am I doing wrong?

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  • Design issue when having classes implement different interfaces to restrict client actions

    - by devoured elysium
    Let's say I'm defining a game class that implements two different views: interface IPlayerView { void play(); } interface IDealerView { void deal(); } The view that a game sees when playing the game, and a view that the dealer sees when dealing the game (this is, a player can't make dealer actions and a dealer can't make player actions). The game definition is as following: class Game : IPlayerView, IDealerView { void play() { ... } void deal() { ... } } Now assume I want to make it possible for the players to play the game, but not to deal it. My original idea was that instead of having public Game GetGame() { ... } I'd have something like public IPlayerView GetGame() { ... } But after some tests I realized that if I later try this code, it works: IDealerView dealerView = (IDealerView)GameClass.GetGame(); this works as lets the user act as the dealer. Am I worrying to much? How do you usually deal with this patterns? I could instead make two different classes, maybe a "main" class, the dealer class, that would act as factory of player classes. That way I could control exactly what I would like to pass on the the public. On the other hand, that turns everything a bit more complex than with this original design. Thanks

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  • Javascript object encapsulation that tracks changes

    - by Raynos
    Is it possible to create an object container where changes can be tracked Said object is a complex nested object of data. (compliant with JSON). The wrapper allows you to get the object, and save changes, without specifically stating what the changes are Does there exist a design pattern for this kind of encapsulation Deep cloning is not an option since I'm trying to write a wrapper like this to avoid doing just that. The solution of serialization should only be considered if there are no other solutions. An example of use would be var foo = state.get(); // change state state.update(); // or state.save(); client.tell(state.recentChange()); A jsfiddle snippet might help : http://jsfiddle.net/Raynos/kzKEp/ It seems like implementing an internal hash to keep track of changes is the best option. [Edit] To clarify this is actaully done on node.js on the server. The only thing that changes is that the solution can be specific to the V8 implementation.

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  • grab inspect the parameters to "use" and pass on the rest?

    - by JoelFan
    I have a Perl module and I'd like to be able to pick out the parameters that my my module's user passed in the "use" call. Whichever ones I don't recognize I'd like to pass on. I tried to do this by overriding the "import" method but I'm not having much luck. EDIT: To clarify, as it is, I can use my module like this: use MyModule qw/foo bar/; which will import the foo and bar methods of MyModule. But I want to be able to say: use MyModule qw/foo doSpecialStuff bar/; and look for doSpecialStuff to check if I need to do some special stuff at the beginning of the program, then pass qw/foo bar/ to the Exporter's import

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  • When to define SDD(System Sequence Diagram) operations System->Actor?

    - by devoured elysium
    I am having some trouble understanding how to make System Sequence Diagrams, as I don't fully grasp why in some cases one should define operations for System - Actor and in others don't. Here is an example: Let's assume the System is a Cinema Ticket Store and the Actor is a client that wants to buy a ticket. 1) The User tells the System that wants to buy some tickets, stating his client number. 2) The System confirms that the given client number is valid. 3) The User tells the System the movie that wants to see. 4) The System shows the set of available sessions and seats for that movie. 5) The System asks the user which session/seat he wants. 6) The User tells the System the chosen session/seat. This would be converted to: a) -----> tellClientNumber(clientNumber) b) <----- validClientNumber c) -----> tellMovieToSee(movie) d) <----- showsAvailableSeatsHours e) -----> tellSystemChosenSessionSeat(session, seat) I know that when we are dealing with SDD's we are still far away from coding. But I can't help trying to imagine how it how it would have been had I to convert it right away to code: I can understand 1) and 2). It's like if it was a C#/Java method with the following signature: boolean tellClientNumber(clientNumber) so I put both on the SDD. Then, we have the pair 3) 4). I can imagine that as something as: SomeDataStructureThatHoldsAvailableSessionsSeats tellSystemMovieToSee(movie) Now, the problem: From what I've come to understand, my lecturer says that we shouldn't make an operation on the SDD for 5) as we should only show operations from the Actor to the System and when the System is either presenting us data (as in c)) or validating sent data (such as in b)). I find this odd, as if I try to imagine this like a DOS app where you have to put your input sequencially, it makes sense to make an arrow even for 5). Why is this wrong? How should I try to visualize this? Thanks

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  • Class architecture, no friends allowed

    - by Captain Comic
    The question of why there are no friends in C# has been extensively discussed. I have the following design problems. I have a class that has only one public function AddOrder(Order ord). Clients are allowed to call only this function. All other logic must be hidden. Order class is listening to market events and must call other other function of TradingSystem ExecuteOrder, so I have to make it public as well. Doing that I will allow clients of Trading system to call this function and I don't want that. class TradingSystem { // Trading system stores list of orders List<Order> _orders; // this function is made public so that Order can call ir public ExecuteOrder(Order ord) { } // this function is made public for external clients public AddOrder(OrderRequest ordreq) { // create order and pass it this order.OnOrderAdded(this); } } class Order { TradingSystem _ts; public void OnOrderAdded(TradingSystem ts) { _ts = ts; } void OnMarketEvent() { _ts.ExecuteOrder() } }

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  • PHP Store User Data without Sessions

    - by Sev
    Is there anyway to store users data such as userid, email, etc to be accessible from all pages of a website after they have logged in, but without using sessions or cookies? For example: class User { var $userid; var $username; var $email; .. methods.. } after they login at login.php $currentUser = new User($_POST['username']) now, how do I access $currentUser from another page, such as index.php if I shouldn't use sessions or cookies at all? so that I could do the following in index.php: if ($currentUser->userid > -1) { echo "you are logged in as: " . $currentUser->username; } else { echo "click here to login"; } i asked a similar question before, here, but the answers didn't fulfill my needs.

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  • Pass object from webserver to client

    - by user362914
    I developed a C# web application that calls a web-service which returns a base64 encoded array (PDF file). I then convert that array into a UCOMIStream object (I know it is obsolete, but the DLL that I am using requires it as a parameter). I use the following code to do the conversion which works perfectly. I can pass this object to the DLL so that I can print the PDF. This works great on the Webserver, but the requirement is to print it locally. Byte[] bBuffer = statementOut.statementcycle.statementdata.content; int size = bBuffer.Length; IntPtr mem = Marshal.AllocHGlobal(size); Marshal.Copy(bBuffer, 0, mem, size); // Create an OLE Stream object. System.Runtime.InteropServices.UCOMIStream str; //obsolete but the createstreamonhglobal outputs it CreateStreamOnHGlobal(mem, true, out str); The DLL resides on the client so I am able to use ActiveX to create the object using javascript and/or VBscript;however, I have not been able to figure out how to get the stream object to the client to pass to the DLL. How can this be achieved?

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  • Should I put actors in the Domain-Model/Class-Diagram?

    - by devoured elysium
    When designing both the domain-model and class-diagrams I am having some trouble understanding what to put in them. I'll give an example of what I mean: I am doing a vacations scheduler program, that has an Administrator and End-Users. The Administrator does a couple of things like registering End-Users in the program, changing their previleges, etc. The End-User can choose his vacations days, etc. I initially defined an Administrator and End-User as concepts in the domain-model, and later as classes in the class-diagram. In the class-diagram, both classes ended up having a couple of methods like Administrator.RegisterNewUser(); Administrator.UnregisterUser(int id); etc. Only after some time I realised that actually both Administrator and End-User are actors, and maybe I got this design totally wrong. Instead of filling Administrator and End-User classes with methods to do what my Use-Cases request, I could define other classes from the domain to do them, and have controllers handle the Use-Cases(actually, I decided to do one for each Use-Case). I could have a UserDatabase.RegisterNewUser() and UserDatabase.UnregisterUser(int id);, for example, instead of having those methods on the Administrator class. The idea would be to try to think of the whole vacation-scheduler as a "closed-program" that has a set of features and doesn't bother with things such as authentication, that should be internal/protected, being that the only public things I'd let the outside world see would be its controllers. Is this the right approach? Or am I getting this totally wrong? Is it generally bad idea to put Actors in the domain-model/class-diagrams? What are good rules of thumb for this? My lecturer is following Applying UML and Patterns, which I find awful, so I'd like to know where I could look up more info on this described actor-models situation. I'm still a bit confused about all of this, as this new approach is radically different from anything I've done before.

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  • Menu MouseOver Image & Image Description Dsiplay from SQL Database

    - by Julu
    Hello, I don't know if this is the right place to post this but here I go. I'm working on a project as a student for my internship and I need help. I have a masterPage with horizontal menu items as shown in the attached screen-captured. What I want to achieved is: Have a default image and description from SQL server database When a user mouse-over the menu item, display an image from a SQL server database and it description based on the mouse-over menu item. When user mouse-out, display default image and description from sql database. I have a also created user interface for inserting images to the database. How do I go about displaying the image and its description based on menu item is my main issue. Here is the link to the screen-captured. http://tinyurl.com/y4p3p32 Thanks a million time

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  • What would be a good starting point for development of a 3D application for representation of struct

    - by Lela Dax
    I was thinking QT on OpenGL. Multiplatform ability and being able to be closed (at no cost) at a later point would be important points. But I'm very interested in finding a way that is not only viable but also has the least amount of reinvention of the wheel. e.g. "Why not Ogre? A ready powerful 3D engine without reinventing that part". But I'm very uncertain in what is the optimal collection of tools for that job.

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  • Display database resume to user

    - by Domnic
    Im using upload control to upload my resume(word document) in sql server 2005 database.and i can download it from database when i click link button...Its all working file...My problem is how can i show my full resume to user (how to display my resume) from my database?

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  • Why can't I create an abstract constructor on an abstract C# class?

    - by Anthony D
    I am creating an abstract class. I want each of my derived classes to be forced to implement a specific signature of constructor. As such, I did what I would have done has I wanted to force them to implement a method, I made an abstract one. public abstract class A { abstract A(int a, int b); } However I get a message saying the abstract modifier is invalid on this item. My goal was to force some code like this. public class B : A { public B(int a, int b) : base(a, b) { //Some other awesome code. } } This is all C# .NET code. Can anyone help me out? Update 1 I wanted to add some things. What I ended up with was this. private A() { } protected A(int a, int b) { //Code } That does what some folks are saying, default is private, and the class needs to implement a constructor. However that doesn't FORCE a constructor with the signature A(int a, int b). public abstract class A { protected abstract A(int a, int b) { } } Update 2 I should be clear, to work around this I made my default constructor private, and my other constructor protected. I am not really looking for a way to make my code work. I took care of that. I am looking to understand why C# does not let you do this.

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  • Simple OOP-related question.

    - by M4design
    This question came to my mind quite a few times. Let my explain my question through an example. Say I've got two classes: 1- Grid. 2- Cell. Now the location of the cell 'should' be stored in the grid class, not in the cell class itself. Say that the cell wanted to get its location through a method in the grid. How can it do that? Keep in mind that the cell was created/initialised by the Grid class. What good OO approach to solve this problem? Thank you

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