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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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  • 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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  • how to get a constant in java with class

    - by vincent
    basically I need to get a constant for a class however I have no instance of the object but only its class. In PHP I would do constant(XYZ); Is there a similar way of retrieving a constant in JAVA? I need it to facilitate a dynamic getMethod call Class parameterType = Class.forName(class_name); object.setProperty(field name, field value, parameterType); the set property method would then get the correct method and set the specified property, however I cant get a method which has int as parameter type without using Interger.TYPE

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  • JS Error:Cannot call method of null

    - by Nadeem
    I have the following method in a js file in ASP.Net web project. This method is giving the error Cannot call method 'split' of null function loadUser_InfoCallBack(res) { var ret=res.value; var senderGUID = ret.split(';')[0]; var senderText = ret.split(';')[1]; if(senderGUID.Length>0) { $('hiddenSender.value')=senderGUID; $('hiddenText.value')=senderText; } } Can anybody suggest the reasons for this error..

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  • C++ allocate objects on heap of base class with protected constructors via inheritance

    - by KRao
    I have a class with protected constructor: class B { protected: B(){}; }; Now I derive from it and define two static functions and I manage to actually create objects of the class B, but not on the heap: class A : public B { public: static B createOnStack() {return B();} //static B* createOnHeap() {return new B;} //Compile time Error on VS2010 }; B b = A::createOnStack(); //This works on VS2010! The question is: 1) Is VS2010 wrong in allowing the first case? 2) Is it possible to create objects of B without modifying B in any way (no friendship and no extra functions). I am asking, because it is possible to make something similar when dealing with instances of B and its member functions, see: http://accu.org/index.php/journals/296 Thank you in advance for any suggestion! Kind regards

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  • How to create GUI as inner class with WindowBuilder

    - by Tim Kemp
    I would like to use WindowBuilder in Eclipse to construct Swing GUIs. The JPanels I need to build will be inner classes in a non-GUI wrapper, like so: public class MyWrapper extends MyBaseClass { ... class MyPanel extends JPanel { ... } } So my question is this: can I construct MyPanel using WindowBuilder? If so, how should I set it up? If anyone is interested, the wrapper is an abstract base class which the plug-ins I am developing for my app must extend; deployment concerns mean that it's not really practical to put the GUIs in a separate JAR either so I pretty much have to do it this way. My current workflow, which is awful, is to build the GUI in NetBeans and paste the entire generated class into Eclipse where I connect it up to the methods in my wrapper. I am very hopeful that WindowBuilder will let me work more reliably and efficiently if I can trick it into generating code in MyPanel, not MyWrapper. Thanks

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  • Session scoped bean as class attribute of Spring MVC Controller

    - by Sotirios Delimanolis
    I have a User class: @Component @Scope("session") public class User { private String username; } And a Controller class: @Controller public class UserManager { @Autowired private User user; @ModelAttribute("user") private User createUser() { return user; } @RequestMapping(value = "/user") public String getUser(HttpServletRequest request) { Random r = new Random(); user.setUsername(new Double(r.nextDouble()).toString()); request.getSession().invalidate(); request.getSession(true); return "user"; } } I invalidate the session so that the next time i got to /users, I get another user. I'm expecting a different user because of user's session scope, but I get the same user. I checked in debug mode and it is the same object id in memory. My bean is declared as so: <bean id="user" class="org.synchronica.domain.User"> <aop:scoped-proxy/> </bean> I'm new to spring, so I'm obviously doing something wrong. I want one instance of User for each session. How?

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  • how many lines of code does my class library have

    - by zachary
    for metrics reasons I need to know how many lines of code my class library has. I'm doing this for code coverage.... So if Class library 1 has 50 lines of code and 100% coverage And if Class library 2 has 500 lines of code and 0% coverage My total coverage is 90% Any idea how to do this? Is there a utility or a way to use Visual Studio?

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  • Why isn't the eigenclass equivalent to self.class, when it looks so similar?

    - by The Wicked Flea
    I've missed the memo somewhere, and I hope you'll explain this to me. Why is the eigenclass of an object different from self.class? class Foo def initialize(symbol) eigenclass = class << self self end eigenclass.class_eval do attr_accessor symbol end end end My train of logic that equates the eigenclass with class.self is rather simple: class << self is a way of declaring class methods, rather than instance methods. It's a shortcut to def Foo.bar. So within the reference to the class object, returning self should be identical to self.class. This is because class << self would set self to Foo.class for definition of class methods/attributes. Am I just confused? Or, is this a sneaky trick of Ruby meta-programming?

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  • Getting An Array Result From A C# Method

    - by Soo
    I am trying to write some code to return an array in C#, but don't know the proper syntax. I think my method is set up correctly, but to set an array to the result of the method is what I'm having difficulty with. Method Declaration: double[,] function(double variable) { ... code ... return array }

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  • Create Class objects based on type signature

    - by Andreas_D
    Class.forName(boolean.class.getName()); This doesn't work in Java - the virtual machine slaps you with a ClassNotFoundException. I was in need for something like that because I wanted to reflect methods based on Strings that included the method signatures, like public void doSomething(boolean yesWeCan, java.lang.String[] presidents); At the end I came up with a custom 'ClassFactory' which translates the type Strings to class objects. This factory includes a lot of handlers for primitive and array type values. The handler for array type objects is something like: if (isArrayOfObjects) { return Class.forName("L["+typeName.replace("[]", "")+";"); } My question is - have I missed something in the Java 1.5+ API that might do the trick?

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  • Inlining an array of non-default constructible objects in a C++ class

    - by porgarmingduod
    C++ doesn't allow a class containing an array of items that are not default constructible: class Gordian { public: int member; Gordian(int must_have_variable) : member(must_have_variable) {} }; class Knot { Gordian* pointer_array[8]; // Sure, this works. Gordian inlined_array[8]; // Won't compile. Can't be initialized. }; As even beginner C++ users know, the language guarantees that all members are initialized when constructing a class. And it doesn't trust the user to initialize everything in the constructor - one has to provide valid arguments to the constructors of all members before the body of the constructor even starts. Generally, that's a great idea as far as I'm concerned, but I've come across a situation where it would be a lot easier if I could actually have an array of non-default constructible objects. The obvious solution: Have an array of pointers to the objects. This is not optimal in my case, as I am using shared memory. It would force me to do extra allocation from an already contended resource (that is, the shared memory). The entire reason I want to have the array inlined in the object is to reduce the number of allocations. This is a situation where I would be willing to use a hack, even an ugly one, provided it works. One possible hack I am thinking about would be: class Knot { public: struct dummy { char padding[sizeof(Gordian)]; }; dummy inlined_array[8]; Gordian* get(int index) { return reinterpret_cast<Gordian*>(&inlined_array[index]); } Knot() { for (int x = 0; x != 8; x++) { new (get(x)) Gordian(x*x); } } }; Sure, it compiles, but I'm not exactly an experienced C++ programmer. That is, I couldn't possibly trust my hacks less. So, the questions: 1) Does the hack I came up with seem workable? What are the issues? (I'm mainly concerned with C++0x on newer versions of GCC). 2) Is there a better way to inline an array of non-default constructible objects in a class?

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  • Regex to match a Java method signature

    - by nitesh
    I am having this particular requirement where a method has to be identified by different regular expressions for different components. For example, there need to be a regex for return parameter, one for method name, one for argument type and one for argument name. I was able to come up with an expression till this step as follows - ([^,]+) ([^,]+)\((([^,]+) ([^,]+))\) It works well for a method signature like - ReturnType foo(Arg parameter) The regular expression identifies ReturnType, foo, Arg and parameter separately. Now the problem is that a method can have no/one/multiple arguments separated by commas. I am not able to get a repeating expression for this. Help will be appreciated.

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  • How to access the next element and check if it has a particular class

    - by NaN
    I need to call a function based on whether the second following td element has a certain class. Here is the HTML <tr id="939"> <td data-id="939">Test2</td> <td class="hold" data-id="939"></td> </tr> <tr id="938"> <td data-id="938">Test1</td> <td class="someotherclass" data-id="938"></td> </tr> Here is the JQuery function $('body').on('click', '#article td:first-child', function(e){ // I need to check the next td for the hold class if($(this).next().hasClass(".hold")){ // Call my function } }); How do I do this? I've tried using next and closest but that yields nothing.

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  • Setting new class variables inside a module

    - by Sean McCleary
    I have a plugin I have been working on that adds publishing to ActiveRecord classes. I extend my classes with my publisher like so: class Note < ActiveRecord::Base # ... publishable :related_attributes => [:taggings] end My publisher is structured like: module Publisher def self.included(base) base.send(:extend, ClassMethods) @@publishing_options = [] # does not seem to be available end module ClassMethods def publishable options={} include InstanceMethods @@publishing_options = options # does not work as class_variable_set is a private method # self.class_variable_set(:@@publishing_options, options) # results in: uninitialized class variable @@publishing_options in Publisher::ClassMethods puts "@@publishing_options: #{@@publishing_options.inspect}" # ... end # ... end module InstanceMethods # results in: uninitialized class variable @@publishing_options in Publisher::InstanceMethods def related_attributes @@publishing_options[:related_attributes] end # ... end end Any ideas on how to pass options to publishable and have them available as a class variable?

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  • rais belong_to which class to choose

    - by Small Wolf
    There is a model relation like this. class A belongs_to :ref_config,:class_name => 'User' end My question is : the A has a attribute named flag, now i want to create a function like this: if flag == 1, I want the class A like this belongs_to :ref_config,:class_name => 'Department and if flag == 2, i want the class A like this belongs_to :ref_config,:class_name => 'User' How can I implement the function Thank you!

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  • How do I create static instances of a class inside that class?

    - by wehas
    I have a class Color that holds values for the red, green, and blue channels of a color. The class constructor lets you create a new color by specifying values for the three channels. However, for convenience, I would also like to have some "premade" colors available for the programmer. For example instead of having something like DrawRectangle(new Color(1, 0, 0)); you would be able to say DrawRectangle(Color.Red); Where Color.Red is an instance of Color that lives inside the Color class. How can I declare these instances of Color inside the Color class? If there is a name for this type of technique I'd like to know it as I had no idea what search terms to use when I was looking for help online.

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  • Reading Connection String from a class Library

    - by devnet247
    Hi all I have a .net class library 2.0 with an app.config with a connectionString section. I have 01 Method that this class library exposes " string GetConnectionString(string name) However even though the app.config in this class library has 3 connstrings it does not read this config.exe.How can I make it read the app.config that resides withing this dll? Again, Usually you will have a web or windows app with a config and it will all work. Mine is a special case I need to read the connectionstring within this class library. How can I do it? thanks a lot

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  • Member variable in C++ class that is always constant for all objects of that class?

    - by user1799323
    I'm constructing a class where I have three member variables that I want to always be the same value NO MATTER WHAT. I have class foo{ public: double var_1, var_2, var_3; double x=1, y=2, z=3; [functions go here] }; that gave me an error since I can't initialize a variable like that. But I want x, y and z to always be 1, 2 and 3 respectively. I tried defining them outside the class but that doesn't work since I want them to be member variables of the class. How do I do this?

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  • Sending and treating text by get method

    - by ilnur777
    Guys, could you help me with treating text sent with GET method. How to detect and treat line foldings in text? The text is sent from textarea through AJAX using GET method. How to detect line foldings in text when it is sent in GET method? And I want to replace all line foldings with special character for example like "|" before sending to PHP script. How to do it?

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