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  • To "null" or not to "null" my class's attributes

    - by Helper Method
    When I write a class in Java, I like to initialize the attributes which are set to a default value directly and attributes which are set by the caller in the constructor, something like this: public class Stack<E> { private List<E> list; private size = 0; public Stack(int initialCapacity) { list = new ArrayList<E>(initialCapacity); } // remainder omitted } Now suppose I have a Tree class: public class Tree<E> { private Node<E> root = null; // no constructor needed, remainder omitted } Shall I set the root attribute to null, to mark that it is set to null by default, or omit the null value?

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  • WPF: Change padding depending of container ?

    - by Alex Ilyin
    I have UserControl named MyUserControl, and another UserControl named MyContainer. I want MyUserControl to have padding 10 if it is placed inside MyContainer and 15 otherwise. Shortly, I want <MyContainer> <MyUserControl> Hello </MyUserControl> </MyContainer> to look like <MyContainer> <UserControl Padding="10"> Hello </UserControl> <MyContainer> and <MyUserControl> Hello </MyUserControl> to look like <UserControl Padding="15"> Hello </UserControl>

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  • Cannot use String.Empty as a default value for an optional parameter in C# - then what's the point?

    - by Mikeyg36
    I am reading Effective C# by Bill Wagner. In Item 14 - Minimize Duplicate Initialization Logic, he shows the following example of using the new optional parameters feature in a constructor: public MyClass(int initialCount = 0, string name = "") Notice that he used "" instead of string.Empty. He comments: You'll note [in an example above] that the second constructor specified "" for the default value on the name parameter, rather than the more customary string.Empty. That's because string.Empty is not a compile-time constant. It is a static property defined in the string class. Because it is not a compile constant, you cannot use it for the default value for a parameter. If we cannot use the string.Empty static in all situations, then doesn't that defeat the purpose of it? I thought that we would use it to be sure that we have a system-independent means of referring to the empty string. Is my understanding wrong? Thanks.

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  • Runtime error in sml function

    - by Rpant
    I am writing this function in sml fun removeNodeswithNoIncoming((x:int,y)::xs,element:int) = if x=element then removeNodeswithNoIncoming (xs , element) else (x,y) :: removeNodeswithNoIncoming (xs , element) | removeNodeswithNoIncoming(nil,element) = nil; the function takes list of tuples [(0,0),(0,1)(1,2)] and another element 0 if first element of the tuples is same as second parameter , it removes it from the list The o/p for the above list should be [(1,2)] Unfortunately , the code is not working for the above input. Though there are other inputs for which it works - removeNodeswithNoIncomingEdge([(0,1),(0,2),(1,2)],0); stdIn:30.1-30.30 Error: unbound variable or constructor: removeNodeswithNoIncomi ngEdge - removeNodeswithNoIncomingEdge([(0,1),(0,2),(1,2),(1,4)],0); stdIn:1.2-1.31 Error: unbound variable or constructor: removeNodeswithNoIncoming Edge

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  • How do I change my current directory from a python script?

    - by misterloogs
    I'm trying to implement my own version of the 'cd' command that presents the user with a list of hard-coded directories to choose from, and the user has to enter a number corresponding to an entry in the list. The program, named my_cd.py for now, should then effectively 'cd' the user to the chosen directory. Example of how this should work: /some/directory $ my_cd.py 1) ~ 2) /bin/ 3) /usr Enter menu selection, or q to quit: 2 /bin $ Currently, I'm trying to 'cd' using os.chdir('dir'). However, this doesn't work, probably because my_cd.py is kicked off in its own child process. I tried wrapping the call to my_cd.py in a sourced bash script named my_cd.sh: #! /bin/bash function my_cd() { /path/to/my_cd.py } /some/directory $ . my_cd.sh $ my_cd ... shows list of dirs, but doesn't 'cd' in the interactive shell Any ideas on how I can get this to work? Is it possible to change my interactive shell's current directory from a python script?

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  • C# DDD Populate Immutable Objects

    - by Russel
    Hi I have a immutable Customer class in my domain assembly. It contains the following GET properties : id, firstname and lastname. I have a CustomerRepository class in my persistence assembly. In turn, this CustomerRepository class should populate and return a Customer object using a remote web-serivce. My Customer class contains no setter properties and it contains a private constructor. The reason - I dont want the UI developer to get the wrong idea - He should not be able to create or change a Customer object. My question: How do I get my CustomerRepository to populate my Customer object. Reflection? Or should I sacrifice my design and enable a public constructor for constructing the customer object?

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  • Locate Database File in SQLITE

    - by Nagendra Baliga
    I have created a file named "MyFile.db" using SQLite3 from my C#.net application. This file got created in my "D:\MyProject\bin" folder. I have created a table named "MyTable" inside "MyFile.db" from same C# app. Now I am running sqlite3.exe from my "C:\" drive to get Command Line Shell For SQLite. How can I get the file "D:\MyProject\bin\MyFile.db" in the SQLite Command Line Shell i.e, how can I locate the file "MyFile.db" in the command shell to get the data from "MyTable".

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  • Please suggest me the best way to design my database.

    - by Raymond Ho
    I have a table named "Pages" and a table named "Categories". Each entry of the table "Pages" is linked to the table "Categories". The "Categories" table have 5 entries, they are: "Car", "Websites", "Technology", "Mobile Phones", and "Interest". So each time I put an entry to the "Pages" table, I need to map it to the "Categories" table so are arranged properly. Here's my table: Pages ______ id [PK] name url Categories ______ id [PK] Categoryname Pages2Categories ______ Pages.id Categories.id So my question is, is this the most efficient way to create this kind of relationships between tables? It seems very amateur

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  • Resharper: how to force introducing new private fields at the bottom of the class?

    - by Igor Brejc
    Resharper offers a very useful introduce and initialize field xxx action when you specify a new parameter in a constructor like: Constructor (int parameter) The only (minor) nuisance is that it puts the new field at the beginning of the class - and I'm a fan of putting private parts as far away as possible from the prying eyes of strangers ;). If, however, you already have some private fields in the class, Resharper will put the new field "correctly" (note the quotes, I don't want to start a flame war over this issue) next to those, even if they are at the end of the class. Is there a way to force Resharper to always put new fields at the end of the class? UPDATE: OK, I forgot to mention I know about the "Type Members Layout in Options" feature, but some concrete help on how to modify the template to achieve fields placement would be nice.

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  • What are the other new features of C# 4.0, after dynamic and optional parameters?

    - by Abel
    So, C# 4.0 came out yesterday. It introduced the much-debated dynamic keyword, named and optional parameters. Smaller improvements were the implicit ref and recognizing of indexed and default properties on COM methods, contra- and co-variance (really a .NET CLR feature, not C# only) and... Is that really it? Are dynamic and optional/named params the only real improvements to C#? Or did I miss something? Not that I'm complaining, but it seems a bit meager after C# 2.0 (generics) and C# 3.0 (lambda, LINQ). Maybe the language just reached actual maturity?

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  • An exception to the "only one implementation" rule ?

    - by ereOn
    While I was reading the accepted answer of this question, I had the following question: Typically, methods are defined in header files (.hpp or whatever), and implementation in source files (.cpp or whatever). One of the main reasons it is bad practice to ever include a "source file" (#include <source_file.cpp>) is that its methods implementation would then be duplicated, resulting in linking errors. When one writes: #ifndef BRITNEYSPEARS_HPP #define BRITNEYSPEARS_HPP class BritneySpears { public: BritneySpears() {}; // Here the constructor has implementation. }; #endif /* BRITNEYSPEARS_HPP */ He is giving the implementation of the constructor (here an "empty" implementation, but still). But why then including this header file multiple times (aka. on different source files) will not generate a "duplicate definition" error at link time ?

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  • Is c++ explicit conversion really that bad?

    - by LoudNPossiblyRight
    My knowledge in c++ at this point is more academic than anything else and in all my reading thus far, the use of explicit conversion with named casts (const_cast, static_cast, reinterpret_cast, dynamic_cast) has come with a big warning label (and it's easy to see why) that pretty much implies explicit conversion is symptomatic of bad design and should only be used as a last resort in desperate circumstances. So i have to ask: Is explicit conversion with named casts really just jury rigging code or is there a more graceful and positive application to this feature? Is there a good example of the latter? Thanks in advance.

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  • Don't understand multiple parameter declarations in objective-c

    - by Blankman
    can someone clarify this for me: When there’s more than one argument, the arguments are declared within the method name after the colons. Arguments break the name apart in the declaration, just as in a message. For example: - (void)setWidth:(float)width height:(float)height; So in the above: method is for instance variables returns void parameter#1 is a float, named width. parameter#2 is a float,named height. But why is it hieght:(float)height; and not just: - (void)setWidth: (float)width (float)height;

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  • Why the compiler doesn't complain about this error ?

    - by M.H
    Hi I am writing some java questions to help my friends in the java exam. I wrote a question and I supposed that three errors will occurred in the code but the compiler complained only about two. the code is : class MyClass { static MyClass() { System.out.println("I am The First Statement here!"); this(); } } I expected the following errors : the constructor can't be static this can't be in a static function (since the constructor isn't valid) this here should be the first statement. NetBeans isn't complaining about the second error here. why ?

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  • Design question - loading info from DB

    - by eriks
    I need to build a class that will represent a row in some table in DB (lets say the table is 'Subscriber' and so is the class). I can have the class Subscriber which constructor receives the Objectkey of subscriber, retrieves info from DB and initializes its members. I add another class - SubscriberLoader which have a static method 'LoadSubscriber'. This method will receive the subscriber objectkey, retrieve info from DB, crate a Subscriber object and initialize its members. Subscriber constructor will be private and SubscirberLoader will be friend class of Subscriber - this way, client could build a Subscriber only using the loader. which of the two in better? any other suggestions?

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  • problem with update the counter value

    - by Edan
    Hello, I having problem to update the counter (integer value). this is the definitions of the class: public class Item_Actions { private final int MAX_ITEMS = 100; private Item myItem[]; private int counter; public Item_Actions() { myItem = new Item[MAX_ITEMS]; counter++; } //Constructor add item into the menu (Description, type & price of Item) public void addItem(Item itm) { myItem[counter] = itm; counter++; }....... Now everytime I call the addItem constructor from another class, the counter always stays on zero. What causing it and how do I save the data inside? thanks

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  • How does a Java Arraylist contains() method evaluate objects?

    - by mvid
    Say i create one object and add it to my ArrayList. If I then create another object with exactly the same constructor input, will the contain() method evaluate the two objects to be the same? Assume the constructor doesn't do anything funny with the input, and the variables stored in both objects are identical. ArrayList<Thing> basket = new ArrayList<Thing>(); Thing thing = new Thing(100); basket.add(thing); Thing another = new Thing(100); basket.contains(another); // true or false?

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  • Making uppercase of std::string

    - by Daniel K.
    Which implementation do you think is better? std::string ToUpper( const std::string& source ) { std::string result; result.reserve( source.length() ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } and... std::string ToUpper( const std::string& source ) { std::string result( source.length(), '\0' ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } Difference is that the first one uses reserve method after the default constructor, but the second one uses the constructor accepting the number of characters.

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  • Is it possible to deny access to SQL Server from specific programs?

    - by Paul McLoughlin
    Currently one of our databases (SQL Server 2008) is accessed via a number of different mechanisms: .Net SqlClient Data Provider; SQL Server Management Studio; various .Net applications and 2007 Microsoft Office system (basically Excel). I see that in the sys.dm_exec_sessions DMV it is possible to see the program name of the program accessing the database for the current sessions. My question is: is it possible for one to deny access from a particular named program? First prize would be if this could be done for any named program, but we would gain a great deal of benefit from being able to deny access to this specific database from all Microsoft Office applications (especially Excel).

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  • Does Qt support virtual pure slots ?

    - by ereOn
    Hi, My GUI project in Qt has a lot of "configuration pages" classes which all inherit directly from QWidget. Recently, I realized that all these classes share 2 commons slots (loadSettings() and saveSettings()). Regarding this, I have two questions: Does it make sense to write a intermediate base abstract class (lets name it BaseConfigurationPage) with these two slots as virtual pure methods ? (Every possible configuration page will always have these two methods, so I would say "yes") Before I do the heavy change in my code (if I have to) : does Qt support virtual pure slots ? Is there anything I should be aware of ? Here is a code example describing everything: class BaseConfigurationPage : public QWidget { // Some constructor and other methods, irrelevant here. public slots: virtual void loadSettings() = 0; virtual void saveSettings() = 0; }; class GeneralConfigurationPage : public BaseConfigurationPage { // Some constructor and other methods, irrelevant here. public slots: void loadSettings(); void saveSettings(); };

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  • Hierarchy of modules in guice

    - by Niko
    Hi, I'd like to run a unit test where a constant is slightly different than in the standard version. That is, in my default module, the following is bindConstant().annotatedWith(Names.named("number of players")).to(4); but in testing, I'd like to try this line instead: bindConstant().annotatedWith(Names.named("number of players")).to(2); Id like to achieve that without copying all of the rest of the module. What I really want is a "default" module that is "below" a more specialized module, such that in case of conflict, the specialized module wins (instead of throwing an exception, which is what guice does). In essence, my question is: how does anybody arrange for more than one module without lots of code duplication?

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  • How to find the entity with the greatest primary key?

    - by simpatico
    I've an entity LearningUnit that has an int primary key. Actually, it has nothing more. Entity Concept has the following relationship with it: @ManyToOne @Size(min=1,max=7) private LearningUnit learningUnit; In a constructor of Concept I need to retrieve the LearningUnit with the greatest primary key. If no LearningUnit exists yet I instantiate one. I then set this.learningUnit to the retrieved/instantied. Finally, I call the empty constructor of Concept in a try-catch block, to have the entitymanager do the cardinality check. If an exception is thrown (I expect one in the case that already another 7 Concepts are referring to the same LearningUnit. In that case, I case instantiate a new LearningUnit with a new greater primary key. Please, also point out, if any, clear pitfalls in my outlined algorithm above.

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  • Getter/Setter from separate class file in Java

    - by Crystal
    I'm new to Java and for a HW assignment, we had to create a Person class that has a constructor, getter/setter for the attributes of firstName, lastName, phone. That is in a separate file from an old HW assignment (Person.java). Now we have to use that Person class in our new HW assignment (LoanApplication.java). So if one of the attributes is private Person client do I need to create getter/setters or a constructor again? Otherwise, how does each LoanApplicaiton instance know which Person attribute it is to go with? How does the JVM know that it can use the Person.class even though my LoanApplicaiton.class does not extend Person.class? Thanks.

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  • Regarding Authlogic and page redirection.

    - by Paddy
    I am using authlogic for authentication in my Rails app. Have named routes for the frequent actions, viz: map.login "login", :controller = "user_sessions", :action = "new" map.logout "logout", :controller = "user_sessions", :action = "destroy" map.register "register", :controller = "users", :action = "new" map.edit 'user/edit/:id', :controller = "users", :action = "edit" But also in my routes.rb i have these automatically created REST routes too: map.resources :user_sessions map.resources :users The problem now is that a user can login from two different routes. Ex: From, http://localhost/login and also from http ://localhost/user_sessions/new. How do i restrict access only from the named route i have defined and not allow from user_sessions/new?

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