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  • Java interface design

    - by Nayn
    Hi, I had an interface initially as below. public interface testMe { public Set<String> doSomething(); } public class A implements testMe { public Set<String> doSomething() { return // Set<String> } } I had similar classes implementing testMe. Now I have to add one more class which returns Set<Some Object> public class X implements testMe() { public Set<Some OBject> doSomething() { } } How could i add this mehtod in the interface without breaking existing classes? Thanks Nayn

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  • PHP object class variable

    - by mck89
    I have built a class in PHP and I must declare a class variable as an object. Everytime I want to declare an empty object I use: $var=new stdClass; But if I use it to declare a class variable as class foo { var $bar=new stdClass; } a parse error occurs. Is there a way to do this or must I declare the class variable as an object in the constructor function? PS: I'm using PHP 4.

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  • Why Java interfaces can't have constructors?

    - by AndrejaKo
    This question showed up on my mid-term exams and I've been searching for correct answer for some time. I know that Java interfaces can't be directly instantiated so they don't need constructors and that they can have only public static final attributes so they don't need constructors to set them up but that's not the expected answer.

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  • Hibernate session method to update object

    - by EugeneP
    I need this roadmap of a Hibernate managed object instance. First, I create an instance with initial properties and persist this object in a db. Then session associated with this object is closed. But still, I serialize my object and on the next step deserialize it, invoke some setters, and again, I need to update what changed in a database. What methods of Hibernate session should I use? persist() or save() on the first step and saveOrUpdate() on the second? In fact I see that saveOrUpdate() can be used on each step. What would you recommend?

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  • Find the right parameters for an event without using Design Mode in Visual Studio 2010

    - by Jason
    Is there a way to know what parameters are needed by an event in Visual Studio 2010? Let's say I have a DropDownList control and I want to bind a method to the "OnSelectedIndexChanged", I would do something like this In the ASPX File: <asp:DropDownList ID="lstMyList" runat="server" OnSelectedIndexChanged="lstMyList_SelectedIndexChanged"></asp:DropDownList> In the codebehind: protected void lstMyList_SelectedIndexChanged(object sender, EventArgs e) { ... } Is there a way to know what parameters the method needs? (In this case, an object for the sender and an EventArgs parameter for the event.) I know you can easily create the method by double-clicking the right event in Design Mode, but it does a mess with your code so I prefer not to use it. Thanks!

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  • Dynamically create and cast objects at runtime

    - by vaibhav bindroo
    Let's say we have 2 classes A and B public class A{ private int member1; A() { member1 = 10; } public getMember(){ return member1; } } Class B is also on the same lines except that its member variable is named member2 and gets intitialized to say 20 inside the constructor. My Requirement : At runtime , I get a string which contains a className ( could be A or B). I want to dynamically create an object of this class along with invoking the constructor. How can I achieve this . I don't want to use interfaces for common functionality of above classes Morever, later on I set the properties of this raw object using Propery Builder Bean Util class based on a list of columns . Class clazz = Class.forName("className"); Obj obj = clazz.newInstance(); How I can dynamically convert that obj to className object.

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  • Google App Engine - Dealing with concurrency issues of storing an object

    - by Spines
    My User object that I want to create and store in the datastore has an email, and a username. How do I make sure when creating my User object that another User object doesn't also have either the same email or the same username? If I just do a query to see if any other users have already used the username or the email, then there could be a race condition. UPDATE: The solution I'm currently considering is to use the MemCache to implement a locking mechanism. I would acquire 2 locks before trying to store the User object in the datastore. First a lock that locks based on email, then another that locks based on username. Since creating new User objects only happens at user registration time, and it's even rarer that two people try to use either the same username or the same email, I think it's okay to take the performance hit of locking. I'm thinking of using the MemCache locking code that is here: http://appengine-cookbook.appspot.com/recipe/mutex-using-memcache-api/ What do you guys think?

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  • How should I declare default values for instance variables in Python?

    - by int3
    Should I give my class members default values like this: class Foo: num = 1 or like this? class Foo: def __init__(self): self.num = 1 In this question I discovered that in both cases, bar = Foo() bar.num += 1 is a well-defined operation. I understand that the first method will give me a class variable while the second one will not. However, if I do not require a class variable, but only need to set a default value for my instance variables, are both methods equally good? Or one of them more 'pythonic' than the other? One thing I've noticed is that in the Django tutorial, they use the second method to declare Models. Personally I think the second method is more elegant, but I'd like to know what the 'standard' way is.

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  • Inheritance from static classes? why not?

    - by Sorush Rabiee
    Hi Why inheritance is not provided for static classes in C#? I know C# has a good reason for everything he implements or doesn't implement. I just wondered, what’s that “good reason” here? semantically, what would be happened if I was able to write a static class that inheritances from another static one? is this an ODD issue? or just programming?

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  • c# - Object reference not set to an instance of an object.

    - by tom
    Line 30: sUsername.Trim(); Line 31: sPassword.Trim(); Line 32: string ConnectionString = WebConfigurationManager.ConnectionStrings["dbnameConnectionString"].ConnectionString; Line 33: SqlConnection myConnection = new SqlConnection(ConnectionString); Line 34: try Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.NullReferenceException: Object reference not set to an instance of an object. Any ideas? I don't understand the error.

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  • populate object graph from database

    - by Rama
    Hi, I would like to know the best way to populate an object that has a collection of child objects and each child object may inturn have a collection of objects, from database without making multiple calls to the database to get child objects for each object. basically in hierarchical format something like for example a customer has orders and each order has order items. is it best to retrieve the data in xml format (SQL server 2005), or retrieve a dataset by joining the related tables together and then map that the data to the object? thanks in advance for your help.

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  • How to access parent window variables from object

    - by Pickle
    I've got an XHTML 1.1 Strict document that is loading another XHTML 1.1 document in an <object> element (as <iframe> isn't part of the XHTML 1.1 spec). I'm having trouble in IE8 (don't care about 6 or 7) with accessing a javascript variable, Lightbox, in the parent window, from the document loaded in the <object>. In Firefox and everywhere I've seen online, I can just use window.parent.Lightbox. In IE8 however, I get it being undefined. window.parent does give me an object but it doesn't have my Lightbox variable. I've also tried window.Lightbox, window.top.Lightbox, and window.top.document.Lightbox, but all return undefined. I should mention I'm using Javascript to set the data property of the <object> - but I don't see how that could affect anything relevant. What Javascript Fu do I need to do to be able to access my Lightbox variable?

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  • vs2003 : assign datarow object

    - by dotnet-practitioner
    currently I am doing this... object s = new object(); ... s = mydatarow["mycolumn"]; What I would like to do is... DataRow r = null; ... r = mydatarow["mycolumn"]; and I get an error saying that can not covert from object to DataRow.. is there a better way of doing this?

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  • Events in Classes (VB.NET)

    - by Otaku
    I find that I write a lot of code within my classes to keep properties in sync with each other. I've read about Events in Classes, but have not been able to wrap my head around how to make them work for what I'm looking for. I could use some advice here. For example, in this one I always want to keep myColor up to date with any change whatsoever in any or all of the Red, Green or Blue properties. Class myColors Private Property Red As Byte Private Property Green As Byte Private Property Blue As Byte Private Property myColor As Color Sub New() myColor = Color.FromArgb(0, 0, 0) End Sub Sub ChangeRed(ByVal r As Byte) Red = r myColor = Color.FromArgb(Red, Green, Blue) End Sub Sub ChangeBlue(ByVal b As Byte) Blue = b myColor = Color.FromArgb(Red, Green, Blue) End Sub End Class If one or more of those changes, I want myColor to be updated. Easy enough as above, but is there a way to work with events that would automatically do this so I don't have to put myColor = Color.FromArgb(Red, Green, Blue) in every sub routine?

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  • How can I define an empty array in a Perl construtor?

    - by Laimoncijus
    I am just beginner with Perl, so if it sounds stupid - sorry for that :) My problem is - I am trying to write a class, which has an empty array, defined in constructor of a class. So I am doing this like this: package MyClass; use strict; sub new { my ($C) = @_; my $self = { items => () }; bless $self, ref $C || $C; } sub get { return $_[0]->{items}; } 1; Later I am testing my class with simple script: use strict; use Data::Dumper; use MyClass; my $o = MyClass->new(); my @items = $o->get(); print "length = ", scalar(@items), "\n", Dumper(@items); And while running the script I get following: $ perl my_test.pl length = 1 $VAR1 = undef; Why am I doing wrong what causes that I get my items array filled with undef? Maybe someone could show me example how the class would need to be defined so I would not get any default values in my array?

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  • C#: why have all static methods/variables in a non-static class?

    - by Craig Johnston
    I have come across a class which is non-static, but all the methods and variables are static. Eg: public class Class1 { private static string String1 = "one"; private static string String2 = "two"; public static void PrintStrings(string str1, string str2) { ... All the variables are static across all instances, so there is no point having separate instances of the class. Is there any reason to create a class such as this?

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  • Using enums or a set of classes when I know I have a finite set of different options?

    - by devoured elysium
    Let's say I have defined the following class: public abstract class Event { public DateTime Time { get; protected set; } protected Event(DateTime time) { Time = time; } } What would you prefer between this: public class AsleepEvent : Event { public AsleepEvent(DateTime time) : base(time) { } } public class AwakeEvent : Event { public AwakeEvent(DateTime time) : base(time) { } } and this: public enum StateEventType { NowAwake, NowAsleep } public class StateEvent : Event { protected StateEventType stateType; public MealEvent(DateTime time, StateEventType stateType) : base(time) { stateType = stateType; } } and why? I am generally more inclined to the first option, but I can't explain why. Is it totally the same or are any advantages in using one instead of the other? Maybe with the first method its easier to add more "states", altough in this case I am 100% sure I will only want two states: now awake, and now asleep (they signal the moments when one awakes and one falls asleep).

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