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  • Problem with object serialization in Applet-Servlet communication

    - by Bruce
    Hi guys, I spent a lot of time on thinking what is wrong with the following code. I send the object from my applet to servlet and then I read the object from servlet. Everything goes fine till reading serialized object from the servlet - I got IOException. Thank you in advance! Here is the code: Applet: try { URL servletURL = new URL(this.getCodeBase().getProtocol(), this.getCodeBase().getHost(), this.getCodeBase().getPort(), "/MyApplet"); URLConnection servletConnection = servletURL.openConnection(); servletConnection.setDoInput( true ); servletConnection.setDoOutput( true ); servletConnection.setUseCaches( false ); servletConnection.setRequestProperty( "Content-Type", "application/x-java-serialized-object" ); ObjectOutputStream output; output = new ObjectOutputStream( servletConnection.getOutputStream( ) ); output.writeObject( someObject ); output.flush( ); output.close( ); ObjectInputStream input = new ObjectInputStream( servletConnection.getInputStream( ) ); // Here I got the exception myObject = ( SomeObject ) input.readObject( ); } catch (java.io.IOException ioe) { System.err.println(ioe.getStackTrace()); } catch (Exception e) { System.err.println(e.getStackTrace()); } Servlet: response.setContentType("application/x-java-serialized-object"); try { ObjectInputStream inputFromApplet = new ObjectInputStream(request.getInputStream()); SomeObject myObject = (SomeObject) inputFromApplet.readObject(); ObjectOutputStream outputToApplet = new ObjectOutputStream(response.getOutputStream()); outputToApplet.writeObject(myObject); outputToApplet.flush(); } catch(Exception e) { // ... }

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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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  • 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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  • Circular dependency with generics

    - by devoured elysium
    I have defined the following interface: public interface IStateSpace<State, Action> where State : IState where Action : IAction<State, Action> // <-- this is the line that bothers me { void SetValueAt(State state, Action action); Action GetValueAt(State state); } Basically, an IStateSpace interface should be something like a chess board, and in each position of the chess board you have a set of possible movements to do. Those movements here are called IActions. I have defined this interface this way so I can accommodate for different implementations: I can then define concrete classes that implement 2D matrix, 3D matrix, graphs, etc. public interface IAction<State, Action> { IStateSpace<State, Action> StateSpace { get; } } An IAction, would be to move up(this is, if in (2, 2) move to (2, 1)), move down, etc. Now, I'll want that each action has access to a StateSpace so it can do some checking logic. Is this implementation correct? Or is this a bad case of a circular dependence? If yes, how to accomplish "the same" in a different way? Thanks

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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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  • 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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  • 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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  • 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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  • 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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  • Accessing property of object vs variable in javascript

    - by Samuel
    Why when I try to access a variable that don't exist, javascript throw an exception but when I try to access a property that don't exist in an object, javascript returns an undefined object? For example, this case returns an undefined object: function Foo(){ console.log(this.bar); } Foo(); But, in this other example, javascript throw an exception: function Foo(){ console.log(bar); } Foo(); ReferenceError: bar is not defined

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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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  • Hibernate Updating an existing entity with a new object

    - by DD
    Hi, Assume I have an entity Foo in the DB. I am parsing some files and creating new Foo objects and would like to check if the parsed Foo object exists in the DB (using a unique attribute). If it exists already update it otherwise save as a new object. What is the best approach? Could I simply set the id and version in the new Foo object? Or would I be better off loading the Foo object from the DB and copying over the properties from the parsed file? Thanks.

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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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  • 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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  • JSON Object XHR and closures

    - by Sara Chipps
    Hi all, I have a JSON object that is populated by an XHR. I then need to update that object with values from a separate XHR call. The issue I am running into is the second call isn't being made at the correct time and I think it's an issue with how I structured my object. Here is what I have: function Proprietary() { var proprietary= this; this.Groups = {}; this.getGroups = function() { $.getJSON(group_url, function(data){proprietary.callReturned(data);}); } this.callReturned = function(data) { //Do stuff for(var i=0; i< data.groups.length; i++) { insparq.Groups[i] = data.groups[i]; $.getJSON(participant_url, function(p){proprietary.Groups[i].participants = p;}); } //the function call below is the action I want to occur after the object is populated. PopulateGroups(); } };

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  • jQuery find events handlers registered with an object

    - by ages04
    I need to find which event handlers an object has registered. eg. $("#el").click(function(){...}); $("#el").mouseover(function(){...}); Is there anyway I can use a function to find out that- $("#el") has click and mouseover registered and possibly iterate over the event handlers. If not a jQuery Object can we find this on a plain DOM object?

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  • Referencing the current jQuery object in a chain?

    - by Lance McNearney
    At DevDays in SF last year (before jQuery 1.4 was released), I thought they mentioned an upcoming feature in 1.4 that would allow you to reference the current jQuery object while in a chain. I've read through all of the 1.4 improvements and wasn't able to find it. Does anyone know how this can be done? Example Being able to access the current jQuery object would be helpful when working with methods that are in relation to the current object like .next(): // Current way var items = $(this).closest('tr'); items = items.add(items.next(':not([id])')); // Magical 1.4 way? Is there a "chain"-like object? var items = $(this).closest('tr') .add(chain.next(':not([id])'));

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