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• permutations gone wrong

  - by vbNewbie

  I have written code to implement an algorithm I found on string permutations. What I have is an arraylist of words ( up to 200) and I need to permutate the list in levels of 5. Basically group the string words in fives and permutated them. What I have takes the first 5 words generates the permutations and ignores the rest of the arraylist? Any ideas appreciated. Private Function permute(ByVal chunks As ArrayList, ByVal k As Long) As ArrayList ReDim ItemUsed(k) pno = 0 Permutate(k, 1) Return chunks End Function Private Shared Sub Permutate(ByVal K As Long, ByVal pLevel As Long) Dim i As Long, Perm As String Perm = pString ' Save the current Perm ' for each value currently available For i = 1 To K If Not ItemUsed(i) Then If pLevel = 1 Then pString = chunks.Item(i) 'pString = inChars(i) Else pString = pString & chunks.Item(i) 'pString += inChars(i) End If If pLevel = K Then 'got next Perm pno = pno + 1 SyncLock outfile outfile.WriteLine(pno & " = " & pString & vbCrLf) End SyncLock outfile.Flush() Exit Sub End If ' Mark this item unavailable ItemUsed(i) = True ' gen all Perms at next level Permutate(K, pLevel + 1) ' Mark this item free again ItemUsed(i) = False ' Restore the current Perm pString = Perm End If Next K above is = to 5 for the number of words in one permutation but when I change the for loop to the arraylist size I get an error of index out of bounds

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• Redirect to another action in an interceptor in struts 2

  - by user292662

  I am currently in the process of learning Struts 2 and I am currently building a simple application where unverified users are redirected to a login form. I have a login form and action functional which takes the users credentials, verifies them and stores a User object in the session however I am now trying to prevent access to pages before the login has taken place and I am trying to do this with an interceptor. My problem is that I have written an interceptor that checks whether the User object has been saved in the session but if it has not I want to redirect to the login page and can't find any way of doing this without bypassing struts and using the HttpServletResponse.sendRedirect method Configuration: <package name="mypackage" extends="struts-default" namespace="/admin"> <interceptors> <interceptor name="login" class="my.LoginInterceptor" /> </interceptors> <default-interceptor-ref name="login"/> <action name="login" class="my.LoginAction"> <result name="input">/admin/login.jsp</result> <result name="success" type="redirect">/admin</result> </action> <action name="private" class="my.PrivateAction"> <result>/admin/private.jsp</result> </action> </package> The interceptor code: @Override public String intercept(ActionInvocation inv) throws Exception { Map<String, Object> session = inv.getInvocationContext().getSession(); Object user = session.get("user"); if(user == null) { // redirect to the 'login' action here } else { return inv.invoke(); } }

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• Is there some advantage to filling a stack with nils and interpreting the "top" as the last non-nil value?

  - by dwilbank

  While working on a rubymonk exercise, I am asked to implement a stack with a hard size limit. It should return 'nil' if I try to push too many values, or if I try to pop an empty stack. My solution is below, followed by their solution. Mine passes every test I can give it in my IDE, while it fails rubymonk's test. But that isn't my question. Question is, why did they choose to fill the stack with nils instead of letting it shrink and grow like it does in my version? It just makes their code more complex. Here's my solution: class Stack def initialize(size) @max = size @store = Array.new end def pop empty? ? nil : @store.pop end def push(element) return nil if full? @store.push(element) end def size @store.size end def look @store.last end private def full? @store.size == @max end def empty? @store.size == 0 end end and here is the accepted answer class Stack def initialize(size) @size = size @store = Array.new(@size) @top = -1 end def pop if empty? nil else popped = @store[@top] @store[@top] = nil @top = @top.pred popped end end def push(element) if full? or element.nil? nil else @top = @top.succ @store[@top] = element self end end def size @size end def look @store[@top] end private def full? @top == (@size - 1) end def empty? @top == -1 end end

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• CF - How to get mouse position when ContextMenu pops up ??

  - by no9

  I have a problem i cannot solve. In my view (that shows a map) i created a contextMenu. When context menu is invoked i need to get the position where the user has clicked on the map. Here is my problem: In the view i already have onMouseDown event that gets me the coordinates where the user clicked. private void MapView_MouseDown(object sender, MouseEventArgs e) { this.lastMouseDownX = e.X; this.lastMouseDownY = e.Y; } When the contextMenu is invoked i need the same data, but the problem is that contextMenu only has EventArgs that dont keep the data i need. Furthermore ... contextMenu is invoked when user presses and holds mouse for a second and when its invoked the code does not enter onMouseDown event ! It just goes into popup event on my context menu.... I tried putting this in my popup event, but the coordinates are not ok. Y coordinate is way off the chart. private void servicesContextMenu_Popup(object sender, EventArgs e) { this.lastMouseUpX = Control.MousePosition.X; this.lastMouseUpX = Control.MousePosition.Y; } I also tried this, but with no success ... the problem remains ... when contextMenu is invoked the code does not fire onMouseDown event. http://www.mofeel.net/58-microsoft-public-dotnet-framework-compactframework/19285.aspx Help?

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• What is the fastest collection in c# to implement a prioritizing queue?

  - by Nathan Smith

  I need to implement a queue for messages on a game server so it needs to as fast as possible. The queue will have a maxiumem size. I need to prioritize messages once the queue is full by working backwards and removing a lower priority message (if one exists) before adding the new message. The appliation is asynchronous so access to the queue needs to be locked. I'm currently implementing it using a LinkedList as the underlying storage but have concerns that searching and removing nodes will keep it locked for too long. Heres the basic code I have at the moment: public class ActionQueue { private LinkedList<ClientAction> _actions = new LinkedList<ClientAction>(); private int _maxSize; /// <summary> /// Initializes a new instance of the ActionQueue class. /// </summary> public ActionQueue(int maxSize) { _maxSize = maxSize; } public int Count { get { return _actions.Count; } } public void Enqueue(ClientAction action) { lock (_actions) { if (Count < _maxSize) _actions.AddLast(action); else { LinkedListNode<ClientAction> node = _actions.Last; while (node != null) { if (node.Value.Priority < action.Priority) { _actions.Remove(node); _actions.AddLast(action); break; } } } } } public ClientAction Dequeue() { ClientAction action = null; lock (_actions) { action = _actions.First.Value; _actions.RemoveFirst(); } return action; } }

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• Jquery autocomplete webservices - what am i doing wrong??

  - by dzajdol

  I created a class for JSON responses: public class PostCodeJson { public String Text { get; private set; } public String Value { get; private set; } #region Constructors /// <summary> /// Empty constructor /// </summary> public PostCodeJson() { this.Text = String.Empty; this.Value = String.Empty; } /// <summary> /// Constructor /// </summary> /// <param name="_text"></param> /// <param name="_value"></param> public PostCodeJson(String _text, String _value) { this.Text = _text; this.Value = _value; } #endregion Constructors } and function returns list of this class using in webservices method: [WebMethod] public List<PostCodeJson> GetPostCodesCompletionListJson(String prefixText, Int32 count) { return LibDataAccess.DBServices.PostCodes.GetPostCodeJson(prefixText, count); } And in aspx i do this that: <script> $(document).ready(function() { $("#<%=pc.ClientID %>").autocomplete( baseUrl + "WebServices/Autocomplete.asmx/GetPostCodesCompletionListJson", { parse: function(data) { var array = new Array(); for (var i = 0; i < data.length; i++) { var datum = data[i]; var name = datum.Text; var display = name; array[array.length] = { data: datum, value: display, result: datum.Value }; } return array; }, dataType: "xml" }); }); </script> and when you enter something in the box i got an error: Request format is unrecognized for URL unexpectedly ending in '/GetPostCodesCompletionListJson What am I doing wrong??

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• LINQtoSQL Custom Constructor off Partial Class?

  - by sah302

  Hi all, I read this question here: http://stackoverflow.com/questions/82409/is-there-a-way-to-override-the-empty-constructor-in-a-class-generated-by-linqtosq Typically my constructor would look like: public User(String username, String password, String email, DateTime birthday, Char gender) { this.Id = Guid.NewGuid(); this.DateCreated = this.DateModified = DateTime.Now; this.Username = username; this.Password = password; this.Email = email; this.Birthday = birthday; this.Gender = gender; } However, as read in that question, you want to use partial method OnCreated() instead to assign values and not overwrite the default constructor. Okay so I got this : partial void OnCreated() { this.Id = Guid.NewGuid(); this.DateCreated = this.DateModified = DateTime.Now; this.Username = username; this.Password = password; this.Email = email; this.Birthday = birthday; this.Gender = gender; } However, this gives me two errors: Partial Methods must be declared private. Partial Methods must have empty method bodies. Alright I change it to Private Sub OnCreated() to remove both of those errors. However I am still stuck with...how can I pass it values as I would with a normal custom constructor? Also I am doing this in VB (converted it since I know most know/prefer C#), so would that have an affect on this?

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• Consistent Equals() results, but inconsistent TreeMap.containsKey() result

  - by smessing

  I have the following object Node: private class Node implements Comparable<Node>(){ private String guid(); ... public boolean equals(Node o){ return (this == o); } public int hashCode(){ return guid.hashCode(); } ... } And I use it in the following TreeMap: TreeMap<Node, TreeSet<Edge>> nodes = new TreeMap<Node, TreeSet<Edge>>(); Now, the tree map is used in a class called Graph to store nodes currently in the graph, along with a set of their edges (from the class Edge). My problem is when I try to execute: public containsNode(n){ for (Node x : nodes.keySet()) { System.out.println("HASH CODE: "); System.out.print(x.hashCode() == n.hashCode()); System.out.println("EQUALS: "); System.out.print(x.equals(n)); System.out.println("CONTAINS: "); System.out.print(nodes.containsKey(n)); System.out.println("N: " + n); System.out.println("X: " + x); } } I sometimes get the following: HASHCODE: true EQUALS: true CONTAINS: false N: foo X: foo Anyone have an idea as to what I'm doing wrong? I'm still new to all this, so I apologize in advance if I'm overlooking something simple (I know hashCode() doesn't really matter for TreeMap, but I figured I'd include it).

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• .Net Finalizer Order / Semantics in Esent and Ravendb

  - by mattcodes

  Help me understand. I've read that "The time and order of execution of finalizers cannot be predicted or pre-determined" Correct? However looking at RavenDB source code TransactionStorage.cs I see this ~TransactionalStorage() { try { Trace.WriteLine( "Disposing esent resources from finalizer! You should call TransactionalStorage.Dispose() instead!"); Api.JetTerm2(instance, TermGrbit.Abrupt); } catch (Exception exception) { try { Trace.WriteLine("Failed to dispose esent instance from finalizer because: " + exception); } catch { } } } The API class (which belongs to Managed Esent) which presumable takes handles on native resources presumably using a SafeHandle? So if I understand correctly the native handles SafeHandle can be finalized before TransactionStorage which could have undesired effects, perhaps why Ayende has added an catch all clause around this? Actually diving into Esent code, it does not use SafeHandles. According to CLR via C# this is dangerous? internal static class SomeType { [DllImport("Kernel32", CharSet=CharSet.Unicode, EntryPoint="CreateEvent")] // This prototype is not robust private static extern IntPtr CreateEventBad( IntPtr pSecurityAttributes, Boolean manualReset, Boolean initialState, String name); // This prototype is robust [DllImport("Kernel32", CharSet=CharSet.Unicode, EntryPoint="CreateEvent")] private static extern SafeWaitHandle CreateEventGood( IntPtr pSecurityAttributes, Boolean manualReset, Boolean initialState, String name) public static void SomeMethod() { IntPtr handle = CreateEventBad(IntPtr.Zero, false, false, null); SafeWaitHandle swh = CreateEventGood(IntPtr.Zero, false, false, null); } } Managed Esent (NativeMEthods.cs) looks like this (using Ints vs IntPtrs?): [DllImport(EsentDll, CharSet = EsentCharSet, ExactSpelling = true)] public static extern int JetCreateDatabase(IntPtr sesid, string szFilename, string szConnect, out uint dbid, uint grbit); Is Managed Esent handling finalization/dispoal the correct way, and second is RavenDB handling finalizer the corret way or compensating for Managed Esent?

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• How to store a public key in a machine-level RSA key container

  - by Andrew Kimball

  I'm having a problem using a machine level RSA key container when storing only the public key of a public/private key pair. The following code creates a public/private pair and extracts the public key from that pair. The pair and the public key are stored in separate key containers. The keys are then obtained from those key containers at which point they should be the same as the keys going into the containers. The code works when CspProviderFlags.UseDefaultKeyContainer is specified for CspParameters.Flags (i.e. the key read back out from the PublicKey container is the same), but when CspProviderFlags.UseMachineKeyStore is specified for CspParameters.Flags the key read back from PublicKey is different. Why is the behaviour different, and what do I need to do differently to retrieve the public key from a machine-level RSA key container? var publicPrivateRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicPrivateKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ) { PersistKeyInCsp = true, }; var publicRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ) { PersistKeyInCsp = true }; //Export the key. publicRsa.ImportParameters(publicPrivateRsa.ExportParameters(false)); Console.WriteLine(publicRsa.ToXmlString(false)); Console.WriteLine(publicPrivateRsa.ToXmlString(false)); //Dispose those two CSPs. using (publicRsa) { publicRsa.Clear(); } using (publicPrivateRsa) { publicRsa.Clear(); } publicPrivateRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicPrivateKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ); publicRsa = new RSACryptoServiceProvider(new CspParameters() { KeyContainerName = "PublicKey", Flags = CspProviderFlags.UseMachineKeyStore //Flags = CspProviderFlags.UseDefaultKeyContainer } ); Console.WriteLine(publicRsa.ToXmlString(false)); Console.WriteLine(publicPrivateRsa.ToXmlString(false)); using (publicRsa) { publicRsa.Clear(); } using (publicPrivateRsa) { publicRsa.Clear(); }

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• How to download .exe file with progress bar - VB 2012

  - by user2839828

  I am trying to create an updater for my program which automatically download's the latest version of my program from the web. Now I want this process to be done using a progress bar (so when the download progress is at 50% the progress bar is half-way through). This is my code: Private Sub client_ProgressChanged(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs) Dim bytesIn As Double = Double.Parse(e.BytesReceived.ToString()) Dim totalBytes As Double = Double.Parse(e.TotalBytesToReceive.ToString()) Dim percentage As Double = bytesIn / totalBytes * 100 client.Value = Int32.Parse(Math.Truncate(percentage).ToString()) End Sub Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click Dim url As String = "MY DOWNLOAD LINK" 'Download Dim client As WebClient = New WebClient AddHandler client.DownloadProgressChanged, AddressOf client_ProgressChanged AddHandler client.DownloadFileCompleted, AddressOf client_DownloadCompleted client.DownloadFileAsync(New Uri(url), "C:\Users\User\Desktop\BACKUP\TESTING\New folder\1.exe") End Sub End Class Now I know that the place where the file is saved has been inputed manually by me , but I will change that later. My problem currently is that the file is not being downloaded. However when I change the DownloadFileAsync method to DownloadFile , my program downloads the file. However with the DownloadFile method I will not be able to use the progress bar to track the download progress. Any help is much appreciated :-)

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• How to use a int2 database-field as a boolean in Java using JPA/Hibernate

  - by mg

  Hello... I write an application based on an already existing database (postgreSQL) using JPA and Hibernate. There is a int2-column (activeYN) in a table, which is used as a boolean (0 = false (inactive), not 0 = true (active)). In the Java application i want to use this attribute as a boolean. So i defined the attribute like this: @Entity public class ModelClass implements Serializable { /*..... some Code .... */ private boolean active; @Column(name="activeYN") public boolean isActive() { return this.active; } /* .... some other Code ... */ } But there ist an exception because Hibernate expects an boolean database-field and not an int2. Can i do this mapping i any way while using a boolean in java?? I have a possible solution for this, but i don't really like it: My "hacky"-solution is the following: @Entity public class ModelClass implements Serializable { /*..... some Code .... */ private short active_USED_BY_JPA; //short because i need int2 /** * @Deprecated this method is only used by JPA. Use the method isActive() */ @Column(name="activeYN") public short getActive_USED_BY_JPA() { return this.active_USED_BY_JPA; } /** * @Deprecated this method is only used by JPA. * Use the method setActive(boolean active) */ public void setActive_USED_BY_JPA(short active) { this.active_USED_BY_JPA = active; } @Transient //jpa will ignore transient marked methods public boolean isActive() { return getActive_USED_BY_JPA() != 0; } @Transient public void setActive(boolean active) { this.setActive_USED_BY_JPA = active ? -1 : 0; } /* .... some other Code ... */ } Are there any other solutions for this problem? The "hibernate.hbm2ddl.auto"-value in the hibernate configuration is set to "validate". (sorry, my english is not the best, i hope you understand it anyway)..

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• Help with error creating SharePoint list (probably due to privilege issues)

  - by Swami

  I'm getting an error when trying to activate a webpart. It activates fine in one setup , but fails in a different one. Administrator in both. Seems like it fails because it's not able to create the list. The error is: Message: Value cannot be null. Stack Trace: at Microsoft.Sharepoint.SPRoleAssignment..ctor at ClientRequestHandler.CreateList(... private static void CreateLists() { try { SPSecurity.RunWithElevatedPrivileges(delegate() { using (SPSite site = SPContext.Current.Site) { using (SPWeb web = site.RootWeb) { string listName = LIST_NAME; bool listExist = ContainList(web, listName); if (!listExist) { AddFieldDelegate _delegate = new AddFieldDelegate(AddAttachmentFields); SPList list = CreateList(web, listName, _delegate); RegisterList(web, list, KEY); } } } }); } catch (Exception ex) { throw new Exception(String.Format("Message: {0} Stack Trace: {1}", ex.Message, ex.StackTrace.ToString())); } } private static SPList CreateList(SPWeb web, string listName, AddFieldDelegate _delegate) { web.AllowUnsafeUpdates = true; SPListTemplateType genericList = new SPListTemplateType(); genericList = SPListTemplateType.GenericList; Guid listGuid = web.Lists.Add(listName, "List", genericList); SPList list = web.Lists[listGuid]; list.Hidden = true; SPView view = _delegate(list); view.Update(); //Remove permissions from the list list.BreakRoleInheritance(false); //Make site owners the list administrators SPPrincipal principal = web.AssociatedOwnerGroup as SPPrincipal; SPRoleAssignment assignment = new SPRoleAssignment(principal); assignment.RoleDefinitionBindings.Add(web.RoleDefinitions.GetByType(SPRoleType.Administrator)); list.RoleAssignments.Add(assignment); //update list changes list.Update(); return list; }

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• Is using YIELD a read-only way to return a collection?

  - by Eric

  I'm writing an interface which has a collection property which I want to be read only. I don't want users of the interface to be able to modify the collection. The typical suggestion I've found for creating a read only collection property is to set the type of the property to IEnumerable like this: private List<string> _mylist; public IEnumerable<string> MyList { get { return this._mylist; } } Yet this does not prevent the user from casting the IEnumerable back to a List and modifying it. If I use a Yield keyword instead of returning _mylist directly would this prevent users of my interface from being able to modify the collection. I think so because then I'm only returning the objects one by one, and not the actual collection. private List<string> _mylist; public IEnumerable<string> MyList { get { foreach(string str in this._mylist) { yield return str; } } }

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• How do I write test code to exercise a C# generic Pair<TKey, TValue> ?

  - by Scott Davies

  Hi, I am reading through Jon Skeet's "C# in Depth", first edition (which is a great book). I'm in section 3.3.3, page 84, "Implementing Generics". Generics always confuse me, so I wrote some code to exercise the sample. The code provided is: using System; using System.Collections.Generic; public sealed class Pair<TFirst, TSecond> : IEquatable<Pair<TFirst, TSecond>> { private readonly TFirst first; private readonly TSecond second; public Pair(TFirst first, TSecond second) { this.first = first; this.second = second; } ...property getters... public bool Equals(Pair<TFirst, TSecond> other) { if (other == null) { return false; } return EqualityComparer<TFirst>.Default.Equals(this.First, other.First) && EqualityComparer<TSecond>.Default.Equals(this.Second, other.Second); } My code is: class MyClass { public static void Main (string[] args) { // Create new pair. Pair thePair = new Pair(new String("1"), new String("1")); // Compare a new pair to previous pair by generating a second pair. if (thePair.Equals(new Pair(new string("1"), new string("1")))) System.Console.WriteLine("Equal"); else System.Console.WriteLine("Not equal"); } } The compiler complains: "Using the generic type 'ManningListing36.Paie' requires 2 type argument(s) CS0305" What am I doing wrong ? Thanks, Scott

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• The Webbrowser DocumentComplited event wont fire c#

  - by Igal B.

  Hi. I have a problem using C# Webbrowser control. the problem is with the event DocumentComplited. Usually the event works fine. the problem is with this page:http://www.voiproblem.com/emulators/Netgear/WGR614v6/fw_forward.html when I (automatically) press on "add" the control navigates to:http://www.voiproblem.com/emulators/Netgear/WGR614v6/pforward.html. but it never firing the DocumentComplited event. I build a simple application that does the same and there it works fine. I mean when the app invokes InvokeMember("click") it does go to the DocumentComplited event. in my real app it doesnt. anyone can help me to figure it up what is the problem? thanks. <code> private void button1_Click(object sender, EventArgs e) { webBrowser1.Navigate("http://www.voiproblem.com/emulators/Netgear/WGR614v6/fw_forward.html"); } private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e) { HtmlElement elm = webBrowser1.Document.GetElementById("Add"); if (elm != null) webBrowser1.Document.GetElementById("Add").InvokeMember("click"); } </code>

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• Index out of bounds exception while iterating through a List<string>.

  - by Sergio Tapia

  I have a List of the location of images on a folder. I have five pictureBoxes that emulate a coverflow type area for users to skim through the images of a given folder. I know that the error is fired because the first image in the collection is set to the first picturebox, then if I click on cycleLeft(), there is a negative number. How can I account for this? For example, if the first image in the List is already set to the farthest left and someone clicks flip left, have that first image put on the last position of the list. Any guidance? private void leftArrow_Click(object sender, EventArgs e) { cycleImagesLeft(); } private void rightArrow_Click(object sender, EventArgs e) { cycleImagesRight(); } public void cycleImagesLeft() { //imageThree is the center image, that's why I use it as a frame of reference. int currentImage = pictures.IndexOf(imageThree.ImageLocation); imageOne.ImageLocation = pictures[currentImage - 3]; imageTwo.ImageLocation = pictures[currentImage - 2]; imageThree.ImageLocation = pictures[currentImage - 1]; imageFour.ImageLocation = pictures[currentImage]; imageFive.ImageLocation = pictures[currentImage + 1]; } public void cycleImagesRight() { int currentImage = pictures.IndexOf(imageThree.ImageLocation); imageOne.ImageLocation = pictures[currentImage - 1]; imageTwo.ImageLocation = pictures[currentImage]; imageThree.ImageLocation = pictures[currentImage + 1]; imageFour.ImageLocation = pictures[currentImage + 2]; imageFive.ImageLocation = pictures[currentImage + 3]; }

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• Invalid method declaration, return type required

  - by Brett Steen

  I am getting an error at public Rectangle(double width, double height){ saying that it's an invalid method declaration, return type required. I'm not sure how to fix it. These are also my instructions for my assignment: Write a super class encapsulating a rectangle. A rectangle has two attributes representing the width and the height of the rectangle. It has methods returning the perimeter and the area of the rectangle. This class has a subclass, encapsulating a parallelepiped, or box. A parallelepiped has a rectangle as its base, and another attribute, its length. It has two methods that calculate and return its area and volume. `public class Rectangle1 { private double width; private double height; public Rectangle1(){ } public Rectangle(double width, double height){ this.width = width; this.height = height; } public double getWidth(){ return width; } public void setWidth(double width) { this.width = width; } public double getHeight(){ return height; } public void setHeight(double height){ this.height = height; } public double getArea(){ return width * height; } public double getPerimeter(){ return 2 * (width + height); } } public class TestRectangle { public static void main(String[] args) { Rectangle1 rectangle = new Rectangle1(2,4); System.out.println("\nA rectangle " + rectangle.toString()); System.out.println("The area is " + rectangle.getArea()); System.out.println("The perimeter is " + rectangle.getPerimeter()); } }`

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• Best practice - When to evaluate conditionals of function execution

  - by Tesserex

  If I have a function called from a few places, and it requires some condition to be met for anything it does to execute, where should that condition be checked? In my case, it's for drawing - if the mouse button is held down, then execute the drawing logic (this is being done in the mouse movement handler for when you drag.) Option one says put it in the function so that it's guaranteed to be checked. Abstracted, if you will. public function Foo() { DoThing(); } private function DoThing() { if (!condition) return; // do stuff } The problem I have with this is that when reading the code of Foo, which may be far away from DoThing, it looks like a bug. The first thought is that the condition isn't being checked. Option two, then, is to check before calling. public function Foo() { if (condition) DoThing(); } This reads better, but now you have to worry about checking from everywhere you call it. Option three is to rename the function to be more descriptive. public function Foo() { DoThingOnlyIfCondition(); } private function DoThingOnlyIfCondition() { if (!condition) return; // do stuff } Is this the "correct" solution? Or is this going a bit too far? I feel like if everything were like this function names would start to duplicate their code. About this being subjective: of course it is, and there may not be a right answer, but I think it's still perfectly at home here. Getting advice from better programmers than I is the second best way to learn. Subjective questions are exactly the kind of thing Google can't answer.

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• Java: Initializing a public static field in superclass that needs a different value in every subclas

  - by BinaryMuse

  Good evening, I am developing a set of Java classes so that a container class Box contains a List of a contained class Widget. A Widget needs to be able to specify relationships with other Widgets. I figured a good way to do this would be to do something like this: public abstract class Widget { public static class WidgetID { // implementation stolen from Google's GWT private static int nextHashCode; private final int index; public WidgetID() { index = ++nextHashCode; } public final int hashCode() { return index; } } public abstract WidgetID getWidgetID(); } so sublcasses of Widget could: public class BlueWidget extends Widget { public static final WidgetID WIDGETID = new WidgetID(); @Override public WidgetID getWidgetID() { return WIDGETID; } } Now, BlueWidget can do getBox().addWidgetRelationship(RelationshipTypes.SomeType, RedWidget.WIDGETID, and Box can iterate through it's list comparing the second parameter to iter.next().getWidgetID(). Now, all this works great so far. What I'm trying to do is keep from having to declare the public static final WidgetID WIDGETID in all the subclasses and implement it instead in the parent Widget class. The problem is, if I move that line of code into Widget, then every instance of a subclass of Widget appears to get the same static final WidgetID for their Subclassname.WIDGETID. However, making it non-static means I can no longer even call Subclassname.WIDGETID. So: how do I create a static WidgetID in the parent Widget class while ensuring it is different for every instance of Widget and subclasses of Widget? Or am I using the wrong tool for the job here? Thanks!

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• ssh_exchange_identification: Connection closed by remote host under Git bash

  - by MoreFreeze

  I work at win7 and set up git server with sshd. I git --bare init myapp.git, and clone ssh://git@localhost/home/git/myapp.git in Cywgin correctly. But I need config git of Cygwin again, I want to git clone in Git Bash. I run "git clone ssh://git@localhost/home/git/myapp.git" and get following message ssh_exchange_identification: Connection closed by remote host then I run "ssh -vvv git@localhost" in Git Bash and get message debug2: ssh_connect: needpriv 0 debug1: Connecting to localhost [127.0.0.1] port 22. debug1: Connection established. debug1: identity file /c/Users/MoreFreeze/.ssh/identity type -1 debug3: Not a RSA1 key file /c/Users/MoreFreeze/.ssh/id_rsa. debug2: key_type_from_name: unknown key type '-----BEGIN' debug3: key_read: missing keytype debug3: key_read: missing whitespace // above it repeats 24 times debug2: key_type_from_name: unknown key type '-----END' debug3: key_read: missing keytype debug1: identity file /c/Users/MoreFreeze/.ssh/id_rsa type 1 debug1: identity file /c/Users/MoreFreeze/.ssh/id_dsa type -1 ssh_exchange_identification: Connection closed by remote host it seems my private keys has wrong format? And I find that there are exactly 25 line in private keys without "BEGIN" and "END". I'm confused why it said NOT RSA1 key, I totally ensure it is RSA 2 key. Any advises are welcome. btw, I have read first 3 pages on google about this problem.

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• singleton factory connection pdo

  - by Scarface

  Hey guys I am having a lot of trouble trying to understand this and I was just wondering if someone could help me with some questions. I found some code that is supposed to create a connection with pdo. The problem I was having was having my connection defined within functions. Someone suggested globals but then pointed to a 'better' solution http://stackoverflow.com/questions/130878/global-or-singleton-for-database-connection. My questions with this code are. PS I cannot format this code on this page so see the link if you cannot read What is the point of the connection factory? What goes inside new ConnectionFactory(...) When the connection is defined $db = new PDO(...); why is there no try or catch (I use those for error handling)? Does this then mean I have to use try and catch for every subsequent query? class ConnectionFactory { private static $factory; public static function getFactory() { if (!self::$factory) self::$factory = new ConnectionFactory(...); return self::$factory; } private $db; public function getConnection() { if (!$db) $db = new PDO(...); return $db; } } function getSomething() { $conn = ConnectionFactory::getFactory()-getConnection(); . . . }

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• How to work threading with ConcurrentQueue<T>.

  - by dboarman

  I am trying to figure out what the best way of working with a queue will be. I have a process that returns a DataTable. Each DataTable, in turn, is merged with the previous DataTable. There is one problem, too many records to hold until the final BulkCopy (OutOfMemory). So, I have determined that I should process each incoming DataTable immediately. Thinking about the ConcurrentQueue<T>...but I don't see how the WriteQueuedData() method would know to dequeue a table and write it to the database. For instance: public class TableTransporter { private ConcurrentQueue<DataTable> tableQueue = new ConcurrentQueue<DataTable>(); public TableTransporter() { tableQueue.OnItemQueued += new EventHandler(WriteQueuedData); // no events available } public void ExtractData() { DataTable table; // perform data extraction tableQueue.Enqueue(table); } private void WriteQueuedData(object sender, EventArgs e) { BulkCopy(e.Table); } } My first question is, aside from the fact that I don't actually have any events to subscribe to, if I call ExtractData() asynchronously will this be all that I need? Second, is there something I'm missing about the way ConcurrentQueue<T> functions and needing some form of trigger to work asynchronously with the queued objects?

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• Objective-C basics: subclassing and member variable accessability

  - by Krumelur

  Hi, Code below is pseudo code. Imagine a class "Fruit" which has a factory method to create a fruit. interface Fruit { } +(Fruit*) createFruit: { return [[Fruit alloc] init autorelease]; } Now I want to subclass the Fruit to get an Apple: interface Apple : Fruit { int iSeeds; } +(Apple*) createAppleWithColor: (int) iSeeds { Apple* oApple = [Apple createFruit:]; oApple.iSeeds = iSeeds; return oApple; } Questions: How can I make "iSeeds" private so it cannot be changed from outside? If I add a "private" keyword it does not build anymore. Still I want to set iSeeds from inside my Apple's factory method. I want users allow to READ the content of iSeeds. So I suppose I should have a getter but I can't get it to work. I always get some error about "LValue assignment". The Fruit's createFruit is making use of autorelease. Does the Apple have to reatin/release anything? René

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• Sending items in a LINQ sequence to a method that returns void

  - by generalt

  Hello all. Often while I'm dealing with LINQ sequences, I want to send each item to a method returning void, avoiding a foreach loop. However, I haven't found an elegant way to do this. Today, I wrote the following code: private StreamWriter _sw; private void streamToFile(List<ErrorEntry> errors) { if (_sw == null) { _sw = new StreamWriter(Path.Combine (Path.GetDirectoryName(_targetDatabasePath), "errors.txt")); } Func<ErrorEntry, bool> writeSelector = (e) => { _sw.WriteLine(getTabDelimititedLine(e)); return true; }; errors.Select(writeSelector); _sw.Flush(); } As you can see, I write a lambda function that just returns true, and I realize that the Select method will return a sequence of booleans- I'll just ignore that sequence. However, this seems a little bit noobish and jank. Is there any elegant way to do this? Or am I just misapplying LINQ? Thanks.

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