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• Serializing a part of object graph

  - by Felix

  Hi all, I have a problem regarding Java custom serialization. I have a graph of objects and want to configure where to stop when I serialize a root object from client to server. Let's make it a bit concrete, clear by giving a sample scenario. I have Classes of type Company Employee (abstract) Manager extends Employee Secretary extends Employee Analyst extends Employee Project Here are the relations: Company(1)---(n)Employee Manager(1)---(n)Project Analyst(1)---(n)Project Imagine, I'm on the client side and I want to create a new company, assign it 10 employees (new or some existing) and send this new company to the server. What I expect in this scenario is to serialize the company and all bounding employees to the server side, because I'll save the relations on the database. So far no problem, since the default Java serialization mechanism serializes the whole object graph, excluding the field which are static or transient. My goal is about the following scenario. Imagine, I loaded a company and its 1000 employees from the server to the client side. Now I only want to rename the company's name (or some other field, that directly belongs to the company) and update this record. This time, I want to send only the company object to the server side and not the whole list of employees (I just update the name, the employees are in this use case irrelevant). My aim also includes the configurability of saying, transfer the company AND the employees but not the Project-Relations, you must stop there. Do you know any possibility of achieving this in a generic way, without implementing the writeObject, readObject for every single Entity-Object? What would be your suggestions? I would really appreciate your answers. I'm open to any ideas and am ready to answer your questions in case something is not clear.

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• Email Collector / Implementation

  - by Tian

  I am implementing a simple RoR webpage that collect emails from visitors and store them as objects. I'm using it as a mini-project to try RoR and BDD. I can think of 3 features for Cucumber: 1. User submits a valid email address 2. User submits an existing email address 3. User submits an invalid email My question is, for scenarios 2 and 3, is it better to handle this via the controller? or as methods in a class? Perhaps something that throws errors if an instance is instantiated in sceanrio 2 or 3? Implementation is below, love to hear some code reviews in addition to answers to questions above. Thanks! MODEL: class Contact < ActiveRecord::Base attr_accessor :email end VIEW: <h1>Welcome To My Experiment</h1> <p>Find me in app/views/welcome/index.html.erb</p> <%= flash[:notice] %> <% form_for @contact, :url => {:action => "index"} do |f| %> <%= f.label :email %><br /> <%= f.text_field :email %> <%= submit_tag 'Submit' %> <% end %> CONTROLLER: class WelcomeController < ApplicationController def index @contact = Contact.new unless params[:contact].nil? @contact = Contact.create!(params[:contact]) flash[:notice] = "Thank you for your interest, please check your mailbox for confirmation" end end end

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• Classification: Dealing with Abstain/Rejected Class

  - by abner.ayala

  I am asking for your input and/help on a classification problem. If anyone have any references that I can read to help me solve my problem even better. I have a classification problem of four discrete and very well separated classes. However my input is continuous and has a high frequency (50Hz), since its a real-time problem. The circles represent the clusters of the classes, the blue line the decision boundary and Class 5 equals the (neutral/resting do nothing class). This class is the rejected class. However the problem is that when I move from one class to the other I activate a lot of false positives in the transition movements, since the movement is clearly non-linear. For example, every time I move from class 5 (neutral class) to 1 I first see a lot of 3's before getting to the 1 class. Ideally, I will want my decision boundary to look like the one in the picture below where the rejected class is Class =5. Has a higher decision boundary than the others classes to avoid misclassification during transition. I am currently implementing my algorithm in Matlab using naive bayes, kNN, and SVMs optimized algorithms using Matlab. Question: What is the best/common way to handle abstain/rejected classes classes? Should I use (fuzzy logic, loss function, should I include resting cluster in the training)?

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• Performance issue on Android's MapView Navigation-App

  - by poeschlorn

  Hey Guys, I've got a question on making an navigation app more faster and more stable. The basic layer of my app is a simple mapview, covered with several overlays (2 markers for start and destination and one for the route). My idea is to implement a thread to display the route, so that the app won't hang up during the calculation of a more complex route (like it does right now). After implementing the thread there are no updates shows any more, maybe you can help me with a short glance at an excerpt of my code below: private class MyLocationListener implements LocationListener { @Override public void onLocationChanged(Location loc) { posUser = new GeoPoint((int) (loc.getLatitude() * 1E6), (int) (loc .getLongitude() * 1E6)); new Thread(){ public void run(){ mapView.invalidate(); // Erase old overlays mapView.getOverlays().clear(); // Draw updated overlay elements and adjust basic map settings updateText(); if(firstRefresh){ adjustMap(); firstRefresh = false; } getAndPaintRoute(); drawMarkers(); } }; } Some features have been summarized to a method like "drawMarkers()" or "updateText()"...(they don't need any more attention ;-))

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• How to implement menuitems that depend on current selection in WPF MVVM explorer-like application

  - by Doug

  I am new to WPF and MVVM, and I am working on an application utilizing both. The application is similar to windows explorer, so consider an app with a main window with menu (ShellViewModel), a tree control (TreeViewModel), and a list control (ListViewModel). I want to implement menu items such as Edit - Delete, which deletes the currently selected item (which may be in the tree or in the list). I am using Josh Smith's RelayCommand, and binding the menuitem to a DeleteItemCommand in the ShellViewModel is easy. It seems like implementing the DeleteItemCommand, however, requires some fairly tight coupling between the ShellViewModel and the two child view models (TreeViewModel and ListViewModel) to keep track of the focus/selection and direct the action to the proper child for implementation. That seems wrong to me, and makes me think I'm missing something. Writing a focus manager and/or selection manager to do the bookkeeping does not seem too hard, and could be done without coupling the classes together. The windowing system is already keeping track of which view has the focus, and it seems like I'd be duplicating code. What I'm not sure about is how I would route the command from the ShellViewModel down to either the ListViewModel or the TreeViewModel to do the actual work without making a mess of the code. Some day, the application will be extended to include more than two children, and I want the shell to be as ignorant of the children as possible to make that extension as painless as possible. Looking at some sample WPF/MVVM applications (Karl Shifflett's CipherText, Josh Smith's MVVM Demo, etc.), I haven't seen any code that does this (or I didn't understand it). Regardless of whether you think my approach is way off base or I'm just missing a small nuance, please share your thoughts and help me get back on track. Thanks!

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• ASP.NET MVC static-asset aides/practices

  - by shannon

  I want to keep assets that are only used by one view in a view-specific folder, so my Search.aspx properly finds images/*.jpg, and helps me maintain my convention: ~/Areas/Candidate/Views/Job/Search.aspx -> ~/Assets/Candidate/Job/Search/images/*.jpg Perhaps with the ability to easily reference controller- or area-common assets manually or automatically: ~/Assets/Candidate/Job/images/*.jpg ~/Assets/Candidate/images/*.jpg If you wonder why I'm doing this, then speak up; I'm probably missing something. But here's why: I don't want stale static assets sitting in my ASP.NET MVC projects, which I expect to be an automatic outcome of the ~/Assets/Images folder: i.e. As a shared asset loses its last reference-count, who knows to delete it, especially with it being so difficult to trace content link validity in MVC projects? How do you, personally, do this? I can imagine, for example: Implement HtmlHelper extension methods for URL-generation. Extending ViewPage and ViewMasterPage with URL-generation methods. Implementing an inbound request filter to search related folders for static assets. and, are there good libraries out there for this? For example, something that also automatically appends timestamps for .JS and .CSS files, writes the / tags for me, and maybe even that allows me to inject includes in the head section from outside head code?

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• Rails 3 get raw post data and write it to tmp file

  - by Andrew

  I'm working on implementing Ajax-Upload for uploading photos in my Rails 3 app. The documentation says: For IE6-8, Opera, older versions of other browsers you get the file as you normally do with regular form-base uploads. For browsers which upload file with progress bar, you will need to get the raw post data and write it to the file. So, how can I receive the raw post data in my controller and write it to a tmp file so my controller can then process it? (In my case the controller is doing some image manipulation and saving to S3.) Some additional info: As I'm configured right now the post is passing these parameters: Parameters: {"authenticity_token"=>"...", "qqfile"=>"IMG_0064.jpg"} ... and the CREATE action looks like this: def create @attachment = Attachment.new @attachment.user = current_user @attachment.file = params[:qqfile] if @attachment.save! respond_to do |format| format.js { render :text => '{"success":true}' } end end end ... but I get this error: ActiveRecord::RecordInvalid (Validation failed: File file name must be set.): app/controllers/attachments_controller.rb:7:in `create'

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• Serial.begin(speed, config) not compiling for Leonardo Board

  - by forgemo

  I would like to configure my serial communication to have no parity, 1 start- and 2 stop-bits. The documentation for Serial.begin(speed, config) states: (...) An optional second argument configures the data, parity, and stop bits. The default is 8 data bits, no parity, one stop bit. The documentation also lists the possible configuration-values. According to my (limited) understanding, I need SERIAL_7N2 or SERIAL_8N2 to meet my requirements. (I'm not sure how the data-bits relate to the the 1-start-bit that I need.) However, I can't even compile because I have no idea how to supply that config value to the begin method. (I don't have much Arduino/C++ experience) I've tried in my code the following two variants: Serial.begin(9600, SERIAL_8N2); Serial.begin(9600, "SERIAL_8N2"); Am I missing something? Additional Information: Serial.begin(speed, config) has been introduced with the latest Arduino 1.0.2 IDE version. The code defining/implementing the begin methods can be found here. HardwareSerial.h HardwareSerial.cpp Edit: According to the replies from PeterJ and borges, the following variant is correct. Serial.begin(9600, SERIAL_8N2); However, it's still not working. I found that the compile error doesn't occur if I change the configured board from my Arduino Leonardo to Arduino uno. Therefore, it could be a bug occurring only with a subset of boards ... or maybe it's not supported?!

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• Embedded non-relational (nosql) data store

  - by Igor Brejc

  I'm thinking about using/implementing some kind of an embedded key-value (or document) store for my Windows desktop application. I want to be able to store various types of data (GPS tracks would be one example) and of course be able to query this data. The amount of data would be such that it couldn't all be loaded into memory at the same time. I'm thinking about using sqlite as a storage engine for a key-value store, something like y-serial, but written in .NET. I've also read about FriendFeed's usage of MySQL to store schema-less data, which is a good pointer on how to use RDBMS for non-relational data. sqlite seems to be a good option because of its simplicity, portability and library size. My question is whether there are any other options for an embedded non-relational store? It doesn't need to be distributable and it doesn't have to support transactions, but it does have to be accessible from .NET and it should have a small download size. UPDATE: I've found an article titled SQLite as a Key-Value Database which compares sqlite with Berkeley DB, which is an embedded key-value store library.

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• Are licenses relevant for small code snippets?

  - by Martin

  When I'm about to write a short algorithm, I first check in the base class library I'm using whether the algorithm is implemented in it. If not, I often do a quick google search to see if someone has done it before (which is the case, 19 times out of 20). Most of the time, I find the exact code I need. Sometimes it's clear what license applies to the source code, sometimes not. It may be GPL, LGPL, BSD or whatever. Sometimes people have posted a code snippet on some random forum which solves my problem. It's clear to me that I can't reuse the code (copy/paste it into my code) without caring about the license if the code is in some way substantial. What is not clear to me is whether I can copy a code snippet containing 5 lines or so without doing a license violation. Can I copy/paste a 5-line code snippet without caring about the license? What about one-liner? What about 10 lines? Where do I draw the line (no pun intended)? My second problem is that if I have found a 10-line code snippet which does exactly what I need, but feel that I cannot copy it because it's GPL-licensed and my software isn't, I have already memorized how to implement it so when I go around implementing the same functionality, my code is almost identical to the GPL licensed code I saw a few minutes ago. (In other words, the code was copied to my brain and my brain after that copied it into my source code).

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• Facebook XFBML Like Button incompatible with FeatureLoader script?

  - by retailevolved

  Facebook gurus, I have been implementing the Facebook Like button for a number of clients lately. To enable the Like Button, the following script has to be run: <div id="fb-root"></div> <script> window.fbAsyncInit = function() { FB.init({appId: '<?php echo Mage::helper("evlike")->getLikeConfig("ev_facebook_app_id") ?>', xfbml: true}); }; (function() { var e = document.createElement('script'); e.async = true; e.src = document.location.protocol + '//connect.facebook.net/en_US/all.js'; document.getElementById('fb-root').appendChild(e); }()); </script> It seems that this is incompatible with the following include: <script src="http://static.ak.connect.facebook.com/js/api_lib/v0.4/FeatureLoader.js.php/en_US" type="text/javascript"></script> It would make sense as I believe that the FeatureLoader performs an initialization. Is this official now? I would ask in official Facebook forums but I get an error every time I attempt to do so...

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• Key Tips in WPF

  - by Brad Leach

  Office 2007 and the Ribbon introduced the concept of "Key Tips". In short, every single command in the Ribbon receives a letter which you can press to activate that command. ... The letters are indicated by small "KeyTips" which indicate the letter to press to activate the control. KeyTips are displayed using the Alt key, so using them feels similar to how menu navigation works in Windows. (Source: http://blogs.msdn.com/jensenh/archive/2006/04/12/574930.aspx) An example of the Key Tips can be shown as follows. In this diagram, the use has pressed the ALT key, and is awaiting further input. Are there any WPF Open Source examples of "Key Tips"? How would you go about implementing something like this feature in a generic way (i.e. not requiring a Ribbon)? How would you implement this using a MVVM pattern (given that ICommand does not support InputBindings). Note: ActiPro have implemented this feature in their implementation of a Ribbon, but they have not released source code.

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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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• Architecture for data layer that uses both localStorage and a REST remote server

  - by Zack

  Anybody has any ideas or references on how to implement a data persistence layer that uses both a localStorage and a REST remote storage: The data of a certain client is stored with localStorage (using an ember-data indexedDB adapter). The locally stored data is synced with the remote server (using ember-data RESTadapter). The server gathers all data from clients. Using mathematical sets notation: Server = Client1 ? Client2 ? ... ? ClientN where, in general, a record may not be unique to a certain client. Here are some scenarios: A client creates a record. The id of the record can not set on the client, since it may conflict with a record stored on the server. Therefore a newly created record needs to be committed to the server - receive the id - create the record in localStorage. A record is updated on the server, and as a consequence the data in localStorage and in the server go out of sync. Only the server knows that, so the architecture needs to implement a push architecture (?) Would you use 2 stores (one for localStorage, one for REST) and sync between them, or use a hybrid indexedDB/REST adapter and write the sync code within the adapter? Can you see any way to avoid implementing push (Web Sockets, ...)?

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• Detecting Singularities in a Graph

  - by nasufara

  I am creating a graphing calculator in Java as a project for my programming class. There are two main components to this calculator: the graph itself, which draws the line(s), and the equation evaluator, which takes in an equation as a String and... well, evaluates it. To create the line, I create a Path2D.Double instance, and loop through the points on the line. To do this, I calculate as many points as the graph is wide (e.g. if the graph itself is 500px wide, I calculate 500 points), and then scale it to the window of the graph. Now, this works perfectly for most any line. However, it does not when dealing with singularities. If, when calculating points, the graph encounters a domain error (such as 1/0), the graph closes the shape in the Path2D.Double instance and starts a new line, so that the line looks mathematically correct. Example: However, because of the way it scales, sometimes it is rendered correctly, sometimes it isn't. When it isn't, the actual asymptotic line is shown, because within those 500 points, it skipped over x = 2.0 in the equation 1 / (x-2), and only did x = 1.98 and x = 2.04, which are perfectly valid in that equation. Example: In that case, I increased the window on the left and right one unit each. My question is: Is there a way to deal with singularities using this method of scaling so that the resulting line looks mathematically correct? I myself have thought of implementing a binary search-esque method, where, if it finds that it calculates one point, and then the next point is wildly far away from the last point, it searches in between those points for a domain error. I had trouble figuring out how to make it work in practice, however. Thank you for any help you may give!

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• How to TDD Asynchronous Events?

  - by Padu Merloti

  The fundamental question is how do I create a unit test that needs to call a method, wait for an event to happen on the tested class and then call another method (the one that we actually want to test)? Here's the scenario if you have time to read further: I'm developing an application that has to control a piece of hardware. In order to avoid dependency from hardware availability, when I create my object I specify that we are running in test mode. When that happens, the class that is being tested creates the appropriate driver hierarchy (in this case a thin mock layer of hardware drivers). Imagine that the class in question is an Elevator and I want to test the method that gives me the floor number that the elevator is. Here is how my fictitious test looks like right now: [TestMethod] public void TestGetCurrentFloor() { var elevator = new Elevator(Elevator.Environment.Offline); elevator.ElevatorArrivedOnFloor += TestElevatorArrived; elevator.GoToFloor(5); //Here's where I'm getting lost... I could block //until TestElevatorArrived gives me a signal, but //I'm not sure it's the best way int floor = elevator.GetCurrentFloor(); Assert.AreEqual(floor, 5); } Edit: Thanks for all the answers. This is how I ended up implementing it: [TestMethod] public void TestGetCurrentFloor() { var elevator = new Elevator(Elevator.Environment.Offline); elevator.ElevatorArrivedOnFloor += (s, e) => { Monitor.Pulse(this); }; lock (this) { elevator.GoToFloor(5); if (!Monitor.Wait(this, Timeout)) Assert.Fail("Elevator did not reach destination in time"); int floor = elevator.GetCurrentFloor(); Assert.AreEqual(floor, 5); } }

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• Caching page by parts; how to pass variables calculated in cached parts into never-cached parts?

  - by Kirzilla

  Hello, Let's imagine that I have a code like this... if (!$data = $cache->load("part1_cache_id")) { $item_id = $model->getItemId(); ob_start(); echo 'Here is the cached item id: '.$item_id; $data = ob_get_contents(); ob_end_clean(); $cache->save($data, "part1_cache_id"); } echo $data; echo never_cache_function($item_id); if (!$data_2 = $cache->load("part2_cache_id")) { ob_start(); echo 'Here is the another cached part of the page...'; $data_2 = ob_get_contents(); ob_end_clean(); $cache->save("part2_cache_id"); } echo $data_2; As far as you can see I need to pass $item_id variable into never_cache_function, but if fist part is cached (part1_cache_id) then I have no way to get $item_id value. I see the only solution - serialize all data from fist part (including $item_id value); then cache serialized string and unserialize it everytime when script is executed... Something like this... if (!$data = $cache->load("part1_cache_id")) { $item_id = $model->getItemId(); $data['item_id'] = $item_id; ob_start(); echo 'Here is the cached item id: '.$item_id; $data['html'] = ob_get_contents(); ob_end_clean(); $cache->save( serialize($data), "part1_cache_id" ); } $data = unserialize($data); echo $data['html'] echo never_cache_function($data['item_id']); Is there any other ways for doing such trick? I'm looking for the most high performance solution. Thank you UPDATED And another question is - how to implement such caching into controller without separating page into two templates? Is it possible? PS: Please, do not suggest Smarty, I'm really interested in implementing custom caching.

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• Pass Result of ASIHTTPRequest "requestFinished" Back to Originating Method

  - by Intelekshual

  I have a method (getAllTeams:) that initiates an HTTP request using the ASIHTTPRequest library. NSURL *httpURL = [[[NSURL alloc] initWithString:@"/api/teams" relativeToURL:webServiceURL] autorelease]; ASIHTTPRequest *request = [[[ASIHTTPRequest alloc] initWithURL:httpURL] autorelease]; [request setDelegate:self]; [request startAsynchronous]; What I'd like to be able to do is call [WebService getAllTeams] and have it return the results in an NSArray. At the moment, getAllTeams doesn't return anything because the HTTP response is evaluated in the requestFinished: method. Ideally I'd want to be able to call [WebService getAllTeams], wait for the response, and dump it into an NSArray. I don't want to create properties because this is disposable class (meaning it doesn't store any values, just retrieves values), and multiple methods are going to be using the same requestFinished (all of them returning an array). I've read up a bit on delegates, and NSNotifications, but I'm not sure if either of them are the best approach. I found this snippet about implementing callbacks by passing a selector as a parameter, but it didn't pan out (since requestFinished fires independently). Any suggestions? I'd appreciate even just to be pointed in the right direction. NSArray *teams = [[WebService alloc] getAllTeams]; (currently doesn't work, because getAllTeams doesn't return anything, but requestFinished does. I want to get the result of requestFinished and pass it back to getAllTeams:)

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• value of Identity column returning null when retrieved by value in dataGridView

  - by Raven Dreamer

  Greetings. I'm working on a windows forms application that interacts with a previously created SQL database. Specifically, I'm working on implementing an "UPDATE" query. for (int i = 0; i < dataGridView1.RowCount; i++) { string firstName = (string)dataGridView1.Rows[i].Cells[0].Value; string lastName = (string)dataGridView1.Rows[i].Cells[1].Value; string phoneNo = (string)dataGridView1.Rows[i].Cells[2].Value; short idVal = (short)dataGridView1.Rows[i].Cells[3].Value; this.contactInfoTableAdapter.UpdateQuery(firstName, lastName, phoneNo, idVal); } The dataGridView has 4 columns, First Name, Last Name, Phone Number, and ID (which was created as an identity column when I initially formed the table in SQL). When I try to run this code, the three strings are returned properly, but dataGridView1.Rows[i].Cells[3].Value is returning "null". I'm guessing this is because it was created as an identity column rather than a normal column. What's a better way to retrieve the relevant ID value for my UpdateQuery?

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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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• Java method keyword "final" and its use

  - by Lukas Eder

  When I create complex type hierarchies (several levels, several types per level), I like to use the final keyword on methods implementing some interface declaration. An example: interface Garble { int zork(); } interface Gnarf extends Garble { /** * This is the same as calling {@link #zblah(0)} */ int zblah(); int zblah(int defaultZblah); } And then abstract class AbstractGarble implements Garble { @Override public final int zork() { ... } } abstract class AbstractGnarf extends AbstractGarble implements Gnarf { // Here I absolutely want to fix the default behaviour of zblah // No Gnarf shouldn't be allowed to set 1 as the default, for instance @Override public final int zblah() { return zblah(0); } // This method is not implemented here, but in a subclass @Override public abstract int zblah(int defaultZblah); } I do this for several reasons: It helps me develop the type hierarchy. When I add a class to the hierarchy, it is very clear, what methods I have to implement, and what methods I may not override (in case I forgot the details about the hierarchy) I think overriding concrete stuff is bad according to design principles and patterns, such as the template method pattern. I don't want other developers or my users do it. So the final keyword works perfectly for me. My question is: Why is it used so rarely in the wild? Can you show me some examples / reasons where final (in a similar case to mine) would be very bad?

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• Post method in Servlet is not being called again after being executed once

  - by SaurabhCsIITKgp

  I am implementing a database based web application using servlets. Now, when I input a parameter using a form in the jsp page, it redirects it to a servlet which subsequently adds the value to the database (the servlet creates a new table if the table doesn't already exist). The creation of the table and the addition of value works fine if the table doesn't already exists. Once it is created however and the parameter is inputted again in the form, the submit button no longer redirects it to the servlet. Nor is the value added to the database. Kindly advise me as to where I am going wrong. Following are the snippets of my code: From the JSP page (/showmanager is the urlpattern of the servlet): <form action="showmanager" method="post"> <h3>Enter name of the show: </h3> <input type="text" name="showname" value=""> <input type="hidden" name="task" value="addshow" /> <input type="button" value="Add Show"> </form> From the servlet (POST method): p rotected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { if(request.getParameter("task").equals("addshow")){ this.addShow(request.getParameter("showname")); response.sendRedirect("showmanager.jsp"); } } Method to add in database: protected boolean addShow(String showname){ try{ statement =con.prepareStatement("INSERT INTO showdb10(name) VALUES ('"+showname+"')"); if(statement.executeUpdate()>0){ return true; } } catch(Exception e) { try{ statement =con.prepareStatement("create table showdb10 (id int NOT NULL AUTO_INCREMENT, name varchar(255) NOT NULL, date varchar(20),time varchar(20), b_total int, o_total int, b_avbl int, o_avbl int, b_price double(10,2), o_price double(10,2), seat_no varchar(20), transaction_id varchar(255), total_sales double(10,2), paymnt_artists double(10,2), paymnt_othr double(10,2), flag varchar(20), PRIMARY KEY(id))"); statement.executeUpdate(); statement =con.prepareStatement("INSERT INTO showdb10(name) VALUES ('"+showname+"')"); if(statement.executeUpdate()>0){ return true; } }catch(Exception e2){} } return false; }

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• Assign a unique client ID to each <rich:dataTable /> row?

  - by Dolph Mathews

  I'm relatively new to working with the UI in Seam, so I'm hoping there is something simple I can replace the three instances of UNIQUE_ID with in the following example (such as #{object.uniqueId}). The goal is to have a <rich:dataTable /> wherein each row has the ability to show/hide a <rich:modalPanel /> with more details about the particular object instance. <rich:dataTable var="object" value="#{bean.myObject}"> <rich:column> <h:outputText value="#{object.summary}" /> </rich:column> <rich:column> <a onclick="Richfaces.showModalPanel('UNIQUE_ID');" href="#">Show Details in ModalPanel</a> <a4j:form> <rich:modalPanel id="UNIQUE_ID" > <a onclick="Richfaces.hideModalPanel('UNIQUE_ID');" href="#">Hide This ModalPanel</a> <h:outputText value="#{object.details}" /> </rich:modalPanel> </a4j:form> </rich:column> </rich:dataTable> If I only had one link/modalPanel pair, this would obviously be trivial, but I don't know what to do within the scope of the <rich:dataTable />'s iteration. Also, in case it complicates things further, the page will also contain many <rich:dataTable />'s, each implementing this behavior.

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• Which DHT algorithm to use (if I want to join two separate DHTs)?

  - by webdreamer

  I've been looking into some DHT systems, specially Pastry and Chord. I've read some concerns about Chord's reaction to churn, though I believe that won't be a problem for the task I have at hands. I'm implementing some sort of social network service that doesn't rely on any central servers for a course project. I need the DHT for the lookups. Now I don't know of all the servers in the network in the beginning. As I've stated, there's no main tracker server. It works this way: each client has three dedicated servers. The three servers have the profile of the client, and it's wall, it's personal info, replicated. I only get to know about other group of servers when the user adds a friend (inputing the client's address). So I would create two separate DHTs on the two groups of three servers and when they friend each other I would like to join the DHTs. I would like to this consistently. I haven't had a lot of time to get all that familiar with the protocols, so I would like to know which one is better if I want to join the two separate DHTs?

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• Password Confirmation Overlay

  - by Alasdair

  Hello, I'm creating a J2EE web application that uses jQuery and Ajax to help with some of the presentation for a user-friendly interface. I've done a lot of work ensuring security around persistant login cookies, and I've decided to request the password from any user that logged in using a persistant login cookie before being allowed to make any changes that could be malicious. This request would only happen once to confirm the user is who they say they are and will last throughout the session. At present, any requests that meet this criteria has their request information stored in session and then the user is forwarded to a page to confirm their password. Once confirmed, the user's original request is then performed and the requestion information removed from session. What I would like to do is avoid all this redirection and minimize what's held in session (even if it's just for a small time), thus improving usability and convenience for the user. I believe that a jQuery overlay could allow me to prompt the user for their password (if required) and then continue to submit the request if successful. I would of originally used ThickBox, but since that's now deprecated I don't see the benefit in implementing it in an application at this development stage. However, I have tried to create an overlay using jQuery but I've scrapped every attempt as I can't seem to make it all come together. My main problem is preventing the submission when the user incorrectly types a password or cancels the overlay. Desired Flow Persistant Login Sensitive Page Submit Password Confirmation Overlay [Continue Submit | (Cancel | Incorrect] I have already created JavaScript code to encrypt the password to be sent in a parameter, but all I need now is a method of controlling the overlay and how best to use Ajax for this purpose. Please ignore the fact that this is a J2EE web application when answering as it is irrelevant really. Thanks in advance, Alasdair

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