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• Programming exercises in Java inheritance for intern

  - by Tenner

  I work for a small software development team, working primarily in Java, for a very large company. Our new intern showed up sight-unseen (not uncommon in my company). He has some C++ experience but no Java. Worse, he's never worked with inheritance in C++. Our code has a great deal of abstraction and a heavy reliance on inheritance. We need to get him up to speed as quickly as possible. Of course the rest of the team is busy, and so we can't take the time out of our day to teach a one-student 200-level CS course. Instead, I'd like to give him an actual programming project to work on which highlights how classes, interfaces, method overrides, etc. work. I've had him look at Project Euler, but most of the solutions end up being procedural, and not object-oriented programs. Do any of you have any somewhat-straightforward (and relatively quick) projects which you would give to an intern in this situation? Or, any recent (or current) students have a school project they'd be willing to share? Anyone else had this experience?

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• Stupid newbie c++ two-dimensional array problem.

  - by paulson scott

  I've no idea if this is too newbie or generic for stackoverlflow. Apologies if that's the case, I don't intend to waste time. I've just started working through C++ Primer Plus and I've hit a little stump. This is probably super laughable but: for (int year = 0; year < YEARS; year++) { cout << "Year " << year + 1 << ":"; for (int month = 0; month < MONTHS; month++) { absoluteTotal = (yearlyTotal[year][year] += sales[year][month]); } cout << yearlyTotal[year][year] << endl; } cout << "The total number of books sold over a period of " << YEARS << " years is: " << absoluteTotal << endl; I wish to display the total of all 3 years. The rest of the code works fine: input is fine, individual yearly output is fine but I just can't get 3 years added together for one final total. I did have the total working at one point but I didn't have the individual totals working. I messed with it and reversed the situation. I've been messing with it for God knows how long. Any idea guys? Sorry if this isn't the place!

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• Rails can't find my route but it exists!

  - by DJTripleThreat

  Ok I have events that I want to publish/unpublish with an extra action (nonRESTful) I watched Ryan Bates' railscast on this: http://railscasts.com/episodes/35-custom-rest-actions and it got me most of the way. I think the problem is that my route is nested in an /admin section so even though when I run rake routes and get: publish_admin_event PUT /admin/events/:id/publish(.:format) {:controller=>"event_services", :action=>"publish"} This won't work in my /views/admin/index.html.erb file: <%= link_to 'Publish', publish_admin_event(event), :method => :put %> because it claims that path doesn't exist! And neither will this: <%= link_to 'Publish', {:controller => :event_services, :action => :publish}, {:method => :put, :id => event} %> and says that "No route matches {:controller=>"event_services", :action=>"publish"}" so what gives? (And I've tried restarting my server so that isn't it.) EDIT: This DOES work: <%= link_to 'Publish', "/admin/events/" + event.id.to_s + "/publish", :method => :put %> But I'd rather NOT do this.

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• Spring MVC: should service layer be returning operation specific DTO's ?

  - by arrages

  In my Spring MVC application I am using DTO in the presentation layer in order to encapsulate the domain model in the service layer. The DTO's are being used as the spring form backing objects. hence my services look something like this: userService.storeUser(NewUserRequestDTO req); The service layer will translate DTO - Domain object and do the rest of the work. Now my problem is that when I want to retrieve a DTO from the service to perform say an Update or Display I can't seem to find a better way to do it then to have multiple methods for the lookup that return different DTO's like... EditUserRequestDTO userService.loadUserForEdit(int id); DisplayUserDTO userService.loadUserForDisplay(int id); but something does not feel right about this approach. The reason do have separate DTO's is that DisplayUserDTO is strongly typed to be read only and also there are many properties of user that are entities from a lookup table in the db (like city and state) so the DisplayUserDTO would have the string description of the properties while the EditUserRequestDTO will have the id's that will back the select drop down lists in the forms. What do you think? thanks

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• Android: CustomListAdapter

  - by primal

  Hi, I have implemented a custom list view which looks like the twitter timeline. adapter = new MyClickableListAdapter(this, R.layout.timeline, mObjectList); setListAdapter(adapter); The constructor for MyClickableListAdapter is as follows private class MyClickableListAdapter extends ClickableListAdapter{ public MyClickableListAdapter(Context context, int viewId, List objects) { super(context, viewId, objects); } ClickableListAdapter extends BaseAdapter and implements the necessary methods. The xml code for the list view is as follows <ListView android:id="@+id/android:list" android:layout_width="fill_parent" android:layout_height="wrap_content" /> This is what it looks like. I have 3 questions 1) I tried registering a context menu for the list view by adding the line after setting the list adapter registerforContextMenu(getListView()); But on long-click the menu doesnt get displayed. I cannot understand what I am doing wrong! 2) Is it possible to display a textview above the listview? I tried it by adding the code for textview above the listview. But then, only the textview gets displayed. 3) I have seen in many twitter clients that on clicking post a window pops up from the top covering only some portion of the screen and rest of the timeline is visible. How can this be done possibly without starting a new activity? Any help would be much appreciated..

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• Why aren't these Canvases rendering?

  - by bpapa

  I'm creating a web app that allows users to enter a number of colors, by specifying RGB values. Upon submission, the user will see a canvas with a solid rectangle drawn in the color chosen. On this page, I have 7 canvases. The first one draws just fine, but none of the rest show up. The browser is Safari. Here's the relevant code: First, the script element in the header, which defines the function I use to draw to the canvas. <script language="JavaScript" TYPE="text/javascript"><!-- function drawCanvas(canvasId, red, green, blue) { var theCanvas = document.getElementById("canvas" + canvasId); var context = theCanvas.getContext("2d"); context.clearRect(0,0,100,100); context.setFillColor(red,green,blue,1.0); context.fillRect(0,0,100,100); } // --> </script> Next, the HTML source, where I have my canvas tags and some embedded Javascript to call my drawCanvas function <canvas id="canvas0" width="100" height="100"> </canvas> <script language="JavaScript" TYPE="text/javascript"><!-- drawCanvas(0,250,0,0); // --> </script> . . //more source . <canvas id="canvas1" width="100" height="100"> </canvas> <script language="JavaScript" TYPE="text/javascript"><!-- drawCanvas(1,4,250,6); // --> </script> Also provided is a screenshot. As you can see, the "red" canvas comes up just fine, but the second one, which should be green, doesn't show up at all. Any ideas?

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• "Subforms" associated with tree view in VB

  - by knomdeguerre

  I am using VB Express 2008 to demonstrate my ideas for an improved UI for an existing product for my colleagues at work. The current UI has a certain page with ten tabs, allowing the user to define up to ten "things". The available choices for each of the ten "things" are all the same. On each of the ten tabs, there is a checkbox to enable that definition. Generally, a user will never use more than 5 or 6 unique definitions, the rest will remain disabled. So far, my prototype has a tree view control with one branch to contain this list of definitions, Add and Delete buttons. My idea is: there is one sub-branch to start with (corresponding to the first tab in the current UI); if the user wants addtional definitions, they click Add and other branches are added to the tree view, up to maximum of ten. I think I should be able to create a "class" that has a sub-UI (like a sub-form in Access) along with behavior code, that can be instantiated with each press of the Add button; each instantiation's settings can be set independently and is displayed in the main UI form )in a panel or frame) when selected in the tree view. For example, suppose the user Adds to make a total of three definitions: the tree view now has three sub-branches, each of which presents the same sub-UI with settings that can be set specific to the selected sub-branch. I'm sure it's possible but not sure how to do it. I know a comprehensive "answer" might be complicated and long, but I may just need some quick hints to get underway - don't be shy! Thanks in advance!

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• Validation problem with a 'JotForm' template

  - by Thomas

  A client sent me a form template they had created using jotform.com to implement on their wordpress site. The form template is supposed to hide part of the form until the user clicks the 'next' button. At which point a script is supposed to validate all of the input fields the user has presumably filled out and then display the rest of the form. While I have successfully managed to get the form to display the next part of the form when the user clicks 'next', it fails to validate the input fields. Its kind of difficult to explain without a huge block of text so it is probably easier to show you: The original working template that the customer sent me: http://www.loftist.com/jotform/List_Your_Loft.html The problem child: http://www.loftist.com/?page_id=78 If you just click on one of the input fields and then click elsewhere on the page, the input fields successfully return a validation error message and prevent the user from clicking on the 'next' button. However, if you simply click on the next button than the next set of fields get displayed. Any thoughts? What am I doing wrong here? Im convinced this must be a really simple problem but Im not sure what it could be....

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• Find and Replace with Notepad++

  - by Levi

  I have a document that was converted from PDF to HTML for use on a company website to be referenced and indexed for search. I'm attempting to format the converted document to meet my needs and in doing so I am attempting to clean up some of the junk that was pulled over from when it was a PDF such as page numbers, headers, and footers. luckily all of these lines that need to be removed are in blocks of 4 lines unfortunately they are not exactly the same therefore cannot be removed with a simple literal replace. The lines contain numbers which are incremental as they correlate with the pages. How can I remove the following example from my html file. Title<br> 10<br> <hr> <A name=11></a>Footer<br> I've tried many different regular expression attempts but as my skill in that area is limited I can't find the proper syntax. I'm sure i'm missing something fairly easy as it would seem all I need is a wildcard replace for the two numbers in the code and the rest is literal. any help is apprciated

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• one two-directed tcp socket OR two one-directed? (linux, high volume, low latency)

  - by osgx

  Hello I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets? The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe). The benefit of 2 uni-directed connections come from linux: http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847 3847/* 3848 * TCP receive function for the ESTABLISHED state. 3849 * 3850 * It is split into a fast path and a slow path. The fast path is 3851 * disabled when: ... 3859 * - Data is sent in both directions. Fast path only supports pure senders 3860 * or pure receivers (this means either the sequence number or the ack 3861 * value must stay constant) ... 3863 * 3864 * When these conditions are not satisfied it drops into a standard 3865 * receive procedure patterned after RFC793 to handle all cases. 3866 * The first three cases are guaranteed by proper pred_flags setting, 3867 * the rest is checked inline. Fast processing is turned on in 3868 * tcp_data_queue when everything is OK. All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive

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• Deserialize json with json.net c#

  - by 76mel

  Hi, am new to Json so a little green. I have a Rest Based Service that returns a json string; {"treeNode":[{"id":"U-2905","pid":"R","userId":"2905"}, {"id":"U-2905","pid":"R","userId":"2905"}]} I have been playing with the Json.net and trying to Deserialize the string into Objects etc. I wrote an extention method to help. public static T DeserializeFromJSON<T>(this Stream jsonStream, Type objectType) { T result; using (StreamReader reader = new StreamReader(jsonStream)) { JsonSerializer serializer = new JsonSerializer(); try { result = (T)serializer.Deserialize(reader, objectType); } catch (Exception e) { throw; } } return result; } I was expecting an array of treeNode[] objects. But its seems that I can only deserialize correctly if treeNode[] property of another object. public class treeNode { public string id { get; set; } public string pid { get; set; } public string userId { get; set; } } I there a way to to just get an straight array from the deserialization ? Cheers

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• Generate random number from an arbitrary weighted list

  - by Fernando

  Here's what I need to do, I'll be doing this both in PHP and JavaScript. I have a list of numbers that will range from 1 to 300-500 (I haven't set the limit yet). I will be running a drawing were 10 numbers will be picked at random from the given range. Here's the tricky part: I want some numbers to be less likely to be drawn up. A small set of those 300-500 will be flagged as "lucky numbers". For example, out of 100 drawings, most numbers have equal chances of being drawn, except for a few, that will only be picked once every 30-50 drawings. Basically I need to artificially set the probability of certain numbers to be picked while maintaining an even distribution with the rest of the numbers. The only similar thing I've found so far is this question: Generate A Weighted Random Number, the problem being that my spec has considerably more numbers (up to 500) so the weights would get very small and supposedly this could be a problem with that solution (Rejection Sampling). I'm still trying it, though, but I wonder if there other solutions. Math is not my thing so I appreciate any input. Thanks.

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• Patterns / Solutions to complicated Feature Management

  - by yclian

  Hi all, My company develops CDN / Web-Hosting solution. We have a middleware that's served as a business logic layer and exposes web service for the front-end. I would like to seek for a clean solution to feature management - there're uncertainties and ugly workarounds/solutions in the software that the dev would say "when it happens or is broken, we will fix it". For example, here're the following features that a web publisher can have: Sites limit Bandwidth limit SSL feature + SSL configuration per site If we downgrade a web publisher, when he's having 10 sites, down to 5 sites, we can choose not to suspend the rest of the 5 sites, or we shall prompt for suspension before the downgrade. For the case of bandwidth limit, the downgrade is easy, when the bandwidth check happens, if the publisher has it exceeded, then we will suspend his account. For the case of SSL feature. Every SSL configuration is tied to a site, what shall happen to these configuration object when the SSL feature is downgraded from enabled to disabled? So as you can see, there're many different situations and there are different ways of handling it. I can make a system that examines the impacts and prompts the user to make changes before the downgrade/upgrade. Or a system that ignores the impacts and just upgrade/downgrade. Bad. Or a system designed in a way that the client code need to be aware of the complex feature matrix (or I can expose a helper to the client code to check if a feature is not DEFUNCT) There can be many ways that I am still thinking but puzzled. I am wondering, how would you tackle this issue and is there any recommended patterns or books or software that you think I can refer to? Appreciate your help.

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• Hibernate not saving foreign key, but with junit it's ok

  - by Leonardo

  Hi All, I have this strange problem. In a J2ee webapp with spring, smartgwt and hibernate, it happens that I have a class A wich has a set of class B, both of them mapped to table A and table B. I wrote a simple test case for testing the service manager which is supposed to do insert, update, delete and everything work as expected especially during insert. In the end I have one record in A and records in B with foreign key to A. But when I try to call the service from the web app, the entity in B are saved without a foreign key reference. I am sure that the service is the same. One thing I noticed is that enabling hibernate logging, seems that when the service is called from the application, one more update is made: insert A insert B update A update B update B (foreign key only) update A <--- ??? update B <--- ??? Instead, when junit test case is run, the update is as follows: insert A insert B update A update B update B (foreign key only) I suppose the latest update is what is causing the erroe, maybe it is overwriting values. Considering that the app is using spring, with the well known mechanism of DAO + Manager, where can I investigate to solve this issue ? Someone told me that the session is not closed, so hibernate would do one more update before release the objects by itself. I am pretty sure that all the configuration hbm, xml, and the rest are fine...but I maybe wrong. thanks

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• Do ORMs normally allow circular relations? If so, how would they handle it?

  - by SeanJA

  I was hacking around trying to make a basic orm that has support for the one => one and one => many relationships. I think I succeeded somewhat, but I am curious about how to handle circular relationships. Say you had something like this: user::hasOne('car'); car::hasMany('wheels'); car::property('type'); wheel::hasOne('car'); You could then do this (theoretically): $u = new user(); echo $u->car->wheels[0]->car->wheels[1]->car->wheels[2]->car->wheels[3]->type; #=> "monster truck" Now, I am not sure why you would want to do this. It seems like it wastes a whole pile of memory and time just to get to something that could have been done in a much shorter way. In my small ORM, I now have 4 copies of the wheel class, and 4 copies of the car class in memory, which causes a problem if I update one of them and save it back to the database, the rest get out of date, and could overwrite the changes that were already made. How do other ORMs handle circular references? Do they even allow it? Do they go back up the tree and create a pointer to one of the parents? DO they let the coder shoot themselves in the foot if they are silly enough to go around in circles?

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• How can I unit test a PHP class method that executes a command-line program?

  - by acoulton

  For a PHP application I'm developing, I need to read the current git revision SHA which of course I can get easily by using shell_exec or backticks to execute the git command line client. I have obviously put this call into a method of its very own, so that I can easily isolate and mock this for the rest of my unit tests. So my class looks a bit like this: class Task_Bundle { public function execute() { // Do things $revision = $this->git_sha(); // Do more things } protected function git_sha() { return `git rev-parse --short HEAD`; } } Of course, although I can test most of the class by mocking git_sha, I'm struggling to see how to test the actual git_sha() method because I don't see a way to create a known state for it. I don't think there's any real value in a unit test that also calls git rev-parse to compare the results? I was wondering about at least asserting that the command had been run, but I can't see any way to get a history of shell commands executed by PHP - even if I specify that PHP should use BASH rather than SH the history list comes up empty, I presume because the separate backticks executions are separate terminal sessions. I'd love to hear any suggestions for how I might test this, or is it OK to just leave that method untested and be careful with it when the app is being maintained in future?

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• Seeking suggestions on redesigning the interface

  - by ratkok

  As a part of maintaining large piece of legacy code, we need to change part of the design mainly to make it more testable (unit testing). One of the issues we need to resolve is the existing interface between components. The interface between two components is a class that contains static methods only. Simplified example: class ABInterface { static methodA(); static methodB(); ... static methodZ(); }; The interface is used by component A so that different methods can use ABInterface::methodA() in order to prepare some input data and then invoke appropriate functions within component B. Now we are trying to redesign this interface for various reasons: Extending our unit test coverage - we need to resolve this dependency between the components and stubs/mocks are to be introduced The interface between these components diverged from the original design (ie. a lots of newer functions, used for the inter-component i/f are created outside this interface class). The code is old, changed a lot over the time and needs to be refactored. The change should not be disruptive for the rest of the system. We try to limit leaving many test-required artifacts in the production code. Performance is very important and should be no (or very minimal) degradation after the redesign. Code is OO in C++. I am looking for some ideas what approach to take. Any suggestions on how to do this efficiently?

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• one two-directed tcp socket of two one-directed? (linux, high volume, low latency)

  - by osgx

  Hello I need to send (interchange) a high volume of data periodically with the lowest possible latency between 2 machines. The network is rather fast (e.g. 1Gbit or even 2G+). Os is linux. Is it be faster with using 1 tcp socket (for send and recv) or with using 2 uni-directed tcp sockets? The test for this task is very like NetPIPE network benchmark - measure latency and bandwidth for sizes from 2^1 up to 2^13 bytes, each size sent and received 3 times at least (in teal task the number of sends is greater. both processes will be sending and receiving, like ping-pong maybe). The benefit of 2 uni-directed connections come from linux: http://lxr.linux.no/linux+v2.6.18/net/ipv4/tcp_input.c#L3847 3847/* 3848 * TCP receive function for the ESTABLISHED state. 3849 * 3850 * It is split into a fast path and a slow path. The fast path is 3851 * disabled when: ... 3859 * - Data is sent in both directions. Fast path only supports pure senders 3860 * or pure receivers (this means either the sequence number or the ack 3861 * value must stay constant) ... 3863 * 3864 * When these conditions are not satisfied it drops into a standard 3865 * receive procedure patterned after RFC793 to handle all cases. 3866 * The first three cases are guaranteed by proper pred_flags setting, 3867 * the rest is checked inline. Fast processing is turned on in 3868 * tcp_data_queue when everything is OK. All other conditions for disabling fast path is false. And only not-unidirected socket stops kernel from fastpath in receive

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• Scheduler with Asp Mvc

  - by Samuel

  Hi, I want to use a Scheduler like Telerik Scheduler in my Mvc project. The problem is that the Scheduler is a Asp.Net WebForm control. For this reason, I must create a WebForm page in my Mvc project to put the Scheduler control. When I show the page, it work fine to render the layout of the control but if I try to interact with it; click for change date, change to day view to week view, the control don't change. I know that postback doesn't work in mvc project but does it work in a WebForm page in a Mvc project? If it doesn't work, it is the reason why when I try to interact with the control, the control don't respond. I think it's because the postback don't work and the Scheduler use 100 % Databinding where when I change date, the postback don't contain any data that I have changed and for this reason, the control can't change is layout. Have you any ideas about postback with WebForm in mvc project? What type of design can I adopt? (Two differents projets: One for my Scheduler with WebForm and another for all the rest of my website in Mvc project) Any other control easily to use with Scheduler? Tips and tricks when needing both WebForm control and Mvc control in Mvc project? Thank you very much.

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• Python: Errors saving and loading objects with pickle module

  - by Peterstone

  Hi, I am trying to load and save objects with this piece of code I get it from a question I asked a week ago: Python: saving and loading objects and using pickle. The piece of code is this: class Fruits: pass banana = Fruits() banana.color = 'yellow' banana.value = 30 import pickle filehandler = open("Fruits.obj","wb") pickle.dump(banana,filehandler) filehandler.close() file = open("Fruits.obj",'rb') object_file = pickle.load(file) file.close() print(object_file.color, object_file.value, sep=', ') At a first glance the piece of code works well, getting load and see the 'color' and 'value' of the saved object. But, what I pursuit is to close a session, open a new one and load what I save in a past session. I close the session after putting the line filehandler.close() and I open a new one and I put the rest of your code, then after putting object_file = pickle.load(file) I get this error: Traceback (most recent call last): File "<pyshell#5>", line 1, in <module> object_file = pickle.load(file) File "C:\Python31\lib\pickle.py", line 1365, in load encoding=encoding, errors=errors).load() AttributeError: 'module' object has no attribute 'Fruits' Can anyone explain me what this error message means and telling me how to solve this problem? Thank so much and happy new year!!

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• What database strategy to choose for a large web application

  - by Snoopy

  I have to rewrite a large database application, running on 32 servers. The hardware is up to date, each machine has two quad core Xeon and 32 GByte RAM. The database is multi-tenant, each customer has his own file, around 5 to 10 GByte each. I run around 50 databases on this hardware. The app is open to the web, so I have no control on the load. There are no really complex queries, so SQL is not required if there is a better solution. The databases get updated via FTP every day at midnight. The database is read-only. C# is my favourite language and I want to use ASP.NET MVC. I thought about the following options: Use two big SQL servers running SQL Server 2012 to serve the 32 servers with data. On the 32 servers running IIS hosting providing REST services. Denormalize the database and use Redis on each webserver. Use booksleeve as a Redis client. Use a combination of SQL Server and Redis Use SQL Server 2012 together with Hadoop Use Hadoop without SQL Server What is the best way for a read-only database, to get the best performance without loosing maintainability? Does Map-Reduce make sense at all in such a scenario? The reason for the rewrite is, the old app written in C++ with ISAM technology is too slow, the interfaces are old fashioned and not nice to use from an website, especially when using ajax. The app uses a relational datamodel with many tables, but it is possible to write one accerlerator table where all queries can be performed on, and all other information from the other tables are possible by a simple key lookup.

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• PHP/Javascript: Need help removing line break from code

  - by Josh K

  I am trying to get names from a .txt file. I am using file('filename.txt') but if i use a php for loop to try and trim the names, it comes out on multiple lines: This is the actual line that prints the javascript (NOTE: I am going to be putting these names into a select box, if you can fix the problem at hand the rest of the code should work so unless you a big problem with it you don't need to comment) <?php for($i=1; $i < 27; $i++){ echo "selbox.options[selbox.options.length] = new Option('".lines[$i]."','".$lines[$i]."');\n"; } ?> Heres how it comes out on the browser: selbox.options[selbox.options.length] = new Option('Djamal ABDOUN ','First1 Last1 '); selbox.options[selbox.options.length] = new Option('Chadli AMRI ','First2 Last2 '); I need those to be on one line so i dont get a unterminated string literal js error Any ideas on what i can do here? EDIT: Oh i should probably mention, the $lines var is initiated like this: $lines = file('filename.txt'); and inside that file i have formatted like this First1 Last1 First2 Last2 First3 Last3 etc. and i hit delete after each Last name until the next first name is touching, then hit enter to put it on a new line (Editor is notepad++)

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• Initial capacity of collection types, i.e. Dictionary, List

  - by Neil N

  Certain collection types in .Net have an optional "Initial Capacity" constructor param. i.e. Dictionary<string, string> something = new Dictionary<string,string>(20); List<string> anything = new List<string>(50); I can't seem to find what the default initial capacity is for these objects on MSDN. If I know I will only be storing 12 or so items in a dictionary, doesn't it make sense to set the initial capacity to something like 20? My reasoning is, assuming the capacity grows like it does for a StringBuiler, which doubles each time the capacity is hit, and each re-allocation is costly, why not pre-set the size to something you know will hold your data, with some extra room just in case? If the initial capacity is 100, and I know I will only need a dozen or so, it seems as though the rest of that allocated RAM is allocated for nothing. Please spare me the "premature optimization" speil for the O(n^n)th time. I know it won't make my apps any faster or save any meaningful amount of memory, this is mostly out of curiosity.

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• Java 8 Stream, getting head and tail

  - by lyomi

  Java 8 introduced a Stream class that resembles Scala's Stream, a powerful lazy construct using which it is possible to do something like this very concisely: def from(n: Int): Stream[Int] = n #:: from(n+1) def sieve(s: Stream[Int]): Stream[Int] = { s.head #:: sieve(s.tail filter (_ % s.head != 0)) } val primes = sieve(from(2)) primes takeWhile(_ < 1000) print // prints all primes less than 1000 I wondered if it is possible to do this in Java 8, so I wrote something like this: IntStream from(int n) { return IntStream.iterate(n, m -> m + 1); } IntStream sieve(IntStream s) { int head = s.findFirst().getAsInt(); return IntStream.concat(IntStream.of(head), sieve(s.skip(1).filter(n -> n % head != 0))); } IntStream primes = sieve(from(2)); PrimitiveIterator.OfInt it = primes.iterator(); for (int prime = it.nextInt(); prime < 1000; prime = it.nextInt()) { System.out.println(prime); } Fairly simple, but it produces java.lang.IllegalStateException: stream has already been operated upon or closed because both findFirst() and skip() is a terminal operation on Stream which can be done only once. I don't really have to use up the stream twice since all I need is the first number in the stream and the rest as another stream, i.e. equivalent of Scala's Stream.head and Stream.tail. Is there a method in Java 8 Stream that I can achieve this? Thanks.

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• How do I create a hyperlink in java?

  - by Justin984

  I'm going through the google app engine tutorials at https://developers.google.com/appengine/docs/java/gettingstarted/usingusers I'm very new to google app engine, java and web programming in general. So my question is, at the bottom of the page it says to add a link to allow the user to log out. So far I've got this: public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException { UserService userService = UserServiceFactory.getUserService(); User user = userService.getCurrentUser(); if(user != null){ resp.setContentType("text/plain"); resp.getWriter().println("Hello, " + user.getNickname()); String logoutLink = String.format("<a href=\"%s\">Click here to log out.</a>", userService.createLogoutURL(req.getRequestURI())); resp.getWriter().println(logoutLink); }else { resp.sendRedirect(userService.createLoginURL(req.getRequestURI())); } } However instead of a link, the full string is printed to the screen including the tags. When I look at the page source, I have no tags or any of the other stuff that goes with a webpage. I guess that makes sense considering I've done nothing to output any of that. Do I just do a bunch of resp.GetWriter().println() statements to output the rest of the webpage, or is there something else I don't know about? Thanks!

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