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  • Why I cannot add a JPanel to JFrame?

    - by Roman
    Here is the code: import javax.swing.SwingUtilities; import javax.swing.JFrame; import javax.swing.JPanel; import javax.swing.JLabel; import java.awt.event.*; import java.awt.*; public class GameWindow { private String[] players; private JFrame frame; // Constructor. public GameWindow(String[] players) { this.players = players; } // Start the window in the EDT. public void start() { SwingUtilities.invokeLater(new Runnable() { public void run() { showWindow(); controller.start(); } }); } // Defines the general properties of and starts the window. public void showWindow() { frame = new JFrame("Game"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(600,400); frame.setVisible(true); } // The thread controlling changes of panels in the main window. private Thread controller = new Thread() { public void run() { frame.add(generatePartnerSelectionPanel()); frame.invalidate(); frame.validate(); } }; // Generate the panel for the selection of a partner. private JPanel generatePartnerSelectionPanel() { JPanel panel = new JPanel(); panel.add(new JLabel("Pleas select a partner:")); return panel; } } I should see "Pleas select the partner" and I don't. Why? I suppose that it's because I do not see frame from the run method of the Thread.

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  • Need help choosing database server

    - by The Pretender
    Good day everyone. Recently I was given a task to develop an application to automate some aspects of stocks trading. While working on initial architecture, the database dilemma emerged. What I need is a fast database engine which can process huge amounts of data coming in very fast. I'm fairly experienced in general programming, but I never faced a task of developing a high-load database architecture. I developed a simple MSSQL database schema with several many-to-many relationships during one of my projects, but that's it. What I'm looking for is some advice on choosing the most suitable database engine and some pointers to various manuals or books which describe high-load database development. Specifics of the project are as follows: OS: Windows NT family (Server 2008 / 7) Primary platform: .NET with C# Database structure: one table to hold primary items and two or three tables with foreign keys to the first table to hold additional information. Database SELECT requirements: Need super-fast selection by foreign keys and by combination of foreign key and one of the columns (presumably DATETIME) Database INSERT requirements: The faster the better :) If there'll be significant performance gain, some parts can be written in C++ with managed interfaces to the rest of the system. So once again: given all that stuff I just typed, please give me some advice on what the best database for my project is. Links or references to some manuals and books on the subject are also greatly appreciated. EDIT: I'll need to insert 3-5 rows in 2 tables approximately once in 30-50 milliseconds and I'll need to do SELECT with 0-2 WHERE clauses queries with similar rate.

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  • How do you remove invalid hexadecimal characters from an XML-based data source prior to constructing

    - by Oppositional
    Is there any easy/general way to clean an XML based data source prior to using it in an XmlReader so that I can gracefully consume XML data that is non-conformant to the hexadecimal character restrictions placed on XML? Note: The solution needs to handle XML data sources that use character encodings other than UTF-8, e.g. by specifying the character encoding at the XML document declaration. Not mangling the character encoding of the source while stripping invalid hexadecimal characters has been a major sticking point. The removal of invalid hexadecimal characters should only remove hexadecimal encoded values, as you can often find href values in data that happens to contains a string that would be a string match for a hexadecimal character. Background: I need to consume an XML-based data source that conforms to a specific format (think Atom or RSS feeds), but want to be able to consume data sources that have been published which contain invalid hexadecimal characters per the XML specification. In .NET if you have a Stream that represents the XML data source, and then attempt to parse it using an XmlReader and/or XPathDocument, an exception is raised due to the inclusion of invalid hexadecimal characters in the XML data. My current attempt to resolve this issue is to parse the Stream as a string and use a regular expression to remove and/or replace the invalid hexadecimal characters, but I am looking for a more performant solution.

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  • Invalid iPhone Application Binary

    - by Kristopher Johnson
    I'm trying to upload an application to the iPhone App Store, but I get this error message from iTunes Connect: The binary you uploaded was invalid. The signature was invalid, or it was not signed with an Apple submission certificate. My guess is that it is not properly signed. I have downloaded my App Store distribution certficate, but I can't figure out how to "sign" my application with it. The SDK's documentation about code signing is not very helpful. (FWIW, I can install the app on my iPhone just fine using the development provisioning profile.) However, it is possible that I screwed things up on a more basic level. Here's what I did to try to prepare it for upload: In Xcode, select the Device|Release target Select the target and click the Info button. Change "Code Signing Identity" to "iPhone Distribution", and change "Code Signing Provisioning Profile" to my App Store distribution profile. Build Go to the directory where the built MyApp.app bundle is, control-click and choose "Compress" to create MyApp.zip Upload MyApp.zip to the App Store via iTunes Connect (which resulted in the above error message). Can anybody give me any hints? Edit: Found someone with the same problem. Unfortunately, he won't tell us how he fixed it. http://www.rhonabwy.com/wp/2008/07/18/seattlebus-diary-ongoing-update-saga/#comments http://www.rhonabwy.com/wp/2008/07/22/seattlebus-diary-update-is-pending-review/ (Note: For general information on submitting iPhone applications to the App Store, see Steps to upload an iPhone application to the AppStore.)

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  • Why does Clojure hang after hacing performed my calculations?

    - by Thomas
    Hi all, I'm experimenting with filtering through elements in parallel. For each element, I need to perform a distance calculation to see if it is close enough to a target point. Never mind that data structures already exist for doing this, I'm just doing initial experiments for now. Anyway, I wanted to run some very basic experiments where I generate random vectors and filter them. Here's my implementation that does all of this (defn pfilter [pred coll] (map second (filter first (pmap (fn [item] [(pred item) item]) coll)))) (defn random-n-vector [n] (take n (repeatedly rand))) (defn distance [u v] (Math/sqrt (reduce + (map #(Math/pow (- %1 %2) 2) u v)))) (defn -main [& args] (let [[n-str vectors-str threshold-str] args n (Integer/parseInt n-str) vectors (Integer/parseInt vectors-str) threshold (Double/parseDouble threshold-str) random-vector (partial random-n-vector n) u (random-vector)] (time (println n vectors (count (pfilter (fn [v] (< (distance u v) threshold)) (take vectors (repeatedly random-vector)))))))) The code executes and returns what I expect, that is the parameter n (length of vectors), vectors (the number of vectors) and the number of vectors that are closer than a threshold to the target vector. What I don't understand is why the programs hangs for an additional minute before terminating. Here is the output of a run which demonstrates the error $ time lein run 10 100000 1.0 [null] 10 100000 12283 [null] "Elapsed time: 3300.856 msecs" real 1m6.336s user 0m7.204s sys 0m1.495s Any comments on how to filter in parallel in general are also more than welcome, as I haven't yet confirmed that pfilter actually works.

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  • stack overflow on XMLListCollection collectionEvent

    - by reidLinden
    I'm working on a Flex 3 project, and I'm using a pair of XMLListCollection(s) to manage a combobox and a data grid. The combobox piece is working perfectly. The XMLListCollection for this is static. The user picks an item, and, on "change", it fires off an addItem() to the second collection. The second collection's datagrid then displays the updated list, and all is well. The datagrid, however, is editable. A further complication is that I have another event handler bound to the second XMLLIstCollection's "change" event, and in that handler, I do make additional changes to the second list. This essentially causes an infinite loop (a stack overflow :D ), of the second lists "change" handler. I'm not really sure how to handle this. Searching has brought up an idea or two regarding AutoUpdate functionality, but I wasn't able to get much out of them. In particular, the behavior persists, executing the 'updates' as soon as I re-enable, so I imagine I may be doing it wrong. I want the update to run, in general, just not DURING that code block. Thanks for your help!

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  • "image contains error", trying to create and display images using google app engine

    - by bert
    Hello all the general idea is to create a galaxy-like map. I run into problems when I try to display a generated image. I used Python Image library to create the image and store it in the datastore. when i try to load the image i get no error on the log console and no image on the browser. when i copy/paste the image link (including datastore key) i get a black screen and the following message: The image “view-source:/localhost:8080/img?img_id=ag5kZXZ-c3BhY2VzaW0xMnINCxIHTWFpbk1hcBgeDA” cannot be displayed because it contains errors. the firefox error console: Error: Image corrupt or truncated: /localhost:8080/img?img_id=ag5kZXZ-c3BhY2VzaW0xMnINCxIHTWFpbk1hcBgeDA import cgi import datetime import urllib import webapp2 import jinja2 import os import math import sys from google.appengine.ext import db from google.appengine.api import users from PIL import Image #SNIP #class to define the map entity class MainMap(db.Model): defaultmap = db.BlobProperty(default=None) #SNIP class Generator(webapp2.RequestHandler): def post(self): #SNIP test = Image.new("RGBA",(100, 100)) dMap=MainMap() dMap.defaultmap = db.Blob(str(test)) dMap.put() #SNIP result = db.GqlQuery("SELECT * FROM MainMap LIMIT 1").fetch(1) if result: print"item found<br>" #debug info if result[0].defaultmap: print"defaultmap found<br>" #debug info string = "<div><img src='/img?img_id=" + str(result[0].key()) + "' width='100' height='100'></img>" print string else: print"nothing found<br>" else: self.redirect('/?=error') self.redirect('/') class Image_load(webapp2.RequestHandler): def get(self): self.response.out.write("started Image load") defaultmap = db.get(self.request.get("img_id")) if defaultmap.defaultmap: try: self.response.headers['Content-Type'] = "image/png" self.response.out.write(defaultmap.defaultmap) self.response.out.write("Image found") except: print "Unexpected error:", sys.exc_info()[0] else: self.response.out.write("No image") #SNIP app = webapp2.WSGIApplication([('/', MainPage), ('/generator', Generator), ('/img', Image_load)], debug=True) the browser shows the "item found" and "defaultmap found" strings and a broken imagelink the exception handling does not catch any errors Thanks for your help Regards Bert

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  • What's it like being a financial programmer?

    - by Mike
    As a student who's done an internship at a Silicon Valley company(non-financial), I'm curious to know what it's like working for a financial company doing software development. I'd expect the hours to be longer, and the pay to be higher. Specifically, I have the following questions: What's the work/life balance really like? Are you expected to work 80 hours a week most weeks? For those who have worked in non-financial software engineering jobs, how does being a financial software engineer compare in terms of work/life balance? How much does it pay? I'm curious as to starting(i.e. just got a BS) pay, as well as "top out" pay. (I'd prefer concrete numbers - ballpark is fine). Also, bonuses would be useful information. What jobs do financial programmers typically have? Are most just general software engineers, or do people typically have very specialized(i.e. AI or systems) backgrounds? Also, do most programmers have PhDs? Are programmers typically required to be at work, or are financial companies generally flexible about letting programmers work from home? When at work, do programmers have to dress formally? What are the technology environments like? Are finance companies using state-of-the-art hardware and software, or are they generally more conservative in upgrading their equipment? What programming languages are typically used? If VBA(shudder) is used, is it a large part of a finance company's workflow? If you could turn back the clock, would you still be a financial programmer? I'm going to keep this post open a little bit longer to get some more responses.

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  • How to maintain an ordered table with Core Data (or SQL) with insertions/deletions?

    - by Jean-Denis Muys
    This question is in the context of Core Data, but if I am not mistaken, it applies equally well to a more general SQL case. I want to maintain an ordered table using Core Data, with the possibility for the user to: reorder rows insert new lines anywhere delete any existing line What's the best data model to do that? I can see two ways: 1) Model it as an array: I add an int position property to my entity 2) Model it as a linked list: I add two one-to-one relations, next and previous from my entity to itself 1) makes it easy to sort, but painful to insert or delete as you then have to update the position of all objects that come after 2) makes it easy to insert or delete, but very difficult to sort. In fact, I don't think I know how to express a Sort Descriptor (SQL ORDER BY clause) for that case. Now I can imagine a variation on 1): 3) add an int ordering property to the entity, but instead of having it count one-by-one, have it count 100 by 100 (for example). Then inserting is as simple as finding any number between the ordering of the previous and next existing objects. The expensive renumbering only has to occur when the 100 holes have been filled. Making that property a float rather than an int makes it even better: it's almost always possible to find a new float midway between two floats. Am I on the right track with solution 3), or is there something smarter?

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  • Accessing class member variables inside a BackgroundWorker's DoWork event handler, and other Backgro

    - by Justin
    Question 1 In the DoWork event handler of a BackgroundWorker, is it safe to access (for both reading and writing) member variables of the class that contains the BackgroundWorker? Is it safe to access other variables that are not declared inside the DoWork event handler itself? Obviously DoWork should not be accessing any UI objects of, say, a WinForms application, as the UI should only be updated from the UI thread. But what about accessing other (not UI-related) member variables? The reason why I ask is that I've seen the occasional comment come up while Googling saying that accessing member variables is not allowed. The only example I can find at the moment is a comment on this MSDN page, which says: Note, that the BGW can cause exceptions if it attempts to access or modify class level variables. All data must be passed to it by delegates and events. And also: NEVER. NEVER. Never try to reference variables not declared inside of DoWork. It may seem to work at times, but in reality you are just getting lucky. As far as I know, MSDN itself does not document any restrictions of this kind (although if I'm wrong, I'd appreciate a link). But comments like these do seem to pop up every now and again. (Of course if DoWork does access/modify a member variable that could be accessed/modified by the main thread at the same time, it is necessary to synchronise access to that field, eg by using a locking object. But the above quotes seem to require a blanket ban of accessing member variables, rather than just synchronising access!) Question 2 To make this into a more general question, are there any other (not documented?) restrictions that users of the BackgroundWorker should be aware of, aside from the above? Any "best practices", perhaps?

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  • What is the relationship between Turing Machine & Modern Computer ?

    - by smwikipedia
    I heard a lot that modern computers are based on Turing machine. I just cannot build a bridge from a conceptual Turing Machine to a real modern computer. Could someone help me build this bridge? Below is my current understanding. I think the computer is a big general-purpose Turing machine. Each program we write is a small specific-purpose Turing machine. The classical Turing machine do its job based on the input and its current state inside and so do our programs. Let's take a running program (a process) as an example. We know that in the process's address space, there's areas for stack, heap, and code. A classical Turing machine doesn't have the ability to remember many things, so we borrow the concept of stack from the push-down automaton. The heap and stack areas contains the state of our specific-purpose Turing machine (our program). The code area represents the logic of this small Turing machine. And various I/O devices supply input to this Turing machine.

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  • Can I create template-based library objects in Dreamweaver CS5?

    - by Danjah
    At work we need two 'streams' of template. The first are general layout templates, like the ones already available in the MX through CS5 packages (except we'd have our own customised ones). The second are more granular objects, some of which are functional. In both cases, I don't want Jimmy to be able to wreak havoc inside anything other than the 'editable regions' which make up the templates. Now this is fine if I stick with the first scenario (layout templates) where there's simply a big chunk of editable region for good ole Jim to sprawl into, think of this as the 'body content' area. But I really do need these granular library (or snippet) objects to work in the same way. Unfortunately with my attempts so far they don't work as I'd have thought - perhaps for good reason? When I create a blank template and throw in my chunk of HTML (unobstrusive JS and external CSS use selectors in this HTML to provide style and function) and save it as a new library item or snippet, all looks well. Then I create a new document based on a layout template and save it as a plain html file (still all good so far). Next I drop in my custom library item... still all good... but then I go to save the document and it only allows me to save it as a new template! I expected it would just allow me to save it as HTML and have it simply respect the defined editable regions, as happens in the containing page 'body content' editable region. Apologies if that got specific and technical quite quickly, but it is quite particular. If you want some example files lemme know and I'll zip some up. Many thanks :) p.s It is not a requirement that library objects must somehow inject their dependency files into the newly created page - I already know what they'll be. Also, I know I must 'detatch from original' once I drop a library item into a document which then allows customisation of the library object.

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  • How do I begin reading source code?

    - by anonnoir
    I understand the value of reading source code, and I am trying my best to read as much as I can. However, every time I try getting into a 'large' (i.e. complete) project of sorts, I am overwhelmed. For example, I use Anki a lot when revising languages. Also, I'm interested in getting to know how an audio player works (because I have some project ideas), hence quodlibet on Google Code. But whenever I open the source code folders for the above programs, there are just so many files that I don't know where or what to begin with. I think that I should start with files marked init.py but I can't see the logical structure of the programs, or what reasoning was applied when the original writer divided his modules the way he did. Hence, my questions: How/where should I begin reading source? Any general tips or ideas? How does a programmer keep in mind the overall structure and logic of the program, especially for large projects, and is it common not to document that structure? As an open source reader, must I look through all of the code and get a bird's eye view of the code and libraries, before even being able to proceed? Would an IDE like Eclipse SDK (with PyDev) help with code-reading? Thanks for the help; I really appreciate your helping me.

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  • Converting a Linq expression tree that relies on SqlMethods.Like() for use with the Entity Framework

    - by JohnnyO
    I recently switched from using Linq to Sql to the Entity Framework. One of the things that I've been really struggling with is getting a general purpose IQueryable extension method that was built for Linq to Sql to work with the Entity Framework. This extension method has a dependency on the Like() method of SqlMethods, which is Linq to Sql specific. What I really like about this extension method is that it allows me to dynamically construct a Sql Like statement on any object at runtime, by simply passing in a property name (as string) and a query clause (also as string). Such an extension method is very convenient for using grids like flexigrid or jqgrid. Here is the Linq to Sql version (taken from this tutorial: http://www.codeproject.com/KB/aspnet/MVCFlexigrid.aspx): public static IQueryable<T> Like<T>(this IQueryable<T> source, string propertyName, string keyword) { var type = typeof(T); var property = type.GetProperty(propertyName); var parameter = Expression.Parameter(type, "p"); var propertyAccess = Expression.MakeMemberAccess(parameter, property); var constant = Expression.Constant("%" + keyword + "%"); var like = typeof(SqlMethods).GetMethod("Like", new Type[] { typeof(string), typeof(string) }); MethodCallExpression methodExp = Expression.Call(null, like, propertyAccess, constant); Expression<Func<T, bool>> lambda = Expression.Lambda<Func<T, bool>>(methodExp, parameter); return source.Where(lambda); } With this extension method, I can simply do the following: someList.Like("FirstName", "mike"); or anotherList.Like("ProductName", "widget"); Is there an equivalent way to do this with Entity Framework? Thanks in advance.

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  • best practice for boolean REST results

    - by Andrew Patterson
    I have a resource /system/resource And I wish to ask the system a boolean question about the resource that can't be answered by processing on the client (i.e I can't just GET the resource and look through the actual resource data - it requires some processing on the backend using data not available to the client). eg /system/resource/related/otherresourcename I want this is either return true or false. Does anyone have any best practice examples for this type of interaction? Possibilities that come to my mind: use of HTTP status code, no returned body (smells wrong) return plain text string (True, False, 1, 0) - Not sure what string values are appropriate to use, and furthermore this seems to be ignoring the Accept media type and always returning plain text come up with a boolean object for each of my support media types and return the appropriate type (a JSON document with a single boolean result, an XML document with a single boolean field). However this seems unwieldy. I don't particularly want to get into a long discussion about the true meaning of a RESTful system etc - I have used the word REST in the title because it best expresses the general flavour of system I am designing (even if perhaps I am tending more towards RPC over the web rather than true REST). However, if someone has some thoughts on how a true RESTful system avoids this problem entirely I would be happy to hear them.

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  • implementing a download manager that supports resuming

    - by Idan K
    hi, I intend on writing a small download manager in C++ that supports resuming (and multiple connections per download). From the info I gathered so far, when sending the http request I need to add a header field with a key of "Range" and the value "bytes=startoff-endoff". Then the server returns a http response with the data between those offsets. So roughly what I have in mind is to split the file to the number of allowed connections per file and send a http request per splitted part with the appropriate "Range". So if I have a 4mb file and 4 allowed connections, I'd split the file to 4 and have 4 http requests going, each with the appropriate "Range" field. Implementing the resume feature would involve remembering which offsets are already downloaded and simply not request those. Is this the right way to do this? What if the web server doesn't support resuming? (my guess is it will ignore the "Range" and just send the entire file) When sending the http requests, should I specify in the range the entire splitted size? Or maybe ask smaller pieces, say 1024k per request? When reading the data, should I write it immediately to the file or do some kind of buffering? I guess it could be wasteful to write small chunks. Should I use a memory mapped file? If I remember correctly, it's recommended for frequent reads rather than writes (I could be wrong). Is it memory wise? What if I have several downloads simultaneously? If I'm not using a memory mapped file, should I open the file per allowed connection? Or when needing to write to the file simply seek? (if I did use a memory mapped file this would be really easy, since I could simply have several pointers). Note: I'll probably be using Qt, but this is a general question so I left code out of it.

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  • PHP - Database schema: version control, branching, migrations.

    - by Billiam
    I'm trying to come up with (or find) a reusable system for database schema versioning in php projects. There are a number of Rails-style migration projects available for php. http://code.google.com/p/mysql-php-migrations/ is a good example. It uses timestamps for migration files, which helps with conflicts between branches. General problem with this kind of system: When development branch A is checked out, and you want to check out branch B instead, B may have new migration files. This is fine, migrating to newer content is straight forward. If branch A has newer migration files, you would need to migrate downwards to the nearest shared patch. If branch A and B have significantly different code bases, you may have to migrate down even further. This may mean: Check out B, determine shared patch number, check out A, migrate downwards to this patch. This must be done from A since the actual applied patches are not available in B. Then, checkout branch B, and migrate to newest B patch. Reverse process again when going from B to A. Proposed system: When migrating upwards, instead of just storing the patch version, serialize the whole patch in database for later use, though I'd probably only need the down() method. When changing branches, compare patches that have been run to patches that are available in the destination branch. Determine nearest shared patch (or oldest difference, maybe) between db table of run patches and patches in destination branch by ID or hash. Could also look for new or missing patches that are buried under a number of shared patches between the two branches. Automatically merge down to the nearest shared patch, using the db table stored down() methods, and then merge up to the branche's latest patch. My question is: Is this system too crazy and/or fraught with consequences to bother developing? My experience with database schema versioning is limited to PHP autopatch, which is an up()-only system requiring filenames with sequential IDs.

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  • How best to use XPath with very large XML files in .NET?

    - by glenatron
    I need to do some processing on fairly large XML files ( large here being potentially upwards of a gigabyte ) in C# including performing some complex xpath queries. The problem I have is that the standard way I would normally do this through the System.XML libraries likes to load the whole file into memory before it does anything with it, which can cause memory problems with files of this size. I don't need to be updating the files at all just reading them and querying the data contained in them. Some of the XPath queries are quite involved and go across several levels of parent-child type relationship - I'm not sure whether this will affect the ability to use a stream reader rather than loading the data into memory as a block. One way I can see of making it work is to perform the simple analysis using a stream-based approach and perhaps wrapping the XPath statements into XSLT transformations that I could run across the files afterward, although it seems a little convoluted. Alternately I know that there are some elements that the XPath queries will not run across, so I guess I could break the document up into a series of smaller fragments based on it's original tree structure, which could perhaps be small enough to process in memory without causing too much havoc. I've tried to explain my objective here so if I'm barking up totally the wrong tree in terms of general approach I'm sure you folks can set me right...

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  • How to improve Java performance on Informix for Windows

    - by Michal Niklas
    I have problem with performance of Java UDR functions on Informix on Windows. On this server I already have some functions in C and SPL. I chose one function to write it in those 3 languages and I measured performance of this function on test table. Function calculates some kind of checksum so it does not use any db libraries etc. only string and math operations. I observed performance on 30k records with SQL like: select function(txt) from _tmp_perf_test and I changed function to 'function_c, function_spl or function_java. My performance tests showed that C function is the fastest, SPL function is about 5 times slower, where Java is 100 (one hundred!) times slower than C. I checked it few times and 1:100 ratio didn't improve. I changed Java function to simply return length of the string but even this do not help so it looks, that there is general problem with Java function invocation, because there was no difference in time between Java function that calculate checksum and Java function that returns length of the string. I increased JVM_MAX_HEAP_SIZE to 128 and it not helped too. I use IBM Informix Dynamic Server Version 11.50.TC6DE. The same test on Linux server: IBM Informix Dynamic Server Version 11.50.FC6 show more "normal" results, i.e. Java is slower from C and SPL but only 2 to 5 times. What can I do to improve Java performance on Informix server on Windows? More info about Java on servers: c:\Informix\extend\krakatoa\jre\bin>java -version java version "1.5.0" Java(TM) 2 Runtime Environment, Standard Edition (build pwi32dev-20081129a (SR9-0 )) IBM J9 VM (build 2.3, J2RE 1.5.0 IBM J9 2.3 Windows Server 2003 x86-32 j9vmwi3223-20081129 (JIT enabled) J9VM - 20081126_26240_lHdSMr JIT - 20081112_1511ifx1_r8 GC - 200811_07) JCL - 20081129 [root@informix11 bin]# ./java -version java version "1.5.0" Java(TM) 2 Runtime Environment, Standard Edition (build pxa64devifx-20071025 (SR6b)) IBM J9 VM (build 2.3, J2RE 1.5.0 IBM J9 2.3 Linux amd64-64 j9vmxa6423-20071005 (JIT enabled) J9VM - 20071004_14218_LHdSMr JIT - 20070820_1846ifx1_r8 GC - 200708_10) JCL - 20071025

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  • Why avoid increment ("++") and decrement ("--") operators in JavaScript?

    - by artlung
    I'm a big fan of Douglas Crockford's writing on JavaScript, particularly his book JavaScript: The Good Parts. It's made me a better JavaScript programmer and a better programmer in general. One of his tips for his jslint tool is this : ++ and -- The ++ (increment) and -- (decrement) operators have been known to contribute to bad code by encouraging excessive trickiness. They are second only to faulty architecture in enabling to viruses and other security menaces. There is a plusplus option that prohibits the use of these operators. This has always struck my gut as "yes, that makes sense," but has annoyed me when I've needed a looping condition and can't figure out a better way to control the loop than a while( a < 10 )do { a++ } or for (var i=0;i<10;i++) { } and use jslint. It's challenged me to write it differently. I also know in the distant past using things, in say PHP like $foo[$bar++] has gotten me in trouble with off-by-one errors. Are there C-like languages or other languages with similarities that that lack the "++" and "--" syntax or handle it differently? Are there other rationales for avoiding "++" and "--" that I might be missing? UPDATE -- April 9, 2010: In the video Crockford on JavaScript -- Part 5: The End of All Things, Douglas Crockford addresses the ++ issue more directly and with more detail. It appears at 1:09:00 in the timeline. Worth a watch.

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  • Suppress Eclipse compiler errors in in a plug-in

    - by Jan Gorzny
    Hi, I'm currently working on a plug-in for Eclipse that translates some custom Java code (which doesn't necessarily run/compile), to runnable Java code. In particular, the plug-in allows code to be written using classes created or imported during the translation. In general, the pre-translation code runs/compiles fine provided the writer uses import statements at the top of their class files. However, it would be convenient for my users if it was not necessary to import these classes. At the moment, the lack of import statements results in (obvious) compiler errors. Would it be possible to empower my plug-in to either a) suppress/ignore these errors, or b) have Eclipse find these classes automatically, without the use of import statements? I should point out that the translated code would these include the required import statements--but this is not a problem for me. I'm also aware that this could lead to lazy programmers and some bad habits. To clarify, consider the following example of pre-translated code: File f = new File("Somefilename.txt"); which clearly requires the possibly imported class File. Without an import statement (import java.io.File;), Eclipse reports that File can not be resolved to a type. This is the error I'd like to hide in files pertaining to projects created for use with my plug-in. (The translated code would include import java.io.File; so that it would be runnable) In closing, I should point out I'm not necessarily looking for code (though I wouldn't be opposed to it), but rather some links to some relevant tutorials (if they exist), or helpful tips/ideas. Also, as this is my first plug-in, it's entirely possible that what I'd like to do is not possible and that I don't realize it--if this is the case, please let me know, preferably with some justification. Thanks!

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  • A queue in C using structs and dynamic memory allocation (linked list)

    - by Martin Pugh
    I am tasked with making a queue data structure in C, as a linked list. Our lecturer gave us a large amount of code to implement a stack, but we have to adapt it to create a queue. The code our lecturer gave us ends up not compiling and segfaulting at the exact same point as the code I wrote for the queue. I'm very new to structs, malloc and C in general, so there could be something painfully obvious I've overlooked. Here is the code I am using: #include <stdio.h> #include <stdlib.h> struct node{ int data; //contains the actual data struct node *prev; //pointer to previous node (Closer to front) struct node *next; //pointer to next node (Closer to back) }; typedef struct node *Nodepointer; struct queue{ Nodepointer front; Nodepointer back; }; typedef struct queue *Queuepointer; main(){ Queuepointer myqueue; //create a queue called myqueue init(myqueue); //initialise the queue Nodepointer new = (Nodepointer)malloc(sizeof(struct node)); myqueue->front = new; } int init(Queuepointer q){ q = (Queuepointer)malloc(sizeof(struct queue)); q->front = NULL; q->back = NULL; } The idea is that the queue struct 'contains' the first and last nodes in a queue, and when a node is created, myqueue is updated. However, I cannot even get to that part (pop and push are written but omitted for brevity). The code is segfaulting at the line myqueue->front = new; with the following gdb output: Program received signal SIGSEGV, Segmentation fault. 0x08048401 in main () at queue.c:27 27 myqueue->front = new; Any idea what I'm doing wrong?

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  • Time complexity with bit cost

    - by Keyser
    I think I might have completely misunderstood bit cost analysis. I'm trying to wrap my head around the concept of studying an algorithm's time complexity with respect to bit cost (instead of unit cost) and it seems to be impossible to find anything on the subject. Is this considered to be so trivial that no one ever needs to have it explained to them? Well I do. (Also, there doesn't even seem to be anything on wikipedia which is very unusual). Here's what I have so far: The bit cost of multiplication and division of two numbers with n bits is O(n^2) (in general?) So, for example: int number = 2; for(int i = 0; i < n; i++ ){ number = i*i; } has a time complexity with respect to bit cost of O(n^3), because it does n multiplications (right?) But in a regular scenario we want the time complexity with respect to the input. So, how does that scenario work? The number of bits in i could be considered a constant. Which would make the time complexity the same as with unit cost except with a bigger constant (and both would be linear). Also, I'm guessing addition and subtraction can be done in constant time, O(1). Couldn't find any info on it but it seems reasonable since it's one assembler operation.

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  • Javascript and webshop tracking/affiliate across websites, how to do?

    - by H4mm3rHead
    Hi, I have a small front end to a webshop. All customers that go through my website and buy an item from the webshop I get back 5% of the amount. I need to find a way af tracking the customers i forward from my webshop to the other webshop. And then get the webshop to reply to me when the purchase has been made. In my webshop i have made a small page: collect.aspx that requests and saves the values passed in the querystring, something like this pseudo code: string orderid = Request["orderid"]; string amount = Request["amount"]; ..save to database On the webshop i forward customers to i get to insert a javascript on the last page in the purchase flow. I have tried a lot of things but it seems that the only thing that works is to fool the browser into thinking im referring a javascript, like this: <script type="text/javascript" src="http://domain.com/mypage.aspx?orderid=4&amount=45/> I saw how other trackers did their bit, and this seems to be the general way of doing it. With this script however, i get all the orders, i only want to log those that belong tome, those who entered through my website. Here is my big problem, how to do this? I added a cookie when the user opens my page, and i want to check for this cookie again when the purchase page make the callback. It weems that i cant get the cookie from the browser when it makes the "" call. This is really buggin me now. Could anyone please tell me how this is generally done, this tracking. And what am i missing in regards to this cookie thing? All ideas on how to do this is very welcome.

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  • Javascript scope chain

    - by Geromey
    Hi, I am trying to optimize my program. I think I understand the basics of closure. I am confused about the scope chain though. I know that in general you want a low scope (to access variables quickly). Say I have the following object: var my_object = (function(){ //private variables var a_private = 0; return{ //public //public variables a_public : 1, //public methods some_public : function(){ debugger; alert(this.a_public); alert(a_private); }; }; })(); My understanding is that if I am in the some_public method I can access the private variables faster than the public ones. Is this correct? My confusion comes with the scope level of this. When the code is stopped at debugger, firebug shows the public variable inside the this keyword. The this word is not inside a scope level. How fast is accessing this? Right now I am storing any this.properties as another local variable to avoid accessing it multiple times. Thanks very much!

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