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  • How to synchronize static method in java.

    - by Summer_More_More_Tea
    Hi there: I come up with this question when implementing singleton pattern in Java. Even though the example listed blow is not my real code, yet very similar to the original one. public class ConnectionFactory{ private static ConnectionFactory instance; public static synchronized ConnectionFactory getInstance(){ if( instance == null ){ instance = new ConnectionFactory(); } return instance; } private ConnectionFactory(){ // private constructor implementation } } Because I'm not quite sure about the behavior of a static synchronized method, I get some suggestion from google -- do not have (or as less as possible) multiple static synchronized methods in the same class. I guess when implementing static synchronized method, a lock belongs to Class object is used so that multiple static synchronized methods may degrade performance of the system. Am I right? or JVM use other mechanism to implement static synchronized method? What's the best practice if I have to implement multiple static synchronized methods in a class? Thank you all! Kind regards!

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  • Aspect Oriented Programming vs List<IAction> To execute methods based on conditions

    - by David Robbins
    I'm new to AOP so bear with me. Consider the following scenario: A state machine is used in a workflow engine, and after the state of the application is changed, a series of commands are executed. Depending on the state, different types of commands should be executed. As I see it, one implementation is to create List<IAction> and have each individual action determine whether it should execute. Would a Aspect Oriented process work as well? That is, could you create an aspect that notifies a class when a property changes, and execute the appropriate processes from that class? Would this help centralize the state specific rules?

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  • What's a good book for learning BCPL?

    - by paxdiablo
    A long time ago, I worked on some BCPL code (very similar to C although even more basic, difficult though that is to imagine). Now, as part of a compiler course, we're going to be setting assignments for building some of the parts of the compiler (lexical and semantic analysis) and I'd like to know what the community thinks is the best book for learning about the language (and concrete why you think it's the best). Not how to write compilers for it, just on how to program in it. It'll be up to the students themselves to figure out how best to develop a compiler. We're using BCPL since the chance of people being able to plagiarise code for a compiler is very slim. Any suggestions?

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  • C++ - how does Sleep() and cin work?

    - by quano
    Just curious. How does actually the function Sleep() work (declared in windows.h)? Maybe not just that implementation, but anyone. With that I mean - how is it implemented? How can it make the code "stop" for a specific time? Also curious about how cin and those actually work. What do they do exactly? The only way I know how to "block" something from continuing to run is with a while loop, but considering that that takes a huge amount of processing power in comparison to what's happening when you're invoking methods to read from stdin (just compare a while (true) to a read from stdin), I'm guessing that isn't what they do.

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  • How to save state of the app when app terminates?

    - by user164589
    Hi guys. I am trying to save the app state by encoding when the app terminates. I've found the solution related this issue. But I don't know how to use. I am really trying to make encoding and decoding like this: http://cocoaheads.byu.edu/wiki/nscoding in CustomObject.h @interface CustomObject : NSObject <NSCoding> { NSArray *someArray; } in CustomObject.m @implementation CustomObject // Other method implementations here - (void) encodeWithCoder:(NSCoder*)encoder { [encoder encodeObject:someArray forKey:@"someArray"]; } - (id) initWithCoder:(NSCoder*)decoder { if (self = [super init]) { someArray = [[decoder decodeObjectForKey:@"someArray"] retain]; } return self; } @end My object to save is another NSArray. Not "someArray" in CustomObject. We call it that "MySaveObject". I want to pass "MySaveObject" to "someArray" in CustomObject. Actually I don't know how to encode "MySaveObject" and to pass to "someArray" in CustomObject. Thanks in advance.

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  • Abstracting the adding of click events to elements selected by class using jQuery

    - by baroquedub
    I'm slowly getting up to speed with jQuery and am starting to want to abstract my code. I'm running into problems trying to define click events at page load. In the code below, I'm trying to run through each div with the 'block' class and add events to some of its child elements by selecting them by class: <script language="javascript" type="text/javascript"> $(document).ready(function (){ $('HTML').addClass('JS'); // if JS enabled, hide answers $(".block").each(function() { problem = $(this).children('.problem'); button = $(this).children('.showButton'); problem.data('currentState', 'off'); button.click(function() { if ((problem.data('currentState')) == 'off'){ button.children('.btn').html('Hide'); problem.data('currentState', 'on'); problem.fadeIn('slow'); } else if ((problem.data('currentState')) == 'on'){ button.children('.btn').html('Solve'); problem.data('currentState', 'off'); problem.fadeOut('fast'); } return false; }); }); }); </script> <style media="all" type="text/css"> .JS div.problem{display:none;} </style> <div class="block"> <div class="showButton"> <a href="#" title="Show solution" class="btn">Solve</a> </div> <div class="problem"> <p>Answer 1</p> </div> </div> <div class="block"> <div class="showButton"> <a href="#" title="Show solution" class="btn">Solve</a> </div> <div class="problem"> <p>Answer 2</p> </div> </div> Unfortunately using this, only the last of the divs' button actually works. The event is not 'localised' (if that's the right word for it?) i.e. the event is only applied to the last $(".block") in the each method. So I have to laboriously add ids for each element and define my click events one by one. Surely there's a better way! Can anyone tell me what I'm doing wrong? And how I can get rid of the need for those IDs (I want this to work on dynamically generated pages where I might not know how many 'blocks' there are...) <script language="javascript" type="text/javascript"> $(document).ready(function (){ $('HTML').addClass('JS'); // if JS enabled, hide answers // Preferred version DOESN'T' WORK // So have to add ids to each element and laboriously set-up each one in turn... $('#problem1').data('currentState', 'off'); $('#showButton1').click(function() { if (($('#problem1').data('currentState')) == 'off'){ $('#showButton1 > a').html('Hide'); $('#problem1').data('currentState', 'on'); $('#problem1').fadeIn('slow'); } else if (($('#problem1').data('currentState')) == 'on'){ $('#showButton1 > a').html('Solve'); $('#problem1').data('currentState', 'off'); $('#problem1').fadeOut('fast'); } return false; }); $('#problem2').data('currentState', 'off'); $('#showButton2').click(function() { if (($('#problem2').data('currentState')) == 'off'){ $('#showButton2 > a').html('Hide'); $('#problem2').data('currentState', 'on'); $('#problem2').fadeIn('slow'); } else if (($('#problem2').data('currentState')) == 'on'){ $('#showButton2 > a').html('Solve'); $('#problem2').data('currentState', 'off'); $('#problem2').fadeOut('fast'); } return false; }); }); </script> <style media="all" type="text/css"> .JS div.problem{display:none;} </style> <div class="block"> <div class="showButton" id="showButton1"> <a href="#" title="Show solution" class="btn">Solve</a> </div> <div class="problem" id="problem1"> <p>Answer 1</p> </div> </div> <div class="block"> <div class="showButton" id="showButton2"> <a href="#" title="Show solution" class="btn">Solve</a> </div> <div class="problem" id="problem2"> <p>Answer 2</p> </div> </div>

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  • form submit not working in firefox but works fine in IE

    - by jestges
    Hi, I want to submit my parent page when I click on submit button of the child page. In my child page I've written my code as string scriptString = "<script language=JavaScript> window.opener.document.forms(0).submit(); </script>"; // ASP.NET 2.0 if (!Page.ClientScript.IsClientScriptBlockRegistered(scriptString)) { Page.ClientScript.RegisterClientScriptBlock(this.GetType(), "script", scriptString); } it is working fine in IE but not working in Firefox. What could be the alternate method for this? Thank in advance

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  • How to detect touchEvent across multiple objects?

    - by RobGThai
    In short: I need to find a way to implement swipe action (touchEvent) for my Calendar just like the default Android Calendar one. I am using GridView to make a calendar for my application. When I touch any date, I launch an activity to display details on that date. My problem is that now I tried to implement swipe to change month/year to display but I dont know a way to do it. I tried to use setOnTouchListener on GridView but it seems like detecting for each grid separately instead of the whole grid as one. Further problem would be that it overridden my onItemClick implementation as well.

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  • Developing a sector based partition copying program?

    - by baltusaj
    Hi, I want to develop a program that copies a partition's 'data' only, to another partition. And I want to do it such that the program starts from the first sector of source partition and checks if a sector is used. If it is used copy it to the destination parition. Else don't copy. In other words it's like copying only the contents of a partition to another, sector-by-sector. Question: Is there a way to check if a particular sector on harddisk is used or not? The programming language I am using is C++ and the underlying filesystem in NTFS. Thanks a lot.

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  • list permutations in haskell

    - by turingcomplete
    So I'm new to haskell and I've been playing with it for a while now. I want to get my function that outputs all list permutations to work. I have written 2 implementations, one works well, the other is giving me an error. Any help would be awesome. This is the first (working) implementation: permute [] = [[]] permute xs = [y| x <- xs, y <- map (x:) $ permute $ delete x xs] This one is giving me an error: permute [] = [[]] permute xs = map (\x -> map (x:) $ permute $ delete x xs) xs and here's the error message: Occurs check: cannot construct the infinite type: t0 = [t0] Expected type: [t0] Actual type: [[t0]] In the expression: map (x :) $ permute $ delete x xs In the first argument of `map', namely `(\ x -> map (x :) $ permute $ delete x xs)' I'd appreciate if someone could explain why I'm getting this error. Thanks

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  • Why I can't called my doSomething method?

    - by Tattat
    This is my DrawSomethingCmd: #import "Command.h"; @interface DrawSomethingCmd : Command { } -(void)doSomething; -(void)execute; @end and the DrawSomethingCmd.m's doSomething method is like that: -(void)doSomething{ NSLog(@"did"); } The Command.h: #import <Foundation/Foundation.h> @interface Command : NSObject { } -(void)execute; And the Command.m: #import "Command.h" @implementation Command -(id)init{ return self; } -(void)execute{ } @end And I have the method like this: DrawSomethingCmd *tempCmd = [[DrawSomethingCmd alloc] init]; [tempCmd doSomething]; But my Console did't show any things on that, what's going on?

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  • gVim and multiple programming languages

    - by Abhi
    My day job involves coding with Perl. At home I play around with Python and Erlang. For Perl I want to indent my code with two spaces. Whereas for Python the standard is 4. Also I have some key bindings to open function declarations which I would like to use with all programming languages. How can this be achieved in gVim? As in, is there a way to maintain a configuration file for each programming language or something of that sort?

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  • SVN merge adding parameters. WTF? Or how to do big merges?

    - by HeavyWave
    I am doing an SVN merge for a branch, and in one of the files I see this: GetQueryReferenceData(int sessionId, Int32 sessionId) Which means that the merge tool just added another parameter without asking any questions. Imagine if it was a call to Substring(0) and in another branch it would be Substring(0,2). That is completely different behavior, how does it even get to decide which one to choose? Good thing it came up during compile time. The problem is that it will not be marked as a conflict and will be merged automatically. That is very dangerous behavior and if you don't have the luxury of having a unit test for every line of code - you are screwed. What am I doing wrong and how to do big merges without the merging tool putting in dangerous changes silently? Is there a merge tool that is not language agnostic? I am using Tortoise SVN.

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  • How to get the computer name (hostname in a web aplication)?

    - by Filipe
    Hi, how can I get the client's computer name in a web application. The user in a network. Regards // Already tryed this option string IP = System.Web.HttpContext.Current.Request.UserHostAddress; string compName = DetermineCompName(IP); System.Net.IPHostEntry teste = System.Net.Dns.GetHostEntry(IP); ssresult = IP + " - " + teste.HostName; // TODO: Write implementation for action private static string DetermineCompName(string IP) { IPAddress myIP = IPAddress.Parse(IP); IPHostEntry GetIPHost = Dns.GetHostEntry(myIP); string[] compName = GetIPHost.HostName.ToString().Split('.'); return compName[0]; } All of that, gives me only the IP :/

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  • How to parse a string to an integer without library functions?

    - by dack
    Hi, I was recently asked this question in an interview: "How could you parse a string of the form '12345' into its integer representation 12345 without using any library functions, and regardless of language?" I thought of two answers, but the interviewer said there was a third. Here are my two solutions: Solution 1: Keep a dictionary which maps '1' = 1, '2' = 2, etc. Then parse the string one character at a time, look up the character in your dictionary, and multiply by place value. Sum the results. Solution 2: Parse the string one character at a time and subtract '0' from each character. This will give you '1' - '0' = 0x1, '2' - '0' = 0x2, etc. Again, multiply by place value and sum the results. Can anyone think of what a third solution might be? Thanks.

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  • Composite primary keys in N-M relation or not?

    - by BerggreenDK
    Lets say we have 3 tables (actually I have 2 at the moment, but this example might illustrate the thought better): [Person] ID: int, primary key Name: nvarchar(xx) [Group] ID: int, primary key Name: nvarchar(xx) [Role] ID: int, primary key Name: nvarchar(xx) [PersonGroupRole] Person_ID: int, PRIMARY COMPOSITE OR NOT? Group_ID: int, PRIMARY COMPOSITE OR NOT? Role_ID: int, PRIMARY COMPOSITE OR NOT? Should any of the 3 ID's in the relation PersonGroupRole be marked as PRIMARY key or should they all 3 be combined into one composite?? whats the real benefit of doing it or not? I can join anyways as far as I know, so Person JOIN PersonGroupRole JOIN Group gives me which persons are in which Groups etc. I will be using LINQ/C#/.NET on top of SQL-express and SQL-server, so if there is any reasons regarding language/SQL that might make the choice more clear, thats the platform I ask about. Looking forward to see what answers pops up, as I have thought of these primary keys/indexes many times when making combined ones.

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  • Making uppercase of std::string

    - by Daniel K.
    Which implementation do you think is better? std::string ToUpper( const std::string& source ) { std::string result; result.reserve( source.length() ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } and... std::string ToUpper( const std::string& source ) { std::string result( source.length(), '\0' ); std::transform( source.begin(), source.end(), result.begin(), std::ptr_fun<int, int>( std::toupper ) ); return result; } Difference is that the first one uses reserve method after the default constructor, but the second one uses the constructor accepting the number of characters.

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  • Gwt-ext. Bean to record and record to bean.

    - by den bardadym
    I write a RIA application and my JPA beans must be decoded to push it in Store. My decisions are: Brute Force. If I have property 'aProp' in bean (and getter/setter for it) i create RecordDef, then Record, then Recrod.set('aProp', bean.getAProp()) and so on.. (it is terrible) I can write generator for creating a Factory of Records (it is my desision and i write it). For example: RecordFactory<User> factory = GWT.create(User.class); //User is entity I now that i need a reflection, BUT GWT have no implementation of reflection (some libraries emulates this, but they builds on generators) Exists the best way? Thanks, Den Bardadym.

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  • How to escape/strip special characters in the LaTeX document?

    - by Igor
    We implemented the online service where it is possible to generate PDF with predefined structure. User can choose a LaTeX template and then compile it with an appropriate inputs. The question we worry about is the security, that the malicious user was not able to gain shell access through the injection of special instruction into latex document. We need some workaround for this or at least a list of special characters that we should strip from the input data. Preferred language would be PHP, but any suggestions, constructions and links are very welcomed. PS. in few word we're looking form mysql_real_escape_string for LaTeX

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  • How to communicate with Telecom infrastructure using .NET

    - by Raiford
    I am currently writing some pretty gnarly C#/C++/Cli code to interface with Telecommunication equipement and GSM Mobile Networks for a couple of the major telecom here and abroad. GSM networks primarily use SS7 Signaling using a protocol called TCAP to send messages back and forth to Signaling Points within the network. The laws of Tcp/ip do not apply here :) I am very interested in hearing from others in this space specifically individuals using the .NET framework most likely using C# / C++. I have not come across any .NET libraries or tools to assist in this sort of development. Most of the software in this industry is "C" / Java based, as a result I have written tons of infrastructure .NET code using C# where possible and C++ / CLI to interface with hardware. Is anyone aware of any .NET language tools for this niche industry?

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  • representing graph using database

    - by prosseek
    I need to represent graph information with database. Let's say, a is connected to b, c, and d. a -- b |_ c |_ d I can have a node table for a, b, c, and d, and I can also have a link table (FROM, TO) - (a,b), (a,c), (a,d). For other implementation there might be a way to store the link info as (a,b,c,d), but the number of elements in the table is variable. Q1 : Is there a way to represent variable elements in a table? Q2 : Is there any general way to represent the graph structure using database?

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  • Special characters incongruence

    - by Enrique
    Hello I'm building a Spring MVC web application that runs on Tomcat 6.0.20 and JDK 1.6.0_19. When I send some special characters through an HTML form some of them are stored as question marks ? For example these symbols are stored correctly: €, á, é, í, ‰, etc But some symbols are replaced with ? like: £, ?, ? MySQL tables charset is utf-8. My jsp also use utf-8 <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8" %> I have included org.springframework.web.filter.CharacterEncodingFilter in web.xml as suggested here When I debug the POST request when sending 3 characters €a£ with firebug I get: %E2%82%ACa%E2%82%A4 which is correct since E2 82 AC is the code for € and E2 82 A4 is the code for £ but £ is stored as ? in the database. When I save £ directly into the database it is displayed correctly in the webpage. How can I fix this?

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  • Java Enum Newbie Question

    - by ikurtz
    i have a situation where i need the Checker enum below used in multiple classes: package Sartre.Connect4; public enum Checker { EMPTY, RED, YELLOW } so i put the Checker in a Checker.java file and then from the classes that need it i simply do the following: example: public Cell(){ currentCell = Checker.EMPTY; } example: public Cell(Checker checker){ currentCell = checker; } and the code compiles fine and runs fine also. so what is my question? well being new to Java i am just wondering if the way i use Checker without encapsulating it in a class is a sound implementation? it may be because of The enum declaration defines a class (called an enum type). as noted in Java docs enum tutorial page. thank you for your insight into this matter.

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  • Declaring and creating an object then adding to collection VS Adding object to collection using new

    - by ZeeMan
    Ok so the title may have been confusing so i have posted 2 code snippets to illustrate what i mean. NOTE: allUsers is just a collection. RegularUser regUser = new RegularUser(userName, password, name, emailAddress); allUsers.Add(regUser); VS allUsers.Add(new RegularUser(userName, password, name, emailAddress)); Which snippet A or B is better and why? What are the advantages or disadvantages? The example i wrote was C# but does the language (C#, Java etc) make a difference?

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  • Manipulate Excel workbooks programmatically

    - by Tom
    I have an Excel workbook that I want to use as a template. It has several worksheets setup, one that produces the pretty graphs and summarizes the numbers. Sheet 1 needs to be populated with data that is generated by another program. The data comes in a tab delimited file. Currently the user imports the tab delimited file into a new Workbook, selects all and copies. Then goes to the template and pastes the data into sheet1. This is a large amount of data, 269 columns and over 135,000 rows. It’s a cumbersome process and the users are not experienced Excel users. All they really want is the pretty graphs. I would like to add a step after the program that generates the data to programmatically automate the process the user currently must do manually. Can anyone suggest the best method/programming language that could accomplish this?

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