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• Single instance of application in C#

  There is some application that we want that only single instance of application works at a time. So here in this article is the logic for doing that.

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• Déploiement d'une instance GNU/Linux Debian 7 sous CloudStack, premier tutoriel d'une série sur Cloudstack

  Bonjour, Citation: CloudStack est un logiciel de cloud computing open source pour la création, la gestion et le déploiement de services de cloud d'infrastructure. Il utilise des hyperviseurs existants tels que KVM, vSphere, XenServer et / XCP pour la virtualisation. En plus de sa propre API, CloudStack prend également en charge les Amazon Web Services. Voici une série de tests effectués par Ikoula sur ce logiciel. Je vous présente ce tutoriel sur Cloudstack:Déploiement d'une instance...

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• When do instance variables get initialized and values assigned?

  - by AKh

  When doees the instance variable get initialized? Is it after the constructor block is done or before it? Consider this example: public abstract class Parent { public Parent(){ System.out.println("Parent Constructor"); init(); } public void init(){ System.out.println("parent Init()"); } } public class Child extends Parent { private Integer attribute1; private Integer attribute2 = null; public Child(){ super(); System.out.println("Child Constructor"); } public void init(){ System.out.println("Child init()"); super.init(); attribute1 = new Integer(100); attribute2 = new Integer(200); } public void print(){ System.out.println("attribute 1 : " +attribute1); System.out.println("attribute 2 : " +attribute2); } } public class Tester { public static void main(String[] args) { Parent c = new Child(); ((Child)c).print(); } } OUTPUT: Parent Constructor Child init() parent Init() Child Constructor attribute 1 : 100 attribute 2 : null When the memory for the atribute 1 & 2 are allocated in the heap ? Curious to know why is attribute 2 is NULL ? Are there any design flaws?

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• Can one use environment variables in Inno Setup scripts?

  - by dicroce

  I need to find a way to reference environment variables INSIDE the Inno Setup script file (.iss)... I've found plenty of references to MODIFYING the environment from an .iss, but none on how to actually use it. Is this possible?

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• How to set global variables to use everywhere in my application?

  - by user502052

  I am using Ruby on Rails 3 and I would like to set some global variable to use those everywhere in my application. In particular, the domain name. If, for example, my website URL is http://subname.domain.com I would like to set or retrieve the subname.domain.com value in order to use that in my application like this request_uri = "http://#{sub_domain_name}" Where and how I have to state\initialize the sub_domain_name variable or other variables at all?

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• [Iphone-Dev] Assigning values : difference between properties and class variables ?

  - by gotye

  Hey guys, I noticed that I rarely use properties, due to the fact that I rarely need to access my object's variables outside my class ;) So I usually do : NSMutableArray *myArray; // not a property ! My question is : even if i don't declare myArray as a property, does iphone make a retain anyway if I do myArray = arrayPassedToMe; I think so but I just wanted to confirm ;) Any thoughts welcome ! Gotye

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• How do I set Environment Variables in Visual Studio 2010?

  - by xarzu

  How do I set Environment Variables in Visual Studio 2010? I found this web page: http://msdn.microsoft.com/en-us/library/ee479070.aspx Which says: From the Project menu, choose Properties. In the left pane, select Configuration Properties, and then select Environment. But when I select "Configuration Properties", there is no "Enviroment" option: http://i67.photobucket.com/albums/h292/Athono/microsoft/newstuff.jpg This is an example in VS 2008: http://i21.photobucket.com/albums/b279/GrunchCan/env.jpg But how is it done in VS 2010?

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• Implicit typing; why just local variables?

  - by edg

  Does anyone know or care to speculate why implicit typing is limited to local variables? var thingy = new Foo(); But why not... var getFoo() { return new Foo(); }

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• Bash: how to process variables from an input file?

  - by gilgongo

  I've got a bash script that reads input from a file like this: while IFS="|" read -r a b do echo "$a something $b somethingelse" done < "$FILE" The file it reads looketh like this: http://someurl1.com|label1 http://someurl2.com|label2 However, I'd like to be able to insert the names of variables into that file when it suits me, and have the script process them when it sees them, so the file might look like this: http://someurl1.com?$VAR|label1 http://someurl2.com|label2 So $VAR could be, for example, today's date, producing an output like this: http://someurl1.com something label1 somethingelse http://someurl2.com?20100320 something label2 somethingelse

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• When should I use session variables instead of cookies?

  - by sprugman

  Session variables and cookies seem very similar to me. I understand the technical differences, but how do you decide when to use one vs. the other?

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• Passing variables from PHP to Javascript back to PHP using Ajax.

  - by ObjectiveJ

  I hope this makes sesne, please bare with me. So I have a PHP page that contains variables, I have some radial boxes, and on click of them, it calculates a price for the item you have clicked on. I do this by activating a js function that I have passed some variables to. Like so. PHP: <?php $result = mssql_query("SELECT * FROM Segments ORDER BY 'Squares'"); if (!$result) { echo 'query failed'; exit; } while ($row = mssql_fetch_array($result)) { ?> <span><?php echo $row["Squares"]; ?></span><input name="squares" type="radio" onclick="ajaxCases('<?php echo $row["Squares"]; ?>', '<?php echo $row["StartCaseID"]; ?>', '<?php echo $row["StartMatrixPrice"]; ?>')" value="<?php echo $row["Squares"]; ?>"<?php if ($row["Squares"] == "1") { ?> checked="checked" <?php }else{ ?> checked="" <?php } ?>/> <?php } ?> As you can see onclick it goes to a function called ajaxcases, this function looks like this. function ajaxCases(squares,start,price){ $('#step1').html('<p style="margin:100px 0px 0px 100px"><img src="images/ajax-loader-bigindic.gif" width="32" height="32" alt="" /></p>'); $('#step1').load("ajax-styles.php?squares="+squares); prevId1 = ""; document.varsForm.caseid.value=start; $('#step1price').html('<span style="margin:0px 0px 0px 30px"><img src="images/ajax-loader-price.gif" width="24" height="24" alt="" /></span>'); $('#step1price').load("ajax-step1-price.php?Squares="+Squares); return true; } This then goes to a php page called ajax-step1-price.php and I try to recall the variable Squares. However it doesn't work, I thought it was a GET however that returns undefined. In Summary: I would like to know how to pass a variable from PHP to JS then back to PHP, or if someone could just tell me where I am going wrong that would be greatly appreciated.

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• Where to store global variables like file paths in java ?

  - by Jules Olléon

  In my application I use some icons. Where should I store the path of the directory containing those icons ? The icons are used in different classes so it doesn't really make sense to store them in one of those classes in particular. I read that global variables are evil, but is it acceptable to use a class (eg Commons) containing only public static final fields to store this king of data ? What solution is used in professional applications ?

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• How are static variables with the same name in different functions identified by the System?

  - by Jay

  AFAIK, we can have two static variables with the same name in different functions? How are these managed by the compiler and symbol table? How are their identities managed seperately?

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• Do I have to initialize simple class member variables?

  - by Frank

  Quick beginner's question: Do I have to initialize simple class member variables, or are they guaranteed to get assigned their default values in any case? Example: class Foo { int i; // is i==0 or do I need the following line for that? Foo() : i(0) {} }; Thanks!

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• in java can one have an array of variables?

  - by David

  in java can you have an array of variables? if so what is the syntax? here's an example if your confused: varint[] ArrayOfVariablesThatAreInts = new varint[#] or var[] ArrayofVariables = new var[#] is something like this legal?

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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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• static block instance block java Order

  - by Rollerball

  Having read this question In what order are the different parts of a class initialized when a class is loaded in the JVM? and the related JLS. I would like to know in more detail why for example having class Animal (superclass) and class Dog (subclass) as following: class Animal { static{ System.out.println("This is Animal's static block speaking"): } { System.out.println("This is Animal's instance block speaking"); } class Dog{ static{ System.out.println("This is Dog's static block speaking"); } { System.out.println("This is Dog's instance block speaking"); } public static void main (String [] args) { Dog dog = new Dog(); } } Ok before instantiating a class its direct superclass needs to be initialized (therefore all the statics variables and block need to be executed). So basically the question is: Why after initializing the static variables and static blocks of the super class, control goes down to the subclass for static variables initialization rather then finishing off the initialization of also the instance member? The control goes like: superclass (Animal): static variables and static blocks subclass (Dog): static variables and static blocks superclass (Animal): instance variables and instance blocks sublcass (Dog):instance variables and instance blocks What is the reason why it is in this way rather than : superclass -> static members superclass -> instance members subclass -> static members sublcass-> instance members

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• AWS Large Instance: /mnt does not show all the space that should be available

  - by Emile Baizel

  I just created a Large (m1.large) 64 bit instance which comes with 850 GB instance storage. Look at the Large Instance http://aws.amazon.com/ec2/instance-types/ A 'df -h' from the root folder gives me the output below. The /mnt is where I'm thinking the instance storage is but here it is only showing me 414G. I have set up two servers and both are showing the same numbers. root@ip-11-11-11-11:/# df -h Filesystem Size Used Avail Use% Mounted on /dev/sda1 7.9G 1.1G 6.5G 14% / none 3.7G 112K 3.7G 1% /dev none 3.7G 0 3.7G 0% /dev/shm none 3.7G 48K 3.7G 1% /var/run none 3.7G 0 3.7G 0% /var/lock /dev/sdb 414G 199M 393G 1% /mnt

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• Unable to connect to a remote SQL Server Instance over a VPN

  - by Jack Njiri

  I'm running SQL Server 2005 on two different servers running Win XP. The two servers are in different physical locations and are connected via a dedecated point to point data link in a virtual private network(VPN). Im only able to connect to the remote instance of SQL Server by specifying the IP address on the server name property. If I provide the actual server name say 'ServerA', then I get an error message. Everything works fine except configuring replication at the subscriber level, which requires the actual name of the instance, not an IP address or alias. I have already configured both instances on allow remote connections and im running the SQL Server Browser. How do I connect to the remote instance by providing the instance name? Alternatively how I configure subscription to a remote publisher without supplying the remote instance name?

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• Google App Engine JDO how to define instance fields ?

  - by Frank

  I have a class like this : import java.io.*; import java.util.*; public class Contact_Info_Entry implements Serializable { public static final long serialVersionUID=26362862L; String Contact_Id,First_Name="",Last_Name="",Company_Name="",Branch_Name="",Address_1="",Address_2="",City="",State="",Zip="",Country="",E_Mail="",Phone; int I_1,I_2; float F_1,F_2; boolean B_1,B_2; GregorianCalendar Date_1, Date_2; Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } If I want to translate it to a class for JDO, do I need to define each field by it self or can I do a group at a time ? For instance do I have to make it like this : @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Long id; @Persistent public static final long serialVersionUID=26362862L; @Persistent String Contact_Id; @Persistent String First_Name; @Persistent String Last_Name; ...... @Persistent int I_1; @Persistent int I_2; ... @Persistent float F_1; ... @Persistent boolean B_1; @Persistent boolean B_2; @Persistent GregorianCalendar Date_1; ... @Persistent Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Or can I do a group at a time like this : @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { @PrimaryKey @Persistent(valueStrategy=IdGeneratorStrategy.IDENTITY) private Long id; @Persistent public static final long serialVersionUID=26362862L; @Persistent String Contact_Id,First_Name,Last_Name=""; ...... @Persistent int I_1=0,I_2=1; ... @Persistent float F_1; ... @Persistent boolean B_1,B_2; @Persistent GregorianCalendar Date_1; ... @Persistent Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Or can I skip the "@Persistent" all together like this : import java.io.*; import java.util.*; @PersistenceCapable(identityType=IdentityType.APPLICATION) public class Contact_Info_Entry implements Serializable { public static final long serialVersionUID=26362862L; String Contact_Id,First_Name="",Last_Name="",Company_Name="",Branch_Name="",Address_1="",Address_2="",City="",State="",Zip="",Country="", E_Mail="",Phone; int I_1,I_2; float F_1,F_2; boolean B_1,B_2; GregorianCalendar Date_1, Date_2; Vector<String> A_Vector=new Vector<String>(); public Contact_Info_Entry() { } ...... } Which are correct ? Frank

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• SQL SERVER – Table Variables and Transactions – SQL in Sixty Seconds #007 – Video

  - by pinaldave

  Today’s SQL in Sixty Seconds video is inspired from my presentation at TechEd India 2012 on Misconception and Resolution. Quite often I have seen people getting confused with certain behavior of the T-SQL. They expect SQL to behave certain way and SQL Server behave differently. This kind of issue often creates confusion and frustration. Sometime I have seen them also confusing it with bug and submitting the bug, where reality is totally different. Similar concept which are going to see today. I have seen quite commonly developer assuming that table various will be rolled back when transaction is rolled back. This sixty seconds video describes that table various are not rolled back when transactions are rolled back. More on Errors: Difference Temp Table and Table Variable – Effect of Transaction Effect of TRANSACTION on Local Variable – After ROLLBACK and After COMMIT Debate – Table Variables vs Temporary Tables – Quiz – Puzzle – 13 of 31 I encourage you to submit your ideas for SQL in Sixty Seconds. We will try to accommodate as many as we can. Reference: Pinal Dave (http://blog.sqlauthority.com) Filed under: Database, Pinal Dave, PostADay, SQL, SQL Authority, SQL in Sixty Seconds, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQLServer, T SQL, Video

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• Recording custom variables to identify individual users with Google Analytics

  - by mrtsherman

  I have been asked by our marketing department to add Google Analytics custom variable tracking to my company's website. As the website uses server side includes, modifications to the tracking tag roll out globally - maintenance is therefore a headache! So, if I add the following code (keeping in mind SSI so every page has the same code): // visitor level tracking, id = 12345 // Record a unique id for each visitor. When they return also track this id _gaq.push(['_setCustomVar', 1, 'id', '12345', 1]); // page level tracking // If the user signs up for our newsletter we set newsletter to true // Each page they subsequently visit should also mark this as true _gaq.push(['_setCustomVar', 1, 'newsletter', 'true', 1]); I don't use GA and the marketing people don't use custom variables, so we don't actually know how or if this will work. Therefore my questions are:- Do I want Page, Session or Visitor level tracking? What happens when the same code is used on every page? Can GA 'overwrite' a setting. For example, if I set newsletter to true on page X and then user navigates to page Y, will the variable also be marked there?

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• How to minimize the usage of static variables and objects

  - by Peter Penzov

  I'm trying to implement this JavaFX code where I want to call remote Java class and pass boolean flag: final CheckMenuItem toolbarSubMenuNavigation = new CheckMenuItem("Navigation"); toolbarSubMenuNavigation.setOnAction(new EventHandler<ActionEvent>() { @Override public void handle(ActionEvent e) { //DataTabs.renderTab = toolbarSubMenuNavigation.isSelected(); DataTabs.setRenderTab(toolbarSubMenuNavigation.isSelected()); // call here the getter setter and send boolean flag System.out.println("subsystem1 #1 Enabled!"); } }); Java class which I want to call: public class DataTabs { private static boolean renderTab; // make members *private* private static TabPane tabPane; public static boolean isRenderTab() { return DataTabs.renderTab; } public static void setRenderTab(boolean renderTab) { DataTabs.renderTab = renderTab; tabPane.setVisible(renderTab); } // somewhere below // set visible the tab pane TabPane tabPane = DataTabs.tabPane = new TabPane(); tabPane.setVisible(renderTab); } This implementation works but I want to optimize it to use less static variables and objects. Can you tell me which sections of the code how can be optimized?

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• Matrices: Arrays or separate member variables?

  - by bjz

  I'm teaching myself 3D maths and in the process building my own rudimentary engine (of sorts). I was wondering what would be the best way to structure my matrix class. There are a few options: Separate member variables: struct Mat4 { float m11, m12, m13, m14, m21, m22, m23, m24, m31, m32, m33, m34, m41, m42, m43, m44; // methods } A multi-dimensional array: struct Mat4 { float[4][4] m; // methods } An array of vectors struct Mat4 { Vec4[4] m; // methods } I'm guessing there would be positives and negatives to each. From 3D Math Primer for Graphics and Game Development, 2nd Edition p.155: Matrices use 1-based indices, so the first row and column are numbered 1. For example, a12 (read “a one two,” not “a twelve”) is the element in the first row, second column. Notice that this is different from programming languages such as C++ and Java, which use 0-based array indices. A matrix does not have a column 0 or row 0. This difference in indexing can cause some confusion if matrices are stored using an actual array data type. For this reason, it’s common for classes that store small, fixed size matrices of the type used for geometric purposes to give each element its own named member variable, such as float a11, instead of using the language’s native array support with something like float elem[3][3]. So that's one vote for method one. Is this really the accepted way to do things? It seems rather unwieldy if the only benefit would be sticking with the conventional math notation.

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• How to input data into user defined variables into MySql query

  - by user292791

  Simple Shell script echo "Enter 1 for month of March" echo "Enter 2 for month of April" echo "Enter 3 for month of May" read Month case "$Month" in 1) echo "enter establishment name" read a; mysql -u root -p $a < "March.sql";; 2) echo "enter establishment name" read b; mysql -u root -p $b < "April.sql";; 3) echo "enter establishment name" read c; mysql -u root -p $c < "May.sql";; esac done In this i have three other query files March.sql, April.sql, May.sql. i'm linking this in shell script . Example of .sql file: SELECT DISTINCT substr( a.case_no, 3, 2 ), b.case_type, b.type_name, a.case_no into outfile '/tmp/April.csv' FIELDS TERMINATED BY ',' ENCLOSED BY '"' LINES TERMINATED BY '\r\n' FROM Civil_t AS a, Case_type_t AS b, disposal_proc AS c WHERE substr( a.case_no, 3, 2 ) = b.case_type AND a.date_of_decision BETWEEN '2014-04-01' AND '2014-04-30' AND a.case_no = c.case_no AND a.court_no =1; I have to alter the .sql script every time. Is there any method to read the variables from shell script and use it in mysql. For example:- echo "enter date" read a #input date Now i have read a "date" and i want to use it in March.sql query in where clause. Is there is any method of using this variable in .sql query.

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