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• Why do we make a copy of final instance variable in a method in Java?

  - by PRK

  For instance: private final Object o; public void doSomething(){ final Object local = this.o; //access methods of local; } This practice is followed in lots of java classes (such as ArrayBlockingQueue). What's the benefit of this?

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• What is better: to delete pointer or set it with a new value?

  - by user63898

  Hi simple question in c++ , say i have a loop and i have function that returns pointer to item so i have to define inner loop pointer so my question is what to do with the pointer inside the loop , delete it ? or to set it with new value is good for example: for(int i =0;i<count();i++) { ptrTmp* ptr = getItemPtr(); // do somthing with the ptr ... // what to do here ? to delete the poinetr or not? delete ptr; // ?? }

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• what is the code for the following?

  - by kkol

  a difficult one.. using classes of primitive types in java, like Integer, Float, Long, etc, write a code fragment using a method to double the value of a variable passed as an argument

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• Spring @Transactional - Can I Override rollbackFor

  - by user475039

  Hi all, I am calling a service which has the following annotation: @Transactional(rollbackFor=ExceptionA.class) public void myMethodA(....) throws ExceptionA { . . } I am calling this method from an other method in another Spring Bean. @Transactional(rollbackFor=ExceptionB.class) public void mainEntryPointMethod(....) throws ExceptionB { . try { myMethodA() } catch (ExceptionA exp) { . } . } My problem is that if myMethodA throws an exception, my transaction (which is passed from mainEntryPointMethod - myMethodA by default propagation) will be marked for rollback. Is there a way in which the 'rollbackFor' for the inner method can be overriden? Thanks in advance Chris

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• Java / MySQL - How to access connection from another class?

  - by Alex

  I'm just getting my head around java (and OOP for that matter), the only thing I am familiar with is MySQL. I need to keep the DB connection open throughout the duration of the application, as well as a server socket. I'm not even sure if they both need separate classes, but here's what I have so far: http://pastebin.com/qzMFFTrY (it wouldn't all go in a code tag) The variable I need is con for line 86.

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• Is an index required for columns in ON clause?

  - by newbie

  Do I have to create an index on columns referenced in Joins? E.g. SELECT * FROM left_table INNER JOIN right_table ON left_table.foo = right_table.bar WHERE ... Should I create indexes on left_table(foo), right_table(bar), or both? I noticed different results when I used EXPLAIN (Postgresql) with and without indexes and switching around the order of the comparison (right_table.bar = left_table.foo) I know for sure that indexes are used for the left of the WHERE clause but I am wondering whether I need indexes for columns listed in ON clauses.

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• purpose of php consutructor

  - by Bharanikumar

  Hi , Am working in the classes and object class structure , but not extream level , Just class and function , then in one place instantiation . that's it , not much big functions like __construct etc , Please tell me very simply , 1.what is th purpose of constructor ad destructor , But i know theoretical explanation school level , But i am expecting something like in real time , which situation we have to use, and is there any example for that please tell me, Regards

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• Do we inherit from Object?

  - by Knowing me knowing you

  Guys do we inherit from Object like from any other class (except of course that we don't have to explicitly state that) or there is some special privileges to Object class and it's not inherited as other classes?

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• MySQL join not returning rows

  - by John

  I'm attempting to create an anti-bruteforcer for the login page on a website. Unfortunately, my query is not working as expected. I would like to test how many times an IP address has attempted to login, and also return the ID of the user for my next step in the login process. However, I'm having a problem with the query... for one thing, this would only return rows if it was the same user as they had been trying to login to before. I need it to be any user. Secondly, regardless of whether I use LEFT JOIN, RIGHT JOIN, INNER JOIN or JOIN, it will not return the user's ID unless there is a row for the user in login_attempts. SELECT COUNT(`la`.`id`), `u`.`id` FROM `users` AS `u` LEFT JOIN `login_attempts` AS `la` ON `u`.`id` = `la`.`user_id` WHERE `u`.`username` = 'admin' AND `la`.`ip_address` = '127.0.0.1' AND `la`.`timestamp` >= '1'

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• Alternatives to persisting objects than using __destruct() in PHP

  - by Michael

  I usually use a classes destructor method __destruct() to persist objects to session or what have you. It is just very convinient, but I'm curious to if there are any other methods that are equally appealing. Do you know of such? The curiousity arose as I was to merge/utilize two frameworks that both made use of __destruct() for persistance resulting in a race-problem.

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• One log4j.xml - many scripts

  - by psed

  One of my utility jar files is used by different nix scripts, located in different categories. Problem: unable to initialize log4j framework (unable to find log4j.xml). Solution, that allows to configure logger correctly while launching jar classes by different scripts - usage of env vars and force configuring using DOMConfigurtor.configure(pathToConfXml) method. is it possible to avoid path hardcoding and configure logger inside of a script? Appreciate all your help. Thanks.

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• C++ Template Usage

  - by MalcomTucker

  If I have a template definition like the one below, can someone provide a code sample for how I would actually instantiate an instance of this with two of my own classes? template <class T1, class T2> class LookUpTable { public: LookUpTable(); void set(Tl x, T2* y); T2* get(Tl x); }; Thanks.

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• guides for writing php libraries?

  - by fayer

  i have studied design patterns and want to use them to code an open source library (not an application). but i have never coded a library before and don't know where should i include files, should i have a bootstrap file that loads everything or should every class load their own classes they are dependent on etc. are there any tutorials for writing libraries in php from start to finnish? thanks

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• What is your most useful C/C++ utility?

  - by maddizzyro

  It seems that every project has an "utility" module with various code snippets used throughout other files and which don't fit any particular pattern. What utility classes, functions, and macros do you find most useful in your C/C++ projects? Please keep the entries small (under 100 lines) and give only one example per post.

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• Is there a good Python library that can parse C++?

  - by csbrooks

  Google didn't turn up anything that seemed relevant. I have a bunch of existing, working C++ code, and I'd like to use python to crawl through it and figure out relationships between classes, etc. EDIT: Just wanted to point out: I don't think I need or want to parse every bit of C++; I just need something smart enough to pick up on class, function and member variable declarations, and to skip over function definitions.

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• Multiple &(AND) fails in query

  - by N e w B e e

  here is my query $sql = 'SELECT * FROM Orders INNER JOIN [Order Details] ON Orders.OrderNumber = [Order Details].OrderNumber WHERE Orders.CartID =2 AND [Order Details].Option10 Is Null AND [Order Details].Status="Shipped"'; this queries when entered in MS_Access sql view, returns the correct results, but when I copy and paste the same query in my php script, it fails and gives the error Too few parameters, expected 1... although data is there, query is working in access... Please note if I omitted on AND condition, it works eg if I removed shipped conidtion or is null condition, it works then too.. any hint? whats wrong with it?? any help?thanks

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• Clarifying... So Background Jobs don't Tie Up Application Resources (in Rails)?

  - by viatropos

  I'm trying to get a better grasp of the inner workings of background jobs and how they improve performance. I understand that the goal is to have the application return a response to the user as fast as it can, so you don't want to, say, parse a huge feed that would take 10 seconds because it would prevent the application from being able to process any other requests. So it's recommended to put any operations that take more than say 500ms to execute, into a queued background job. What I don't understand is, doesn't that just delay the same problem? I know the user who invoked that background job will get an immediate response, but what if another user comes right when that background job starts (and it takes 10 seconds to finish), wont that user have to wait? Or is the main issue that, requests are the only thing that can happen one-at-a-time, while on the other hand a request can start while one+ background jobs are in the middle of running? Is that correct?

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• What is the syntax to declare an event in C#?

  - by Tilendor

  In my class I want to declare an event that other classes can subscribe to. What is the correct way to declare the event? This doesn't work: public event CollectMapsReportingComplete;

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• Rails: i have a class method and i want to modify something of the instance

  - by Totty

  Rails: i have a class method and i want to modify something of the instance something like this: class Test < Main template :box def test # here I want to access the template name, that is box end end class Main def initialize end def self.template(name) # here I have to save somehow the template name # remember is not an instance. end end that is similar to the model classes: # in the model has_many :projects How do I do it?

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• redefinition c++

  - by coubeatczech

  hi, how does header including in c++ work? I have the classes already implemented in .h file and when there is #include in two files, there's this error: files.h:14:7: error: redefinition of ‘class abstract_file’ files.h:14:20: error: previous definition of ‘class abstract_file’ multiple times for each class and enum. Can anyone explain this?

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• Sort vector<int>(n) in O(n) time using O(m) space?

  - by Adam

  I have a vector<unsigned int> vec of size n. Each element in vec is in the range [0, m], no duplicates, and I want to sort vec. Is it possible to do better than O(n log n) time if you're allowed to use O(m) space? In the average case m is much larger than n, in the worst case m == n. Ideally I want something O(n). I get the feeling that there's a bucket sort-ish way to do this: unsigned int aux[m]; aux[vec[i]] = i; Somehow extract the permutation and permute vec. I'm stuck on how to do 3. In my application m is on the order of 16k. However this sort is in the inner loops and accounts for a significant portion of my runtime.

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• why the String class in java does not implement Iterable?

  - by xyzzyz

  Hey, many builtin classes in Java implement Iterable, however String does not. It makes sense to iterate over chars in the String, just as one can iterate over items in regular array. Is there a reason behind it?

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• Documenting functions in C++ with Doxygen

  - by Paul

  I've got a project that I'm using Doxygen to generate documentation to. The documentation of the classes is fine, but I've also got some functions that I use in main() to create objects etc. I'd also like to have these into my documentation, but I have not figured how to do that. Any suggestions?

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• Are there any data-binding solution that works in C++ and GWT and supports structures polymorphism?

  - by user116854

  I expect it should share a common description, like XmlSchema or IDL and should generate classes for target language. I found Thrift and it's really nice solution, but it doesn't support structures polymorphism. I would like to have collections of base class objects, where I could place instances of subclasses, serialize this and deserialize at the opposite side. Some mechanism of polymorphic behavior support, like Visitor, would be a perfect. Does anybody know something suitable for these requirements?

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• Why doesn't the String class in Java implement Iterable?

  - by xyzzyz

  Many Java framework classes implement Iterable, however String does not. It makes sense to iterate over characters in a String, just as one can iterate over items in a regular array. Is there a reason why String does not implement Iterable?

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