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Avoid an "out of memory error" in Java(eclipse), when using large data structure?

- by gnomed

OK, so I am writing a program that unfortunately needs to use a huge data structure to complete its work, but it is failing with a "out of memory error" during its initialization. While I understand entirely what that means and why it is a problem, I am having trouble overcoming it, since my program needs to use this large structure and I don't know any other way to store it. The program first indexes a large corpus of text files that I provide. This works fine. Then it uses this index to initialize a large 2D array. This array will have nXn entries, where "n" is the number of unique words in the corpus of text. For the relatively small chunk I am testing it on(about 60 files) it needs to make approximately 30,000x30,000 entries. this will probably be bigger once I run it on my full intended corpus too. It consistently fails every time, after it indexes, while it is initializing the data structure(to be worked on later). Things I have done include: revamp my code to use a primitive "int[]" instead of a "TreeMap" eliminate redundant structures, etc... Also, I have run eclipse with "eclipse -vmargs -Xmx2g" to max out my allocated memory I am fairly confident this is not going to be a simple line of code solution, but is most likely going to require a very new approach. I am looking for what that approach is, any ideas? Thanks, B.

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I just need one dependent module , but don't need its dependencies (Maven)

- by smallufo

In my project , there is a spring XML config that utilizes ehcache to cache method returns. xml snippet : http://www.springmodules.org/schema/ehcache http://www.springmodules.org/schema/cache/springmodules-ehcache.xsd <ehcache:config configLocation="classpath:ehcache.xml"/> <ehcache:proxy id="explainRetriever" refId="explainRetrieverImpl"> <ehcache:caching methodName="get*" cacheName="explainCache"/> </ehcache:proxy> but in runtime , server complains it cannot find definitions of http://www.springmodules.org/schema/ehcache , I know I have to add "spring-modules-cache.jar" to WEB-INF/lib directory. But my project is maintained by maven , if I add "spring-modules-cache" to the runtime dependency , it will bring a lot of dependencies to my WAR file , filling my WAR with a lot of unnecessary jars. I just need one declaration in it , not all of its dependencies ... Is there any way to tell maven not to include its dependencies to the project ? Or ... another way , when packaging WAR , just copy another prepared spring-modules-cache.jar to WEB-INF/lib , how to do this ? Thanks !

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How to visually reject user input in a table?

- by FX

In the programming of a table-based application module (i.e. the user mostly enters tabular data in an already laid-out table), how would you reject user input for a given cell? The scenario is: the user edits the cell, enters something (text, picture, ...) and you want them to notice when they finish editing (hitting enter, for example) that their entry is not valid for your given "format" (in the wider meaning: it can be that they entered a string instead of a number, that their entry is too long, too short, they include a picture while it's not acceptable, ...). I can see two different things happening: You can rather easily fit their entry into your format, and you do so, but you want them to notice it so they can change if your guess is not good enough (example: they entered "15.47" in a field that needs to be an integer, so your program makes it "15") You cannot guess what to do with their entry, and want to inform them that it's not valid. My question specifically is: what visual display can you offer to inform the user that his input is invalid? Is it preferable to refuse to leave the editing mode, or not? The two things I can imagine are: using colors (red background if invalid, yellow background for my case 1 above) when you reject an input, do something like Apple does for password entry of user accounts: you make the cell "shaking" (i.e. oscillating left and right) for one second, and keep the focus/editing in their so they don't loose what they've typed. Let's hear your suggestions. PS: This question is, at least in my thought process, somehow a continuation and a specialization of my previous question on getting users to read error messages. PPS: Made this community wiki, was that the right thing to do on this kind of question or not?

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Using fopen and str_replace to auto fill a select option

- by Anders Kitson

Hi Everyone, I have this file 'gardens.php', which pulls data from a table called 'generalinfo' and I use fopen to send that data to a file called 'index.html'. Here is the issue, only one option is filled. I have a demo running here Garden Demo <-- this is a new updated page and location, there are more errors than I have locally If anyone could help me fix them Username:stack1 Password:stack1 Is there a better way to achieve what I want to? Thanks! Always. GARDENS.PHP <?php include("connect.php"); $results = mysql_query("SELECT * FROM generalinfo"); while($row = mysql_fetch_array($results)){ $country = $row['country']; $province = $row['province']; $city = $row['city']; $address = $row['address']; //echo $country; //echo $province; //echo $city; //echo $address; } $fd = fopen("index.html","r") or die ("Can not fopen the file"); while ($buf =fgets($fd, 1024)){ $template .= $buf; } $template = str_replace("<%country%>",$country,$template); echo $template; ?> INDEX.PHP SNIPPET <form name="filter" method="get" action="filter.php"> <select class="country" name="country"> <option><%country%></option> </select> </form>

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base destructor called twice after derived object?

- by sil3nt

hey there, why is the base destructor called twice at the end of this program? #include <iostream> using namespace std; class B{ public: B(){ cout << "BC" << endl; x = 0; } virtual ~B(){ cout << "BD" << endl; } void f(){ cout << "BF" << endl; } virtual void g(){ cout << "BG" << endl; } private: int x; }; class D: public B{ public: D(){ cout << "dc" << endl; y = 0; } virtual ~D(){ cout << "dd" << endl; } void f(){ cout << "df" << endl; } virtual void g(){ cout << "dg" << endl; } private: int y; }; int main(){ B b, * bp = &b; D d, * dp = &d; bp->f(); bp->g(); bp = dp; bp->f(); bp->g(); }

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NSNotification vs. Delegate Protocols?

- by jr

I have an iPhone application which basically is getting information from an API (in XML, but maybe JSON eventually). The result objects are typically displayed in view controllers (tables mainly). Here is the architecture right now. I have NSOperation classes which fetch the different objects from the remote server. Each of these NSOperation classes, will take a custom delegate method which will fire back the resulting objects as they are parsed, and then finally a method when no more results are available. So, the protocol for the delegates will be something like: (void) ObjectTypeResult:(ObjectType *)result; (void) ObjectTypeNoMoreResults; I think the solution works well, but I do end up with a bunch of delegate protocols around and then my view controllers have to implement all these delegate methods. I don't think its that bad, but I'm always on the lookout for a better design. So, I'm thinking about using NSNotifications to remove the use of the delegates. I could include the object in the userInfo part of the notification and just post objects as received, and then a final event when no more are available. Then I could just have one method in each view controller to receive all the data, even when using multiple objects in one controller.† So, can someone share with me some pros/cons of each approach. Should I consider refactoring my code to use Events rather then the delegates? Is one better then the other in certain situations? In my scenario I'm really not looking to receive notifications in multiple places, so maybe the protocol based delegates are the way to go. Thanks!

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Google App Engine datastore encoding?

- by sernaferna

I'm using the GAE datastore for a Java application, and storing some text that will be in numerous languages. In my servlet, I'm first checking to see if there's any data in the data store, and, if not, I'm creating some, similar to the following: ArrayList<Lang> list = new ArrayList<Lang>(); list.add(new Lang("EN", "English", 1)); list.add(new Lang("ES", "Español", 0)); //more languages here... PersistenceManager pm = PMF.get().getPersistenceManager(); for(Lang l : list) { pm.makePersistent(l); } Since this is using JDO, I guess I should include the relevent parts of the Lang class too: @PersistenceCapable public class Lang { @PrimaryKey private String code; @Persistent private String name; @Persistent private int popularity; // getters & setters & constructors... } However, the non-ASCII characters are giving me grief. I've set my Eclipse project to use the UTF-8 encoding instead of the default Cp1252, so I think I'm okay from that perspective, but when I use the App Engine Data Viewer to look at my data, that Español entry becomes EspaÃ±ol, and when I click on it to view it, I get a 500 Server Error. (There are some other entries with right-to-left text that don't even show up in the Data Viewer at all, but one problem at a time...) Is there anything special I can do in my code to set the character encoding, or specify to GAE that the data I'm storing is UTF-8? Or is the problem on the Eclipse side, and is there something I should be doing with my Java code?

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git push says everything up to date when it definitely is not

- by Wolf

I have a public repository. No one else has forked, pulled, or done anything else to it. I made some minor changes to one file, successfully committed them, and tried to push. It says 'Everything up-to-date'. There are no branches. I'm very, very new to git and I don't understand what on earth is going on. git remote show origin tells me: HEAD branch: master Remote branch: master tracked Local ref configured for 'git push': master pushes to master (up to date) Any ideas what I can do to make this understand that it's NOT up to date? Thanks Updates: git status: # On branch master # Untracked files: # (use "git add ..." to include in what will be committed) # # histmarkup.el # vendor/yasnippet-0.6.1c/snippets/ no changes added to commit (use "git add" and/or "git commit -a") git branch -a: * master remotes/origin/master git fsck: dangling tree 105cb101ca1a4d2cbe1b5c73eb4a238e22cb4998 dangling tree 85bd0461f0fcb1618d46c8a80d3a4a7932de34bb Update 2: I re-opened the modified file, and the modifications I KNOW I had made were gone. So I added them again, went through the rigamarole of git status, git add filename, git commit -m "(message)", and git push origin master, and all of a sudden it works the way it's supposed to.

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What is the purpose of the Html "no-js" class?

- by Swader

I notice that in a lot of template engines, in the HTML5 Boilerplate, in various frameworks and in plain php sites there is the no-js class added onto the html element. Why is this done? Is there some sort of default browser behavior that reacts to this class? Why include it always? Does that not render the class itself obsolete, if there is no no-"no-js" case and html can be addressed directly? Here is an example from the HTML5 Boilerplate index.html:      <html lang="en" class="no-js">  As you can see, the html element will always have this class. Can someone explain why this is done so often?

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When is the reintegrate option really necessary?

- by Tor Hovland

If you always sync a feature branch before you merge it back, why do you really have to use the --reintegrate option? The Subversion book says: When merging your branch back to the trunk, however, the underlying mathematics is quite different. Your feature branch is now a mishmosh of both duplicated trunk changes and private branch changes, so there's no simple contiguous range of revisions to copy over. By specifying the --reintegrate option, you're asking Subversion to carefully replicate only those changes unique to your branch. (And in fact, it does this by comparing the latest trunk tree with the latest branch tree: the resulting difference is exactly your branch changes!) So the --reintegrate option only merges the changes that are unique to the feature branch. But if you always sync before merge (which is a recommended practice, in order to deal with any conflicts on the feature branch), then the only changes between the branches are the changes that are unique to the feature branch, right? And if Subversion tries to merge code that is already on the target branch, it will just do nothing, right? In this blog post, Mark Phippard writes: http://blogs.open.collab.net/svn/2008/07/subversion-merg.html If we include those synched revisions, then we merge back changes that already exist in trunk. This yields unnecessary and confusing conflicts. Can somebody give me an example of when dropping reintegrate gives me unnecessary conflicts?

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jquery with php loading file

- by Marcus Solv

I'm trying to use jquery with a simple php code: $('#some').click(function() { <?php require_once('some1.php?name="some' + index + '"'); ?> }); It shows no error, so I don't know what is wrong. In some1 I have: <?php //Start session session_start(); //Include database connection details require_once('../sql/config.php'); //Connect to mysql server $link = mysql_connect(DB_HOST, DB_USER, DB_PASSWORD); if(!$link) { die('Failed to connect to server: ' . mysql_error()); } //Select database $db = mysql_select_db(DB_DATABASE); if(!$db) { die("Unable to select database"); } //Function to sanitize values received from the form. Prevents SQL injection function clean($str) { $str = @trim($str); if(get_magic_quotes_gpc()) { $str = stripslashes($str); } return mysql_real_escape_string($str); } //Sanitize the POST values $name = clean($_GET['name']); ?> It's not complete because I want to make a sql command (insert). I want when I click in #some to execute that file (create a entry in the table that isn't define yet).

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Documentation about difference between javacript src and javascript library in grails

- by damian

I know that if you write in a view: <g:javascript src="myscript.js" /> <g:javascript src="myscript.js" /> <g:javascript src="myscript.js" />  <g:javascript library="myscript" /> <g:javascript library="myscript" /> <g:javascript library="myscript" /> It will out output: <script type="text/javascript" src="/vip/js/myscript.js"></script> <script type="text/javascript" src="/vip/js/myscript.js"></script> <script type="text/javascript" src="/vip/js/myscript.js"></script>  <script type="text/javascript" src="/vip/js/myscript.js"></script> Conclution: with library it will try to include only once. I have been try to find documentation about it without success. Do you have any pointer?

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How can I restore the "auto" values with for list-style-type in nested unordered lists with CSS?

- by Michael

By default, an unstyled set of nested <ul> lists looks like this (in Chrome, Firefox, and IE at least): The top level has a list-style-type of disc, the next level is circle, and subsequent levels are square. If I include a stylesheet that changes the list-style-type to none, is there a simple way to revert back to the "automatic bullet types" later in the document? (e.g., override with a subsequent CSS definition or JavaScript style change) Basically, I'm looking for something like list-style-type: auto; (which is apparently not valid and has no effect): <style type="text/css"> ul { list-style-type: none; } ul { list-style-type: auto; } /* Does not work */ </style> Setting the list-style-type back to disc changes every bullet in the list and I no longer see different bullets at different levels, so that doesn't work either. Is the only way to accomplish this by explicitly defining styles for every level? e.g.: <style type="text/css"> ul { list-style-type: disc; } ul ul { list-style-type: circle; } ul ul ul { list-style-type: square; } </style>

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Segmentation fault in C recursive Combination (nCr)

- by AruniRC

PLease help me out here. The program is supposed to recursively find out the combination of two numbers. nCr = n!/ (r!(n-r)! ). I'm getting this error message when i compile it on GCC. Here's what the terminal shows: Enter two numbers: 8 4 Segmentation fault (Program exited with code:139) The code is given here: #include<stdio.h> float nCr(float, float, float); int main() { float a, b, c; printf("Enter two numbers: \n"); scanf("%f%f", &a, &b); c = nCr(a, b, a-b); printf("\n%.3f", c); return 0; } float nCr(float n, float r, float p) { if(n<1) return (1/(p*r))*(nCr(1, r-1, p-1)); if(r<1) return (n/(p*1))*(nCr(n-1, 1, p-1)); if(p<1) return (n/r)*(nCr(n-1, r-1, 1)); return ( n/(p*r) )*nCr(n-1, r-1, p-1); }

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Good Replacement for User Control?

- by David Lively

I found user controls to be incredibly useful when working with ASP.NET webforms. By encapsulating the code required for displaying a control with the markup, creation of reusable components was very straightforward and very, very useful. While MVC provides convenient separation of concerns, this seems to break encapsulation (ie, you can add a control without adding or using its supporting code, leading to runtime errors). Having to modify a controller every time I add a control to a view seems to me to integrate concerns, not separate them. I'd rather break the purist MVC ideology than give up the benefits of reusable, packaged controls. I need to be able to include components similar to webforms user controls throughout a site, but not for the entire site, and not at a level that belongs in a master page. These components should have their own code not just markup (to interact with the business layer), and it would be great if the page controller didn't need to know about the control. Since MVC user controls don't have codebehind, I can't see a good way to do this. I've searched previous SO questions, and have yet to find a good answer. Options so far In an attempt to avoid turning the comments section into a discussion... RenderAction This allows the view to call another controller, which will be responsible for interacting with the BLL and whatever data is necessary to its corresponding view. The calling view needs to be aware of the sub controller. This seems to provide a nice way to encapsulate partial views and controls, without having to modify the calling controller. RenderPartial The calling controller is still responsible for executing whatever code is associated with the partial view, and making sure that the model passed to the partial view contains the data it expects. Effectively, modifying the partial view potentially means modifying the calling controller. Annoying especially if this is used in multiple places. Portable Areas Place each control in its own project/area?

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Modify existing struct alignment in Visual C++

- by Crend King

Is there a way to modify the member alignment of an existing struct in Visual C++? Here is the background: I use an 3rd-party library, which uses several structs. To fill up the structs, I pass the address of the struct instance to some functions. Unfortunately, the functions only returns unaligned buffer, so that data of some members are always wrong. /Zp is out of choice, since it breaks the other parts of the program. I know #pragma pack modifies the alignment of the following struct, but I do not want to copy the structs into my code, for the definitions in the library might change in the future. Sample code: test.h: struct am_aligned { BYTE data1[10]; ULONG data2; }; test.cpp: include "test.h" // typedef alignment(1) struct am_aligned am_unaligned int APIENTRY wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow) { char buffer[20] = {}; for (int i = 0; i < sizeof(unaligned_struct); i++) { buffer[i] = i; } am_aligned instance = *(am_aligned*) buffer; return 0; } instance.data2 is 0x0f0e0d0c, while 0x0d0c0b0a is desired. The commented line does not work of course. Thanks for help!

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Android lifecycle of thread-based game

- by ehehhh

I ran into a bit of trouble while trying to get my game to work correctly after being put to the background by the user or a phone call for example. My app has a SurfaceView class called GameView, which has the onDraw() method to do all the necessary drawing for my game and two threads - one for calling the onDraw() and one for doing the necessary calculations for the game's logic. I succesfully implemented onPause() and onResume(). (I paused both threads when back button was pressed and resumed them after user cancelled in the AlertDialog.) Now I would like to have the game paused the same way when onStop() gets called. I put both threads on pause and saved my characters location in the savedInstanceState, but when I start my app again, no method gets called (I checked with Logcat). I believe onRestart() should be called first, then onStart() and then onResume(), but none of that happens. What am I doing wrong? (Didn't include any code, because it seems to be a problem of me not understanding the lifecycle, not a problem in code. If it seems necessary, I'll post the parts you request.)

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Need some clarification on the ANSI/SPARC 3-tier database architecture.

- by Moonshield

Hi there, I'm currently revising for a databases exam and looking over some past papers, but there's one question that I'm slightly unsure about and was wondering if someone could offer some assistance. "Describe EACH of the THREE levels of the ANSI SPARC 3 level architecture. Your answer should include the purpose of EACH of the schemas, the level of abstraction they provide and the software tools that would be used to access and support them." As I understand it (although please correct me if I'm wrong): the internal schema specifies the physical storage of the data; the conceptual schema specifies the structure of the database and the domains; and the external schemas are how the database is viewed by "users" (applications, etc.). As for the abstraction, I understand that the conceptual layer means that the physical data storage can be altered without the end user being affected, likewise the The bit that I'm not sure about is what tools are used to access and support each layer. Would the internal schema be handled by the DBMS, the conceptual schema handled by some sort of DDL interpreter and the external schema handled by a DML interpreter (or have I misunderstood what each level does)? Any assistance would be greatly appreciated. Thanks, Moonshield

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Compound Primary Key in Hibernate using Annotations

- by Rich

Hi, I have a table which uses two columns to represent its primary key, a transaction id and then the sequence number. I tried what was recommended http://docs.jboss.org/hibernate/stable/annotations/reference/en/html_single/#entity-mapping in section 2.2.3.2.2, but when I used the Hibernate session to commit this Entity object, it leaves out the TXN_ID field in the insert statement and only includes the BA_SEQ field! What's going wrong? Here's the related code excerpt: @Id @Column(name="TXN_ID") private long txn_id; public long getTxnId(){return txn_id;} public void setTxnId(long t){this.txn_id=t;} @Id @Column(name="BA_SEQ") private int seq; public int getSeq(){return seq;} public void setSeq(int s){this.seq=s;} And here are some log statements to show what exactly happens to fail: In createKeepTxnId of DAO base class: about to commit Transaction :: txn_id->90625 seq->0 ...<Snip>... Hibernate: insert into TBL (BA_ACCT_TXN_ID, BA_AUTH_SRVC_TXN_ID, BILL_SRVC_ID, BA_BILL_SRVC_TXN_ID, BA_CAUSE_TXN_ID, BA_CHANNEL, CUSTOMER_ID, BA_MERCHANT_FREETEXT, MERCHANT_ID, MERCHANT_PARENT_ID, MERCHANT_ROOT_ID, BA_MERCHANT_TXN_ID, BA_PRICE, BA_PRICE_CRNCY, BA_PROP_REQS, BA_PROP_VALS, BA_REFERENCE, RESERVED_1, RESERVED_2, RESERVED_3, SRVC_PROD_ID, BA_STATUS, BA_TAX_NAME, BA_TAX_RATE, BA_TIMESTAMP, BA_SEQ) values (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?) [WARN] util.JDBCExceptionReporter SQL Error: 1400, SQLState: 23000 [ERROR] util.JDBCExceptionReporter ORA-01400: cannot insert NULL into ("SCHEMA"."TBL"."TXN_ID") The important thing to note is I print out the entity object which has a txn_id set, and then the following insert into statement does not include TXN_ID in the listing and thus the NOT NULL table constraint rejects the query.

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What's the best technique to protect my framework from visitors who are not logged in?

- by Hermet

First of all, I would like to say that I have used the search box looking for a similar question and was unsuccessful, maybe because of my poor english skills. I have a a 'homemade' framework. I have certain PHP files that must only be visible for the admin. The way I currently do this is check within every single page to see if a session has been opened. If not, the user gets redirected to a 404 page, to seem like the file which has been requested doesn't exist. I really don't know if this is guaranteed to work or if there's a better and more safe way because I'm currently working with kind of confidential data that should never become public. Could you give me some tips? Or leave a link where I could find some? Thank you very much, and again excuse me for kicking the dictionary. EDIT What I usually write in the top of each file is something like this <?php include("sesion.php"); $rs=comprueba(); //'check' if ($rs==1) { ?> And then, at the end <?php } ?> Is it such a butched job, isn't it? EDIT Let's say I have a customers list in a file named customers.php That file may be currently on http://www.mydomain.com/admin/customers.php and it must only be visible for the admin user. Once the admin user has been logged in, I create a session variable. That variable is what I check on the top of each page, and if it exists, the customers list is shown. If not, the user gets redirected to the 404 page. Thank you for your patience. I really appreciate.

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What's the best Linux backup solution?

- by Jon Bright

We have a four Linux boxes (all running Debian or Ubuntu) on our office network. None of these boxes are especially critical and they're all using RAID. To date, I've therefore been doing backups of the boxes by having a cron job upload tarballs containing the contents of /etc, MySQL dumps and other such changing, non-packaged data to a box at our geographically separate hosting centre. I've realised, however that the tarballs are sufficient to rebuild from, but it's certainly not a painless process to do so (I recently tried this out as part of a hardware upgrade of one of the boxes) long-term, the process isn't sustainable. Each of the boxes is currently producing a tarball of a couple of hundred MB each day, 99% of which is the same as the previous day partly due to the size issue, the backup process requires more manual intervention than I want (to find whatever 5GB file is inflating the size of the tarball and kill it) again due to the size issue, I'm leaving stuff out which it would be nice to include - the contents of users' home directories, for example. There's almost nothing of value there that isn't in source control (and these aren't our main dev boxes), but it would be nice to keep them anyway. there must be a better way So, my question is, how should I be doing this properly? The requirements are: needs to be an offsite backup (one of the main things I'm doing here is protecting against fire/whatever) should require as little manual intervention as possible (I'm lazy, and box-herding isn't my main job) should continue to scale with a couple more boxes, slightly more data, etc. preferably free/open source (cost isn't the issue, but especially for backups, openness seems like a good thing) an option to produce some kind of DVD/Blu-Ray/whatever backup from time to time wouldn't be bad My first thought was that this kind of incremental backup was what tar was created for - create a tar file once each month, add incrementally to it. rsync results to remote box. But others probably have better suggestions.

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Should conditional expressions go inside or outside of classes?

- by Rupert

It seems that often I will want to execute some methods from a Class when I call it and choosing which function will depend on some condition. This leads me to write classes like in Case 1 because it allows me to rapidly include their functionality. The alternative would be Case 2 which can take a lot of time if there is a lot of code and also means more code being written twice when I drop the Class into different pages. Having said that, Case 1 feels very wrong for some reason that I can't quite put my finger on. I haven't really seen any classes written like this, I suppose. Is there anything wrong with writing classes like in Case 1 or is Case 2 superior? Or is there a better way? What the advantages and disadvantages of each? Case 1 class Foo { public function __construct($bar) { if($bar = 'action1') $this->method1(); else if($bar = 'action2') $this->method2(); else $this->method1(); } public function method1() { } public function method2() { } } $bar = 'action1' $foo = new Foo($bar); Case 2 class Foo { public function __construct() { } public function method1() { } public function method2() { } } $foo = new Foo; $bar = 'action1'; if($bar == 'action1') $foo->method1(); else if($bar == 'action2') $foo->method2(); else $foo->method1();

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Are application servers necessary? Advantages of using one? (And other JEE questions)

- by Mike

Apologies for the long question.. there seems to be other similar questions on here but none really clear up my confusion. I'd be really grateful if someone could confirm or correct my understanding: Java Enterprise Edition is a set of APIs for building enterprise applications, which take away the burden of developing parts of the system that aren't actually features of the application you are trying to build (i.e. messaging, transactions etc). To do this, you can use an application server, which implements these APIs. So you could use JBoss, Glassfish, WebSphere, WebLogic etc which would provide your application with these enterprise services. However, there are many other implementations of these individual services available such as ActiveMQ for messaging, Hibernate for persistence, OpenEJB etc. You can download these implementations as Java libraries and include them in your application, and use the services they provide in a similar way to using the services provided by an application server. So if my understanding is correct, my questions are: I've read a lot of places that application servers are necessary for JEE features like EJB, but can't you just use an implementation such as OpenEJB and not need an application server at all? Are there any features that an application server provides which you cannot get from another source? Why would/wouldn't I choose an application server over a custom stack such as Tomcat, OpenEJB, ActiveMQ, and Hibernate? Is Spring a complete alternative to JEE? Does it ever require an application server or always just a servlet container? Why would someone choose Spring over JEE? Any help would be much appreciated!

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Copy constructor called even when returning by reference?

- by Johnyy

Hi, I am testing the return of local objects by reference. My original test went well but something else happens unexpected. #include <iostream> using namespace std; class MyInt { public: MyInt(int i){ value = new int(i); } ~MyInt(){ delete value; } int getValue(){ return *value; } MyInt(const MyInt &b){ cout<<"Copy"<<endl; } private: int* value; }; MyInt& returnref(){ MyInt a(10); cout<<"Returning from returnref()"<<endl; return a; } int main(){ MyInt a = returnref(); cout<<a.getValue()<<endl; return 0; } My console prints "Returning from ..." then "Copy" then a random value. My understanding of pass by reference is that it does not need to make any copy. Why is it not doing what I expected?

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Explanation of `self` usage during dealloc?

- by Greg

I'm trying to lock down my understanding of proper memory management within Objective-C. I've gotten into the habit of explicitly declaring self.myProperty rather than just myProperty because I was encountering occasional scenarios where a property would not be set to the reference that I intended. Now, I'm reading Apple documentation on releasing IBOutlets, and they say that all outlets should be set to nil during dealloc. So, I put this in place as follows and experienced crashes as a result: - (void)dealloc { [self.dataModel close]; [self.dataModel release], self.dataModel = nil; [super dealloc]; } So, I tried taking out the "self" references, like so: - (void)dealloc { [dataModel close]; [dataModel release], dataModel = nil; [super dealloc]; } This second system seems to work as expected. However, it has me a bit confused. Why would self cause a crash in that case, when I thought self was a fairly benign reference more used as a formality than anything else? Also, if self is not appropriate in this case, then I have to ask: when should you include self references, and when should you not?

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