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  • JAR files, don't they just bloat and slow Java down?

    - by Josamoto
    Okay, the question might seem dumb, but I'm asking it anyways. After struggling for hours to get a Spring + BlazeDS project up and running, I discovered that I was having problems with my project as a result of not including the right dependencies for Spring etc. There were .jars missing from my WEB-INF/lib folder, yes, silly me. After a while, I managed to get all the .jar files where they belong, and it comes at a whopping 12.5MB at that, and there's more than 30 of them! Which concerns me, but it probably and hopefully shouldn't be concerned. How does Java operate in terms of these JAR files, they do take up quite a bit of hard drive space, taking into account that it's compressed and compiled source code. So that can really quickly populate a lot of RAM and in an instant. My questions are: Does Java load an entire .jar file into memory when say for instance a class in that .jar is instantiated? What about stuff that's in the .jar that never gets used. Do .jars get cached somehow, for optimized application performance? When a single .jar is loaded, I understand that the thing sits in memory and is available across multiple HTTP requests (i.e. for the lifetime of the server instance running), unlike PHP where objects are created on the fly with each request, is this assumption correct? When using Spring, I'm thinking, I had to include all those fiddly .jars, wouldn't I just be better off just using native Java, with say at least and ORM solution like Hibernate? So far, Spring just took extra time configuring, extra hard drive space, extra memory, cpu consumption, so I'm concerned that the framework is going to cost too much application performance just to get for example, IoC implemented with my BlazeDS server. There still has to come ORM, a unit testing framework and bits and pieces here and there. It's just so easy to bloat up a project quickly and irresponsibly easily. Where do I draw the line?

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  • Manipulate data in the DB query or in the code

    - by DrDro
    How do you decide on which side you perform your data manipulation when you can either do it in the code or in the query ? When you need to display a date in a specific format for example. Do you retrieve the desired format directly in the sql query or you retrieve the date then format it through the code ? What helps you to decide : performance, best practice, preference in SQL vs the code language, complexity of the task... ?

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  • What is a mantainable way of saving "star rating" in a database?

    - by Montecristo
    I'll use the jQuery plugin for presenting the user with a nice interface The request is to display 5 stars, up to a total score of 10 (2 points per star). By now I thought about using 7/10 as a format for that value, but what if at some point in the future I'll receive a request like We would like to give users more choice, let's increase the total score to 20 (so that each star contributes with a maximum of 4 points) I'll end up with a table with mixed values for the "star rating" column: some will be like 7/10 while others will be like 14/20. Is it ok for you to have this difference in the database and deal with it in the logic layer to have it consistent? Or is preferred another way so that querying the table will not result in inconsistent results outside the application? Maybe floating point values could help me, is it better to store that value as a number less than or equal to one? So in each of the two examples the resulting value stored in the database would be 0,7, as a number, not a varchar, which can be queried also outside the application. What do you think?

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  • SELECT product from subclass: How many queries do I need?

    - by Stefano
    I am building a database similar to the one described here where I have products of different type, each type with its own attributes. I report a short version for convenience product_type ============ product_type_id INT product_type_name VARCHAR product ======= product_id INT product_name VARCHAR product_type_id INT -> Foreign key to product_type.product_type_id ... (common attributes to all product) magazine ======== magazine_id INT title VARCHAR product_id INT -> Foreign key to product.product_id ... (magazine-specific attributes) web_site ======== web_site_id INT name VARCHAR product_id INT -> Foreign key to product.product_id ... (web-site specific attributes) This way I do not need to make a huge table with a column for each attribute of different product types (most of which will then be NULL) How do I SELECT a product by product.product_id and see all its attributes? Do I have to make a query first to know what type of product I am dealing with and then, through some logic, make another query to JOIN the right tables? Or is there a way to join everything together? (if, when I retrieve the information about a product_id there are a lot of NULL, it would be fine at this point). Thank you

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  • using ref to view error

    - by Avram
    Hello. I working now on firm that using ref in every function. The reason, is to catch errors. There example : //return true if the read is success //otherwise writing to the error ,the problem bool ReadFile(ref string error) Question: How do you catching errors? Using ref,exceptions or other way?

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  • How to avoid nested functions when using AJAX?

    - by Fletcher Moore
    Sequential Asynchronous calls are gross. Is there a more readable solution? The problem is this is hard to follow: ajaxOne(function() { // do something ajaxTwo(function() { // do something ajaxThree() }); }); where the anonymous functions are callbacks that are called on server response. I'm using a third party API to make the AJAX calls, so I need a generic solution.

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  • One class per file rule in .NET?

    - by Joan Venge
    I follow this rule but some of my colleagues disagree with it and argue that if a class is smaller it can be left in the same file with other class(es). Another argument I hear all the time is "Even Microsoft don't do this, so why should we?" What's the general consensus on this? Are there cases where this should be avoided?

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  • Why do people keep parsing HTML using regex? [closed]

    - by polygenelubricants
    As much as I love regular expressions, it's obvious to me that it's not the best tool for parsing HTML, especially given the numerous good HTML parsers out there. And yet there are numerous questions on stackoverflow that attempts to parse HTML using regex. And people would always point out what a bad idea that is in the comments. And the accepted answer would often have a disclaimer how this isn't really the ideal way of doing things. But based on the constant flow of questions, it still seems that people keep parsing HTML using regex, despite the perceived difficulty in reading and maintaining it (and that's putting correctness aside for now). So my question is: why? Is it because it's easy to learn? Is it because it's faster? Is it because it's the industry standard? Is it because there are already so many reusable regexes to build from? Is it because 100% correctness is never really the objective? (90% good enough?) etc... I'd also like to hear from the downvoters why they did so. Is it because: There's absolutely nothing wrong with using regex to parse HTML and asking "Why?" is just dumb? The premise of the question is flawed because the people who are using regex to parse HTML is such a small minority?

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  • Where to put a piece of code in Ruby on Rails?

    - by yuval
    I have a post controller that has many comments. The post model has a field called has_comments which is a boolean (so I can quickly select from the database only posts that have comments). To create a new comment for a post, I use the create action of my comments controller. After I create the comment I need to update my post's has_comments field and set it to true. I can update this field from the create action of my comments controller, but that doesn't seem right - I feel that I should really be using the post's update action, but I'm not sure if it's right to call it (via send?) from the create action of the comments controller. Where should the code for updating the post be? Thank you!

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  • Finding relative libraries when using symlinks to ruby executables

    - by dgtized
    Imagine you have an executable foo.rb, with libraries bar.rb layed out in the following manner: <root>/bin/foo.rb <root>/lib/bar.rb In the header of foo.rb you place the following require to bring in functionality in bar.rb: require File.dirname(__FILE__)+"../lib/bar.rb" This works fine so long as all calls to foo.rb are direct. If you put as say $HOME/project, and symlink foo.rb into $HOME/usr/bin, then __FILE__ resolves to $HOME/usr/bin/foo.rb, and is thus unable to locate bar.rb in relation to the dirname for foo.rb. I realize that packaging systems such as rubygems fix this by creating a namespace to search for the library, and that it is also possible to adjust the load_path using $: to include $HOME/project/lib, but it seems as if a more simple solution should exist. Has anyone had experience with this problem and found a useful solution or recipe?

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  • Are there any inherent benefits or drawbacks to choosing Google Code vs. SourceForge vs. Codeplex?

    - by kdmurray
    I've got a couple of different projects that I'd like to post up as open source. I've been trying to decide which of the three big open-source project hosting sites makes the most sense, or if I should just host it myself. Are there any inherent drawbacks or benefits to these three? Is there a "best" place to host a project? Do different sites make more sense for different kinds of projects?

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  • Why cast null before checking if object is equal to null?

    - by jacerhea
    I was looking through the "Domain Oriented N-Layered .NET 4.0 Sample App" project and ran across some code that I do not understand. In this project they often use syntax like the following to check arguments for null: public GenericRepository(IQueryableContext context,ITraceManager traceManager) { if (context == (IQueryableContext)null) throw new ArgumentNullException("context", Resources.Messages.exception_ContainerCannotBeNull); Why would you cast null to the type of the object you are checking for null?

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  • What is the standard way to bundle OSGi dependent libraries?

    - by Chris
    Hi, I have a project that references a number of open source libraries, some new, some not so new. That said, they are all stable and I wish to stick with my chosen versions until I have time to migrate to the newer versions (I tested hsqldb 2.0 yesterday and it contains many api changes). One of the libraries I have wish to embed is Jasper Reports, but as you all surely know, it comes with a mountain of supporting jar files and I have only need a subset of the mountain (known) therefore I am planning to custom bundle all of my dependant libraries. So: Does everyone custom-make their own OSGi bundles for open-source libraries they are using or is there a master source of OSGi versions of common libraries? Also, I was thinking that it would be far simpler for each of my bundles simply to embed their dependent jars within the bundle itself. Is this possible? If I choose to embed the 3rd party foc libraries within a bundle, I assume I will need to produce 2 jar files, one without the embedded libraries (for libraries to be loaded via the classpath via standard classloader), and one osgi version that includes the embedded libraryy, therefore should I choose a bundle name like this <<myprojectname>>-<<subproject>>-osgi-.1.0.0.jar ? If I cannot embed the open source libraries and choose to custom bundle the open source libraries (via bnd), should I choose a unique bundle name to avoid conflict with a possible official bundle? e.g. <<myprojectname>>-<<3rdpartylibname>>-<<3rdpartylibversion>>.jar ? My non-OSGi enabled project currently scans for custom plugins via scanning the META-INF folders in my various plugin jars via Service.providers(...). If I go OSGi, will this mechanism still work?

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  • Building a life-critical System using Agile

    - by Ben Breen
    Looking at the general trend of comments in my question about Building an Aircraft using Agile, the biggest problem other than cost appears to be safety. Do people feel that it is not possible to build a safe system (or prove it is safe) using agile? Doesn’t all the iterative testing mitigate this? Is it likely that a piece of software developed using agile will never be as reliable as counterparts such as waterfall?

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  • Should you always write code for else cases that "can never happen"?

    - by johnswamps
    Take some code like if (person.IsMale()) { doGuyStuff(); } else { doGirlOtherStuff(); } (Yes, I realize this is bad OO code, it's an example) Should this be written so that to explicitly check if person.isFemale(), and then add a new else that throws an exception? Or maybe you're checking values in an enum, or something like that. You think that no one will add new elements to the enum, but who knows? "Can never happen" sounds like famous last words.

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  • How should I ethically approach user password storage for later plaintext retrieval?

    - by Shane
    As I continue to build more and more websites and web applications I am often asked to store user's passwords in a way that they can be retrieved if/when the user has an issue (either to email a forgotten password link, walk them through over the phone, etc.) When I can I fight bitterly against this practice and I do a lot of ‘extra’ programming to make password resets and administrative assistance possible without storing their actual password. When I can’t fight it (or can’t win) then I always encode the password in some way so that it at least isn’t stored as plaintext in the database—though I am aware that if my DB gets hacked that it won’t take much for the culprit to crack the passwords as well—so that makes me uncomfortable. In a perfect world folks would update passwords frequently and not duplicate them across many different sites—unfortunately I know MANY people that have the same work/home/email/bank password, and have even freely given it to me when they need assistance. I don’t want to be the one responsible for their financial demise if my DB security procedures fail for some reason. Morally and ethically I feel responsible for protecting what can be, for some users, their livelihood even if they are treating it with much less respect. I am certain that there are many avenues to approach and arguments to be made for salting hashes and different encoding options, but is there a single ‘best practice’ when you have to store them? In almost all cases I am using PHP and MySQL if that makes any difference in the way I should handle the specifics. Additional Information for Bounty I want to clarify that I know this is not something you want to have to do and that in most cases refusal to do so is best. I am, however, not looking for a lecture on the merits of taking this approach I am looking for the best steps to take if you do take this approach. In a note below I made the point that websites geared largely toward the elderly, mentally challenged, or very young can become confusing for people when they are asked to perform a secure password recovery routine. Though we may find it simple and mundane in those cases some users need the extra assistance of either having a service tech help them into the system or having it emailed/displayed directly to them. In such systems the attrition rate from these demographics could hobble the application if users were not given this level of access assistance, so please answer with such a setup in mind. Thanks to Everyone This has been a fun questions with lots of debate and I have enjoyed it. In the end I selected an answer that both retains password security (I will not have to keep plain text or recoverable passwords), but also makes it possible for the user base I specified to log into a system without the major drawbacks I have found from normal password recovery. As always there were about 5 answers that I would like to have marked correct for different reasons, but I had to choose the best one--all the rest got a +1. Thanks everyone!

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  • Reference table values in a war against magic numbers

    - by Alex N.
    This question bugged me for years now and can't seem to find good solution still. I working in PHP and Java but it sounds like this maybe language-agnostic :) Say we have a standard status reference table that holds status ids for some kind of entity. Further let's assume the table will have just 5 values, and will remain like this for a long time, maybe edited occasionally with addition of a new status. When you fetch a row and need to see what status it is you have 2 options(as I see it at least) - put it straight ID values(magic numbers that is) or use a named constant. Latter seem much cleaner, the question though is where those named constants should leave? In a model class? In a class that uses this particular constant? Somewhere else?

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  • Best practice for near reuse of model components?

    - by Chris Knight
    I have a requirement to use a Fund model in my code. It will contain a fund name and fund code. In the interest of reuse I've poked around the package containing the other models used and found an existing Fund model. However the issue here is that, in addition to fund name and code, it also contains an amount. Amount isn't directly relevant in my context. So, do I: 1) Use the existing Fund model as is, ignoring the setters/getters for fund amount. 2) Put a FundDescription interface onto the existing Fund model for accessing only the information I'm interested in. 3) Make a FundDescription base class from which the existing Fund model could now extend 4) Create a whole new seperate model since the two are slightly contextually different

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  • Is it a good idea to define a variable in a local block for a case of a switch statement?

    - by Paperflyer
    I have a rather long switch-case statement. Some of the cases are really short and trivial. A few are longer and need some variables that are never used anywhere else, like this: switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: { int specialVariable = 5; // Do something complex with specialVariable } break; } The alternative would be to declare that variable before going into the switch like this: int specialVariable = 5; switch (action) { case kSimpleAction: // Do something simple break; case kComplexAction: // Do something complex with specialVariable break; } This can get rather confusing since it is not clear to which case the variable belongs and it uses some unnecessary memory. However, I have never seen this usage anywhere else. Do you think it is a good idea to declare variables locally in a block for a single case?

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  • Python-based password tracker (or dictionary)

    - by Arrieta
    Hello: Where we work we need to remember about 10 long passwords which need to change every so often. I would like to create a utility which can potentially save these passwords in an encrypted file so that we can keep track of them. I can think of some sort of dictionary passwd = {'host1':'pass1', 'host2':'pass2'}, etc, but I don't know what to do about encryption (absolutely zero experience in the topic). So, my question is really two questions: Is there a Linux-based utility which lets you do that? If you were to program it in Python, how would you go about it? A perk of approach two, would be for the software to update the ssh public keys after the password has been changed (you know the pain of updating ~15 tokens once you change your password). As it can be expected, I have zero control over the actual network configuration and the management of scp keys. I can only hope to provide a simple utility to me an my very few coworkers so that, if we need to, we can retrieve a password on demand. Cheers.

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  • Asynchronous SQL Operations

    - by Paul Hatcherian
    I've got a problem I'm not sure how best to solve. I have an application which updates a database in response to ad hoc requests. One request in particular is quite common. The request is an update that by itself is quite simple, but has some complex preconditions. For this request the business layer first requests a set of data from the data layer. The business logic layer evaluated the data from the database and parameters from the request, from this the action to be performed is determined, and the request's response message(s) are created. The business layer now executes the actual update command that is the purpose of the request. This last step is the problem, this command is dependent on the state of the database, which might have changed since the business logic ran. Locking down the data read in this operation across several round-trips to the database doesn't seem like a good idea either. Is there a 'best-practice' way to accomplish something like this? Thanks!

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  • Why doesn't String's hashCode() cache 0?

    - by polygenelubricants
    I noticed in the Java 6 source code for String that hashCode only caches values other than 0. The difference in performance is exhibited by the following snippet: public class Main{ static void test(String s) { long start = System.currentTimeMillis(); for (int i = 0; i < 10000000; i++) { s.hashCode(); } System.out.format("Took %d ms.%n", System.currentTimeMillis() - start); } public static void main(String[] args) { String z = "Allocator redistricts; strict allocator redistricts strictly."; test(z); test(z.toUpperCase()); } } Running this in ideone.com gives the following output: Took 1470 ms. Took 58 ms. So my questions are: Why doesn't String's hashCode() cache 0? What is the probability that a Java string hashes to 0? What's the best way to avoid the performance penalty of recomputing the hash value every time for strings that hash to 0? Is this the best-practice way of caching values? (i.e. cache all except one?) For your amusement, each line here is a string that hash to 0: pollinating sandboxes amusement & hemophilias schoolworks = perversive electrolysissweeteners.net constitutionalunstableness.net grinnerslaphappier.org BLEACHINGFEMININELY.NET WWW.BUMRACEGOERS.ORG WWW.RACCOONPRUDENTIALS.NET Microcomputers: the unredeemed lollipop... Incentively, my dear, I don't tessellate a derangement. A person who never yodelled an apology, never preened vocalizing transsexuals.

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