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• When is BIG, big enough for a database?

  - by David ???

  I'm developing a Java application that has performance at its core. I have a list of some 40,000 "final" objects, i.e., I have an initialization input data of 40,000 vectors. This data is unchanged throughout the program's run. I am always preforming lookups against a single ID property to retrieve the proper vectors. Currently I am using a HashMap over a sub-sample of a 1,000 vectors, but I'm not sure it will scale to production. When is BIG, actually big enough for a use of DB? One more thing, an SQLite DB is a viable option as no concurrency is involved, so I guess the "threshold" for db use, is perhaps lower.

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• Groovy: Dynamically addings methods with a specific signature.

  - by Reverend Gonzo

  So, I need to dynamically create (or inject) methods into an object that have a specific return type and method signature, because a Java tool we're using will be finding this methods via Reflection and checks for void type. Method names will be determined at runtime. Using metaClass. = { ... } however adds a closure which doesn't show up as a regular method (even if it can be used as one) and also has a return type. I can't modify the method finding code, and it it not Groovy-aware. I can't use methodMissing() or invokeMethod() because the method needs to actually exist. If I could overload class.getMethods() I think it would be possible, but I can't figure out how. Is there any way to do this in Groovy?

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• Refactoring if/else logic

  - by David

  I have a java class with a thousand line method of if/else logic like this: if (userType == "admin") { if (age > 12) { if (location == "USA") { // do stuff } else if (location == "Mexico") { // do something slightly different than the US case } } else if (age < 12 && age > 4) { if (location == "USA") { // do something slightly different than the age > 12 US case } else if (location == "Mexico") { // do something slightly different } } } else if (userType == "student") { if (age > 12) { if (location == "USA") { // do stuff } else if (location == "Mexico") { // do something slightly different than the US case } } else if (age < 12 && age > 4) { if (location == "USA") { // do something slightly different than the age > 12 US case } else if (location == "Mexico") { // do something slightly different } } How should I refactor this into something more managable?

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• How to store matrix information in MySQL?

  - by dedalo

  Hi, I'm working on an application that analizes music similarity. In order to do that I proccess audio data and store the results in txt files. For each audio file I create 2 files, 1 containing and 16 values (each value can be like this:2.7000023942731723) and the other file contains 16 rows, each row containing 16 values like the one previously shown. I'd like to store the contents of these 2 file in a table of my MySQL database. My table looks like: Name varchar(100) Author varchar (100) in order to add the content of those 2 file I think I need to use the BLOB data type: file1 blob file2 blob My question is how should I store this info in the data base? I'm working with Java where I have a double array containing the 16 values (for the file1) and a matrix containing the file2 info. Should I process the values as strings and add them to the columns in my database? Thanks

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• Applet in client-server infrastructure

  - by Andrey

  Hello! I have a general question concerning client-server design. We have a Java server with Spring, a GWT client program and some HTTP-servlets for our site. At the moment we also want to develop an applet which would communicate with that server in such a way GWT-client and site requests do. Is it a good idea to communicate with the server from applet by RMI? I.e. to create some Remote services, register them with Spring and call them from applet? Thanks in advance!

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• Using JLists and ListModels

  - by devoured elysium

  I have defined a DirectoryListModel class that extends the AbstractListModel class from the Java Api. Internally, I have a list of File objects. I have defined the getElementAt(int index) method as: @Override public Object getElementAt(int index) { return directoryElements.get(index) } The problem is that when I try to run my JList with my DirectoryListModel, it is going to show up the full paths of files instead of just the filenames. I could change this code to: @Override public Object getElementAt(int index) { return directoryElements.get(index).getName(); } and it'd work wonders, but the problem is that in the onclick event I'll want to have the File objects so I can do some checking with them (check if they're directories, etc). If I make getElementAt() return a String, I'm losing that possibility, thus I'd like to konw if there is a way I can format my File objects before the JList shows them in my window. Thanks

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• Need suggestions on which web frameworks to use?

  - by satish

  I want to build a site where people can create their personal websites quickly. All their websites will be hosted on my single web application (i.e. there will be only one database which contains info of all the websites). Each person will have an account where he can customize his website (template, content etc.). They can access their website from .mysite.com or mysite.com/xyz. I should be able to add different modules frequently, which will immediately reflect in all the websites created through my site. Based on the above requirements, please suggest me if there are any frameworks to use which can ease my job. Also suggest me which language to use (php or java). Which one would be better.

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• Why does Ordered[A] use a compare method instead of reusing compareTo?

  - by soc

  trait Ordered[A] extends java.lang.Comparable[A] { def compare(that: A): Int def < (that: A): Boolean = (this compare that) < 0 def > (that: A): Boolean = (this compare that) > 0 def <= (that: A): Boolean = (this compare that) <= 0 def >= (that: A): Boolean = (this compare that) >= 0 def compareTo(that: A): Int = compare(that) } Isn't it a bit useless to have both compare and compareTo? What is the huge benefit I'm missing here? If they had just used compareTo I could just had replaced Comparable with Ordered in my code and be done.

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• Does XSD allow simpleContent and complexContent at the same time?

  - by Willi Schönborn

  I want to write an xsd for the xmlrpc spec (and generate java classes out of it using jaxb). The xmlrpc spec allows values like: <value><int>123</int></value> <value><boolean>1</boolean></value> But at the same time it requires: If no type is indicated, the type is string. Which means i could receive something like this: <value>test123</value> which is equivalent to <value><string>test123</string></value> Is there a way to define this in an xsd.

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• How to keep statefull web clients in sync, when multiple clients are looking at the same data?

  - by Hilbrand

  In a RIA web client, created with GWT, the state is maintained in the web client, while the server is (almost) stateless (this is the preferred technique to keep the site scalable). However, if multiple users looking at the same data in their browser and one user changes something, which is send to the server and stored in the database, the other users still have the old data in their browser state. For example a tree is shown and one of the users adds/removes an item from the tree. Since there can be a lot of state in the client, what is the best technique to keep the state in the clients in sync? Are there any java frameworks that take care of this?

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• Updating the Jpanel of a class

  - by ivor

  Hi, After some advice on using jpanel - I'm new to java and playing around with the GUI elements. Bascially what I'm curious about is if I can set up a Jpanel in one class, then somehow add labels etc to the that container, but from another class. Is this possible ? or do i have to set the entire GUI up in one class, but then I guess I would have the same issue, if I wanted to update those fields I had set up in the main class from another class? Apologies I don't really have any code that's usefull to demostrate here - I'm just trying to get the idea going, working out if its possible before I go ahead. And I'm not even sure if this is possible. Any advice would be greatly appreciated. Thanks

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• How can I treat a sequence value like a generated key?

  - by Jeff Knecht

  Here is my situation and my constraints: I am using Java 5, JDBC, and DB2 9.5 My database table contains a BIGINT value which represents the primary key. For various reasons that are too complicated to go into here, the way I insert records into the table is by executing an insert against a VIEW; an INSTEAD OF trigger retrieves the NEXT_VAL from a SEQUENCE and performs the INSERT into the target table. I can change the triggers, but I cannot change the underlying table or the general approach of inserting through the view. I want to retrieve the sequence value from JDBC as if it were a generated key. Question: How can I get access to the value pulled from the SEQUENCE. Is there some message I can fire within DB2 to float this sequence value back to the JDBC driver?

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• what happen if I delete the xx.jar file after I started to execute the xx.jar

  - by ogzylz

  I have a server program running a java binary code (xx.jar file) While it is running I erranously delete the xx.jar file. The program continues to run. But I am not sure if the results will be correct, and I am not sure if the program will fail? When I delete the xx.jar file, the program was in a method for a long time and still it is in that method call. When it calls another method call will my program fail? I am asking this question because If deleting the file has no harm I will be gaining about 3-4h on a server machine

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• Is it bad practice to use Reflection in Unit testing?

  - by Sebi

  During the last years I always thought that in Java, Reflection is widely used during Unit testing. Since some of the variables/methods which have to be checked are private, it is somehow necessary to read the values of them. I always thought that the Reflection API is also used for this purpose. Last week i had to test some packages and therefore write some JUnit tests. As always i used Reflection to access private fields and methods. But my supervisor who checked the code wasn't really happy with that and told me that the Reflection API wasn't meant to use for such "hacking". Instead he suggested to modifiy the visibility in the production code. Is it really bad practice to use Reflection? I can't really believe that

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• No mapping for LONGVARCHAR in Hibernate 3.2

  - by jimbokun

  I am running Hibernate 3.2.0 with MySQL 5.1. After updating the group_concat_max_len in MySQL (because of a group_concat query that was exceeding the default value), I got the following exception when executing a SQLQuery with a group_concat clause: "No Dialect mapping for JDBC type: -1" -1 is the java.sql.Types value for LONGVARCHAR. Evidently, increasing the group_concat_max_len value causes calls to group_concat to return a LONGVARCHAR value. This appears to be an instance of this bug: http://opensource.atlassian.com/projects/hibernate/browse/HHH-3892 I guess there is a fix for this issue in Hibernate 3.5, but that is still a development version, so I am hesitant to put it into production, and don't know if it would cause issues for other parts of my code base. I could also just use JDBC queries, but then I have to replace every instance of a SQLQuery with a group_concat clause. Any other suggestions?

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• How to Get the Method/Function Call Trace for a Specific Run?

  - by JackWM

  Given a Java or JavaScript program, after its execution, print out a sequence of calls. The calls are in invocation order. E.g. main() { A(); } A() { B(); C(); } Then the call trace should be: main -> A() -> B() -> C() Is there any tool that can profile and output this kind of information? It seems this is common a need for debugging or performance tuning. I noticed that some profilers can do this, but I prefer a simpler/easy-to-use one. Thanks!

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• Concatinate integer arrays iteratively

  - by Ojtwist

  I have a methode in2.getImagesOneDim() which gives me an array of integers, to be more precise the pixel values of an image. Now i want to create one big array with all the pixel values of all the images. Therefore I have to call this method several times. Now I would like to concatenate the previous output to the current output until all images are read. In some kind of pseudo code, where the + is a concatination ... : for (int i = 1; i < 25; i++) { ConArray = ConArray + in2.getImagesOneDim("../images/"+i); } How would I do this in java ?

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• Localizing a JSF 1.2 application with UTF-8 resources

  - by Filini

  (WARNING: this is my first java application, coming from .NET, so don't bash me if I write too much garbage) I'm developing a simple JSF 1.2 web application which should support Russian, Chinese, and other languages outside ISO 8859-1, which is automatically used in Properties.load(). Is there a way to use the Properties loaded from XML files, with Properties.loadFromXml(), inside JSF, without writing too much code? I know there are alternative ways to do so (writing my own loader, escaping the characters...), but I'd really love to find a simple solution, and I don't see it in all the forums I checked. Thanks in advance for any help

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• JSP::Confused with the session objects

  - by Legend

  I just started exploring Java Servlets and JSP and am a little confused about the sessions object. Inside a servlet I have this: public class SampleServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException { HttpSession session = request.getSession(true); session.setAttribute("_session", "_value"); response.sendRedirect("page2.jsp"); } } Now, inside page2.jsp, there is a session object as well, but when I do this <% out.print(session.getAttribute("_session")) %> it gives me an error. Can someone tell me the right way of doing this? As to what I am trying to do, I want to share some session variables.

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• building an XML service parsing library

  - by DanInDC

  This is more of a design question I suppose. My company offers a web service to our client that spits data out in a custom xml format. I'd like to build a java library we can offer so our customers can just feed it the url and we will turn it into a set of POJOs built from the response. I can obviously just create a library that will do some simple xml parsing and building of the POJOs but I'm looking to build something a bit more robust. My brain is pulling me in a million directions, wondering if anyone has some pointers or some code to poke at. Was thinking about adding an Abdera extension, but it's not really a syndication format that fits the Abdera model. And most of the popular service libraries (twitter, facebook) all rely on standards format parsers, of which our format isn't.

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• HashMap "WriteOnce" Implementation .. need help

  - by JavaNewbie

  import java.util.*; public class HashMapExample { public static class WriteOnceMap<K, V> extends HashMap<K, V> { public V put(K key, V value) { /* WriteOnceMap is a map that does not allow changing value for a particular key. It means that put() method should throw IllegalArgumentException if the key is already assosiated with some value in the map. Please implement this method to conform to the above description of WriteOnceMap. */ } public void putAll(Map<? extends K, ? extends V> m) { /* Pleaase implement this method to conform to the description of WriteOnceMap above. It should either (1) copy all of the mappings from the specified map to this map or (2) throw IllegalArgumentException and leave this map intact if the parameter already contains some keys from this map. */ } } }

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• Mercurial - Files nog showing on server (ls command)

  - by Bumbolt

  I'm trying to setup a java buildserver with jenkins,maven and mercurial. Now my mercurial server is working i can push, pull and commit. Running the command 'hg serve' on the server allows me to see commits from my clients. But when i go manually into the repository (cd in server-terminal) and do an 'ls' command i can't see any file. When i clone the repository onto a new client i DO recieve the files pushed by the other clients. This is somewhat strange behaviour. Does anyone recognize this? What should i do to fix this?

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• Game Server Language Selection

  - by mr.LiKaShing

  I am planning to make a online-multiplayer game with my friends. The game is a browser card game (so, players act in turns) and players could host rooms in a lobby. Flex + actionscript will be used to write for the client side. We are discussing what should be used for the server side. I suggested C#/Java and my friend suggested PHP. I kw there are couple of questions asking for what language to use but I think it should depend on specific conditions. Is there any suggestion for us? Thanks.

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• Does the OS make a significant difference for Ruby Development ?

  - by Bragaadeesh

  Hi, I have been working in Java for the past 4 years and I am currently switching over to Ruby. I am so excited about it and I feel good to finally get a hands on experience on a scripting language first time. The task assigned to me is to first pick a OS of my choice and setup a Ruby in it and study for 2 weeks. I have been developing applications in windows and Linux is not my cup of tea. Some part of me wants to try out Linux but I want to first convince myself whether OS really matters for Ruby development. If Linux does matter, which distribution can I start looking at? Please advise.

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• Write file in sub-directory in Android

  - by Davide Vosti

  I'm trying to save a file in a subdirectory in Android 1.5. I can successfully create a directory using _context.GetFileStreamPath("foo").mkdir(); (_context is the Activity where I start the execution of saving the file) but then if I try to create a file in foo/ by _context.GetFileStreamPath("foo/bar.txt"); I get a exception saying I can't have directory separator in a file name ("/"). I'm missing something of working with files in Android... I thought I could use the standard Java classes but they don't seem to work... I searched the Android documentation but I couldn't fine example and google is not helping me too... I'm asking the wrong question (to google)... Can you help me out with this? Thank you!

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