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• how do i close a frame yet open a new frame?(revisited)

  - by altvali

  I'm new at Java and I'm trying to do what the title says, my application has page A, a jpanel with some controls and a specific button, and when the user clicks the button i want page A to disappear and page B to appear (page B has controls that depend on the choices that are made by the user on page A). This has been asked before but there was no satisfactory answer. In the ActionListener implementation, namely public void ActionPerformed(ActionEvent e) from my jpanelForPageA class i can comfortably write this.setVisible(false), but how can i set page B to a visible state?

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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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• Formal name of Magento’s Class Override Design Pattern?

  - by Alan Storm

  Magento is a newish (past 5 years) PHP based Ecommerce system with an architecture that's similar to the Java Spring framework (or so I've been told) One of the features of the Framework is certain classes are not directly instantiated. Rather than do something like $model = new Mage_Foo_Model_Name(); you pass an identifier into a static method on a global application object $model = Mage::getModel('foo/name'); and this instantiates the class for you. One of the wins with this approach is getModel checks a global configuration system for the foo/name identifier, and instantiates the class name it finds in the configuration system. This allows you to change the behavior of a Model system wide with a single configuration change. Is there a formal, Gang of Four or otherwise, name that describes this system/design pattern? The instantiation itself looks like a classic Factory pattern, but I'm specifically interested in the whole "override a class in the system via configuration" aspect. Is there a name/concept that covers this, or is it contained within the worldview of a Factory?

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• How to update mutual entries in DB?

  - by Sthita

  I am not able to perform mutual update to my Database. My Requirement is like this : Insert IDS UPDate DB Entries ID ConnectedTo ID connectedTo connectedVia 2 1 --- No Entry ----- 2 3 -- No Entry ----- When ID 1 Comes in to picture (Enties happened to Table) 1 4 1 3 2 1 5 2 4 1 1 2 2 5 1 When ID 3 Comes into picture (Enties happened to Table) 3 4 3 5 1 3 1 ---- 3 2 ---- Similarly when ID 4 Comes in to picture 4 9 4 2 3 4 10 4 5 1 4 3 4 2 1 4 1 1 9 4 1 10 4 Its basically Updating the mutual connections.No Duplicate entries should happen. Like for example 2 3 and 3 2 are mutually connected and 1 is associated with them so there is no need to insert (3 2 via 1). I think this is my requirement. Anything possible combinations i have missed please let me know. i will Update. Please help me writing the logic or any example using jdbc and java.

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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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• 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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• 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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• 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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• 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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• 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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• 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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• Accessing and encoding of properties files

  - by NoozNooz42

  I'm used to work with properties files, for example from Ant. Where I can simply reference the property file doing something like that: <property file="webapp_DO_NOT_COMMIT.properties"/> (the file is so named because our DVCS is configured as to never commit files containing "DO_NOT_COMMIT" to prevent committing credentials/passwords/etc.) Here's a very simple .properties file example: passwd=brokencleartextpassword Now I want to put some configuration in another, similar, properties file that I need to access from my Java code. How should I go about it? I also have another related question: is the character encoding of .properties file defined by any spec?

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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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• Regex to find the text without a special character

  - by Hunter

  I have a paragraph, in that, some of the texts are surrounded with a specific html tag. I need to to find the text which are not surrounded by that specific html tag. For example AVG Antivirus for Smartphones and Tablets detects harmful apps and SMS. <font color='black'>AVG</font> Mobilation™ AntiVirus Pro for Android™ is a mobile security solution that helps protect your mobile device from viruses, malware, spyware and online exploitation in real-time. avg blah blah... I want to find the word AVG (case insensitive) which is not surrounded by <font color='black'> </font>. It can be part the word or single whole word. In the case of part of the text, the whole word containing the word AVG should not surrounded by that html tag How can I do it with Java?

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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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• 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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• How is a constructor executed?

  - by simion

  I am doing some reviison from the lecture slides and it says a constructor is executed in the following way; If the constructor starts with this, recursively execute the indicated constructor, then go to step 4. Invoke the explicitly or implicitly indicated superclass constructor (unless this class is java.lang.Object) Initialise the fields of the object in the order in which they were declared in this class Execute the rest of the body of this constructor. What i dont undertsand is that, a constructor can never "start" with this, because even if it forms no class heirarchy/relationship then super() is inserted by default. How would this fit in with the description above? Thanks

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• Send data over telnet without pressing enter

  - by Matt

  I've recently started messing around with Java sockets and telnet... I want the user to be able to connect to the server, just type a letter and have it sent to the server, without pressing enter to send it. I'm sure there's no way for the server to set this up, but maybe telnet has a parameter or something which could allow this? Maybe if I got the user to type stty cbreak or stty raw before running telnet, this would work? (UNIX only, I know!) If I can get telnet to do this then it saves me having to write a special client just for this feature...

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• NullPointerException when accessing image files in a .jar file

  - by user548240

  Hi, I have pretty much tried everything but still have this same problem. I have the following setup: I have a images.jar containing a folder called 'images' in which there are multiple image files. I add images.jar to the java build path of the project in eclipse, and i've been trying to use the following code to access the individual images in the jar: URL url = this.getClass().getResource("images/a.png"); ImageIcon icon = new ImageIcon (url); Unfortunately, the URL object is always NULL. I don't think this has anything to do with where I put images.jar file as it is added to the classpath in eclipse. I have also tried using the path '/images/a.png', but still the same problem. Any suggestion would be extremely welcome! Thanks.

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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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• Web applet game design

  - by Vlad

  I making web games in java and having troubles each time when getting to the GUI design, usually I'm looking at others codes and copy most of the design, and I can't decide which design should I use. I used Applet, Canvas, JFrame. What i need is the main loop and draw function that changing between different games. So what class should I use and what design, which is better, why, maybe links to useful tutorials and examples... Please explain. Thanks.

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• What happens when a OSGi service using JNI is unregistered while in use?

  - by schngrg

  As I understand, OSGi services can be unregistered anytime, including when they are in use. Consider an OSGi service which internally makes a long-running JNI call. And while that JNI call is executing, the service is unregistered by OSGi. Will the JNI call be allowed to finish or terminated mid-way? What if it was just a normal non-jni long running Java call? Will that call be allowed to finish execution or will OSGi terminate everything immediately and unregister? What is the expected behavior in such a case? Does the expected behavior depend on if the service was loaded using a 'tracker' or not? SG

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• Hibernate + Spring + session + cache

  - by andromeda

  We are using Hibernate with Spring for our Java application. We find out that when a session update something in database other sessions can not see the update. For example user1 get the account balance from database then user2 increase the balance , if user1 get the object another time he see the account balance before updating (seems that session use the value from its cache) but we want to get the updated object with new account balance. User1 use one session during all activity that is different from user2 session. Is any configuration to force to get the updated object from database? or any other help?

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