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• How to keep Hibernate mapping use under control as requirements grow

  - by David Plumpton

  I've worked on a number of Java web apps where persistence is via Hibernate, and we start off with some central class (e.g. an insurance application) without any time being spent considering how to break things up into manageable chunks. Over time as features are added we add more mappings (rates, clients, addresses, etc.) and then amount of time spent saving and loading an insurance object and everything it connects to grows. In particular you get close to a go-live date and performance testing with larger amounts of data in each table is starting to demonstrate that it's all too slow. Obviously there are a number of ways that we could attempt to partition things up, e.g. map only the client classes for the client CRUD screens, etc., which would have been better to get in place earlier rather than trying to work it in at the end of the dev cycle. I'm just wondering if there are recommendations about ways to handle/mitigate this.

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• What is the possible benefit (if any) of allowing recursive contructors?

  - by Penang

  In Java, constructors cannot be recursive. Compile time error: "recursive constructor invocation". Let's assume that we did not have this restriction. Things to keep in mind: The return type of a constructor is void. Since it is a void method you can't harness the complete power of recursion. A constructor can invoke itself (or any other constructor) using this(). But a "call to this must be first statement in constructor" We could use non local data between consecutive calls to still have some possible gain from recursive constructors. Would there be any benefit from allowing recursive constructors?

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• Netbeans GUI Form corrupted?

  - by hubpages-my

  I was making a java gui application through netbeans IDE. All was working fine but yesterday when I opened the form in Netbeans, it said that the form had been corrupted and it could only open that form in read-only mode. When I opened that form in read-only mode, I found that the code was incomplete as severals lines of coding wasn't there at the end. Could anybody tell me how to recover the form. The form is perfect in lookwise but the generated code is incomplete. The code is too long to write it again. The Netbeans told me to get help from http://wiki.netbeans.org/FormGuardedBlockError but I didn't find any helpful information there.

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• What is a good practice to access class attributes in class methods?

  - by Clem

  I always wonder about the best way to access a class attribute from a class method in Java. Could you quickly convince me about which one of the 3 solutions below (or a totally different one :P) is a good practice? public class Test { String a; public String getA(){ return this.a; } public setA(String a){ this.a = a; } // Using Getter public void display(){ // Solution 1 System.out.println(this.a); // Solution 2 System.out.println(getA()); // Solution 3 System.out.println(this.getA()); } // Using Setter public void myMethod(String b, String c){ // Solution 1 this.a = b + c; // Solution 2 setA(b + c); // Solution 3 this.setA(b + c); } }

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• executing a class in remote jvm

  - by redzedi

  Hi All, I have a small test class that i want to run on a particular jvm that's already up and running (basically it's an web application running on Tomcat) . The reason i want to do this is i want to execute a small test class (with the main method and all) within that jvm so that i get the same environment (loaded and initialized classes) for my test class. Is it possible to indicate that ,say through a jvm parameter, that it should not initialize a new vm to execute my class but instead go and execute on the remote vm and show me the result here, on my console. So the local jvm acts as a kind of thin proxy ? I am not aware in case there are some tools that should make this possible ... also heard somewhere that java 6 jvm comes with an option like this , is that true ?? Please help me. Thanks,

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• I'm having a hard time calling the variable from first frame.

  - by iownfloppydisk

  here is how should my program be. In first frame, there is a textfield1 where a user input text and when he press a button, a new frame will be display with a textfield2 that displays the inputted text from the textfield1. please help me with the syntax. i'm still a beginner in java. much thanks guys. First Frame: textfield= new JTextField(); textfield.setPreferredSize( new Dimension(200,30) ) ; textfield.setSize( textfield.getPreferredSize() ) ; textfield.setLocation(95,198) ; textfield.setSize(175,28); cont.add(textfield); public void actionPerformed(ActionEvent e) { this.setVisible(false); new Frame2().setVisible(true); //displays the 2nd frame right? } now i don't know what to do on my 2nd frame or where to start because i can't get the variable from the first frame

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• C++: Create abstract class with abstract method and override the method in a subclass

  - by Martijn Courteaux

  Hi, How to create in C++ an abstract class with some abstract methods that I want to override in a subclass? How should the .h file look? Is there a .cpp, if so how should it look? In Java it would look like this: abstract class GameObject { public abstract void update(); public abstract void paint(Graphics g); } class Player extends GameObject { @Override public void update() { // ... } @Override public void paint(Graphics g) { // ... } } // In my game loop: for (int i = 0; i < objects.size(); i++) { objects.get(i).update(); } for (int i = 0; i < objects.size(); i++) { objects.get(i).paint(g); } Translating this code to C++ is enough for me.

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• How to setup Main class in manifest file in jar produced by NetBeans project

  - by Leni Kirilov

  I have the following problem. I have a Java project in my NetBeans IDE 6.8. When I compile it and it produces a .jar file containing everything possible, the META-INF is not right. It doesn't contain the class to be executed - with main() method. When I click the Run button inside the IDE, everything works. The settings of the project are also set the right way - pointing to a class in my project. I tried adding a folder META-INF with manifest file but I didn't manage. Is there a way to do this manually in NetBeans, because I found that if I add the missing Main class in the manifest, everything works.

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• Manage duplicate jar files using ant and ivy.

  - by lawardy

  HI, I am using ant build script to build my java app and utilizing Ivy to manage its dependency. As my application is dependent/subset of other application(Main App), when running it, I set the classpath to point to lib jars of the Main App. As I tried to build the kit using ant and ivy, it includes/retrieve all the jars that is required as specified in ivy.xml The problem is, some of the jar files are duplicated with with jars file in the main app folders. Is there a way to set the classpath in build.xml to ignore retrieving jar files that already exist in the main app's lib folder. Thanks

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• BlackBerry project version number

  - by Seva Alekseyev

  I have a BlackBerry Java project in Eclipse. It has version number written down in four different spots: in the project properties, under "BlackBerry Project Settings/General" in the JAD file, under MIDlet-1 in the JAD file, under MIDlet-Version in the ALX file, under <version> And they seem uncorrelated. Changing either of these affects none of the rest. The third one is what the users sees during over-the-air setup and under Options/Advanced. Questions - why do we need all these? Are there contexts where numbers 1, 2, 4 come up? It's my understanding that the ALX is generated during compilation - where does the version # come from? Is there a way to learn at least one of those programmatically (without signing the app)?

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• xDocklet, Maven and Hibernate

  - by Vinothbabu

  I am having some trouble setting up xDocklet and getting this error. Error resolving version for plugin 'xdoclet:maven2-xdoclet2-plugin' from the repositories <pluginRepositories> <pluginRepository> <id>codehaus-plugins</id> <url>http://dist.codehaus.org/</url> <layout>legacy</layout> <snapshots> <enabled>true</enabled> </snapshots> <releases> <enabled>true</enabled> </releases> </pluginRepository> </pluginRepositories> <plugin> <groupId>xdoclet</groupId> <artifactId>maven2-xdoclet2-plugin</artifactId> <executions> <execution> <id>xdoclet</id> <phase>generate-sources</phase> <goals> <goal>xdoclet</goal> </goals> </execution> </executions> <dependencies> <dependency> <groupId>xdoclet-plugins</groupId> <artifactId>xdoclet-plugin-qtags</artifactId> <version>1.0.4-SNAPSHOT</version> </dependency> <dependency> <groupId>xdoclet-plugins</groupId> <artifactId>xdoclet-taglib-qtags</artifactId> <version>1.0.4-SNAPSHOT</version> </dependency> </dependencies> <goals> <goal>xdoclet</goal> </goals> <configuration> <configs> <config> <components> <component> <classname>org.xdoclet.plugin.qtags.impl.QTagImplPlugin</classname> </component> <component> <classname>org.xdoclet.plugin.qtags.impl.QTagLibraryPlugin</classname> <params> <packagereplace>org.xdoclet.plugin.${xdoclet.plugin.namespace}.qtags</packagereplace> </params> </component> <component> <classname>org.xdoclet.plugin.qtags.doclipse.QTagDoclipsePlugin</classname> <params> <filereplace>qtags.xml</filereplace> <namespace>${xdoclet.plugin.namespace}</namespace> </params> </component> <component> <classname>org.xdoclet.plugin.qtags.confluence.QTagConfluencePlugin</classname> <params> <destdir>${project.build.directory}/tag-doc</destdir> <namespace>${xdoclet.plugin.namespace}</namespace> <filereplace>${xdoclet.plugin.namespace}.confluence</filereplace> </params> </component> </components> <includes>**/*.java</includes> <params> <destdir>${project.build.directory}/generated-resources/xdoclet</destdir> </params> </config> </configs> </configuration> </plugin> Some of my questions. Would you recommend me with going with xDocklet. Is there any alternative for it? Is it one of the best way, as hbm's does get generated automatically. Any suggestions on the way how my Java Objects should get persisted in the DB? Any good tutorials over xDocklet Maven and Hibernate. I am using xDocklet to generate HBM's automatically by annotating my POJO's.

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• JFrame.setBackground() not working -- why?

  - by devoured elysium

  JFrame mainFrame = new JFrame(); mainFrame.setSize(100, 100); mainFrame.setBackground(Color.CYAN); mainFrame.setVisible(true); My intent is to create a window with a cyan background. What is wrong with this? My window doesn't get cyan, as I'd expect! Also, could anyone point out why I seem to have all the colors in duplicate (there's a Color.CYAN and a Color.cyan). Is there any difference at all between the two? Maybe the older one was a constant from before there were enums in Java and the second one is from the Enum? Thanks

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• Log RuntimeException thrown from thread created by Spring via the @Async annotation

  - by Eugen

  I'm having some difficulty logging RuntimeException from a thread. My system is: Java 7 (b118), Spring 3.0.5. The threads are not created by hand, but via Spring's @Async annotation, which creates it's own executor behind the scenes, so I don't really have the option of overriding any methods of the thread, FutureTask or anything low level. So my question is if Spring has any support or if there are any best practices for handling (logging) these type of exceptions? Any suggestions are appreciated. Thanks.

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• Build Interactive Floor With Projection !?

  - by Synxmax

  Dear Guys I am somehow newbie and sometimes guru , but at this moment i don't have enough time to research My nightmare is , my boss ask me to create an interactive floor ( he just saw in an exhibition ) , he ask me to create one of them instead of buying , i am an actionscript crawler and developer with some skills in java and c# programming , i just made some track motion with a simple web cam , and this idea came to my mind if i can use an infrared or thermographic camera instead of simple camera so i can get better positioning if camera place at top of floor ! Now i just came here to ask you guys is there any resource , tip , help i can know before getting into this deal !? is there any lib or api out to deal with this ?! EVEN, if there is any resource , article from another language c++ , c , .... could help i just didn't have enough time to test lot of ways If you search interactive floors , or interactive floor projection you can find some companies who provide such a thing Thanks in advance ( and sorry for my damn poor english , français could be better :D )

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• Monitoring Reasoning Progress using the Pellet Reasoner

  - by Nico

  I am currently constructing an OWL ontology, which - until very recently classified rapidly using the Pellet reasoner. However, since the introduction of several new classes, the reasoning performance has slowed to a crawl. Although the reasoner completes and the ontology does not contain any unsatisfiable concepts etc, the time the reasoning takes is unacceptable. I am currently trying to track down the offending classes/class that may have led to the slowdown. Here's my question: is it possible to log the reasoning progreess of Pellet? I.e. is it possible to produce some output that will document how long pellet has spent on certain reasoning tasks/traces how long reasoning over any given class and axiom takes? If so, does anyone have some java code they could post up? Thanks in advance for your answers!

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• tomcat multithreading problem

  - by jutky

  Hi all I'm writing a java application that runs in Tomcat, on a multi-core hardware. The application executes an algorithm and returns the answer to the user. The problem is that even when I run two requests simultaneously, the tomcat process uses at most one CPU core. As far as I understand each request in Tomcat is executed in separate thread, and JVM should run each thread on separate CPU core. What could be the problem that bounds the JVM or Tomcat to use no more than one core? Thanks in advance.

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• How to use Map element as text of a JComboBox

  - by llm

  I am populating a JComboBox (using addItem()) with all the elements of a collection. Each element in the collection is a HashMap (so its a ComboBox of Hashmaps..). My question is - Given that I need each item to be a HashMap how do I set the text to apear in the combobox on the GUI? It needs to be the value of a certain key in the map. Normally if I am populating a combobox with my own type, I would just overide the toString() method...but I am not sure how to acheive this since I am using a Java HashMap. Any ideas (if possible, without implementing my own HashMap)? Update: It seems like there isn't anyway to avoid having the object int the JComboBox overide toString() if I want custom functionality..I wish there was a way to (1) specify the objects to be loaded into the JComboBox and (2) specify how these objects are to appear in the GUI.

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• how do i use a .dat file as a model for an entity in minecraft?

  - by user1835502

  the entity does not have to do anything, just stand there like a statue, or it doesn't have to be an entity at all, just so the .dat file renders in minecraft i saw this http://pastebin.com/jP4diLJ9 in a java file that came with a .exe, and in the .exe you can choose one of the .dat files and it will show you it as a model, i also asked on minecraft forums and someone said it was possible but i have no idea how maybe has something to do with this try { FileOutputStream fileoutputstream = new FileOutputStream("./Models/"+id+".dat"); fileoutputstream.write(b, 0, b.length); fileoutputstream.close(); } catch(Throwable _ex) {} or if(i 0) {//grabs all models System.out.println("Sending request for Model: "+i); addRequest( 7, i); byte b[] = pack.unpack(download().buffer); if(pack.unpacked) { savemodel(i,b); System.out.println("Model Saved"); }else{ System.out.println("Model Grabbing Complete"); break;

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• How can I create a new class instance from a class within a (static) class?

  - by Mervin

  I'm new to Java (have experience with C#), This is what i want to do: public final class MyClass { public class MyRelatedClass { ... } } public class OtherRandomClass { public void DoStuff() { MyRelatedClass data = new MyClass.MyRelatedClass(); } } which gives this error in Eclipse: "No enclosing instance of type BitmapEffects is accessible. Must qualify the allocation with an enclosing instance of type BitmapEffects (e.g. x.new A() where x is an instance of BitmapEffects)." this is possible in C# with static classes , how should it be done here?

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• What are the pro and cons of having localization files vs hard coded variables in source code?

  - by corgrath

  Definitions: Files: Having the localization phrases stored in a physical file that gets read at application start-up and the phrases are stored in the memory to be accessed via util-methods. The phrases are stored in key-value format. One file per language. Variables: The localization texts are stored as hard code variables in the application's source code. The variables are complex data types and depending on the current language, the appropriate phrase is returned. Background: The application is a Java Servlet and the developers use Eclipse as their primary IDE. Some brief pro and cons: Since Eclipse is use, tracking and finding unused localizations are easier when they are saved as variables, compared to having them in a file. However the application's source code becomes bigger and bloated. What are the pro and cons of having localization text in files versus hard coded varibles in source code? What do you do and why?

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• Tuning JVM (GC) for high responsive server application

  - by elgcom

  I am running an application server on Linux 64bit with 8 core CPUs and 6 GB memory. The server must be highly responsive. After some inspection I found that the application running on the server creates rather a huge amount of short-lived objects, and has only about 200~400 MB long-lived objects(as long as there is no memory leak) After reading http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html I use these JVM options -Xms2g -Xmx2g -XX:MaxPermSize=256m -XX:NewRatio=1 -XX:+UseConcMarkSweepGC Result: the minor GC takes 0.01 ~ 0.02 sec, the major GC takes 1 ~ 3 sec the minor GC happens constantly. How can I further improve or tune the JVM? larger heap size? but will it take more time for GC? larger NewSize and MaxNewSize (for young generation)? other collector? parallel GC? is it a good idea to let major GC take place more often? and how?

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• swing: event listener support class

  - by Jason S

  Is there any preexisting class that helps support add/remove EventListener operations? (kind of like PropertyChangeSupport) I'm trying to partition my code into a model and view in Java. I have some data that arrives erratically, and would like the model to support some kind of EventListener so that a view can subscribe to changes in the model. The data is numerous + complicated enough that I don't want to have to do the whole fine-grained Javabeans property change support; rather I would just like to allow notification that the model has changed in a coarse way. how can I best do this?

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• Does this variable need to be declared volatile?

  - by titaniumdecoy

  Does the out variable in the MyThread class need to be declared volatile in this code or will the "volatility" of the stdout variable in the ThreadTest class carry over? import java.io.PrintStream; class MyThread implements Runnable { int id; PrintStream out; // should this be declared volatile? MyThread(int id, PrintStream out) { this.id = id; this.out = out; } public void run() { try { Thread.currentThread().sleep((int)(1000 * Math.random())); out.println("Thread " + id); } catch (InterruptedException e) { e.printStackTrace(); } } } public class ThreadTest { static volatile PrintStream stdout = System.out; public static void main(String[] args) { for (int i = 0; i < 10; i++) { new Thread(new MyThread(i, stdout)).start(); } } }

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• How created method with signature as List

  - by London

  Hi all, I'm very new to Java programming language so this is probably dumb question but I have to ask it because I can't figure it out on my own. Here is the deal. I want to create method which extracts certain object type from a list. So the method should receive List as argument, meaning list should contain either Object1 or Object2. I've tried like this : public Object1 extractObject(List<?>){ //some pseudo-code ... loop trough list and check if list item is instance of object one return that instance } The problem with declaring method with List<?> as method argument is that I receive compilation error from eclipse Syntax error on token ">", VariableDeclaratorId expected after this token. How do I set the method signature properly to accept object types either Object1 or Object2 ? Thank you

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• Embedded MongoDB when running integration tests

  - by seanhodges

  My question is a variation of this one. Since my Java Web-app project requires a lot of read filters/queries and interfaces with tools like GridFS, I'm struggling to think of a sensible way to simulate MongoDB in the way the above solution suggests. Therefore, I'm considering running an embedded instance of MongoDB alongside my integration tests. I'd like it to start up automatically (either for each test or the whole suite), flush the database for every test, and shut down at the end. These tests might be run on development machines as well as the CI server, so my solution will also need to be portable. Can anyone with more knowledge on MongoDB help me get idea of the feasibility of this approach, and/or perhaps suggest any reading material that might help me get started? I'm also open to other suggestions people might have on how I could approach this problem...

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