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• how to draw rectangle around mouse cursor in java?

  - by Nitz

  hey guys i had made one module in my project, on which user can draw any thing using pencil now i want to create eraser for that drawing module so i need that as soon as user click on that eraser button then, around my mouse cursor i want little rectangle shape around it. so user can use it to erase the some parts in drawing. may be smilier kind of things happen in mspaint but i am doing this in java - swing. how to do this, any suggestion? thanks in advance... nitz.

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• Java Swing - How to access a JComponent of one JPanel from other JPanel, both added to the JFrame?

  - by Yatendra Goel

  I am developing a Java Desktop Application with GUI implemented in SWING. I hava a JFrame. I have added three JPanels on that. One JPanel panel1 has a Start Button. Now I want to disable various componets on other JPanels when a user presses the start button on the panel1. Now how can I access the components of those other panels from panel1. I know that one approach is to first get the container of panel1 panel1.getParent(); Then get the components of the container container.getComponents(); and use them as per need. Q1. Is there any other way by which I can perform the same task? (I think this is the only way) Q2. After getting the components list of the container, how to differentiate one container with other?

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• How do you force a Linux process (Java webstart App) to stop locking a Filesystem (CD-ROM) WITHOUT k

  - by Blake

  In Linux (CentOS 5.4), how do you force a process to stop locking a file system without killing the process? I am trying to get my Java Webstart Application, running locally, to eject a CD. I do not have this problem if I am just browsing through the files using a JFileChooser, but once I read the contents of a file, I can no longer eject the CD...even after removing ALL references to any files. Hitting the eject button will give the error (Title - "Cannot Eject Volume"): "An application is preventing the volume 'volume name' from being ejected" Thus, my goal is to tell the process to stop targeting the CD-ROM in order to free it up. Thank you for any help or direction!! Attempted Fix: -running the commands: sudo umount -l /media/Volume_Name //-l Lazy Unmount forces the unmount sudo eject Problem: When a new CD is inserted, it is no longer mounted automatically probably because the process is still "targeting" it.

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• complex thinking on simple java challenge, how can i fix it?

  - by Rachel

  Simple stuff but somehow not able to crack it, below piece of code is throwing unexpected token at try/catch and unhandled exception:java.io.FileNotFound String fileName = "C:\\GS.xlsx"; try{ CSVReader reader = new CSVReader(new FileReader(fileName)); }catch(Exception e){ } What is the possible issue in here, i know there is something really goofy that am doing in here... public class PositionParserGS { String fileName = "C:\\GS.xlsx"; try{ CSVReader reader = new CSVReader(new FileReader(fileName)); }catch(Exception e){ } } that's the complete code...

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• How to find out on which internet addresses a java program can listen.

  - by tzador

  My program needs to listen incoming socket connections (lets agree on port 8765), but it doesn't know which addresses it can bind on a particular machine. Of, course, it could simply to listen to all of them, but it need to send to the client program over a different(slower) channel the addresses which it should try in order to rich me on port 8765. So the flow is like this: My program lisens on all available interfaces on port 8765 Finds out a list of inet4 adresses by which it can be possibly reached (this step is the actual question) Posts that address on a whiteboard (blogpost or something) Interested clients try out all of them, to see using which one they can reach my program. This is all is to be done in java ofcourse :)

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• How do I get a MessageBox like information window to appear in Java?

  - by John McClane

  I'm learning Java and I have no idea how to do this. I dragged a button on the form in Netbeans, double clicked it and it created this event: @Action public void HelloClickMethod() { JOptionPane.showMessageDialog(this, "The message!", "This is supposed to be the MessageBox title."); } This is the exception the IDE brings up. Cannot find symbol. Symbol: showMessageDialog() Edit 1 Now I changed it to this: @Action public void HelloClickMethod() { JOptionPane.showMessageDialog(this, "The message!", "This is supposed to be the MessageBox title.",JOptionPane.ERROR_MESSAGE); } However the IDE is saying I have an error in the word 'this'. "Cannot find symbol". I don't understand. Why is it so dificult and why are the errors so esoteric. :P

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• Why is super.super.method(); not allowed in Java?

  - by Tim Büthe

  I read this question and thought that would easily be solved (not that it isn't solvable without) if one could write: @Override public String toString() { return super.super.toString(); } I'm not sure if it is useful in many cases, but I wonder why it isn't and if something like this exists in other languages. What do you guys think? EDIT: To clarify: yes I know, that's impossible to at to Java and I don't really miss it. This is nothing I expected to work and was surprised getting a compiler error. I just had the idea and like to discuss it.

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• How to open the command prompt and insert commands using Java?

  - by 404 Not Found

  There have been a few other questions on here sort of like this, but none seem to have any answers. Is it possible to open the command prompt (and I guess any other terminal for other systems), and execute commands in the newly opened window? Currently what I have is this: Runtime rt = Runtime.getRuntime(); rt.exec(new String[]{"cmd.exe","/c","start"}); I've tried adding the next command after the "start", I've tried running another rt.exec containing my command, but I can't find a way to make it work. If it matters, I'm trying to run a command similar to this: java -flag -flag -cp terminal-based-program.jar

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• Would it be useful to change java to support both static and dynamic types?

  - by James A. N. Stauffer

  What if a Java allow both static and dynamic types. That might allow the best of both worlds. i.e.: String str = "Hello"; var temp = str; temp = 10; temp = temp * 5; Would that be possible? Would that be beneficial? Do any languages currently support both and how well does it work out? Here is a better example (generics can't be used but the program does know the type): var username = HttpServletRequest.getSession().getAttribute("username");//Returns a String if(username.length() == 0) { //Error }

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• Does declaring many identical anonymous classes waste memory in java?

  - by depsypher

  I recently ran across the following snippet in an existing codebase I'm working on and added the comment you see there. I know this particular piece of code can be rewritten to be cleaner, but I just wonder if my analysis is correct. Will java create a new class declaration and store it in perm gen space for every call of this method, or will it know to reuse an existing declaration? protected List<Object> extractParams(HibernateObjectColumn column, String stringVal) { // FIXME: could be creating a *lot* of anonymous classes which wastes perm-gen space right? return new ArrayList<Object>() { { add(""); } }; }

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• How do i setup Login module in my web application? in Java?

  - by Nitesh Panchal

  Hello, I am making web application in java. My username and passwords as well as roles are stored in database. I could use jdbcRealm, but it forces me to use a specific structure which i dont have in my project. So, how do i do it? I am using Glassfish v3.0 with Netbeans 6.8. I read few tutorials about custom LoginModule but i am not getting anything out of it. How do you all people do it practically in your projects? If you can show me code of custom LoginModule then also it will do. Waiting for replies.

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• Java Interfaces Methodology: Should every class implement an interface?

  - by Amir Rachum

  I've been programming in Java for a few courses in the University and I have the following question: Is it methodologically accepted that every class should implement an interface? Is it considered bad practice not to do so? Can you describe a situation where it's not a good idea to use interfaces? Edit: Personally, I like the notion of using Interfaces for everything as a methodology and habit, even if it's not clearly beneficial. Eclipse automatically created a class file with all the methods, so it doesn't waste any time anyway.

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• Is there an equivalent to C++'s "friend class" in Java?

  - by Ricket

  In C++ there is a concept of a "friend", which has access to a class's private variables and functions. So if you have: class Foo { friend class Bar; private: int x; } then any instance of the class Bar can modify any Foo instance's x member, despite it being private, because Bar is a friend of Foo. Now I have a situation in Java where this functionality would come in handy. There are three classes: Database, Modifier, Viewer. The Database is just a collection of variables (like a struct). Modifier should be "friends" with Database; that is, it should be able to read and write its variables directly. But Viewer should only be able to read Database's variables. How is this best implemented? Is there a good way to enforce Viewer's read-only access of Database?

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• How can I Submit client side answers (to a question) to the server using JAVA?

  - by mdrafi

  How can I Submit client side computer user's answers(to a multiple choice question) to the server using JAVA I have a centralized server and about 1000 client systems. In these 1000 systems students take multiple choice quiz at at time (in some 2 hrs time). Now i've to send all these answers of these questions to the server in an asynchronous threaded queue when the student answer each question (all 1000 students) Also client have to wait if the server connection is a failure, in this case students should be able to continue taking quiz/exam. When I get the connection these answers in queue should be submitted to the server system. How can I solve this problem? Please suggest/help me in this.

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• What in-client caching options work well with Cassandra and Java?

  - by sanity

  I'm currently architecting a system that must be capable of dealing with tens of thousands of writes per second. I am more-or-less settled on using Apache Cassandra for the persistence layer, and will be using Java for the application layer, but there are situations where I need to quickly access data in a way that picks up any changes within seconds. Hitting Cassandra every single time I need to check this data for changes will be too slow, which means I need to use some kind of application layer caching. To ensure that the cached data remains current, ideally it would support some kind of multicast-based cache invalidation. What are my options?

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• Is the development stack of java/spring/hibernate/eclipse/tomcat/mysql riddled with config hacking?

  - by Blankman

  From a M$ development perspective, using things like vs.net/c#/asp.net/asp.net mvc/sql server, things are pretty much smooth. (Obviously for someone coming from a microsoft background like me). Now I love the idea of open source, linux and terminal servering into the computer and doing things via the command line, no license issues really, etc. I've tried firing up eclipse etc., but I always seem to get stuck on some configuration issue or another. Does it get easier or is it just the territory when you are dealing with the java stack?

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• Is it possible to pass arithmetic operators to a method in java?

  - by drJames

  Right now I'm going to have to write a method that looks like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { if (Operator.equals("+")) { return String.valueOf(Operand1 + Operand2); } else if (Operator.equals("-")) { return String.valueOf(Operand1 - Operand2); } else if (Operator.equals("*")) { return String.valueOf(Operand1 * Operand2); } else { return "error..."; } } It would be nice if I could write the code more like this: public String Calculate(String Operator, Double Operand1, Double Operand2) { return String.valueOf(Operand1 Operator Operand2); } So Operator would replace the Arithmetic Operators (+, -, *, /...) Does anyone know if something like this is possible in java?

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• Online compilers/runtime for Java, C++, Python and ObjC?

  - by Nocturne

  Does anyone know of a good online compiler/runtime (for C++, Java, Python, ObjC etc.) that I can access on the web? What I'm looking for is something that would allow me to type in a program in a web form and to run the program and see the results online. (Let's not get into the why for now. Suffice it to say for the moment that I don't always have access to a compiler/runtime, and firing up an IDE is just overkill for testing out some code snippets) I know of codepad.org -- but I'm looking for something better.

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• Java: How do I get the IP of the local interface that can reach a remote IP?

  - by Per Fagrell

  I have a Java application that registers a server component in a service provider, and then sends the service name to a client. The client uses the service name to get an address out of the service provider to the server. However, the server has several interfaces only 1 of which the client get get at, so the service must be registered with the right IP. We discovered the client through a broadcast, so I have the client IP and an Enumeration of the computers network interfaces. How do I match the IP to an interface, not knowing what the netmask of the client IP is? Spontaneously I imagine turning all the addresses to ints and chomping the local ips with their netmask and looking for a 'best match', but I wonder if there is a better way? (this is an enterprise(tm) solution, so cutting out the service provider isn't an option, at least not w/o a political campaign first ;) )

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• Java how does Key Event Handling Mechanism(KeyListeners notified) work ?

  - by Carbonizer

  How does application/JVM know which classes if implemented key handling interfaces ? Does it use java Reflections or does it check all the classes for methods ? How can a application or executing JVM understanding to deliver the user event or call the specific methods on a class that implemented the keylistener interface. Does it look at all the classes if those methods are implemented or how does it know which classes implmented keylistener interface ? If you dont implement the keylistener Interface for a class but still implmentation all its methods. Do the class still process the user event occurred ?

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• Java sockets: can I write a TCP server with one thread?

  - by hmp

  From what I read about Java NIO and non-blocking [Server]SocketChannels, it should be possible to write a TCP server that sustains several connections using only one thread - I'd make a Selector that waits for all relevant channels in the server's loop. Is that right, or am I missing some important detail? What problems can I encounter? (Background: The TCP communication would be for a small multiplayer game, so max. 10-20 simultaneous connections. Messages will be sent about every few seconds.)

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• Create a graph image (png, jpg ..) from an XML file with Java

  - by alibm

  Hello, I have an XML file and I want to create a graph with some entities, then store this graph in an image, JPG or PNG. So is there a library in Java do like this?? Or is there some tricks by parsing XML files and ... ??? Here an example XML file: <?xml version="1.0"?> <process> <p n=1>Tove</p> <p n=2>Jani</p> <p n=2>Bill</p> <p n=4>John</p> </process> And the output will be like this. http://i.imgur.com [slash] YevGX.png Please change [slash] by / to see the image. Thanks in advance. Best Regards, AliBM

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• What web application is recommended when programming in Java for beginners?

  - by user1710260

  I am a beginner (almost no knowledge) to web applications. I have been programming in Java for about a year now. I have being doing some research on the different frameworks that are available and I want to find which one is right for me. From what I found: Play, Stripes, and Spring are good choices for beginners, but how can I compare these frameworks together. What is it that I need to look for when comparing them? My project that I am starting to work on is similar to an App Store. Basically an info site on different apps. Any advise will be appreciated.

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• How to enforce DB field size limit to related Java String?

  - by Sri Sankaran

  What is the correct way to defend against trying to store more text than can be accommodated in a VARCHAR2 database field? Say the PARTNER_ROLE field of the REGISTRATIONS table is declared as VARCHAR2(80). This field is mapped in the Registration class in Java as public class Registration { @Column(name=”PARTNER_ROLE” length=”80”) private String partnerRole; } However, the setPartnerRole() method allows the user to stuff a string of any length. The problem is encountered only when one subsequently tries to insert or update the REGISTRATIONS record. Oracle complains. What is the correct way to handle this situation?

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• Does invoking System.gc() in java suggest garbage collection of the tenured generation as well as th

  - by Markus Jevring

  When invoking System.gc() in java (via JMX), it will dutifully (attempt to) clean the young generation. This generally works very well. I have never seen it attempt to clean the tenured generation, though. This leads me to two questions: Can the tenured generation even be collected (i.e. is there actually garbage in this generation, or do all objects in the tenured generation actually still have live references to them)? If the tenured generation can be collected, can this be done via System.gc(), or is there another way to do it (unlikely), or will I simply have to wait until I run out of space in the tenured generation?

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