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• Java Swing architecture for flipping through JPane based views

  - by imhotep

  Hi all, I have done a couple of simple swing based apps with static layout, but now I've run into a problem while trying to create an app containing multiple views which are changed by pressing appropriate navigational button. You could compare the idea to a website so that every view has buttons to access certain other views but this would work inside a single JFrame. I've found that maybe CardLayout (Cardlayout example) might be appropriate solution for this kind of structure, but I'm unable to figure out a way to switch the views from the buttons which are inside of the JPanes that I've implemented in their separate classes, Of course one way would be to instantiate everything in the parent class like in the small java tutorial example, but this isn't quite clean nor modular for multiple views, isn't it. How can this be implemented so that I can access the view switching method?

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• java reflection

  - by user622222

  Hi all, System.out.println("Class name : "); BufferedReader reader= new BufferedReader(new InputStreamReader(System.in)); String line = reader.readLine(); Class<?> writeoutClass = Class.forName(line); Method Writeout = null; for (Method mth : writeoutClass.getDeclaredMethods()) { if (mth.getName().startsWith("Writeout")) { Writeout = mth; break; } It's giving error like that; java.lang.ClassNotFoundException: a How can i generate that class?

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• Java Passing variables around classes

  - by nazerb

  I am new to java and am trying to pass variables like in the following example from one class to another, im wondering is this possible and how i would go about it if it is. As this code does not work as it is not static. Main Class public class testAll { public static void main(String[] args) { One one = new One(); Two two = new Two(); } } The first class: public class One { public int test = 4; public int getTest() { return this.test; } } The second class: public class Two { public void value() { System.out.print("Var is: " + One.getTest()); } } Thanks, Naz

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• Java Swing - Problem in JSpinner

  - by Yatendra Goel

  I am developing a Java Desktop Application and designing the GUI with the help of Netbeans Swing GUI builder. I want to use a JSpinner in my app. I have dragged and dropped it to a JPanel. Now, I want to set its two properties: First, It should display numbers in the range of 1 to 50. Neither less than 1 nor greater than 50. How can I set that range? Second, when I try to get the value of it by spinner.getValue() it returns an Object. As my spinner's data type is Integer, would it be better to downcast the Object into Integer or Is there any other way to get that numeric value?

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• Clean way in GWT/Java to wait for multiple asynchronous events to finish

  - by gerdemb

  What is the best way to wait for multiple asynchronous callback functions to finish in Java before continuing. Specifically I'm using GWT with AsyncCallback, but I think this is a generic problem. Here's what I have now, but surely there is cleaner way... AjaxLoader.loadApi("books", "0", new Runnable(){ public void run() { bookAPIAvailable = true; ready(); }}, null); AjaxLoader.loadApi("search", "1", new Runnable(){ public void run() { searchAPIAvailable = true; ready(); }}, null); loginService.login(GWT.getHostPageBaseURL(), new AsyncCallback<LoginInfo>() { public void onSuccess(LoginInfo result) { appLoaded = true; ready(); } }); private void ready() { if(bookAPIAvailable && searchAPIAvailable && appLoaded) { // Everything loaded } }

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• Sqlite + Java: table not updating

  - by Ben L

  I'm using a Java wrapper for SQLite called SQLiteJDBC - this may have some bearing on any answers... I have a table which I've displayed in a GUI, within that UI I have a button for the fields for an individual row of that table. When I save my changes I do this... Statement stmt = connection.createStatement(); stmt.execute("update 'tableName' set 'fieldName'=1 where userid=1"); int updateCount = stmt.getUpdateCount(); My connection is valid, I get no exceptions thrown and getUpdateCount() returns '1' indicating that one row has been updated. However my table is not updated. I've spent the last few hours trying to work out what's going on but I'm not having any luck. Help!!

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• Count in base 2, 3, 4 etc in Java and output all permutations

  - by tree-hacker

  I want to write a function in Java that takes as input an integer and outputs every possible permutation of numbers up to that integer. For example: f(1) 0 f(2) should output: 00 01 10 11 f(3) should output: 000 001 002 010 011 012 020 021 022 100 .... 220 221 222 That is it should output all 27 permutations of the digits of the numbers 0, 1, 2. f(4) should output 0000 0001 0002 0003 0010 ... 3330 3331 3332 3333 f(4) should output 00000 00001 ... 44443 44444 I have been trying to solve this problem but cannot seem to work out how to do it and keep getting confused by how many loops I need. Does anyone know how to solve this problem? Thanks in advance.

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• Java reduce CPU usage

  - by steve

  Greets- We gots a few nutters in work who enjoy using while(true) { //Code } in their code. As you can imagine this maxes out the CPU. Does anyone know ways to reduce the CPU utilization so that other people can use the server as well. The code itself is just constantly polling the internet for updates on sites. Therefore I'd imagine a little sleep method would greatly reduce the the CPU usage. Also all manipulation is being done in String objects (Java) anyone know how much StringBuilders would reduce the over head by? Thanks for any pointers

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• Java: Extend SimpleDateFormat with new pattern letters

  - by Adam Matan

  Java's SimpleDateFormat is used to format a Date object to a string. The formatter supports various pattern letters, which denote textual representation of a Date field. For example, yy is two-letter year, yyyy is four-letter year, and E is day of week. For example, A SimpleDateFormat initialized with yyyy.MM.dd G 'at' HH:mm:ss z will format a date to something like 2001.07.04 AD at 12:08:56 PDT. I would like to add some pattern letters to SimpleDateFormat. For example, want C to denote Hebrew weekday (??? ?????, ??? ???, ...). What's the right way to extend SimpleDateFormat with these new pattern letters? The only online example I could find seems somewhat complicated. I can live with formatting only, without parsing.

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• How to rate a connect four game situation in java

  - by MrPink

  Hey, I am trying to write a simple AI for a "Get four" game. The basic game principles are done, so I can throw in coins of different color, and they stack on each other and fill a 2D Array and so on and so forth. until now this is what the method looks like: public int insert(int x, int color) //0 = empty, 1=player1 2=player2" X is the horizontal coordinate, as the y coordinate is determined by how many stones are in the array already, I think the idea is obvious. Now the problem is I have to rate specific game situations, so find how many new pairs, triplets and possible 4 in a row I can get in a specific situation to then give each situation a specific value. With these values I can setup a "Game tree" to then decide which move would be best next (later on implementing Alpha-Beta-Pruning). My current problem is that I can't think of an efficient way to implement a rating of the current game situation in a java method. Any ideas would be greatly appreciated! greetings from Germany Mr. Pink

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• Create instance of generic type in Java?

  - by David Citron

  Is it possible to create an instance of a generic type in Java? I'm thinking based on what I've seen that the answer is "no" (due to type erasure), but I'd be interested if anyone can see something I'm missing: class SomeContainer<E> { E createContents() { return what??? } } EDIT: It turns out that Super Type Tokens could be used to resolve my issue, but it requires a lot of reflection-based code, as some of the answers below have indicated. I'll leave this open for a little while to see if anyone comes up with anything dramatically different than Ian Robertson's Artima Article.

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• Copying files from one directory to another in Java

  - by user42155

  Hello, I want to copy files from one directory to another (subdirectory) using Java. I have a directory, dir, with text files. I iterate over the first 20 files in dir, and want to copy them to another directory in the dir directory, which I have created right before the iteration. In the code, I want to copy the review (which represents the ith text file or review) to trainingDir. How can I do this? There seems not to be such a function (or I couldn't find). Thank you. boolean success = false; File[] reviews = dir.listFiles(); String trainingDir = dir.getAbsolutePath() + "/trainingData"; File trDir = new File(trainingDir); success = trDir.mkdir(); for(int i = 1; i <= 20; i++) { File review = reviews[i]; }

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• Can I add and remove elements of enumeration at runtime in Java

  - by Brabster

  It is possible to add and remove elements from an enum in Java at runtime? For example, could I read in the labels and constructor arguments of an enum from a file? @saua, it's just a question of whether it can be done out of interest really. I was hoping there'd be some neat way of altering the running bytecode, maybe using BCEL or something. I've also followed up with this question because I realised I wasn't totally sure when an enum should be used. I'm pretty convinced that the right answer would be to use a collection that ensured uniqueness instead of an enum if I want to be able to alter the contents safely at runtime.

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• Full stack framework for Java

  - by Jonathan Barbero

  Hello everyone, I'm looking for a full stack framework (from persistency to view generation (CRUD)) for Java. I don't have experience with Rails style frameworks, like Grails, but I worked a lot with Hibernate, Struts, Spring ... I prefer a framework that let you naturally modify the business domain design with the less effort ( i.e. writing the sql querys to modify the tables and constrains, change the view pages, etc ... ). I was looking a bit about this topic, I saw Naked Objects for example but its development has stopped. So, I want to hear about your experience. Thanks in advance.

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• Minimizing Java Thread Context Switching Overhead

  - by binil

  I have a Java application running on Sun 1.6 32-bit VM/Solaris 10 (x86)/Nahelem 8-core(2 threads per core). A specific usecase in the application is to respond to some external message. In my performance test environment, when I prepare and send the response in the same thread that receives the external input, I get about 50 us advantage than when I hand off the message to a separate thread to send the response. I use a ThreadPoolExecutor with a SynchronousQueue to do the handoff. In your experience what is the acceptable delay between scheduling a task to a thread pool and it getting picked up for execution? What ideas had worked for you in the past to try improve this?

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• Network programming on java

  - by maks

  I have written a simple network program on java using sockets. Program has a client and a server. When user types a word on client side, server simply return this word to client. On server side I use Serversocket and bind it to port 4444. Why does not firewall block this connection on my server PC? I ask this question because earlier I wrote this program using corba technology, and firewall on my server PC was blocking the connection to this port; when I disabled the firewall the program worked fine.

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• Selectively parsing log files using Java

  - by GPX

  I have to parse a big bunch of log files, which are in the following format. SOME SQL STATEMENT/QUERY DB20000I The SQL command completed successfully. SOME OTHER SQL STATEMENT/QUERY DB21034E The command was processed as an SQL statement because it was not a valid Command Line Processor command. EDIT 1: The first 3 lines (including a blank line) indicate an SQL statement executed successfully, while the next three show the statement and the exception it caused. darioo's reply below, suggesting the use of grep instead of Java, works beautifully for a single line SQL statement. EDIT 2: However, the SQL statement/query might not be a single line, necessarily. Sometimes it is a big CREATE PROCEDURE...END PROCEDURE block. Can this problem be overcome using only Unix commands too? Now I need to parse through the entire log file and pick all occurrences of the pair of (SQL statement + error) and write them in a separate file. Please show me how to do this!

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• when to use StringBuilder in java

  - by kostja

  It is supposed to be generally preferable to use a StringBuilder for String concatenation in Java. Is it always the case? What i mean is : Is the overhead of creating a StringBuilder object, calling the append() method and finally toString() smaller then concatenating existing Strings with + for 2 Strings already or is it only advisable for more Strings? If there is such a threshold, what does it depend on (the String length i suppose, but in which way)? And finally - would you trade the readability and conciseness of the + concatenation for the performance of the StringBuilder in smaller cases like 2, 3, 4 Strings?

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• How to stop Interruptible Threads in Java

  - by Dr.Lesh

  I have a Java application that I CAN'T EDIT that starts a Thread wich has this run method: public void run(){ while(true){ System.out.println("Something"); } } And at a certain moment I wanna stop it, but if I use thread.interrupt(); it won't work. If I use thread.stop(); it works, but this method is deprecated and its use is discouraged because soon it will be removed from JVM. Does anyone knows how to do it? Thank you.

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• Java: how to represent graphs?

  - by Rosarch

  I'm implementing some algorithms to teach myself about graphs and how to work with them. What would you recommend is the best way to do that in Java? I was thinking something like this: public class Vertex { private ArrayList<Vertex> outnodes; //Adjacency list. if I wanted to support edge weight, this would be a hash map. //methods to manipulate outnodes } public class Graph { private ArrayList<Vertex> nodes; //algorithms on graphs } But I basically just made this up. Is there a better way? Also, I want it to be able to support variations on vanilla graphs like digraphs, weighted edges, multigraphs, etc.

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• Encoding problem in Java Server Side application.

  - by NikolayGS

  Hi! I have following problem - i`m running Java WS application. The server side (Axis2 WS Modules on Apache Tomcat) is running at Ubuntu server. The problem is when i get some information from client side in cyrilic and store in database it goes like "?????". If i add data in db directly(From Remote MYSQL Console - there is NO problem). Before move to ubuntu server side was at Windows XP and there was no problem? Sorry for bad explanation, but i have no idea where to start! Thanks in advance!

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• Fast way to pass a simple java object from one thread to another

  - by Adal

  I have a callback which receives an object. I make a copy of this object, and I must pass it on to another thread for further processing. It's very important for the callback to return as fast as possible. Ideally, the callback will write the copy to some sort of lock-free container. I only have the callback called from a single thread and one processing thread. I only need to pass a bunch of doubles to the other thread, and I know the maximum number of doubles (around 40). Any ideas? I'm not very familiar with Java, so I don't know the usual ways to pass stuff between threads.

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• Global Exception Handlers in Java

  - by Samuh

  I am thinking of setting up a global, default Exception handler for my (Android) Mobile application(which uses Java syntax) using Thread.setDefaultUncaughtExceptionHandler(...) call. I am thinking of just displaying an Alert Dialog with appropriate message to the user. Are there any gotchas, caveats and rules that one needs to follow when setting DefaultExceptionHandlers? Any best practices like making sure that the process is killed, full stack trace is written to logs etc. ? Links to documentation, tutorials etc. that can throw some light on this are welcome. Thanks.

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• while loop / string input not working java

  - by Mikeecb

  I have looked online and all of the tutorials / questions have pointed me to this. I can't see why this isn't working. Any help would be much appreciated. Thanks import java.util.*; public class test { static Scanner userInput = new Scanner(System.in); public static void main(String[] args) { String textEntered = userInput.next(); if (textEntered == "hello") { System.out.println("Hello to you too!"); } } } I enter "hello" but nothing is printed. Also I have tried next() and nextLine();

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• [java] how to parse XML document?

  - by user32167

  I have xml document in variable (not in file). How can i get data storaged in that? I don't have any additional file with that, i have it 'inside' my sourcecode. When i use DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); Document doc = db.parse(XML); (XML is my xml variable), i get an error java.io.FileNotFoundException: C:\netbeans\app-s7013\<network ip_addr="10.0.0.0\8" save_ip="true"> File not found.

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