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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 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• 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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• [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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• Extracting methods body from a class of Java Source Code

  - by Muhammad Asaduzzaman

  Hi, I want to extract method body from a Java Source Code. Suppose I have the following code: public class A{ public void print(){ System.out.println("Print This thing"); System.out.println("Print This thing"); System.out.println("Print This thing"); } } My objective is not to extract the method name (in this case print) but also the bode of the method(In this case the three print statement inside the print method). Can anyone suggest how can I do so? Is their any library available for doing so.

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• How does array class work in Java?

  - by oks16

  In Java, array is a class and extends Object. I am curious to know about this special array class. I don't find the class definition anywhere. Doing a getClass().getName() gives strange result. String[] array = new String[]{"one","two"}; System.out.println(array.getClass().getName()); // prints [Ljava.lang.String; I want to understand how array works under the hood. Is the array class definition hardcoded in the JVM? Any resources, books, links on this will be helpful. Thank you.

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• generating function arguments in java

  - by aloishis89

  I'm very new to java and am working on my first Android app. I am using the webview demo as a template. I am trying to generate a random integer between 1 and 12 and then call a certain javascript function based on the result. Here's what I have: int number = 1 + (int)(Math.random() * ((12 - 1) + 1)); number = (int) Math.floor(number); String nextQuote = "javascript:wave" + number + "()"; mWebView.loadUrl(nextQuote); So mWebView.loadUrl(nextQuote) will be the same as something like mWebView.loadUrl("javascript:wave1()") I just want to know if what I have here is correct and will work the way I think it will. The application isn't responding as expected and I suspect this bit of code is the culprit.

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• Forcibly clear memory in java

  - by MBennett

  I am writing an application in java that I care about being secure. After encrypting a byte array, I want to forcibly remove from memory anything potentially dangerous such as the key used. In the following snippet key is a byte[], as is data. SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES"); Cipher cipher = Cipher.getInstance("AES"); cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec); byte[] encData = cipher.doFinal(data, 0, data.length); Arrays.fill(key, (byte)0); As far as I understand, the last line above overwrites the key with 0s so that it no longer contains any dangerous data, but I can't find a way to overwrite or evict secretKeySpec or cipher similarly. Is there any way to forcibly overwrite the memory held by secretKeySpec and cipher, so that if someone were to be able to view the current memory state (say, via a cold boot attack), they would not get access to this information?

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• Sort Java List/Map by order in which items are in an XML File

  - by Brandon Smith

  Hello everyone, What I'm looking to do is to sorta a Java List or Map in the order the items are in a XML File. For Example I have a list of function names as so: functionOne functionThree functionTwo The XML File looks like this: <xml> <function>functionOne</function> <function>functionTwo</function> <function>functionThree</function> </xml> So I would like to sort the list so the function names are as so: functionOne functionTwo functionThree Now Im trying to do this for Variables as well, so there are around 500+ unique 'items'. Does anyone have any idea how I can go about doing this? Now for the file that determines that sort order doesn't have to be XML it just what I use the most, it can be anything that can get the job done. Thanks in advance for your time.

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