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• Math operation in Java

  - by joroj

  Hello, what "^" operator does? when I try this: int a = 5^n; it gives me: for n = 5, returns 0 for n = 4, returns 1 for n = 6, returns 3 What is this?

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• java tracing spaghetti code

  - by Amarsh

  Folks, I have just joined this company which has a huge source tree based upon JSP/Servlet and EJB 1.2. No documentation exists. The code has been written over seven years, with a large number of undocumented changes. Are there any tool tah can assist me in tracing the execution? Putting a breakpoint is not helping me much.

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• Java Matcher groups: Understanding The difference between "(?:X|Y)" and "(?:X)|(?:Y)"

  - by user358795

  Can anyone explain: Why the two patterns used below give different results? (answered below) Why the 2nd example gives a group count of 1 but says the start and end of group 1 is -1? public void testGroups() throws Exception { String TEST_STRING = "After Yes is group 1 End"; { Pattern p; Matcher m; String pattern="(?:Yes|No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } { Pattern p; Matcher m; String pattern="(?:Yes)|(?:No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } } Which gives the following output: Pattern=(?:Yes|No)(.*)End Found=true Group count=1 Start of group 1=9 End of group 1=21 Pattern=(?:Yes)|(?:No)(.*)End Found=true Group count=1 Start of group 1=-1 End of group 1=-1

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• Which Queue implementation to use in Java?

  - by devoured elysium

  I need to use a FIFO structure in my application. It needs to have at most 5 elements. I'd like to have something easy to use (I don't care for concurrency) that implements the Collection interface. I've tried the LinkedList, that seems to come from Queue, but it doesn't seem to allow me to set it's maximum capacity. It feels as if I just want at max 5 elements but try to add 20, it will just keep increasing in size to fit it. I'd like something that'd work the following way: XQueue<Integer> queue = new XQueue<Integer>(5); //where 5 is the maximum number of elements I want in my queue. for (int i = 0; i < 10; ++i) { queue.offer(i); } for (int i = 0; i < 5; ++i) { System.out.println(queue.poll()); } That'd print: 5 6 7 8 9 Thanks

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• RSA implementations for Java, alternative to BC

  - by Tom Brito

  The RSA implementation that ships with Bouncy Castle only allows the encrypting of a single block of data. The RSA algorithm is not suited to streaming data and should not be used that way. In a situation like this you should encrypt the data using a randomly generated key and a symmetric cipher, after that you should encrypt the randomly generated key using RSA, and then send the encrypted data and the encrypted random key to the other end where they can reverse the process (ie. decrypt the random key using their RSA private key and then decrypt the data). I can't use the workarond of using symmetric key. So, are there other implementations of RSA than Bouncy Castle?

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• Date conversion in Java

  - by llm

  How can I take a string in a format such as: 2008-06-02 00:00:00.0 and convert it to: 02-Jun-2008? Can I somehow take the original string, convert it to a Date object, then use a formatter to get the final output (rather than parsing the string myself)? Thanks!

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• Java Interfaces/Implementation naming convention

  - by Amir Rachum

  How do you name different classes / interfaces you create? Sometimes I don't have implementation information to add to the implementation name - like interface FileHandler and class SqlFileHandler. hen this happens I usually name the interface in the "normal" name, like Truck and name the actual class TruckClass. How do you name interfaces and classes in this regard?

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• Java Hibernate id auto increment

  - by vinise

  Hy I'v a little problem with hibernate on netbeans. I've a table with an Auto increment id : CREATE TABLE "DVD" ( "DVD_ID" INT not null primary key GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1), "TITLE" VARCHAR(150), "COM" LONG VARCHAR, "COVER" VARCHAR(150) ); But this auto increment is not properly detected with Reverse Engineering. I get a map file with this : <id name="dvdId" type="int"> <column name="DVD_ID" /> <generator class="assigned" /> </id> i've looked on google and on this site ... foud some stuf but i'm still stuck.. i've tried to add insert="false" update="false" on the map file but i get back : Caused by: org.xml.sax.SAXParseException: Attribute "insert" must be declared for element type "id". Anny help will be pleased Vincent

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• What is the best blog for Java development?

  - by John Channing

  Please reply with just one blog per answer to allow the voting system to bring the best/most popular to the top.

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• Java: Ignoring escapes when parsing XML

  - by Personman

  I'm using a DocumentBuilder to parse XML files. However, the specification for the project requires that within text nodes, strings like " and < be returned literally, and not turned into the corresponding ASCII values. A previous similar question, http://stackoverflow.com/questions/1979785/read-escaped-quote-as-escaped-quote-from-xml, received one answer that seems to be specific to Apache, and another that appears to simply not not do what it says it does. I'd love to be proven wrong on either count, however :) For reference, here is some code: file = new File(fileName); DocBderFac = DocumentBuilderFactory.newInstance(); DocBder = DocBderFac.newDocumentBuilder(); doc = DocBder.parse(file); NodeList textElmntLst = doc.getElementsByTagName(text); Element textElmnt = (Element) textElmntLst.item(0); NodeList txts = textElmnt.getChildNodes(); String txt = ((Node) txts.item(0)).getNodeValue(); System.out.println(txt); I would like that println() to produce things like &quot;3&gt;2&quot; instead of "3>2" which is what currently happens. Thanks!

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• Java - PriorityQueue vs sorted LinkedList

  - by msr

  Hello, Which implementation is less "heavy": PriorityQueue or a sorted LinkedList (using a Comparator)? I want to have all the items sorted. The insertion will be very frequent and ocasionally I will have to run all the list to make some operations. Thank you!

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• Java Data Structure

  - by Joe

  Hi there, I'm looking for a data structure that will act like a Queue so that I can hava First In First Out behaviour, but ideally I would also be able to see if an element exists in that Queue in constant time as you can do with a HashMap, rather than the linear time that you get with a LinkedList. I thought a LinkedHashMap might do the job, but although I could make an iterator and just take and then remove the first element of the iteration to produce a sort of poll() method, I'm wondering if there is a better way. Many thanks in advance

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• program for calculating metrics in java

  - by senzacionale

  i need to calculate few metrics (CBO, NOC, DAC, LCOM, WMC, RFC and DIT metric). Program is written in jdeveloper and i do not know how to calculate this metrics. Migration to eclipse is not possible becouse code is not compiled. Does anyone know any good program for calculating metrics?

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• Java threads not working correctly with linkedlist

  - by user69514

  Hi I am working on the sleeping barber problem. with the addition of having priority customer when they arrive they go in the front of the line and they are the next ones to get a haircut. I'm using a linkedlist and if I see a priority customer I put him in the beginning of the list, if the customer is not priority he goes to the end of the list. then I call the wantHaircut method getting the first element of the list. my problem is that the customer are being processed in the order they arrive, and the priority customer have to wait. here is the code where it all happens. any ideas what I am doing wrong? thanks public void arrivedBarbershop(Customer c){ if(waiting < numChairs && c.isPriority()){ System.out.println("Customer " + c.getID() + ": is a priority customer - SITTING -"); mutex.up(); customer_list.addFirst(c); } else if(waiting >= numChairs && c.isPriority()){ System.out.println("Customer " + c.getID() + ": is a priority customer - STANDING -"); mutex.up(); customer_list.addFirst(c); } else if(waiting < numChairs && !c.isPriority()){ waiting++; System.out.println("Customer " + c.getID() + ": arrived, sitting in the waiting room"); customer_list.addLast(c); customers.up(); // increment waiting customers } else if(waiting >= numChairs && !c.isPriority()) { System.out.println("Customer " + c.getID() + ": went to another barber because waiting room was full - " + waiting + " waiting"); mutex.up(); } if(!customer_list.isEmpty()){ this.wantHairCut(customer_list.removeFirst()); } } public void wantHairCut(Customer c) { mutex.up(); barber.down(); // waits for being allowed in barber chair System.out.println("Customer " + c.getID() + ": getting haircut"); try { /** haircut takes between 1 and 2 seconds **/ Thread.sleep(Barbershop.randomInt(1, 2) * 1000); } catch (InterruptedException e) { } System.out.println("Barber: finished cutting customer " + c.getID() + "'s hair"); c.gotHaircut = true; cutting.up(); // signals cutting has finished /** customer must pay now **/ this.wantToCashout(c); }

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• Java: Embedding Soundbank file in JAR

  - by Pyroclastic

  If I have a soundbank stored in a JAR, how would I load that soundbank into my application using resource loading...? I'm trying to consolidate as much of a MIDI program into the jar file as I can, and the last thing I have to add is the soundbank file I'm using, as users won't have the soundbanks installed. I'm trying to put it into my jar file, and then load it with getResource() in the Class class, but I'm getting an InvalidMidiDataException on a soundbank that I know is valid. Here's the code, it's in the constructor for my synthesizer object: try { synth = MidiSystem.getSynthesizer(); channels = synth.getChannels(); instrument = MidiSystem.getSoundbank(this.getClass().getResource("img/soundbank-mid.gm")).getInstruments(); currentInstrument = instrument[0]; synth.loadInstrument(currentInstrument); synth.open(); } catch (InvalidMidiDataException ex) { System.out.println("FAIL"); instrument = synth.getAvailableInstruments(); currentInstrument = instrument[0]; synth.loadInstrument(currentInstrument); try { synth.open(); } catch (MidiUnavailableException ex1) { Logger.getLogger(MIDISynth.class.getName()).log(Level.SEVERE, null, ex1); } } catch (IOException ex) { Logger.getLogger(MIDISynth.class.getName()).log(Level.SEVERE, null, ex); } catch (MidiUnavailableException ex) { Logger.getLogger(MIDISynth.class.getName()).log(Level.SEVERE, null, ex); }

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• Date Comparison using Java

  - by Lakshman

  I have two dates: toDate (user input in MM/dd/yyyy format) currentDate (obtained by new Date()) I need to compare the currentDate with toDate. I have to display a report only when the toDate is equal to or more than currentDate. How can I do that?

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• replace values in a String from a Hashtable in Java

  - by Adnan

  My string looks like; String values = "I am from UK, and you are from FR"; and my hashtable; Hashtable countries = new Hashtable(); countries.put("United Kingdom", new String("UK")); countries.put("France", new String("FR")); What would be the most effective way to change the values in my string with the values from the hashtable accordingly. These are just 2 values to change, but in my case I will have 100+

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• Java ternary operator and boxing Integer/int?

  - by Markus

  I tripped across a really strange NullPointerException the other day caused by an unexpected type-cast in the ternary operator. Given this (useless exemplary) function: Integer getNumber() { return null; } I was expecting the following two code segments to be exactly identical after compilation: Integer number; if (condition) { number = getNumber(); } else { number = 0; } vs. Integer number = (condition) ? getNumber() : 0; . Turns out, if condition is true, the if-statement works fine, while the ternary opration in the second code segment throws a NullPointerException. It seems as though the ternary operation has decided to type-cast both choices to int before auto-boxing the result back into an Integer!?! In fact, if I explicitly cast the 0 to Integer, the exception goes away. In other words: Integer number = (condition) ? getNumber() : 0; is not the same as: Integer number = (condition) ? getNumber() : (Integer) 0; . So, it seems that there is a byte-code difference between the ternary operator and an equivalent if-else-statement (something I didn't expect). Which raises three questions: Why is there a difference? Is this a bug in the ternary implementation or is there a reason for the type cast? Given there is a difference, is the ternary operation more or less performant than an equivalent if-statement (I know, the difference can't be huge, but still)?

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• How does one implement a truly asynchronous java thread

  - by Ritesh M Nayak

  I have a function that needs to perfom two operations, one which finishes fast and one which takes a long time to run. I want to be able to delegate the long running operation to a thread and I dont care when the thread finishes, but the threads needs to complete. I implemented this as shown below , but, my secondoperation never gets done as the function exits after the start() call. How I can ensure that the function returns but the second operation thread finishes its execution as well and is not dependent on the parent thread ? public void someFunction(String data) { smallOperation() Blah a = new Blah(); Thread th = new Thread(a); th.Start(); } class SecondOperation implements Runnable { public void run(){ // doSomething long running } }

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• Java OS X - No app icon in dock

  - by Jacob

  I am using Jar Bundler to create a .app file out of my .jar file. When I launch the app, I do not want a dock icon to show at all. I have already tried modifying my .plist file to include: <string>NSUIElement</string> <key>1</key> But it does not work... Any help?

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• Getting specific values with regex [JAVA, ANDROID]

  - by David

  I need to knowingly isolate each row of the vcard and get its value. For instance, I want to get "5555" from X-CUSTOMFIELD. So far, my thoughts are: "X-CUSTOMFIELD;\d+" I have been looking at some tutorials and I am a little confused with what function to use? What would my regex above return? Would it give me the whole line or just the numerical part (5555)? I was thinking I i get the whole row, I can use substring to get the digits? BEGIN:VCARD VERSION:2.1 N:Last;First; FN:First Last TEL;HOME;VOICE:111111 TEL;MOBILE;VOICE:222222 X-CUSTOMFIELD;5555 END:VCARD

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• Java downcasting dilemma

  - by Shades88

  please have a look at this code here. class Vehicle { public void printSound() { System.out.print("vehicle"); } } class Car extends Vehicle { public void printSound() { System.out.print("car"); } } class Bike extends Vehicle{ public void printSound() { System.out.print("bike"); } } public class Test { public static void main(String[] args) { Vehicle v = new Car(); Bike b = (Bike)v; v.printSound(); b.printSound(); Object myObj = new String[]{"one", "two", "three"}; for (String s : (String[])myObj) System.out.print(s + "."); } } Executing this code will give ClassCastException saying inheritance.Car cannot be cast to inheritance.Bike. Now look at the line Object myObj = new String[]{"one", "two", "three"};. This line is same as Vehicle v = new Car(); right? In both lines we are assigning sub class object to super class reference variable. But downcasting String[]myObj is allowed but (Bike)v is not. Please help me understand what is going on around here.

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• Read / Write XML file from Java application bundle

  - by Peter

  Hi there! I've got an XML file that is parsed and written in my application. From within my IDE (Eclipse) I simply address it like this: Reading: private String xmlFile = "file.xml"; and then I build the document: doc = sax.build(xmlFile); Writing is done like this: writer = new FileWriter("file.xml"); Runs great so far, but after bundling my application, the file is no longer accessible. What exactly do I have to do to make it accessible from within an application bundle? I'm absolutely not familiar with the classpath or whatever I need for that, so please go easy on me! Thank you very much!

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• Java FileFilter

  - by Mr CooL

  public class DocFilter extends FileFilter { public boolean accept(File f) { if (f.isDirectory()) { return true; } String extension = Utils.getExtension(f); if (extension != null) { if (extension.equals(Utils.doc) || extension.equals(Utils.docx) ) { return true; } else { return false; } } return false; } //The description of this filter public String getDescription() { return "Just Document Files"; } } Netbeans compiler warned with the error, "No interface expected here" for above code Anyone has idea what was the problem?? I tried changing the 'extends' to 'implements', however, it didn't seem to work that way. and when I changed to implements, the following code cannot work, chooser.addChoosableFileFilter(new DocFilter()); and with this error, "method addChoosableFileFilter in class javax.swing.JFileChooser cannot be applied to given types required: javax.swing.filechooser.FileFilter" Can anyone help on this? Thanks..

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• Polling servers at the same port - Threads and Java

  - by John

  Hi there. I'm currently busy working on an IP ban tool for the early versions of Call of Duty 1. (Apparently such a feature wasn't implemented in these versions). I've finished a single threaded application but it won't perform well enough for multiple servers, which is why I am trying to implement threading. Right now, each server has its own thread. I have a Networking class, which has a method; "GetStatus" -- this method is synchronized. This method uses a DatagramSocket to communicate with the server. Since this method is static and synchronized, I shouldn't get in trouble and receive a whole bunch of "Address already in use" exceptions. However, I have a second method named "SendMessage". This method is supposed to send a message to the server. How can I make sure "SendMessage" cannot be invoked when there's already a thread running in "GetStatus", and the other way around? If I make both synchronized, I will still get in trouble if Thread A is opening a socket on Port 99999 and invoking "SendMessage" while Thread B is opening a socket on the same port and invoking "GetStatus"? (Game servers are usually hosted on the same ports) I guess what I am really after is a way to make an entire class synchronized, so that only one method can be invoked and run at a time by a single thread. Hope that what I am trying to accomplish/avoid is made clear in this text. Any help is greatly appreciated.

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