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• implementing keepalives with Java

  - by Bilal

  Hi All, I am biulding a client-server application where I have to implement a keepalive mechanism in order to detect that the client has crashed or not. I have separate threads on both client and server side. the client thread sends a "ping" then sleeps for 3 seconds, while the server reads the BufferedInput Stream and checks whether ping is received, if so it makes the ping counter eqauls zero, else it increments the counter by +1, the server thread then sleeps for 3 seconds, if the ping counter reaches 3, it daclares the client as dead. The problem is that when the server reads the input stream, its a blocking call, and it blocks untill the next ping is received, irrespective of how delayed it is, so the server never detects a missed ping. any suggestions, so that I can read the current value of the stream and it doesn't block if there is nothing on the incoming stream. Thanks,

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• Java Applet - ArrayIndexOutOfBoundsException

  - by Dan

  OK so I am getting an ArrayIndexOutofBoundsException. I don't know why. Here's my code: http://www.so.pastebin.com/y5MjD1k3 The thing is when I go to the red brick at board[2][2]... I go there. Then I go up... then I TRY go to back down but that error pops up. Also when I go to the right 8 squares... I ALSO get that error. ALSO, pretend my 2d map is split into FOUR squares... well square one is the top left... if I go ANYWHERE else ... I get that error. What am I doing wrong? Thanks.

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• Implementing Clonable in Java

  - by Artium

  In which cases should I use this way: public A clone() throws CloneNotSupportedException { A clone = (A)super.clone(); clone.x= this.x; return clone; } And in which cases should I use that way: public ShiftedStack clone() throws CloneNotSupportedException { return new A(this.x); } What should I do if x is final and I want to use the first way? Regarding the first way, I understand it like this: we clone the super class and up-cast it, leading to some members uninitialized. After this initialize these members. Is my understanding correct? Thank you.

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• delete item from array in java

  - by davit-datuashvili

  hello can anybody tell me what is wrong here? i want delete item from array but it shows me error ArrayIndexOutBound exception public class delete{ public static void main(String[]args){ int i; //delete item from array int k[]=new int[]{77,99,44,11,00,55,66,33,10}; //delete 55 int searchkey=55; int nums=k.length; for ( i=0;i<nums;i++) if (k[i]==searchkey) break; for (int t=i;t<nums;t++) k[t]=k[t+1]; nums--; for (int m=0;m<nums;m++){ System.out.println(k[m]); } } }

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• Java - 'continue' loop iteration after certain timeout period

  - by Matt

  Is there a way to exit ('continue;') a loop iteration after a certain timeout period? I have a loop that will run gathering data from the web and then use this data to make a calculation. The data become obsolete after about 1 to 2 seconds so if the loop iteration takes longer than 1 second then i want it to 'continue' to the next iteration. Sometimes gathering the data can take time but sometimes the calculation can take longer than 1 second so a HTTP timeout won't work for what i need. Also, while doing the calculation the thread i am using is blocked so i cannot check System.currentTimeMillis(); Is there a way to use another Thread to check the time and force the original for loop to continue.

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• Java Thread - Synchronization issue

  - by Yatendra Goel

  From Sun's tutorial: Synchronized methods enable a simple strategy for preventing thread interference and memory consistency errors: if an object is visible to more than one thread, all reads or writes to that object's variables are done through synchronized methods. (An important exception: final fields, which cannot be modified after the object is constructed, can be safely read through non-synchronized methods, once the object is constructed) This strategy is effective, but can present problems with liveness, as we'll see later in this lesson. Q1. Is the above statements mean that if an object of a class is going to be shared among multiple threads, then all instance methods of that class (except getters of final fields) should be made synchronized, since instance methods process instance variables?

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• using itext how to extracta string in java

  - by user2455183

  I am finding the string in between 123 and 321 and making it as bold. For that I used the Pattern to get the string before 123, text between 123 and 321 and text after 321. Could anyone please help me get all the strings between 123 and 321. Pattern p = Pattern.compile("^.*?(123)"); Matcher m = p.matcher(meredithEditorialSectionSegment); while (m.find()) { String desc = m.group(); String segDesc = (desc.substring(0, desc.length() - 3)); segmentDesc.add(new Chunk(segDesc, sectionDescriptionFont)); } descBold = meredithEditorialSectionSegment.substring(meredithEditorialSectionSegment.indexOf("123") + 3); descBold = descBold.substring(0, descBold.indexOf("321")); segmentDesc.add(new Chunk(descBold, sectionDescriptionBoldFont)); Matcher matcher = Pattern.compile("(?<=321).*").matcher(meredithEditorialSectionSegment); matcher.find(); segmentDesc.add(new Chunk(matcher.group(), sectionDescriptionFont));

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• Issue with WatchService in java 7

  - by user972590

  I'm using jdk7's WatchService API for monitoring the folder on file system.I'm sending a new file through email to that folder, when the file comes into that folder i m triggering the ENTRY_CRATE option. its working fine. But the issue is its generating two events of ENTRY_CREATE instead of one event which i'm invoking. BELOW IS THE CODE: Path dir = Paths.get(/var/mail); WatchService watcher = dir.getFileSystem().newWatchService(); dir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE); System.out.println("waiting for new file"); WatchKey watckKey = watcher.take(); List<WatchEvent<?>> events = watckKey.pollEvents(); System.out.println(events.size()); for(WatchEvent<?> event : events){ if(event.kind() == StandardWatchEventKinds.ENTRY_CREATE){ String fileCreated=event.context().toString().trim(); } } In the above code I'm gettng the events size as 2. Can any one please help me in finding out the reason why i'm getting two events.

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• Freeing Java memory at a specific point in time

  - by Marcus

  Given this code, where we load a lot of data, write it to a file, and then run an exe.. void myMethod() { Map stuff = createMap(); //Consumes 250 MB memory File file = createFileInput(stuff); //Create input for exe runExectuable(file); //Run Windows exe } What is the best way to release the memory consumed by stuff prior to running the exe? We don't need this in memory any more as we have dumped the data to a file for input to the exe... Is the best method to just set stuff = null prior to runExecutable(file)?

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• java: how to parse html-like xml

  - by Yang

  I have an html-like xml, basically it is html. I need to get the elements in each . Each element looks like this: <line tid="744476117"> <attr>1414</attr> <attr>31</attr><attr class="thread_title">title1</attr><attr>author1</attr><attr>date1</attr></line> My code is as below, it does recognize that there are 50 in the file, but it gives me NULLPointException when parsing NodeList fstNmElmntLst = fstElmnt.getElementsByTagName("attr"); Any idea why this is happening? The same code has been used for other applications without problems. DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); InputSource is = new InputSource(); is.setCharacterStream(new StringReader(cleanxml)); Document doc = db.parse(is); doc.getDocumentElement().normalize(); System.out.println("Root element " + doc.getDocumentElement().getNodeName()); NodeList nodeLst = doc.getElementsByTagName("line"); for (int s = 0; s < nodeLst.getLength(); s++) { System.out.println(nodeLst.getLength()); Node fstNode = nodeLst.item(s); if (fstNode.getNodeType() == Node.ELEMENT_NODE) { Element fstElmnt = (Element) fstNode; NodeList fstNmElmntLst = fstElmnt.getElementsByTagName("attr"); Element fstNmElmnt = (Element) fstNmElmntLst.item(0); NodeList fstNm = fstNmElmnt.getChildNodes(); System.out.println("attr : " + ((Node) fstNm.item(0)).getNodeValue()); } }

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• java Swing Listeners: components listening at each others.

  - by Pierre

  Hi all, I want to code two JList (categories and items). When I click one category it should select all the items for that category and when I click on one item it should select its categories. So both JList will have a ListSelectionListener listening at each other and changing the selection. Should I fear about some a of "loop" ? Is there a way to tell that an Event has been consumed ? how do people manage that kind of situation ? Thanks

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• Java OCR Help Needed

  - by maSnun

  Hello, How do I detect all the characters in an image? The image is in png and the font is constant. For simplicity, lets assume that the image has only numeric digits and there are only 4 digits on an image. I need to read all of them and output the text. Can you help? Thanks in advance.

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• Java Swing: JTextArea columns question

  - by battousai622

  How do i put the text in specific columns with jTextArea? private javax.swing.JTextArea jTextArea1; jTextArea1.setColumns(4); jTextArea1.insert(price, 0); //column 1 jTextArea1.insert(cost, 0); //column 2 jTextArea1.insert(quantity, 0); //column ect.. jTextArea1.insert(itemName, 0); jTextArea1.insert("\n", 0);

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• Simple Question:Output of below Java program

  - by Abhishek Jain

  public class abc1 { private String s; public abc1(String s){this.s=s;} public static void main(String args[]) { HashSet<Object> hs=new HashSet<Object>(); abc1 a1= new abc1("abc"); abc1 a2= new abc1("abc"); String s1= new String("abc"); String s2= new String("abc"); hs.add(a1); hs.add(a2); hs.add(s1); hs.add(s2); System.out.println(hs.size()); } } Why above program output is 3?

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• Java Days & Bookings

  - by sys_debug

  Ok this is an extension of a question I asked about earlier yet this is the next step that is unclear to me. Everything else will be ready and this part is driving me mad! some members provided great help and I already made progress with that info, but this is just another obstacle. I am creating a booking object (as was suggested) that will have a start date and end date. each booking will also have a number of seats associated with it (that I require to reserve). The total available number of seats any given day 46 (as the total capacity of the hall is 46 seats). so in assumption that I have a booking to be made in the system, and start date is 1st jan and end date is 10th jan. The question is how can I check the remaining seats in all those days between the range to see if requested number could be hosted or not? and then when the second booking is made, it will have to see that the days in this range already have less than 46 and decrement further if possible to host the reservation. one of the members, and I appreciate his effort, gladly contributed a method to compare if this booking is after or before the existing bookings. The code provided is here: public boolean overlapsWithExisting(Booking booking) { final Date early = booking.getStart(); final Date late = booking.getEnd(); for(Booking existing : existingBookings) { if(!(early.isAfter(existing.getEnd() || late.isBefore(existing.getStart())) return true; } return false; } I just want to know how to associate 46 with each day and keep record of days that are decremented by bookings. Thanks and reallllllly appreciated :D

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• Same loop giving different output. Java IO

  - by Nitesh Panchal

  Hi, I am facing a very strange problem where the same loop keeps giving me different different output on change of value of BUFFER final int BUFFER = 100; char[] charArr = new char[BUFFER]; StringBuffer objStringBuffer = new StringBuffer(); while (objBufferedReader.read(charArr, 0,BUFFER) != -1) { objStringBuffer.append(charArr); } objFileWriter.write(objStringBuffer.toString()); When i change BUFFER size to 500 it gives me a file of 7 kb when i change BUFFER size to 100000 it gives a file of 400 kb where the contents are repeated again and again. Please help. What should i do to prevent this?

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• How are ambigous methods resolved in java ?

  - by Jijoy

  Hi, I have a question. package org.study.algos; public class Study { public static void main(String[] args) { A a = new A(); a.m1(null); } } class A { public void m1(String s) { System.out.println("String"); System.out.println(s); } public void m1(Object obj) { System.out.println("Object"); System.out.println(obj); } } Here, the output is String null Why does the JVM resolve the method to one with a String argument? Thanks in advance J

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• Java Synchronized function

  - by leon

  Hi I have a question. In the following code, if a thread were blocked at wait statement, and another thread attempts to execute foo(), would the hello wolrd message be printed? and Why? Many Thanks synchronized foo(){ system.out.println("hello world"); ..... wait(); ..... }

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• Java GUI guidance on building a chat box

  - by Allen

  I'm just looking for a little guidance as to how i might implement a chat box. There needs to be a text area for user entry, and a scrolling list of past messages. Is there an easy/standard way of going about doing this? Thanks

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• Blackberry (Java) - drawing text in two different fonts

  - by paullb

  using the g.drawText function (two calls one for each text) is it possible to write text in two different sizes? g.drawText("abc",0,0); //whatever code to change font goes here g.drawText("def",30,30);

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• Why is Java String indexOf failing?

  - by Binaryrespawn

  Hi all, this must be quite simple but I am having great difficulty. You see I am trying to find a string within another string as follows. e = input.indexOf("-->"); s = input.indexOf("<!--"); input = input.replace(input.substring(s, e + 3), " "); The integers e and s are returning -1 in that it was not found and this is causing the replace method to fail. The test string I am using is "Chartered Certified<!--lol--> Accountants (ACCA)". I tried to creat a new string object and pass in the string as an argument as follows e=input.indexOf(new String("<!--")); This yielded the same result. Any ideas ?

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• Java regex to get part number

  - by Blankman

  I have HTML that I need to extract a part number from, the HTML looks like: javascript:selectItem('ABC123 1', '..... I need to get the ABC123 from the above. My code snippet: Patterp p = Pattern.Compile("?????"); Matcher m = p.matcher(html); if(m.find()) partNumber = m.group(1).trim(); BTW, in the pattern, how do I escape for the character ( I now for quotes I do \" thanks allot!

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• Java's Swing Threading

  - by nevets1219

  My understanding is that if I start up another thread to perform some actions, I would need to SwingUtilities.invokeAndWait or SwingUtilities.invokeLater to update the GUI while I'm in said thread. Please correct me if I'm wrong. What I'm trying to accomplish is relatively straightforward: when the user clicks submit, I want to (before performing any actions) disable the submit button, perform the action, and at the end of the action re-enable the button. My method to perform the action updates the GUI directly (displays results) when it gets the results back. This action basically queries a server and gets some results back. What I have so far is: boolean isRunning = false; synchronized handleButtonClick() { if ( isRunning == false ) { button.setEnabled( false ); isRunning = true; doAction(); } } doAction() { new Thread() { try { doAction(); // Concern A } catch ( ... ) { displayStackTrace( ... ); // Concern B } finally { SwingUtilities.invokeLater ( /* simple Runnable to enable button */ ); isRunning = false; } } } For both of my concerns above, do I would have to use SwingUtilities.invokeAndWait since they both will update the GUI? All GUI updates revolve around updating JTextPane. Do I need to in my thread check if I'm on EDT and if so I can call my code (regardless of whether it updates the GUI or not) and NOT use SwingUtilities.invokeAndWait?

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• Java Download Concurrent Data

  - by xger86x

  Hi, i'm developing an app which download map tiles around different places in a city. To do this, i have one thread for each place in which i select the tiles and create a thread to download each. Well, the question is how to avoid creating a thread for a tile that already exists in the thread pool. Should not just check if the file exists, since it is possible that the thread for that tile already exists (other place already need that tile) but the file has not been created- Any idea? Thanks

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• java problem about ResultSet

  - by vipul

  Hello Friends, I want to merge two Resultset Object into third one. If you have any idea then reply.. vipul

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