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  • Java: Set<E> collection, where items are identified by its class

    - by mschayna
    I need Set collection, where its items will be identified by items class. Something like ReferenceIdentityMap from Appache Collections, but on class scope i.e. two different instances of same class must be identified as same in this collection. You know, it is a violation of equals()/hashCode() identity principle but in occasional use it makes sense. I have done this in simple class backing with Map<Class<? extends E>, E>, but due to simplicity it doesn't implement Set<E>. There may be a more elegant solution, decorator of any Set<E> would be great. Is there any implementation of such collection there (Apache/Google/something/... Collections)?

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  • Java Runtime.freeMemory() returning bizarre results when adding more objects

    - by Sotirios Delimanolis
    For whatever reason, I wanted to see how many objects I could create and populate a LinkedList with. I used Runtime.getRuntime().freeMemory() to get the approximation of free memory in my JVM. I wrote this: public static void main(String[] arg) { Scanner kb = new Scanner(System.in); List<Long> mem = new LinkedList<Long>(); while (true) { System.out.println("Max memory: " + Runtime.getRuntime().maxMemory() + ". Available memory: " + Runtime.getRuntime().freeMemory() + " bytes. Press enter to use more."); String s = kb.nextLine(); if (s.equals("m")) for (int i = 0; i < 1000000; i++) { mem.add(new Long((new Random()).nextLong())); } } } If I write in m, the app adds a million Long objects to the list. You would think the more objects (to which we have references, so can't be gc'ed), the less free memory. Running the code: Max memory: 1897725952. Available memory: 127257696 bytes. m Max memory: 1897725952. Available memory: 108426520 bytes. m Max memory: 1897725952. Available memory: 139873296 bytes. m Max memory: 1897725952. Available memory: 210632232 bytes. m Max memory: 1897725952. Available memory: 137268792 bytes. m Max memory: 1897725952. Available memory: 239504784 bytes. m Max memory: 1897725952. Available memory: 169507792 bytes. m Max memory: 1897725952. Available memory: 259686128 bytes. m Max memory: 1897725952. Available memory: 189293488 bytes. m Max memory: 1897725952. Available memory: 387686544 bytes. The available memory fluctuates. How does this happen? Is the GC cleaning up other things (what other things are there on the heap to really clean up?), is the freeMemory() method returning an approximation that's way off? Am I missing something or am I crazy?

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  • remove duplicates from object array data java

    - by zahir hussain
    hi i want to know how to remove duplicates in object. for example cat c[] = new cat[10]; c[1].data = "ji"; c[2].data = "pi"; c[3].data = "ji"; c[4].data = "lp"; c[5].data = "ji"; c[6].data = "pi"; c[7].data = "jis"; c[8].data = "lp"; c[9].data = "js"; c[10].data = "psi"; i would like to remove the duplicates value from object array. thanks and advance

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  • Java regex basic usage problem

    - by Ernelli
    The following code works: String str= "test with foo hoo"; Pattern pattern = Pattern.compile("foo"); Matcher matcher = pattern.matcher(str); if(matcher.find()) { ... } But this example does not: if(Pattern.matches("foo", str)) { ... } And neither this version: if(str.matches("foo")) { ... } In the real code, str is a chunk of text with multiple lines if that is treated differently by the matcher, also in the real code, replace will be used to replace a string of text. Anyway, it is strange that it works in the first version but not the other two versions.

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  • Extracting Mail from Microsoft Exchange server 2007 through IMAPS in java

    - by abhishekgem84
    props.put("mail.debug", "true"); props.setProperty("mail.store.protocol","imaps"); props.setProperty("mail.imaps.auth.plain.disable","false"); props.setProperty("mail.imaps.host","Mail3.connect.com"); props.setProperty("mail.imaps.port","135"); props.setProperty("mail.imaps.user","test"); props.setProperty("mail.imaps.pwd","123"); props.setProperty("mail.imaps.ssl.protocols","SSL"); props.setProperty("mail.imaps.socketFactory.class", "javax.net.ssl.SSLSocketFactory"); props.setProperty("mail.imaps.socketFactory.fallback", "false"); props.setProperty("mail.imaps.socketFactory.port", "135"); i have done all this but it still says javax.mail.AuthenticationFailedException: failed to connect, no password specified? kindly help me out thanks

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  • java filenames filter pattern

    - by Sergey
    Hello, I need to implement File[] files = getFiles( String folderName, String ptrn ); Where ptrn is a command prompt style pattern like "*2010*.txt" I'm familar with FilenameFilter class, but can't implement public boolean accept(File dir, String filename) because String.matches() doesn't accept such patterns. Thanks!

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  • Can Java's random function be zero?

    - by ThirdD3gree
    Just out of curiosity, can Math.random() ever be zero? For example, if I were to have: while (true){ if (Math.random() == 0) return 1; } Would I ever actually get a return of one? There's also rounding error to consider because Math.random() returns a double. I ask because my CS professor stated that random() goes from 0 to 1 inclusive, and I always thought it was exclusive.

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  • Java Binary Tree. Priting InOrder traversal

    - by user69514
    I am having some problems printing an inOrder traversal of my binary tree. Even after inserting many items into the tree it's only printing 3 items. public class BinaryTree { private TreeNode root; private int size; public BinaryTree(){ this.size = 0; } public boolean insert(TreeNode node){ if( root == null) root = node; else{ TreeNode parent = null; TreeNode current = root; while( current != null){ if( node.getData().getValue().compareTo(current.getData().getValue()) <0){ parent = current; current = current.getLeft(); } else if( node.getData().getValue().compareTo(current.getData().getValue()) >0){ parent = current; current = current.getRight(); } else return false; if(node.getData().getValue().compareTo(parent.getData().getValue()) < 0) parent.setLeft(node); else parent.setRight(node); } } size++; return true; } /** * */ public void inOrder(){ inOrder(root); } private void inOrder(TreeNode root){ if( root.getLeft() !=null) this.inOrder(root.getLeft()); System.out.println(root.getData().getValue()); if( root.getRight() != null) this.inOrder(root.getRight()); } }

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  • java asynchronous task.

    - by Tony
    For some of HTTP requests from clients, there was very complex business logic in server side. Some of these business logics doesn't require to response to the client immediately, like sending a email to somebody. Can I put those tasks in an asynchronous method.

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  • Java Conversion of byte[] into a srting and then back to a byte[]

    - by Sid
    I am working on a proxy server. I am getting data in byte[] which i convert into a string to perform certain operations. Now when i convert this new string back into a byte [] it causes unkonw problems. So mainly its like i need to know how to correctly convert a byte[] into a string and then back into a byte[] again. I tried to just convert the byte[] to string and then back to byte[] again (to make sure thats its not my operations that are causing problems). So its like: // where reply is a byte[] String str= new String(reply,0, bytesRead); streamToClient.write(str.getBytes(), 0, bytesRead); is not equivalent to streamToClient.write(reply, 0, bytesRead); my proxy works fine when i just send the byte[] without any conversion but when i convert it from byte[] to a string and then back to a byte[] its causes problems. can some one please help? =]

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  • Second level cache for java web app and its alternatives

    - by EugeneP
    Between the transitions of the web app I use a Session object to save my objects in. I've heard there's a program called memcached but there's no compiled version of it on the site, besides some people think there are real disadvantages of it. Now I wanna ask you. What are alternatives, pros and cons of different approaches? Is memcached painpul for sysadmins to install? Is it difficult to embed it to the existing infrastructure from the perspective of a sysadmin? What about using a database to hold temporary data between web app transitions? Is it a normal practice?

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  • Java/swing: console component?

    - by Jason S
    I am looking for a component I can use in Swing that acts as a GUI console which has a text area with scrollbars that can be set to a particular font has an InputStream and an OutputStream that a host application can obtain accepts keyboard input, prints it onto the end of the console text, and sends that input to the InputStream prints the OutputStream text to the end of the console has some kind of FIFO-ish property whereby the amount of text displayed in the console can be limited by automatically discarding the oldest text, when appropriate allows copy (but not cut or paste or any other editing) of the console text to the system clipboard This is kind of like the Console tab in Eclipse. Are there any good libraries that provide this?

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  • Java Time Zone When Parsing DateFormat

    - by shipmaster
    I had code that parses date as follows: String ALT_DATE_TIME_FORMAT = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"; SimpleDateFormat sdf = new SimpleDateFormat( ALT_DATE_TIME_FORMAT); Date date = sdf.parse(requiredTimeStamp); And it was working fine, suddenly, this stopped working. It turns out an admin made some config changes on the server and the date is currently being returned as "2010-12-27T10:50:44.000-08:00" which is not parse-able by the above pattern. I have two questions: The first would be what pattern would parse the date being returned by the JVM in the format above (specifically, just '-08:00' as the time zone)? And second, where exactly would one change such settings on a linux RHEL 5 server so that we are aware of such changes in the future?

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  • Loading data in constructors and not in constructors [JAVA]

    - by Richeve S. Bebedor
    i just want to know the difference between loading the data inside the constructor and loading the data outside the constructor but not inside any methods example: Loading inside constructor public class Model{ Object testobject; public Model(){ testobject=new Object(); } } VS example: Loading outside constructor public class Model{ Object testobject=new Object(); public Model(){ } }

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  • Data table with legends in JfreeChart/Java

    - by TiNS
    Hi All, I am using JFreeChart to generate images. I am trying to create barchart like below. I am able to create it successfully without data table. I tried to get more information from the jfreechar forums and found this post. According to the post , its not supported by JfreeChart. Is it still not supported by jfreechart API ? If yes, can I use any other charting (open source) tool to generate chart with data table ? Thanks

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  • Problem loading java properties

    - by markovuksanovic
    I am trying to load properties from a file (test.properties) The code I use is as follows: URL url = getClass().getResource("../resources/test.properties"); properties.load(url.openStream()); But when executing the second line I get a NPE. (null pointer exception) I'm not sure what's wrong here... I have checked that the file exists at the location where URL points to... Any help is appreciated....

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  • get static initialization block to run in a java without loading the class

    - by TP
    I have a few classes as shown here public class TrueFalseQuestion implements Question{ static{ QuestionFactory.registerType("TrueFalse", "Question"); } public TrueFalseQuestion(){} } ... public class QuestionFactory { static final HashMap<String, String > map = new HashMap<String,String>(); public static void registerType(String questionName, String ques ) { map.put(questionName, ques); } } public class FactoryTester { public static void main(String[] args) { System.out.println(QuestionFactory.map.size()); // This prints 0. I want it to print 1 } } How can I change TrueFalseQuestion Type so that the static method is always run so that I get 1 instead of 0 when I run my main method? I do not want any change in the main method. I am actually trying to implement the factory patterns where the subclasses register with the factory but i have simplified the code for this question.

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  • Deleting from arraylist and exporting back to .buab file(Java)

    - by Dave
    Ive made an address book. I can currently write to the arraylist and save it back to the .buab file, but I cant delete from the arraylist and export it back to the .buab file? Im pretty much stuck on this. Im able to retrive contacts from the .buab and scroll through them using the JTextFields and buttons ive created. Any help will be dearly appreciated. Ive set up seprate classes for all operations (newcontacts, nextcontact etc). If you need the code posted let me know.. Cheers Dave

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  • Are there any other Java schedulers besides Quartz(FOSS) and Flux(Commercial)

    - by mP
    I am interested in finding out about other job scheduling packages besides Quartz and Flux. Given the plethora of web frameworks i find it perculiar that there is really only one scheduler. Are there others that perhaps are very much unknown/unpopular ? Spring Batch Not really a scheduling solution but rather a batch job coordinator etc. http://static.springsource.org/spring-batch/faq.html#schedulers How does Spring Batch differ from Quartz? Is there a place for them both in a solution? Spring Batch and Quartz have different goals. Spring Batch provides functionality for processing large volumes of data and Quartz provides functionality for scheduling tasks. So Quartz could complement Spring Batch, but are not excluding technologies. A common combination would be to use Quartz as a trigger for a Spring Batch job using a Cron expression and the Spring Core convenience SchedulerFactoryBean .

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  • Java Netscape LDAP Remove One Attribute

    - by spex
    Hi, I have LDAP schema where are users. I need remove one attribute named "notify" which have values: phone number or mail or remove attribute from user. I found method LDAPConnection myCon = new LDAPConnection("localhost",389); myCon.delete("uid=test1, ou=People, o=domain.com, o=isp"); but this remove whole user and i need remove only one attribute "notifyTo" of this user. I need remove whole attribute not only its value. Thanks for reply

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  • How is Java Process.getOutputStream() Implemented?

    - by Amit Kumar
    I know the answer depends on the particular JVM, but I would like to understand how it is usually implemented? Is it in terms of popen (posix)? In terms of efficiency do I need to keep something in mind (other than using a Buffered stream as suggested by the javadoc). I would be interested to know if there is a general reference about implementations of JVMs which answers such questions.

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