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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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  • When can Java produce a NaN (with specific code question)

    - by Brent
    I'm a bit perplexed by some code I'm currently writing. I am trying to preform a specific gradient descent (main loop included below) and depending on the initial conditions I will alternatively get good looking results (perhaps 20% of the time) or everything becomes NaN (the other 80% of the time). However it seems to me that none of the operations in my code could produce NaN's when given honest numbers! My main loop is: // calculate errors delta = m1 + m2 - M; eta = f1 + f2 - F; for (int i = 0; i < numChildren; i++) { epsilon[i] = p[i]*m1+(1-p[i])*m2+q[i]*f1+(1-q[i])*f2-C[i]; } // use errors in gradient descent // set aside differences for the p's and q's float mDiff = m1 - m2; float fDiff = f1 - f2; // first update m's and f's m1 -= rate*delta; m2 -= rate*delta; f1 -= rate*eta; f2 -= rate*eta; for (int i = 0; i < numChildren; i++) { m1 -= rate*epsilon[i]*p[i]; m2 -= rate*epsilon[i]*(1-p[i]); f1 -= rate*epsilon[i]*q[i]; f2 -= rate*epsilon[i]*(1-q[i]); } // now update the p's and q's for (int i = 0; i < numChildren; i++) { p[i] -= rate*epsilon[i]*mDiff; q[i] -= rate*epsilon[i]*fDiff; } This behavior can be seen when we have rate = 0.01; M = 30; F = 30; C = {15, 25, 35, 45}; with the p[i] and q[i] chosen randomly uniformly between 0 and 1, m1 and m2 chosen randomly uniformly to add to M, and f1 and f2 chosen randomly uniformly to add up to F. Does anyone see anything that could create these NaN's?

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  • Maven easyb plugin java heap space settings?

    - by vinnu
    Hi, I attempted to change my heap size for maven easyb plugin http://www.easyb.org/maven-easyb-plugin/. In my easyb test I added standard code to print the heap size using the code Runtime.getFreeMemory() and Runtime.getTotalMemory(). I tried setting the MAVEN_OPTS=-Xmx1024m -Xms1024m and also set the maven opts in Maven surefire plugin. Now when I run the same class from the Junit I can see the getTotalMemory() displaying a number close 1Gig but the when the same classes are invoked from easyb plugin they do not reflect the memory size. Shouldn't there be a way of passing JVM opts to maven easyb plugin when it runs these easyb tests? At the very minimum it should atleast pick up the MAVEN_OPTS settings from the environment. Has someone bumped into problems like this? (A search on this group's archive does not reveal much)

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  • permute data for a HashMap in Java

    - by tuxou
    hi i have a linkedhashmap and i need to permute (change the key of the values) between 2 random values example : key 1 value 123 key 2 value 456 key 3 value 789 after random permutation of 2 values key 1 value 123 key 2 value 789 key 3 value 456 so here I permuted values between key 2 and key 3 thank you; sample of the code of my map : Map map = new LinkedHashMap(); map =myMap.getLinkedHashMap(); Set key = map.keySet(); for(Iterator it = cles.iterator(); it.hasNext();) { Integer cle = it.next(); ArrayList values = (ArrayList)map.get(cle);//an arrayList of integers int i = 0; while(i < values.size()) { //i donno what to do here i++; } }

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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: refactoring static constants

    - by akf
    We are in the process of refactoring some code. There is a feature that we have developed in one project that we would like to now use in other projects. We are extracting the foundation of this feature and making it a full-fledged project which can then be imported by its current project and others. This effort has been relatively straight-forward but we have one headache. When the framework in question was originally developed, we chose to keep a variety of constant values defined as static fields in a single class. Over time this list of static members grew. The class is used in very many places in our code. In our current refactoring, we will be elevating some of the members of this class to our new framework, but leaving others in place. Our headache is in extracting the foundation members of this class to be used in our new project, and more specifically, how we should address those extracted members in our existing code. We know that we can have our existing Constants class subclass this new project's Constants class and it would inherit all of the parent's static members. This would allow us to effect the change without touching the code that uses these members to change the class name on the static reference. However, the tight coupling inherent in this choice doesn't feel right. before: public class ConstantsA { public static final String CONSTANT1 = "constant.1"; public static final String CONSTANT2 = "constant.2"; public static final String CONSTANT3 = "constant.3"; } after: public class ConstantsA extends ConstantsB { public static final String CONSTANT1 = "constant.1"; } public class ConstantsB { public static final String CONSTANT2 = "constant.2"; public static final String CONSTANT3 = "constant.3"; } In our existing code branch, all of the above would be accessible in this manner: ConstantsA.CONSTANT2 I would like to solicit arguments about whether this is 'acceptable' and/or what the best practices are.

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  • How to append to an array that contains blank spaces - Java

    - by Cameron Townley
    I'm trying to append to a char[] array that contains blank spaces on the end. The char array for example contains the characters 'aaa'. When I append the first time the method functions properly and outputs 'aaabbb'. The initial capacity of the array is set to 80 or multiples of 80. The second time I try and append my output looks like"aaabbb bbb". Any psuedocode would be great.

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  • Exception and Inheritance in JAVA

    - by user1759950
    Suppose we have this problem public class Father{ public void method1(){...} } public class Child1 extends Father{ public void method1() throws Exception{ super.method1(); ... } } Child1 extends Father and override method1 but given implementation Child1.method1 now throws a exception, this wont compile as override method can't throw new exceptions. What is the best solution? Propagate the required exception to the Father.. to me this is against encapsulation, inheritance and general OOP ( the father potentially throw and exception that will never happen ) Use a RuntimeException instead? This solution wont propagate the Exception to the father but I read In Oracle docs and others sources states class of exceptions should be used when "Client code cannot do anything" this is not that case, this exception will b useful to recover blablabla ( why is wrong to use RuntimeException instead? ) Other.. thanks, Federico

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  • Java, let CookieHandler work on only one instance.

    - by user435657
    Hi all, I don't know how CookieHandler works system wide, I did view the source of CookieHandler but found no more information except the get/set methods. Where do TCP/HTTP connections use instance of CookieHandler, which I set by CookieHandler.setDefault(...) Which source file I should refer to? URLConnection & HttpURLConnection don't seem have things to do with it. Help, thanks in advance.

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  • How does file creation work in Java

    - by Ankur
    I am trying to create a file using File newFile = new File("myFile"); However no file called "myFile" is created. This is within a Web application Project i.e. proper form to be pakaged as a WAR but I am calling it as part of a main method (just to see how this works). How can I make it so that a new file is created at a location relative to the current one i.e not have to put in an absolute path.

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  • Output Parameter in java

    - by soclose
    Hi, could u give me a sample code of using output parameter in function? I tried to google it but just found it in function. I'd like to use this output value in another function. I will use this code in Android.

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  • Java Object Creation Error

    - by ikurtz
    package Sartre.Connect4; import javax.swing.*; public class ChatGUI extends JDialog { public ChatGUI(){ setTitle("Chat"); } } when i do this in another class in the same package: ChatGUI chatGUI = new ChatGUI(); i end up with a situation: Cannot Find Symbol please help?

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  • Strange numbers in java socket output

    - by user293163
    I have small test app: Socket socket = new Socket("jeck.ru", 80); PrintWriter pw = new PrintWriter(socket.getOutputStream(), false); pw.println("GET /ip/ HTTP/1.1"); pw.println("Host: jeck.ru"); pw.println(); pw.flush(); BufferedReader rd = new BufferedReader(new InputStreamReader(socket.getInputStream())); String str; while ((str = rd.readLine()) != null) { System.out.println(str); } It`s output: HTTP/1.1 200 OK Date: Sat, 13 Mar 2010 22:06:51 GMT Content-Type: text/html;charset=utf-8 Transfer-Encoding: chunked Connection: keep-alive Keep-Alive: timeout=5 Server HTTP/1.1 200 OK Date: Sat, 13 Mar 2010 22:06:51 GMT Content-Type: text/html;charset=utf-8 Transfer-Encoding: chunked Connection: keep-alive Keep-Alive: timeout=5 Server: Apache Cache-Control: max-age=0 Expires: Sat, 13 Mar 2010 22:06:51 GMT 123 <!DOCTYPE html> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> <title>??? IP</title> </head> <body> <div style='text-align: center; font: 32pt Verdana;margin-top: 300px'> ??? IP &#151; 94.103.87.153 </div> </body> </html> 0 Whence these numbers (123 an 0) takes?

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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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  • Transfering a set with a Wildcarded Generic to a List in Java

    - by Daniel Bingham
    I have a data type that contains a set and a method that expects List<? extends MyClass>. The data type has Set<? extends MyClass>. I need to be able to move the stuff out of the set and into the List. The order it goes into the list doesn't matter, it just needs to start keeping track of it so that it can be reordered when displayed. Suffice to say that changing the Set into a List in the data type is out of the question here. This seems pretty easy at first. Create a new method that takes a Set instead of a List, changes it into a list and then passes it on to the old method that just took a list. The problem comes in changing the set to a list. public void setData(Set<? extends MyClass> data) { List<? extends Myclass> newData = ArrayList< /* What goes here? */ >(); for(ConcordaEntityBean o : data) { newData.add(o); } setData(newData); } Obviously, I can't instantiate an ArrayList with a wildcard, it chokes. I don't know the type at that point. Is there some way to pull the type out of data and pass it to ArrayList? Can I just instantiate it with MyClass? Is there some other way to do this?

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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 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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  • 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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  • What is an Enterprise Java Bean really?

    - by HDave
    On the Tomcat FAQ it says: "Tomcat is not an EJB server. Tomcat is not a full J2EE server." But if I: use Spring to supply an application context annotate my entities with JPA annotations (and use Hibernate as a JPA provider) configure C3P0 as a connection pooling data source annotate my service methods with @Transactional (and use Atomikos as JTA provider) Use JAXB for marshalling and unmarshalling and possibly add my own JNDI capability then don't I effectively have a JEE application server? And then aren't my beans EJBs? Or is there some other defining characteristic? What is it that a JEE compliant app server gives you that you can't easily/readily get from Tomcat with some 3rd party subsystems?

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  • Java File manipulation

    - by user69514
    So I have an application with a JFileChooser from which I select a file to read. Then I change some words and write a new file. The problem that I am having is that when I write the new file it's saved in the project directory. How do I save it in the same directory as the file that I chose using the JFileChooser. Note: I don't want to use the JFileChooser to choose the location. I just need to save the file in the same directory as the original file that I read.

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