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  • What is Chain Matrix Multiplication ?

    - by Hellnar
    Hello, I am trying to understand what is a chain matrix multiplication and how it is different from a regular multiplication. I have checked several sourcers yet all seem to be very academically explained for me to understand. I guess it is a form of dynamic programming algorithm to achieve the operation in an optimised way but I didn't go any further. Thanks

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  • In JSF, how to handle repeating over a list that mutates

    - by Jon
    Hello, In a JSF page, I am iterating over a list of items provided by a session-scoped backing bean. The list needs to be kept up-to-date, so it is replaced with a fresh list every X minutes by a thread (in a thread-safe way). On my page, for each item I provide some text inputs and an "Update" button. If the list is refreshed before I hit "Update", the update does not happen (which is my problem). I happen to be using a4j:repeat, but I think this could also apply to other methods of iteration, including using dataTables. Any thoughts on how I can do this in a non-hackish way? Thanks!

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  • interfacing: simplified

    - by code wombat
    i've been doing some research on interfaces and a simple layman's explanation for what it truly is. For some reason people love using overly complex explanations and jargon to explain truly simple concepts (guess it makes them feel big) and i have a gut feeling it's the same in this case. so from what i could grasp, it seems like interfaces are nothing more than a way to reserve method names, their return type if any, and the type and amount of arguments they accept. so when a class implements an interface (or interfaces) it is forced to define the body of each method from the interface(s). Am i on the nose with this one or do i need to keep digging? p.s. i know javascript doesn't have support for interfaces, but i still need to understand the concept because there are quite a few places where it's shown how to emulate to an extent.

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  • Jsp declaration element

    - by Stardust
    <%! class father { static int s = 0; } %> <% father f1 = new father(); father f2 = new father(); f1.s++; out.println(f2.s); // It must print "1" %> When I run the file, I got this error. Can anybody explain? "The field s cannot be declared static; static fields can only be declared in static or top level types"

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  • Hibernate - get the size of a list in a property

    - by mada
    I have a class A which have a list of B elements. In my A class i would like to add: int size; which will be valued with the number of B elements. So when I would call myA.getSize() I will have it. Is it possible to map a count query with a single property in the hibernate mapping? I don't want to load the list that is why i would like to add a size property.

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  • JPA: what is the proper pattern for iterating over large result sets?

    - by Caffeine Coma
    Let's say I have a table with millions of rows. Using JPA, what's the proper way to iterate over a query against that table, such that I don't have all an in-memory List with millions of objects? I suspect that the following will blow up if the table is large: List<Model> models = entityManager().createQuery("from Model m", Model.class).getResultList(); for (Model model : models) { // do something with model } Is pagination (looping and manually updating setFirstResult()/setMaxResult()) really the best solution?

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  • Questions about my program and Polymorphism

    - by Strobe_
    Ok, so basically I'm creating a program which allows the user to select a shape (triangle, square, circle) and then it takes in a int and calculates the boundary length and area. I have no problem doing this and have a program that's working perfectly. (https://gist.github.com/anonymous/c63a03c129560a7b7434 4 classes) But now I have to implement this with polymorphism concepts and I'm honestly struggling as to how to do it. I have a basic idea of what I want to do when it comes to inheritance Main | Shapes / | \ triangle circle square But I don't understand how I'm supposed to override when all the methods within the triangle/square/circle classes are unique, there are no "abstract" methods as such that I could inherit from the "Shapes" class. If somebody could make look quickly at the code I linked and suggest a way to do this it would be much appreciated. Sorry if I was bad at explaining this. Thanks.

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  • JSF: attach rich:toggleControl to radio buttons or select items.

    - by arw
    Has anyone had any success attaching a rich:toggleControl component to a radio button component (h:selectOneRadio) or alternatively any of its children select items (in this case s:enumItem). Basic code example: <h:selectOneRadio value="#{backingValue}"> <s:enumItem enumValue="VAL_1" itemLabel="Value One" /> <s:enumItem enumValue="VAL_2" itemLabel="Value Two" /> <s:convertEnum /> </h:selectOneRadio> The ideal thing would be to attach the toggle control to the enumItems so I could have it switch to a particular state. However at this point I'd be happy if the toggle control can just be attached to the selectOneRadio. I've tried the toggle control as a child of the selectOneRadio and enumItems; neither works. I've also tried wrapping the toggleControl around the selectOneRadio, the toggle control works in this case but the radio buttons don't :(

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  • log4j rootLogger seems to inherit log level of other logger. Why?

    - by AndrewR
    I've got a log4J setup in which the root logger is supposed to log ERROR level messages and above to the console and another logger logs everything to syslog. log4j.properties is: # Root logger option log4j.rootLogger=ERROR,R log4j.appender.R=org.apache.log4j.ConsoleAppender log4j.appender.R.layout=org.apache.log4j.PatternLayout log4j.appender.R.layout.ConversionPattern=%d %p %t %c - %m%n log4j.logger.SGSearch=DEBUG,SGSearch log4j.appender.SGSearch=org.apache.log4j.net.SyslogAppender log4j.appender.SGSearch.SyslogHost=localhost log4j.appender.SGSearch.Facility=LOCAL6 log4j.appender.SGSearch.layout=org.apache.log4j.PatternLayout log4j.appender.SGSearch.layout.ConversionPattern=[%-5p] %m%n In code I do private static final Logger logger = Logger.getLogger("SGSearch"); . . . logger.info("Commencing snapshot index [" + args[1] + " -> " + args[2] + "]"); What is happening is that I get the console logging for all logging levels. What seems to be happening is that the level for SGSearch overrides the level set for the root logger somehow. I can't figure it out. I have confirmed that Log4J is reading then properties file I think it is, and no other (via the -Dlog4j.debug option)

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  • Using exponential smoothing with NaN values

    - by Eric
    I have a sample of some kind that can create somewhat noisy output. The sample is the result of some image processing from a camera, which indicates the heading of a blob of a certain color. It is an angle from around -45° to +45°, or a NaN, which means that the blob is not actually in view. In order to combat the noisy data, I felt that exponential smoothing would do the trick. However, I'm not sure how to handle the NaN values. On the one hand, involving them in the math would result in a NaN average, which would then prevent any meaningful results. On the other hand, ignoring NaN values completely would mean that a "no-detection" scenario would never be reported. And just to complicate things, the data is also noisy in that it can get false NaN value, which ideally would be smoothed somehow to prevent random noise. Any ideas about how I could implement such an exponential smoother?

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  • Setting up Matcher for String phrase match in file

    - by randomCoder
    Having trouble figuring out how to match a phrase string to a phrase in file stream. The file I'm dealing with contains random words such as: 3 little pigs built houses and 1 little pig went to the market etc. for many lines Using "little pig" as my pattern and matcher.find() I can locate 2 matches: "little pig" and "little pigs". However, I only want it to match "little pig". What can I do? I thought about using matcher.lookingAt() but I wouldn't know how to set a proper region when I can't rely on the file string phrases I'm matching being on separate lines.

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  • Where to put common setUp-code for differen testclasses?

    - by Benedikt
    I have several different test classes that require that certain objects are created before those tests can be run. Now I'm wondering if I should put the object initialization code into a separate helper class or superclass. Doing so would surely reduce the amount of duplicate code in my test classes but it would also make them less readable. Is there a guideline or pattern how to deal with common setUp-code for unit tests?

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  • Question about factory classes

    - by devoured elysium
    Currently I have created a ABCFactory class that has a single method creating ABC objects. Now that I think of it, maybe instead of having a factory, I could just make a static method in my ABC Method. What are the pro's and con's on making this change? Will it not lead to the same? I don't foresee having other classes inherit ABC, but one never knows! Thanks

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  • Android HTTP Connection

    - by Ubersoldat
    Can anybody tell my why this doesn't work in the Android emulator? From the browser I have access and the server is internal. All I can think of is that I'm missing some configuration on my app so it can access the network layer. try { InetAddress server = Inet4Address.getByName("thehost"); //Doesn't work either //or InetAddress server2 = Inet4Address.getByAddress(new String("192.168.1.30").getBytes()); if(server.isReachable(5000)){ Log.d(TAG, "Ping!"); } Socket clientsocket = new Socket(server, 8080); } catch (UnknownHostException e) { Log.e(TAG, "Server Not Found"); } catch (IOException e) { Log.e(TAG, "Couldn't open socket"); } Throws an UnknownHostException Thanks

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  • Long running method causing race condition

    - by keeleyt83
    Hi, I'm relatively new with hibernate so please be gentle. I'm having an issue with a long running method (~2 min long) and changing the value of a status field on an object stored in the DB. The pseudo-code below should help explain my issue. public foo(thing) { if (thing.getStatus() == "ready") { thing.setStatus("finished"); doSomethingAndTakeALongTime(); } else { // Thing already has a status of finished. Send the user back a message. } } The pseudo-code shouldn't take much explanation. I want doSomethingAndTakeALongTime() to run, but only if it has a status of "ready". My issue arises whenever it takes 2 minutes for doSomethingAndTakeALongTime() to finish and the change to thing's status field doesn't get persisted to the database until it leaves foo(). So another user can put in a request during those 2 minutes and the if statement will evaluate to true. I've already tried updating the field and flushing the session manually, but it didn't seem to work. I'm not sure what to do from here and would appreciate any help. PS: My hibernate session is managed by spring.

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  • stop thread that does not get interrupted

    - by prmatta
    I have a thread that sits and reads objects off of an ObjectInputStream: public void run() { try { ois = new ObjectInputStream(clientSocket.getInputStream()); Object o; while ((o = ois.readObject()) != null) { //do something with object } } catch (Exception ex) { //Log exception } } readObject does not throw InterruptedException and as far as I can tell, no exception is thrown when this thread is interrupted. How do I stop this thread?

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  • What is annotations and how do it actually works for frameworks like Spring ?

    - by Rachel
    I am new to Spring and now a days I hear a lot about Spring Framework. I have two sets of very specific questions: Set No. 1: What are annotations in general ? How does annotations works specifically with Spring framework ? Can annotations be used outside Spring Framework or are they Framework specific ? Set No. 2: What module of Spring Framework is widely used in Industry ? I think it is Spring MVC but why it is the most used module, if am correct or correct me on this ? I am newbie to Spring and so feel free to edit this questions to make more sense.

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  • Using HSQLDB in production environments

    - by lewap
    I want to use HSQLDB in a production environment for stroring some data in memory and for data export using files. Does anybody have experience with using hsqldb in production environments? Is hsqldb treating server resources gracefully and does it cleanup unused resources properly?

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  • HIbernate query language problem.....

    - by mslatf
    I have a Project class that has a Set of userstories called userStories12many. I'm having troubles trying to get the project that has a certain userstory in its set getComponent(int userStoryID) I think im on the right track but i dont know what i did wrong public Projects getComponent(int userStoryID) { Session session = SessionFactoryHelper.getSessionFactory() .getCurrentSession(); session.beginTransaction(); List<Projects> compo = session.createQuery("select p " + "from Projects as p inner join fetch p.userStories12many as u " + "where u.storyId='" + userStoryID + "'").list(); session.getTransaction().commit(); return compo.get(0); }

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  • why toString method does not work here??

    - by user329820
    Hi this is my whole class ,I have added number 2 to the doubly linked list and then I want it to be be print in the concole but it will show this "datastructureproject.Node@f62373" thanks! package datastructureproject; public class DoublyLinkedList { private Node head = new Node(0); private Node tail = new Node(0); private int length = 0; public DoublyLinkedList() { head.setPrev(null); head.setNext(tail); tail.setPrev(head); tail.setNext(null); } public void add(int index, int value) throws IndexOutOfBoundsException { Node cursor = get(index); Node temp = new Node(value); temp.setPrev(cursor); temp.setNext(cursor.getNext()); cursor.getNext().setPrev(temp); cursor.setNext(temp); length++; } private Node get(int index) throws IndexOutOfBoundsException { if (index < 0 || index > length) { throw new IndexOutOfBoundsException(); } else { Node cursor = head; for (int i = 0; i < index; i++) { cursor = cursor.getNext(); } return cursor; } } public long size() { return length; } public boolean isEmpty() { return length == 0; } @Override public String toString() { StringBuffer result = new StringBuffer(); result.append("(head) - "); Node temp = head; while (temp.getNext() != tail) { temp = temp.getNext(); result.append(temp.getValue() + " - "); } result.append("(tail)"); return result.toString(); } public static void main(String[] args){ DoublyLinkedList list = new DoublyLinkedList(); list.add(0,2 ); System.out.println(list.get(0).toString()); } }

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  • http_access.log on WebSphere 6.1.0.29

    - by DavidG
    I am running WebSphere 6.1.0.29 and I need to track the requests being made to an Enterprise Application. Previously I did this by routing the requests through a proxy server, but I need to repeat the exercise and I figure there must be a simpler way. Does anyone know how to enable HTTP access logging? I have been through the console an thought I had enabled http_access.log and http_error.log via: Application servers server1 HTTP error and NCSA access logging (where 'server1' is the application server) I've enabled the service at startup, and ticked the boxes to enable access logging and error logging - however... nothing has happened. I have restarted the server, restarted the Enterprise apps and even did a "find . -name" for the log files - but they don't seem to be anywhere on the system. I saw on a JavaRanch thread someone suggested writing a custom filter for requests in an application, but this seems like wild overkill - plus I am doing the logs to test a pre-built binary, so I don't want to mess with the code. Anyone have any ideas/suggestions? Help! :-)

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  • Strange IP addresses in tomcat

    - by mdev
    Some where I have this in some generic class. public static String getRequestIp (HttpServletRequest request){ String ipaddr = request.getHeader("X-FORWARDED-FOR"); if (ipaddr == null)ipaddr = request.getRemoteAddr(); return ipaddr; } For every request i call that method and in a certain moment i insert a record in a mysql database. In most cases it works normally and i can see a record for every request with a valid ip address in the right field. But sometimes where the IP should be there is something like this. "unknown, 93.186.30.120" or "10.0.1.169, 186.38.84.3" Apache is at the front listening at port 80 and used as proxy to Tomcat that listens at port 8081. My router config would not allow to pass any conection that come by any port other than 80. Any Help? Thanks in advance.

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