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  • Why is BigDecimal.equals specified to compare both value and scale individually?

    - by bacar
    This is not a question about how to compare two BigDecimal objects - I know that you can use compareTo instead of equals to do that, since equals is documented as: Unlike compareTo, this method considers two BigDecimal objects equal only if they are equal in value and scale (thus 2.0 is not equal to 2.00 when compared by this method). The question is: why has the equals been specified in this seemingly counter-intuitive manner? That is, why is it important to be able to distinguish between 2.0 and 2.00? It seems likely that there must be a reason for this, since the Comparable documentation, which specifies the compareTo method, states: It is strongly recommended (though not required) that natural orderings be consistent with equals I imagine there must be a good reason for ignoring this recommendation.

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  • Does thread pool size keep growing for scheduledthreadpoolexecutor?

    - by Sourajit Basak
    Imagine a situation where tasks are being added to scheduledthreadpoolexecutor. Each of these tasks will keep on running at different periodic intervals. Although all such tasks will not be running at the same time because each is set at different intervals, there may be a situation where a high number of threads are competing for execution. Is there any restriction on total number of threads ? It seems there is a restriction on the total number of idle threads. And does this concept of idle thread imply that long running tasks (thread) may be destroyed and recreated when needed ?

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  • Is this safe on a production server?

    - by Camran
    I have a database application (or search engine) which is called Solr. I connect to it via port 8983. I do this from php code, so I add and remove records from it via php. On my server I have a firewall. I have set this firewall to only allow connections to and from this port (8983) from the ip adress of my own server. In other words, only allow servers IP to access this port. Is that safe? Or am I thinking all wrong here? Will others be able to "simulate" my ip adress and act as the server? This is because otherwise others may add/remove records as they want from their own ip adresses... Thanks

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  • Obtaining memory available to JVM at runtime

    - by Bo Tian
    I'm trying to sort a bunch of data such that that the size of data input to the program can be larger than the memory available to the JVM, and handling that requires external sort which is much slower than Quicksort. Is there any way of obtaining memory available to the JVM at runtime such that I could use in place sorting as much as possible, and only switch to Mergesort when data input is too large?

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  • Correct usage of "<T extends SuperClass>"

    - by yusaku
    I am not familiar with "Generics". Is it a correct use of "<T extends SuperClass>" ? And do you agree that the codes after using generics are better? Before using Generics ================================================= public abstract class SuperSample { public void getSomething(boolean isProcessA) { doProcessX(); if(isProcessA){ doProcessY(new SubASample()); }else{ doProcessY(new SubBSample()); } } protected abstract void doProcessX(); protected void doProcessY(SubASample subASample) { // Nothing to do } protected void doProcessY(SubBSample subBSample) { // Nothing to do } } public class SubASample extends SuperSample { @Override protected void doProcessX() { System.out.println("doProcessX in SubASample"); } @Override protected void doProcessY(SubASample subASample) { System.out.println("doProcessY in SubASample"); } } public class Sample { public static void main(String[] args) { SubASample subASample = new SubASample(); subASample.getSomething(true); } } After using Generics ================================================= public abstract class SuperSample { public void getSomething(boolean isProcessA) { doProcessX(); if(isProcessA){ doProcessY(new SubASample()); }else{ doProcessY(new SubBSample()); } } protected abstract void doProcessX(); protected abstract <T extends SuperSample> void doProcessY(T subSample); } public class SubASample extends SuperSample { @Override protected void doProcessX() { System.out.println("doProcessX in SubASample"); } @Override protected <T extends SuperSample> void doProcessY(T subSample) { System.out.println("doProcessY in SubASample"); } } public class Sample { public static void main(String[] args) { SubASample subASample = new SubASample(); subASample.getSomething(true); } }

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  • How to load an entity by a key other than primary key?

    - by stacker
    In a customized servlet (seam 2.1.2) this works fine TableNameHome tableNameHome = (TableNameHome) Component.getInstance( "tableNameHome " ); tableName entity = tableNameHome.getInstance(); entity.setXXX(); tableNameHome.persit(); However this one fails: entityManager = tableNameHome .getEntityManager(); Query query = entityManager.createQuery( "SELECT b FROM tablename b WHERE b.box_id = :key2nd" ); query.setParameter( "key2nd", value); List results = query.getResultList(); and leads to this error message: org.hibernate.hql.ast.QuerySyntaxException: tablename is not mapped [SELECT b FROM tablename b WHERE b.key2nd = :key2nd] In EJB 2.1 I could implement other finder-methods. EntityHome.find() searches only by primary key. What do I need to do in order to query by a different criteria than primary key?

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  • using JDBC with persistence.xml

    - by moshe shamy
    I am building a framework that manage the access to the database. the framework getting tasks from the user and handle a connection pooling that manage the access to the database. the user just send me SQL commands. One of the feature that i would like to support is working with JPA, in this case i will provide entity manager. in some cases i would like to provide JDBC access as well as JPA access. the arguments for the database are written in XML file. so for JPA i need to write the property in persistence.xml so it will be not so smart to write again the same arguments for JDBC. do you know if i can get the arguments of the database from persistence.xml, do you know if there is a source code that do it. or should i parse persistence.xml by myself?

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  • How to use SQLiteOpenHelper without or less restrictive use of Context?

    - by Pentium10
    If you extend SQLiteOpenHelper, for the Constructor you have to use a Context. I am wondering if there is a way to leave this out, and be able to work with database tables without a Context. Or at least be least restrictive, I mean a way of project/class structure that will make history the several context passings I have to do now. As it is my application has several level of classes, chained in each other, and there are a few that connects to the database, but have no whatsoever influence on the interface, so they don't actually need the Context. Are you creating your classes in the way that you pass each time a Context to them? If not, how you do, how you reuse a Context in a short class?

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  • Encog 3.0 backpropagation

    - by Mohamed Shouman
    I have a question...I am using Encog framework to train a network using BP. I am training the network using images that has some object say a cat, telling the network which images are cats and which are not. Bellow are my Neural Network results actual=0.1545868370551181 ideal=0.0,actual=0.797896306829758 ideal=1.0,actual=0.1545868370551181 ideal=0.0,actual=0.797896306829758 ideal=1.0 It is my understanding that since different pictures are presented to network some look like cat for example then they should have higher percentage...but i keep getting same percentage for any pic that has a cat which is 0.79 and for other pics i get 0.15...how can i solve this issue!, what is the intuition behind whats going on! Many thanks

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  • Threading in Android

    - by virsir
    I am currently developing Android app, it needs download content from internet. I use thread to do that and then call runOnUiThread method to update GUI. I placed a refresh menu on it, if user tried to refresh the content, the download thread will be created and started. The problem is that how can I control the thread order, I need to accept the latest request's response and abandon previous thread requests if there were some other requests still running because the request parameters may have been changed by user. Currently I was using a threadId to do this thing, when a thread finished, it will check its threadId, if it was the latest recored one, it then takes control and render the response. My question is that is there any other proper better solution for this? Do I need to stop threads when user exit the app? I remember that some book said that do not try stop thread manually and wait itself finish is a good practice, is that true? Should I stop them by calling "stop" or "interrupt" method? I read some documents around threading in Android and found the class HandlerThread, what is it? In what kind of situation I need to use it?

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  • What else I must do allow my method to handle any type of objects

    - by NewHelpNeeder
    So to allow any type object I must use generics in my code. I have rewrote this method to do so, but then when I create an object, for example Milk, it won't let me pass it to my method. Ether there's something wrong with my generic revision, or Milk object I created is not good. How should I pass my object correctly and add it to linked list? This is a method that causes error when I insert an item: public void insertFirst(T dd) // insert at front of list { Link newLink = new Link(dd); // make new link if( isEmpty() ) // if empty list, last = newLink; // newLink <-- last else first.previous = newLink; // newLink <-- old first newLink.next = first; // newLink --> old first first = newLink; // first --> newLink } This is my class I try to insert into linked list: class Milk { String brand; double size; double price; Milk(String a, double b, double c) { brand = a; size = b; price = c; } } This is test method to insert the data: public static void main(String[] args) { // make a new list DoublyLinkedList theList = new DoublyLinkedList(); // this causes: // The method insertFirst(Comparable) in the type DoublyLinkedList is not applicable for the arguments (Milk) theList.insertFirst(new Milk("brand", 1, 2)); // insert at front theList.displayForward(); // display list forward theList.displayBackward(); // display list backward } // end main() } // end class DoublyLinkedApp Declarations: class Link<T extends Comparable<T>> {} class DoublyLinkedList<T extends Comparable<T>> {}

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  • using context resource in gwt 2 hosted mode

    - by rafael
    Hello all, I am moving a web app from gwt 1.5 to gwt 2.0. I am trying to connect to the a database resource I have in my context.xml file.In gwt 1.5 I had set up root.xml in tomcat-conf-gwt-localhost. I have no idea where to set up the resource in GWT 2.0. I tried placing my context.xml file in war-META-INF with no luck. Anyone have an idea where to place the context.xml file to be able to use a jndi database resource in GWT 2.0? Thanks in advanced

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  • Image creation performance / image caching

    - by Kilnr
    Hello, I'm writing an application that has a scrollable image (used to display a map). The map background consists of several tiles (premade from a big JPG file), that I draw on a Graphics object. I also use a cache (Hashtable), to prevent from having to create every image when I need it. I don't keep everything in memory, because that would be too much. The problem is that when I'm scrolling through the map, and I need an image that wasn't cached, it takes about 60-80 ms to create it. Depending on screen resolution, tile size and scroll direction, this can occur multiple times in one scroll operation (for different tiles). In my case, it often happens that this needs to be done 4 times, which introduces a delay of more than 300 ms, which is extremely noticeable. The easiest thing for me would be that there's some way to speed up the creation of Images, but I guess that's just wishful thinking... Besides that, I suppose the most obvious thing to do is to load the tiles predictively (e.g. when scrolling to the right, precache the tiles to the right), but then I'm faced with the rather difficult task of thinking up a halfway decent algorithm for this. My actual question then is: how can I best do this predictive loading? Maybe I could offload the creation of images to a separate thread? Other things to consider? Thanks in advance.

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  • Struts 1 - problem in showing ActionMessages through a JSP page

    - by Yatendra Goel
    I am using Struts 1.3.10. I am trying to display ActionMessage and ActionError set by Action class through a JSP page. The problem is that the ActionErrors are displaying well but ActionMessages are not displaying. When I debug the application, I found that the messages (reference variable of ActionMessages) contains messages. I also saved those messages through saveMessages(request, messages) method of Action class. So, I think that the problem is in the JSP code through which I am trying to display those messages. The JSP code is as follows: <logic:messagesPresent> <ul id="messsages"> <html:messages id="msg" message="true"> <li><bean:write name="msg"/> </li> </html:messages> </ul> </logic:messagesPresent>

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  • Releasing from development into production in maven

    - by Bruce
    Hi all, I'm confused about the use of maven in development and production environments - I'm sure it's something simple that I'm missing. Grateful for any help.. I set up maven inside eclipse on my local machine and wrote some software. I really like how it's made things like including dependent jars very easy. So that's my development environment. But now I want to release the project to production on a remote server. I've searched the documentation, but I can't figure out how it's supposed to work or what the maven best practice is.. Are you supposed to: a) Also be running maven on your production environment, and upload all your files to your production environment and rebuild your project there? (Something in me baulks at the idea of rebuilding 'released' code on the production server, so I'm fairly sure this isn't right..) b) use mvn:package to create your jar file and then copy that up to production? (But then what of all those nice dependencies? Isn't there a danger that your tested code is now going to be running against different versions of the dependent jars in the production environment, possibly breaking your code? Or missing a jar..?) c) Something else that I'm not figuring out.. Thanks in advance for any help!

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  • Can we view objets in the JVM memory?

    - by Sebastien Lorber
    Hey, At work we found that on some instances (particulary the slow ones) we have a different behaviour, acquired at the reboot. We guess a cache is not initialized correctly, or maybe a concurrency problem... Anyway it's not reproductible in any other env than production. We actually don't have loggers to activate... it's an old component... Thus i'd like to know if there are tools that can help us to see the different objets present in the JVM memory in order to check the content of the cache... Thank you!

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