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  • Is this an example of polymorphism?

    - by computer-science-student
    I'm working on a homework assignment (a project), for which one criterion is that I must make use of polymorphism in a way which noticeably improves the overall quality or functionality of my code. I made a Hash Table which looks like this: public class HashTable<E extends Hashable>{ ... } where Hashable is an interface I made that has a hash() function. I know that using generics this way improves the quality of my code, since now HashTable can work with pretty much any type I want (instead of just ints or Strings for example). But I'm not sure if it demonstrates polymorphism. I think it does, because E can be any type that implements Hashable. In other words HashTable is a class which can work with (practically) any type. But I'm not quite sure - is that polymorphism? Perhaps can I get some clarification as to what exactly polymorphism is? Thanks in advance!

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  • How do I stop the m2eclipse plugin interfering with command line mvn builds?

    - by locka
    I use the m2eclipse plugin in Eclipse so that I can import a Maven project. The plugin reads the pom.xml and sorts out the dependencies in the projects in an Eclipse friendly way so I'm not looking at a sea of broken references and errors. I use Eclipse for code development however I usually build the projects from the command line, e.g. "mvn clean install". Unfortunately when I do this, m2eclipse detects disk activity and attempts to rebuild the workspace. This interferes with the command line build and sometimes results in a race condition. For example the command line might be in its clean phase but fails because it tries to delete a file or directory which is locked during the workspace rebuild. Aside from that workspace rebuilding is incredibly slow, and between failed builds and wasted CPU my build process is 2-3x longer than it should be. It isn't an option to not use Eclipse (e.g. to use Netbeans), or to disable m2eclipse. It is a useful plugin except for this behaviour. So my question is, how do I stop m2eclipse from rebuilding the workspace all the time? Can I invoke a manual refresh and otherwise disable this behaviour?

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  • How does lookup work?

    - by badgirl
    Hello. I have BeanTreeView, and some nodes in it. Every node has constructor public class ProjectNode extends AbstractNode { public ProjectNode(MainProject obj, DiagramsChildren childrens) { super (new ProjectsChildren(), Lookups.singleton(obj)); setDisplayName ( obj.getName()); } I set Rootnode as a root for tree in ExplorerTopComponent as this: private final ExplorerManager mgr = new ExplorerManager(); public ExplorerTopComponent(){ associateLookup (ExplorerUtils.createLookup(mgr, getActionMap())); mgr.setRootContext(new RootNode()); } And now, how I can get MainProject obj from some node? I need to get it in another class.

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  • copy or clone a HSSFWorkbook

    - by Fortega
    Hi, Currently I am doing the following in a loop (at least 300 times): - create a HSSFWorkbook from a template file - add some values to specific cells in the workbook - save the workbook as a new excel file The first line takes about 70% of the time (reading excel file). What I would like to do is to take this out of the loop, and read the file only once. In the loop, I would like to copy or clone the template HSSFWorkbook. However, I can't find anything about copying/cloning a HSSFWorkbook. Did some of you do this before? Any tips?

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  • Playing around with Eclipse features - Project files are now hidden?

    - by Daddy Warbox
    I don't even remember how, but somehow I managed to make all of my project's source files hidden in Eclipse's Package and Project Explorer panels. Go figure. 'Show Filtered Children (alt+click)' temporarily reveals the files, and only in Package Explorer can I double-click to reopen them from this view. They go back into hiding after I select another item, though. Plus, now I'm getting other annoyances, such as all of the folded non-hidden trees altogether expanding when I click on any item, and the entire file folder tree of my project now being shown in these panels (including my .svn subversion folders... which shouldn't be any of Eclipse's business, presently). Long story short, my Package/Project Explorers' just blew up on me, and I want to know how to fix this. Thanks in advance. P.S. What's a good guide I can use to learn my way around this silly contraption, anyway?

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  • WAS Server - Apache critical problem

    - by murali
    hi, I am facing critical problem for integration of WAS Server-Apache Server.I am using the WAS server for the connection pooling for the database calling...and my webpage is hosted in the apache server and the webpage serarch box is calling the WAS Server and i am using struts frame work for autocomplete action... but it is working in IE of all versions.. but it is not working any browser... the JS file HTTPsuggestions are going to the structs frame work... but the response is is giving as null even i am giving the xmlHttpGetSuggestions.status =200 || xmlHttpGetSuggestions.status =0 but i am not getting the autocomplete feature. can you please help to slove this problem..... Thanks, Murali

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  • Declarative JDOQL vs Single-String JDOQL : performance

    - by DrDro
    When querying with JDOQL is there a performance difference between using the declarative version and the Single-String version: Example from the JDOQL doc: //Declarative JDOQL : Query q = pm.newQuery(org.jpox.Person.class, "lastName == \"Jones\" && age < age_limit"); q.declareParameters("double age_limit"); List results = (List)q.execute(20.0); //Single-String JDOQL : Query q = pm.newQuery("SELECT FROM org.jpox.Person WHERE lastName == \"Jones\"" + " && age < :age_limit PARAMETERS double age_limit"); List results = (List)q.execute(20.0); Other then performance, are there any reasons for which one is better to use then the other or is it just about the one with which we feel more comfortable.

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  • Ten latest files on disk

    - by Artic
    I need effective algorithm to keep only ten latest files on disk in particular folder to support some kind of publishing process. Only 10 files should present in this folder at any point of time. Please, give your advises what should be used here.

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  • Getting following exception javax.sound.sampled.LineUnavailableException: line with format ULAW 800

    - by angelina
    Dear All, I tried to play and get duration of a wave file using code below but got following exception.please resolve.I m using a wave file format. URL url = new URL("foo.wav"); Clip clip = AudioSystem.getClip(); AudioInputStream ais = AudioSystem.getAudioInputStream(url); clip.open(ais); System.out.println(clip.getMicrosecondLength()); **javax.sound.sampled.LineUnavailableException: line with format ULAW 8000.0 Hz, 8 bit, mono, 1 bytes/frame, not supported.**

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  • Quartz Cron Trigger with Spring - triggering new cron before last ended

    - by Trick
    Simple question, I think. I have org.springframework.scheduling.quartz.CronTriggerBean triggering one job once a day. Because this method can last a long time (over 24 hours), will the next day at the same time a new job be executed if the last one is not ended yet? If yes - is it possible to turn off executing new jobs until the last one is finished? My method is trans-coding videos and some days there a lot of videos and could last long.

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  • Invalid method declaration, return type required

    - by Brett Steen
    I am getting an error at public Rectangle(double width, double height){ saying that it's an invalid method declaration, return type required. I'm not sure how to fix it. These are also my instructions for my assignment: Write a super class encapsulating a rectangle. A rectangle has two attributes representing the width and the height of the rectangle. It has methods returning the perimeter and the area of the rectangle. This class has a subclass, encapsulating a parallelepiped, or box. A parallelepiped has a rectangle as its base, and another attribute, its length. It has two methods that calculate and return its area and volume. `public class Rectangle1 { private double width; private double height; public Rectangle1(){ } public Rectangle(double width, double height){ this.width = width; this.height = height; } public double getWidth(){ return width; } public void setWidth(double width) { this.width = width; } public double getHeight(){ return height; } public void setHeight(double height){ this.height = height; } public double getArea(){ return width * height; } public double getPerimeter(){ return 2 * (width + height); } } public class TestRectangle { public static void main(String[] args) { Rectangle1 rectangle = new Rectangle1(2,4); System.out.println("\nA rectangle " + rectangle.toString()); System.out.println("The area is " + rectangle.getArea()); System.out.println("The perimeter is " + rectangle.getPerimeter()); } }`

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  • Blob object not working properly even though the class is seralized

    - by GustlyWind
    I have class which is seralized and does convert a very large amount of data object to blob to save it to database.In the same class there is decode method to convert blob to the actual object.Following is the code for encode and decode of the object. private byte[] encode(ScheduledReport schedSTDReport) { byte[] bytes = null; try { ByteArrayOutputStream bos = new ByteArrayOutputStream(); ObjectOutputStream oos = new ObjectOutputStream(bos); oos.writeObject(schedSTDReport); oos.flush(); oos.close(); bos.close(); //byte [] data = bos.toByteArray(); //ByteArrayOutputStream baos = new ByteArrayOutputStream(); //GZIPOutputStream out = new GZIPOutputStream(baos); //XMLEncoder encoder = new XMLEncoder(out); //encoder.writeObject(schedSTDReport); //encoder.close(); bytes = bos.toByteArray(); //GZIPOutputStream out = new GZIPOutputStream(bos); //out.write(bytes); //bytes = bos.toByteArray(); } catch (Exception e) { _log.error("Exception caught while encoding/zipping Scheduled STDReport", e); } decode(bytes); return bytes; } /* * Decode the report definition blob back to the * ScheduledReport object. */ private ScheduledReport decode(byte[] bytes) { ByteArrayInputStream bais = new ByteArrayInputStream(bytes); ScheduledReport sSTDR = null; try { ObjectInputStream ois = new ObjectInputStream(bais); //GZIPInputStream in = new GZIPInputStream(bais); //XMLDecoder decoder = new XMLDecoder(in); sSTDR = (ScheduledReport)ois.readObject();//decoder.readObject(); //decoder.close(); } catch (Exception e) { _log.error("IOException caught while decoding/unzipping Scheduled STDReport", e); } return sSTDR; } The problem here is whenver I change something else in this class means any other method,a new class version is created and so the new version the class is unable to decode the originally encoded blob object. The object which I am passing for encode is also seralized object but this problem exists. Any ideas thanks

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  • Do Blob properties on entities affect query performance?

    - by Jaroslav Záruba
    Hello I'm trying to make my mind on whether to store a binary representation of an entity as its Blob property, or whether I better keep the blobs in some separate 'wrapping' class. Possible impact on memory heap and/or a query execution time are my concerns in the first case, complexity votes against the other one. I know Blobs are not indexed, i.e. index size is not what I'm worrying about. Also I assume for blobs Datastore puts defaultFetchGroup to false, but does it mean that blobs don't make a difference in queries? Regards J. Záruba

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  • Is it possible to build a JPA entity by extending a POJO?

    - by Freiheit
    Lets say I have the following POJO: public class MyThing { private int myNumber; private String myData; //assume getter/setter methods } Is it now possible to extend this POJO as a JPA entity? @Entity @Table(name = "my_thing") public class MyThingEntity extends MyThing implements Serializable { @Column(name = "my_number") //????????? @Column(name = "my_data") //???????? } I want to keep the POJO separate from the JPA entity. The POJO lives in a different project and is often used without a persistence layer, my project wants to persist it in a database and do so without the overhead of mapping from a POJO to an entity and back. I understand that JPA entities are POJOs, but in order to use it I would have to include a library that implements javax.persistence and the other projects using the same base object have no use for a persistence layer. Is this possible? Is this a good idea?

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  • Disabling JComboBox and retaining original item list

    - by n002213f
    My action listener on a JComboBox invokes a thread. I would like the component to be disabled until the thread completes. I have tried calling seEnabled(false) when the thread start and setEnabled(true) when it completes. Unfortunately setEnabled(false) clears the combo box list as well. Is there a way of disabling the component but retain the original list?

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  • How to stream XML data using XOM?

    - by Jonik
    Say I want to output a huge set of search results, as XML, into a PrintWriter or an OutputStream, using XOM. The resulting XML would look like this: <?xml version="1.0" encoding="UTF-8"?> <resultset> <result> [child elements and data] </result> ... ... [1000s of result elements more] </resultset> Because the resulting XML document could be big (tens or hundreds of megabytes, perhaps), I want to output it in a streaming fashion (instead of creating the whole Document in memory and then writing that). The granularity of outputting one <result> at a time is fine, so I want to generate one <result> after another, and write it into the stream. Assume there's already a method that helps with iterating the results and generating Element objects: public nu.xom.Element getNextResult(); So I'd simply like to do something like this pseudocode (automatic flushing enabled, so don't worry about that) : open stream/writer write declaration write start tag for <resultset> while more results: write next <result> element write end tag for <resultset> close stream/writer I've been looking at Serializer, but the necessary methods, writeStartTag(Element), writeEndTag(Element), write(DocType) are protected, not public! Is there no other way than to subclass Serializer to be able to use those methods, or to manually write the start and end tags directly into the stream as Strings, bypassing XOM altogether? (The latter wouldn't be too bad in this simple example, but in the general case it would get quite ugly.) Am I missing something or is XOM just not made for this? With dom4j I could do this easily using XMLWriter - it has constructors that take a Writer or OutputStream, and methods writeOpen(Element), writeClose(Element), writeDocType(DocumentType) etc. Compare to XOM's Serializer where the only public write method is the one that takes a whole Document. Please refrain from answering if you're not familiar with XOM! I specifically want to know if and how you can do this kind of streaming with that library. (This is related to my question about the best dom4j replacement where XOM is a strong contender.)

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