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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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  • Specifying distinct sequence per table in Hibernate on subclasses

    - by gutch
    Is there a way to specify distinct sequences for each table in Hibernate, if the ID is defined on a mapped superclass? All entities in our application extend a superclass called DataObject like this: @MappedSuperclass public abstract class DataObject implements Serializable { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE) @Column(name = "id") private int id; } @Entity @Table(name = "entity_a") public class EntityA extends DataObject { ... } @Entity @Table(name = "entity_b") public class EntityB extends DataObject { ... } This causes all entities to use a shared sequence, the default hibernate_sequence. What I would like to do is use a separate sequence for each entity, for example entity_a_sequence and entity_b_sequence in the example above. If the ID were specified on the subclasses then I could use the @SequenceGenerator annotation to specify a sequence for each entity, but in this case the ID is on the superclass. Given that ID is in the superclass, is there a way I can use a separate sequence for each entity — and if so, how? (We are using PostgreSQL 8.3, in case that's relevant)

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  • Handling Character Encoding in URI on Tomcat

    - by ZZ Coder
    On the web site I am trying to help with, user can type in an URL in the browser, like following Chinese characters, http://localhost:8080?a=?? On server, we get GET /a=%E6%B5%8B%E8%AF%95 HTTP/1.1 As you can see, it's UTF-8 encoded, then URL encoded. We can handle this correctly by setting encoding to UTF-8 in Tomcat. However, sometimes we get Latin1 encoding on certain browsers, http://localhost:8080?a=ß turns into GET /a=%DF HTTP/1.1 Is there anyway to handle this correctly in Tomcat? Looks like the server has to do some intelligent guessing. We don't expect to handle the Latin1 correctly 100% but anything is better than what we are doing now by assuming everything is UTF-8. The server is Tomcat 5.5. The supported browsers are IE 6+, Firefox 2+ and Safari on iPhone.

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  • Tomcat reporting 404 error on all of newly deployed WAR files?

    - by dacracot
    I deployed a WAR file into $TOMCAT_HOME/webapps by copying the file into the directory, just like I've done a thousand times before. Tomcat detects the WAR and inflates it. I can traverse the directory tree on my server at the command line (it's Fedora). But when I address the webapp within my client machine's browser, I get nothing but 404 errors. This has happened to the last two deployments of completely separate WARs. The first was a replacement of an existing WAR. I first deleted the WAR and its inflated directory, and then copied in the WAR which inflated... 404. I deleted everything again, put back the previously working WAR from backup. It inflated and worked. The second was a completely new, never before deployed WAR... nothing but 404. Other WARs are working, but now I'm afraid to change anything until I know what is going on. Any clues? Edit: From my comment you can see that the logs included "SEVERE: Error listenerStart" after the WAR was deployed by Tomcat. There were no stack traces or other errors reported.

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  • JMX - MBean automated registration on application deployment

    - by Gadi
    Hi All, I need some direction with JMX and J2EE. I am aware (after few weeks of research) that the JMX specification is missing as far as deployment is concerned. There are few vendor specific implementations for what I am looking for but none are cross vendor. I would like to automate the deployment of MBeans and registration with the Server. I need the server to load and register my MBeand when the application is deployed and remove when the application is un-deployed. I develop with: NetBean 6.7.1, GlassFish 2.1, J2EE5, EJB3 More specific, I need a way to manage timer service runs. My application need to run different archiving agents and batch reporting. I was hoping the JMX will give me remote access to create and manage the timer services and enable the user to create his own schedule. If the JMX is auto registered on application deployment the user can immediately connect and manage the schedule. On the other hand, how can an EJB connect/access an MBean? Many thanks in advance. Gadi.

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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