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  • How do I ensure my abstract class's function can only operate on extenders of the same type as the c

    - by incrediman
    For example, let's say this is my abstract class: abstract class A{ int x; int y; void foo(A fooMe); } ...and B and C are two classes which extend A. What I want is for B to only be able to call foo() on other Bs, and for C to only be able to call foo() on other Cs. But I want this to be out of the hands of the programmer who's extending my A class - that is, I want a way to ensure this functionality within As code alone. What can I do? (If possible) I'd like to avoid any hack or generics solution that's too messy - I still want foo to be able to be called like this, for example: B b=new B(); B bb=new B(); bb.foo(b);

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  • Set the Size of a FrameView programmatically.

    - by npinti
    Hi guys, I am making a Desktop Application using Netbeans 6.8. What I would like to do is to programmatically set the size of my Application so that it fills the entire screen. I have looked around and it seems to be quite a nasty problem. I have been trying the code shown here, but it doesn't seem to be working. Anyone has any idea on how I can solve it?

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  • Why is the output like this?

    - by javatechi
    class another { public void method(Object o) { System.out.println("This is in method which takes object"); } public void method(String s) { System.out.println("This is method which takes string"); } } public class NewClass { public static void main(String args[]) { another an = new another(); an.method(null); } } When I try to execute this, I get This is method which takes string as the output. Why not "This is in method which takes object"? Object can also be null and string can also be null, why doesn't it invoke first method?

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  • Project Euler #3

    - by Alex
    Question: The prime factors of 13195 are 5, 7, 13 and 29. What is the largest prime factor of the number 600851475143? I found this one pretty easy, but running the file took an extremely long time, it's been going on for a while and the highest number I've got to is 716151937. Here is my code, am I just going to have a wait or is there an error in my code? //User made class public class Three { public static boolean checkPrime(long p) { long i; boolean prime = false; for(i = 2;i<p/2;i++) { if(p%i==0) { prime = true; break; } } return prime; } } //Note: This is a separate file public class ThreeMain { public static void main(String[] args) { long comp = 600851475143L; boolean prime; long i; for(i=2;i<comp/2;i++) { if(comp%i==0) { prime = Three.checkPrime(i); if(prime==true) { System.out.println(i); } } } } }

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  • jsf custom control strange behaviour

    - by Cristian Boariu
    hi, I have a jsf custom control which contains this: <rich:column> <c:if test="#{not empty columnTitle}"> <f:facet name="header"> <rich:spacer/> </f:facet> </c:if> <s:link view="#{view}" value="#{messages['edit']}" propagation="#{propagation}"> <f:param name="${paramName}" value="${paramValue}"/> </s:link> &#160; <h:commandLink action="#{entityHome.removeMethodName(entity)}" value="#{messages['remove']}"/> </rich:column> You see that command link action. I want it to call an action like this: action="#{documentHome.removeProperty(property)"} Well, in order to do this i call the control like: <up:columnDetails view="/admin/property.xhtml" columnTitle="yes" entity="#{property}" paramValue="#{property.propertyId}" propagation="nest" entityHome="documentHome" removeMethodName="removeProperty"/> So, i hardcode entityHome and removeMethodName. Well an error is firing. Caused by javax.servlet.ServletException with message: "#{entityHome.removeMethodName(entity)}: javax.el.MethodNotFoundException It seems that it cannot interpret "removeMethodName". If i print entityHome or removeMethodName it correctly shows the values i pass. But i think jsf has an error like not beeing able to "believe" that after an object.something, that something can be a parameter... Can anyone guide me...?

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  • Best practice when removing entity regarding mappedBy collections?

    - by Daniel Bleisteiner
    I'm still kind of undecided which is the best practice to handle em.remove(entity) with this entity being in several collections mapped using mappedBy in JPA. Consider an entity like a Property that references three other entities: a Descriptor, a BusinessObject and a Level entity. The mapping is defined using @ManyToOne in the Property entity and using @OneToMany(mappedBy...) in the other three objects. That inverse mapping is defined because there are some situations where I need to access those collections. Whenever I remove a Property using em.remove(prop) this element is not automatically removed from managed entities of the other three types. If I don't care about that and the following page load (webapp) doesn't reload those entities the Property is still found and some decisions might be taken that are no longer true. The inverse mappings may become quite large and though I don't want to use something like descriptor.getProperties().remove(prop) because it will load all those properties that might have been lazy loaded until then. So my currently preferred way is to refresh the entity if it is managed: if (em.contains(descriptor)) em.refresh(descriptor) - which unloads a possibly loaded collection and triggers a reload upon the next access. Is there another feasible way to handle all those mappedBy collections of already loaded entites?

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  • What GC parameters is a JVM running with?

    - by skaffman
    I'm still investigating issues I have with GC tuning (see prior question), which involves lots of reading and experimentation. Sun Java5+ JVMs attempt to automatically select the optimal GC strategy and parameters based on their environment, which is great, but I can't figure out how to query the running JVM to find out what those parameters are. Ideally, I'd like to see what values of the various GC-related -XX options are being used, as selected automatically by the VM. If I had that, I could have a baseline to begin tweaking. Anyone know to recover these values from a running VM?

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  • Printing a JFrame and its components

    - by Alex Terreaux
    I have been working in a big program and one of its functionalities should be to print the contents of the main window. I checked the API and found this example: http://docs.oracle.com/javase/tutorial/2d/printing/gui.html it was very helpful, I tried to use that code in my program by placing this inside the actionperformed method of my print button: PrinterJob job = PrinterJob.getPrinterJob(); job.setPrintable(this); boolean ok = job.printDialog(); if (ok) { try { job.print(); } catch (PrinterException ex) { /* The job did not successfully complete */ } } If I click the print button, I get a printer dialog and when I tell it to print, it just prints a blank document. I know the above code is not all I need, as I've seen in the API's examples there is a print() method, but apparently they never call it, so it is pretty confusing. I've tried calling and using it many times, but with no success. Also, I think that when I finally get it to print, my window will need to be printed in the landscape orientation, it even may need some scaling. Any ideas on how to do that? I would like any useful help to help me implement this code successfully. I know I should be able to do it by myself just by checking the documentation (I've tried for almost 2 days now) but I can't get it to work. I've learned all the programming I know through the internet. Any help will be greatly appreciated.

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  • Hibernate many-to-many relationship

    - by Capitan
    I have two mapped types, related many-to-many. @Entity @Table(name = "students") public class Student{ ... @ManyToMany(fetch = FetchType.EAGER) @JoinTable( name = "students2courses", joinColumns = { @JoinColumn( name = "student_id", referencedColumnName = "_id") }, inverseJoinColumns = { @JoinColumn( name = "course_id", referencedColumnName = "_id") }) public Set<Course> getCourses() { return courses; } public void setCourses(Set<Course> courses) { this.courses = courses; } ... } __ @Entity @Table(name = "courses") public class Course{ ... @ManyToMany(fetch = FetchType.EAGER, mappedBy = "courses") public Set<Student> getStudents() { return students; } public void setStudents(Set<Student> students) { this.students = students; } ... } But if I update/delete Course entity, records are not created/deleted in table students2courses. (with Student entity updating/deleting goes as expected) I wrote abstract class HibObject public abstract class HibObject { public String getRemoveMTMQuery() { return null; } } which is inherited by Student and Course. In DAO I added this code (for delete() method): String query = obj.getRemoveMTMQuery(); if (query != null) { session.createSQLQuery(query).executeUpdate(); } and I ovrerided method getRemoveMTMQuery() for Course @Override @Transient public String getRemoveMTMQuery() { return "delete from students2courses where course_id = " + id + ";"; } Now it works but I think it's a bad code. Is there a best way to solve this problem?

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  • Unable to use JAR in Eclipse

    - by Myn
    Hi guys, I have just created my first JAR in Eclipse, just a simple program with a single class Database.class. It is not in a package. public class Database { public Database() { int dbInit = 1; } } I have added it as an external JAR to the build path libraries for another project in Eclipse, but for some reason I cannot get Database db = new Database(), the default constructor, to work - it's as if the contents of the JAR are not being recognised. Could anyone please offer any advice on this? Thanks very much, M

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  • Runtime of optimized Primehunter

    - by Setton
    Ok so I need some serious runtime help here! This method should take in an int value, check its primality, and return true if the number is indeed a prime. I understand why the loop only needs to go up to i squared, I understand that the worst case scenario is the case in which either the number is prime (or a multiple of a prime). But I don't understand how to quantify the actual runtime. I have done the loop myself by hand to try to understand the pattern or correlation of the number (n) and how many loops occur, but I literally feel like I keep falling into the same trap every time. I need a new way of thinking about this! I have a hint: "Think about the SIZE of the integer" which makes me want to quantify the literal number of integers in a number in relation to how many iterations it does in the for loop (floor log(n)) +1). BUT IT'S NOT WORKIIIING?! I KNOW it isn't square root n, obviously. I'm asking for Big O notation. public class PrimeHunter { public static boolean isPrime(int n) { boolean answer = (n > 1) ? true : false; //runtime = linear runtime for (int i = 2; i * i <= n; i++) //runtime = ????? { if (n % i == 0) //doesn't occur if it is a prime { answer = false; break; } } return answer; //runtime = linear runtime } }

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  • Junit test that creates other tests

    - by Benju
    Normally I would have one junit test that shows up in my integration server of choice as one test that passes or fails (in this case I use teamcity). What I need for this specific test is the ability to loop through a directory structure testing that our data files can all be parsed without throwing an exception. Because we have 30,000+ files that that 1-5 seconds each to parse this test will be run in its own suite. The problem is that I need a way to have one piece of code run as one junit test per file so that if 12 files out of 30,000 files fail I can see which 12 failed not just that one failed, threw a runtimeexception and stopped the test. I realize that this is not a true "unit" test way of doing things but this simulation is very important to make sure that our content providers are kept in check and do not check in invalid files. Any suggestions?

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  • Hibernate reverse engineering

    - by EugeneP
    I have a structure where the main table is USER, other tables include CATEGORY (contains user_id). What I got after the standard reverse engineering procedure was: the class User contained a collection of categories, the class Category didn't contain the foreign key (user_id) but it did contain the User object. Why did it not contain the foreign key as a class property? And how do I join these two tables in HQL without that glue? HQL - please explain this part.

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  • Automatically Add a Prefix to Column Names for @Embeddable Classes

    - by VeeArr
    I am developing a project in which I am persisting some POJOs by adding Hibernate annotations. One problem I am running into is that code like this fails, as Hibernate tries to map the sub-fields within the Time_T onto the same column (i.e. startTime.sec and stopTime.sec both try to map to the colum sec, causing an error). @Entity public class ExampleClass { @Id long eventId; Time_T startTime; Time_T stopTime; } @Embeddable public class Time_T { int sec; int nsec; } As there will be many occurrences like this throughout the system, it would be nice if there was an option to automatically append a prefix to the column name (e.g. make the columns be startTime_sec, startTime_nsec, stopTime_sec, stopTime_nsec), without having to apply overrides on a per-field basis. Does Hibernate have this capability, or is there any other reasonable work-around?

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  • Join data from two Lists into one object

    - by Petr Mensik
    I ran into following situation and I am wondering about best solution. Let's say I have List<Object1> and List<Object2>, these lists are result of two separated queries. Both of them have the same size and there is relationship 1:1 between elements in the lists based on ID. I know that best solution would be fetching data in one DB query but that's possible right now. So my question is, what is the best way to join these lists into let's say List<Object3>?

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  • How to create live stream audio for web-sites ???

    - by Kathir
    Hi All, We are storing sound from mic to pc via sound forge. We would like to broadcast the sound which comes from the mic to the pc as live streaming audio. Basically a person speaks in a mic, we like to give it as live stream audio. The web-site is hosted on yahoo server. Can you please let me know in what are the ways we can achieve this? Thanks, Kathir

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  • jaxb: How can I bind nested element

    - by user368532
    There is my xml: <parent> <children> <child>1</child> <child>2</child> </children> </parent> I want to have the following Parent class: @XmlRootElement Parent{ @XmlElement(name="children/child") List<Child> children; } I don't want to have class for element 'children'. How should I map field children ?

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  • Keeping track of threads when creating them recursively

    - by 66replica
    I'm currently working on some code for my Programming Languages course. I can't post the code but I'm permitted to talk about some high level concepts that I'm struggling with and receive input on them. Basically the code is a recursive DFS on a undirected graph that I'm supposed to convert to a concurrent program. My professor already specified that I should create my threads in the recursive DFS method and then join them in another method. Basically, I'm having trouble thinking of how I should keep track of the threads I'm creating so I can join all of them in the other method. I'm thinking an array of Threads but I'm unsure how to add each new thread to the array or even if that's the right direction.

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  • Merge object from list by comparing one value

    - by Bala
    I have two List of Objects (one is master list and other is error list) and if there is a match of one value when compared two lists then merge all other error list values into mast list value (only one object). Other than iterating is there any other way to compare a value and then merge that object. Object is a Value object with some setters and getters. Appreciate your help. List<OrderVO> masterList; List<OrderVO> errorList; If errorList.OrderVO.getOrderID = masterList.OrderVO.getOrderID then masterList.OrderVO.merge(errorList.OrderVO) or copy all values of masterList.OrderVO.copy(errorList.OrderVO). Hoper this is clear

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  • JVM with no garbage collection

    - by HH
    I've read in many threads that it is impossible to turn off garbage collection on Sun's JVM. However, for the purpose of our research project we need this feature. Can anybody recommend a JVM implementation which does not have garbage collection or which allows turning it off? Thank you.

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