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  • JAVA Casting error

    - by user1612725
    Im creating a program that uses Dijksrtras algorithm, im using nodes that represent cities on an imported map, and you can create edges between two cities on the map. My problem is every edge has a "weight" where it will represent distance in minutes and i have a function where i want to see the distance between the two edges. But i keep getting the error "Cannot cast from Stad to Edge" at the line Edge<Stad> selectedEdge = (Edge) fvf.visaFörbLista.getSelectedValue(); where "Stad" represents the city and "Edge" an edge. FormVisaförbindelse fvf = new FormVisaförbindelse(); for(;;){ try{ int svar = showConfirmDialog(null, fvf, "Ändra Förbindelser", JOptionPane.OK_CANCEL_OPTION); if (svar != YES_OPTION) return; if (fvf.visaFörbLista.isSelectionEmpty() == true){ showMessageDialog(mainMethod.this, "En Förbindelse måste valjas.","Fel!", ERROR_MESSAGE); return; } Edge<Stad> selectedEdge = (Edge) fvf.visaFörbLista.getSelectedValue(); FormÄndraförbindelse faf = new FormÄndraförbindelse(); faf.setförbNamn(selectedEdge.getNamn()); for(;;){ try{ int svar2 = showConfirmDialog(mainMethod.this, faf, "Ändra Förbindelse", OK_CANCEL_OPTION); if (svar2 != YES_OPTION) return; selectedEdge.setVikt(faf.getförbTid()); List<Edge<Stad>> edges = lg.getEdgesBetween(sB, sA); for (Edge<Stad> edge : edges){ if (edge.getNamn()==selectedEdge.getNamn()){ edge.setVikt(faf.getförbTid()); } } return; } catch(NumberFormatException e){ showMessageDialog(mainMethod.this, "Ogiltig inmatning.","Fel!", ERROR_MESSAGE); }

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  • Static variables in Java for a test oObject creator

    - by stevebot
    Hey, I have something like the following TestObjectCreator{ private static Person person; private static Company company; static { person = new Person() person.setName("Joe"); company = new Company(); company.setName("Apple"); } public Person createTestPerson(){ return person; } public Person createTestCompany(){ return company; } } By applying static{} what am I gaining? I assume the objects are singletons as a result. However, if I did the following: Person person = TestObjectCreator.createTestPerson(); person.setName("Jill"); Person person2 = TestObjectCreator.createTestPerson(); would person2 be named Jill or Joe?

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  • Java anonymous class efficiency implications

    - by Po
    Is there any difference in efficiency (e.g. execution time, code size, etc.) between these two ways of doing things? Below are contrived examples that create objects and do nothing, but my actual scenarios may be creating new Threads, Listeners, etc. Assume the following pieces of code happen in a loop so that it might make a difference. Using anonymous objects: void doSomething() { for (/* Assume some loop */) { final Object obj1, obj2; // some free variables IWorker anonymousWorker = new IWorker() { doWork() { // do things that refer to obj1 and obj2 } }; } } Defining a class first: void doSomething() { for (/* Assume some loop */) { Object obj1, obj2; IWorker worker = new Worker(obj1, obj2); } } static class Worker implements IWorker { private Object obj1, obj2; public CustomObject(Object obj1, Object obj2) {/* blah blah */} @Override public void doWork() {} }; Thank you :)

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  • Java Generics : What is PECS?

    - by peakit
    Hi, I came across PECS (short for Producer extends and Consumer super) while reading on Generics. Can someone explain me how to use PECS to resolve confusion between extends and super? Thanks in advance !

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  • Detecting incorrect key using AES/GCM in JAVA

    - by 4r1y4n
    I'm using AES to encrypt/decrypt some files in GCM mode using BouncyCastle. While I'm proving wrong key for decryption there is no exception. How should I check that the key is incorrect? my code is this: SecretKeySpec incorrectKey = new SecretKeySpec(keyBytes, "AES"); IvParameterSpec ivSpec = new IvParameterSpec(ivBytes); Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "BC"); byte[] block = new byte[1048576]; int i; cipher.init(Cipher.DECRYPT_MODE, incorrectKey, ivSpec); BufferedInputStream fis=new BufferedInputStream(new ProgressMonitorInputStream(null,"Decrypting ...",new FileInputStream("file.enc"))); BufferedOutputStream ro=new BufferedOutputStream(new FileOutputStream("file_org")); CipherOutputStream dcOut = new CipherOutputStream(ro, cipher); while ((i = fis.read(block)) != -1) { dcOut.write(block, 0, i); } dcOut.close(); fis.close(); thanks

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  • How to pause a thread in java?

    - by mithun1538
    Consider the following code: while(true) { someFunction(); Thread.sleep(1000); } What I want is that, someFunction() be called once every 10 seconds. But this is not the case. It is being called every second. I tried Thread.wait(1000), but even that doesnt help. I removed of the while part, just kept the body, and at the end wrote : Thread.start(); But it throwed an exception. Is there any other solution to this?

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  • Java XMLRPC request-String

    - by Philip
    Hi, I'm using Apache XML-RPC 3.1.2 to talk to an online-service. They have something special, they need a hash over the whole XML with a secret key for some kind of security, like this: String hash = md5(xmlRequest + secretKey); String requestURL = "http://foo.bar/?authHash=" + hash; So I need the XML-request like this: <?xml version="1.0"?> <methodCall> <methodName>foo.bar</methodName> <params> <param> <value><struct> <member><name>bla</name> <value><int>1</int></value> </member> <member><name>blubb</name> <value><int>2</int></value> </member> </struct></value> </param> </params> </methodCall> But how do I get this String-representation of the XMLRPC-Request with the lib Apache XML-RPC?

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  • Inheritance in Java

    - by Mandar
    Hello, recently I went through the inheritance concept. As we all know, in inheritance, superclass objects are created/initialized prior to subclass objects. So if we create an object of subclass, it will contain all the superclass information. But I got stuck at one point. Do the superclass and the subclass methods are present on separate call-stack? If it is so, is there any specific reason for same? If it is not so, why they don't appear on same call-stack? E.g. // Superclass class A { void play1( ) { // .... } } // Subclass class B extends A { void play2( ) { //..... } } Then does the above 2 methods i.e play1( ) and play2( ) appear on separate call stack? Thanks.

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  • Java method keyword "final" and its use

    - by Lukas Eder
    When I create complex type hierarchies (several levels, several types per level), I like to use the final keyword on methods implementing some interface declaration. An example: interface Garble { int zork(); } interface Gnarf extends Garble { /** * This is the same as calling {@link #zblah(0)} */ int zblah(); int zblah(int defaultZblah); } And then abstract class AbstractGarble implements Garble { @Override public final int zork() { ... } } abstract class AbstractGnarf extends AbstractGarble implements Gnarf { // Here I absolutely want to fix the default behaviour of zblah // No Gnarf shouldn't be allowed to set 1 as the default, for instance @Override public final int zblah() { return zblah(0); } // This method is not implemented here, but in a subclass @Override public abstract int zblah(int defaultZblah); } I do this for several reasons: It helps me develop the type hierarchy. When I add a class to the hierarchy, it is very clear, what methods I have to implement, and what methods I may not override (in case I forgot the details about the hierarchy) I think overriding concrete stuff is bad according to design principles and patterns, such as the template method pattern. I don't want other developers or my users do it. So the final keyword works perfectly for me. My question is: Why is it used so rarely in the wild? Can you show me some examples / reasons where final (in a similar case to mine) would be very bad?

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  • Java NumberFormatException

    - by Bragaadeesh
    Hi, I am trying to do a conversion of a String to integer for which I get a NumberFormatException. The reason is pretty obvious. But I need a workaround here. Following is the sample code. public class NumberFormatTest { public static void main(String[] args) { String num = "9.18E+09"; try{ long val = Long.valueOf(num); }catch(NumberFormatException ne){ //Try to convert the value to 9180000000 here } } } I need the logic that goes in the comment section, a generic one would be nice. Thanks.

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  • Simple way to repeat a String in java

    - by e5
    I'm looking for a simple commons method or operator that allows me to repeat some String n times. I know I could write this using a for loop, but I wish to avoid for loops whenever necessary and a simple direct method should exist somewhere. String str = "abc"; String repeated = str.repeat(3); repeated.equals("abcabcabc"); Related to: repeat string javascript Create NSString by repeating another string a given number of times Edited I try to avoid for loops when they are not completely necessary because: They add to the number of lines of code even if they are tucked away in another function. Someone reading my code has to figure out what I am doing in that for loop. Even if it is commented and has meaningful variables names, they still have to make sure it is not doing anything "clever". Programmers love to put clever things in for loops, even if I write it to "only do what it is intended to do", that does not preclude someone coming along and adding some additional clever "fix". They are very often easy to get wrong. For loops that involving indexes tend to generate off by one bugs. For loops often reuse the same variables, increasing the chance of really hard to find scoping bugs. For loops increase the number of places a bug hunter has to look.

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  • Java How to call method of grand parents?

    - by Arkaha
    Let's assume I have 3 classes A, B and C, each one extending the previous one. How do I call the code in A.myMethod() from C.myMethod() if B also implements myMethod? class A { public void myMethod() { // some stuff for A } } class B extends A { public void myMethod() { // some stuff for B //and than calling A stuff super.myMethod(); } } class C extends B { public void myMethod() { // some stuff for C // i don't need stuff from b, but i need call stuff from A // something like: super.super.myMethod(); ?? how to call A.myMethod(); ?? } }

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  • Java ArrayList initialization

    - by Jonathan
    I am aware that you can initialize an array during instantiation as follows: String[] names = new String[] {"Ryan", "Julie", "Bob"}; Is there a way to do the same thing with an ArrayList? Or must I add the contents individually with array.add()? Thanks, Jonathan

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  • Why isn't JML implemented as Annotations in Java?

    - by devoured elysium
    Contrary to Code Contracts in C#, in JML Code Contracts are just text that's used in the form of comments in the header of a method. Wouldn't it be better to have them exposed as Annotations, then? That way even when compiling the information would persist on the .class's metadata, contrary to comments, that get erased. Am I missing something? Thanks

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  • Java Swing TanleModel fireTableRowsInserted on EDT

    - by Ayman
    I have a TableModel that is populated from a background running thread. I am calling fireTableRowsInserted when data is inserted, which is NOT on the EDT. My question is, do I need to use invokeLater for the fireTableRowsInserted? In other words, is the below correct: public void putData(TableRow row) { // we are not on the EDT here... rows.add(row); fireTableRowsInserted(rows.size()-1, rows.size()-1); }

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  • N-tier architecture and unit tests (using Java)

    - by Alexandre FILLATRE
    Hi there, I'd like to have your expert explanations about an architectural question. Imagine a Spring MVC webapp, with validation API (JSR 303). So for a request, I have a controller that handles the request, then passes it to the service layer, which passes to the DAO one. Here's my question. At which layer should the validation occur, and how ? My though is that the controller has to handle basic validation (are mandatory fields empty ? Is the field length ok ? etc.). Then the service layer can do some tricker stuff, that involve other objets. The DAO does no validation at all. BUT, if I want to implement some unit testing (i.e. test layers below service, not the controllers), I'll end up with unexpected behavior because some validations should have been done in the Controller layer. As we don't use it for unit testing, there is a problem. What is the best way to deal with this ? I know there is no universal answer, but your personal experience is very welcomed. Thanks a lot. Regards.

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  • IBM RAD With Java 1.5 wont compile code with generics

    - by Matt1776
    Hello I have some code that has generic references in it and my IBM RAD IDE will not compile the code, instead treating it as an error. I have checked the version of the JRE its pointing to across all the Enterprise Project's and it is 1.5 which I am told does support generics. Also I checked that all the libraries for WAS were pointing to the correct version and that the Compiler Compliance Level was set correctly (which it was at 5.0 and i changed it to 6.0 with no luck either) Does anyone have any suggestions as to anything else I can try? I have issues like this with RAD all the time and I dont know about anyone else but they took eclipse and made it complicated and dysfunctional.

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  • Filtering records in app-engine (Java)

    - by Manjoor
    I have following code running perfectly. It filter records based on single parameter. public List<Orders> GetOrders(String email) { PersistenceManager pm = PMF.get().getPersistenceManager(); Query query = pm.newQuery(Orders.class); query.setFilter("Email == pEmail"); query.setOrdering("Id desc"); query.declareParameters("String pEmail"); query.setRange(0,50); return (List<Orders>) query.execute(email); } Now i want to filter on multiple parameters. sdate and edate is Start Date and End Date. In datastore it is saved as Date (not String). public List<Orders> GetOrders(String email,String icode,String sdate, String edate) { PersistenceManager pm = PMF.get().getPersistenceManager(); Query query = pm.newQuery(Orders.class); query.setFilter("Email == pEmail"); query.setFilter("ItemCode == pItemCode"); query.declareParameters("String pEmail"); query.declareParameters("String pItemCode"); .....//Set filter and declare other 2 parameters .....// ...... query.setRange(0,50); query.setOrdering("Id desc"); return (List<Orders>) query.execute(email,icode,sdate,edate); } Any clue?

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  • java source code doubt

    - by abson
    this compiles class ex1 { public int show() { try { int a=10/10; return 10;} catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally");} System.out.println("hello"); return 20; } } on the other hand this doesn't class ex15 { public int show() { try { int a=10/0; return 10;} catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally"); return 40;} System.out.println("hello"); return 20; } } why is it so?

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  • How to extract paragraphs instead of whole texts only for XWPFWordExtractor (POI Library) Java

    - by Mr CooL
    Hello, I know the following code could extract whole texts of the docx document, however, I need to extract paragraph instead. Is there are possible way?? public static String extractText(InputStream in) throws Exception { JOptionPane.showMessageDialog(null, "Start extracting docx"); XWPFDocument doc = new XWPFDocument(in); XWPFWordExtractor ex = new XWPFWordExtractor(doc); String text = ex.getText(); return text; } Any helps would much appreciated. I need this so urgently.

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