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  • Static initializer in Java

    - by Szere Dyeri
    My question is about one particular usage of static keyword. It is possible to use static keyword to cover a code block within a class which does not belong to any function. For example following code compiles: public class Test { private static final int a; static { a = 5; doSomething(a); } private static int doSomething(int x) { return (x+5); } } If you remove the static keyword it complains because the variable a is final. However it is possible to remove both final and static keywords and make it compile. It is confusing for me in both ways. How am I supposed to have a code section that does not belong to any method? How is it possible to invoke it? In general, what is the purpose of this usage? Or better, where can I find documentation about this?

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  • Read-only view of a Java list with more general type parameter

    - by Michael Rusch
    Suppose I have class Foo extends Superclass. I understand why I can't do this: List<Foo> fooList = getFooList(); List<Superclass> supList = fooList; But, it would seem reasonable for me to do that if supList were somehow "read-only". Then, everything would be consistent as everything that would come out of an objList would be a Foo, which is a Superclass. I could probably write a List implementation that would take an underlying list and a more general type parameter, and would then return everything as the more general type instead of the specific type. It would work like the return of Collections.unmodifiableList() except that the type would be made more general. Is there an easier way? The reason I'm considering doing this is that I am implementing an interface that requires that I return an (unmodifiable) List<Superclass>, but internally I need to use Foos, so I have a List<Foo>. I can't just cast.

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  • java jama array problem

    - by agazerboy
    Hi All, I asked a question before but duffymo said it is not clear so i am going to post it again here. I am using Jama api for SVD calculation. I know very well about jama and SVD. Jama does not work if your column are more than rows. I have this situation. What should I do?? any help? I can't transpose the matrix too as it can produce wrong results. Thanks. P.S: I am calculating LSI with the help of jama. I am going like column(docs) and rows ( terms )

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  • How to get more details of a java compilation

    - by Farid
    Hi, We are using an ant script in order to build our application. I recently made a change in one jar required by our app. However, when running the ant script, the compilation fails and the error message shown let me think that the compiler is using a previous version of the jar. Also, compilation throug my IDE works fine. Manual compilation with the javac command and specifying my new jar works as well. When looking at the classpath used by ant to build, I can see that the jar seems to be the correct one. So I am a bit lost actually, don't know where to look at ... Any ideas ? I also wanted to know if this is possible to get the path of the jar javac is really using when compiling a particular class .. Thanks and regards

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  • Java Junit testing problem

    - by agazerboy
    Hi All, I am using Junit 4. My whole program is working fine. I am trying to write a test case. But there is one error... here is very basic sample test public class di extends TestCase{ private static Records testRec; public void testAbc() { Assert.assertTrue( "There should be some thing.", di.testRec.getEmployee() > 0); } } and when i run this it give me error that fName can not be null if i use super and do like this public TestAgnes() { super("testAbc"); } it work all fine. It wasn't this before with JUnit 3.X am I doing wrong or they changed it :( Sorry if I am not clear Is there any way to executre test without super? or calling functions etc. ?

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  • Java repaint is slow under certain conditions.

    - by Gabriel A. Zorrilla
    I'm doing a simple grid which each square is highlighted by the cursor: They are a couple of JPanels, mapgrid and overlay inside a JLayeredPane, with mapgrid on the bottom. Mapgrid just draws on initialization the grid, its paint metodh is: public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); for (int i = 0; i < h; i++) { for (int j = 0; j < w; j++) { g2d.setColor(new Color(128, 128, 128, 255)); g2d.drawRect(tileSize * j, i * tileSize, tileSize, tileSize); } } In the overlay JPanel is where the highlighting occurs, this is what is repainted when the mouse is moved: public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2d = (Graphics2D) g; g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g2d.setColor(new Color(255, 255, 128, 255)); g2d.drawRect((pointerX/tileSize)*tileSize,(pointerY/ tileSize)*tileSize, tileSize, tileSize); } I noticed that even though the base layer (mapgrid) is NOT repainted when the mouse moves, just the transparent overlay layer, the performance is lacking. If i give the overlay JPanel a background, its way faster. If i remove the mapgrid Antialiasing, its a bit faster too. I don't know why giving a background to the overlay layer (and thus, hiding the mapgrid) or disabling antialiasing in the mapgrid leads to much better performance. Is there a better way to do this? Why does this happen?

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  • Java - Regex problem

    - by Yatendra Goel
    I want a regex to find the following types of strings: http://anything.abc.tld http://anything.abc.tld/ where abc - abc always remains abc anything - it could be any string tld - it could be any tld (top-level-domain) like .com .net .co.in .co.uk etc.

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  • Java variadic function parameters

    - by Amir Rachum
    Hi, I have a function that accepts a variable number of parameters: foo (Class... types); In which I get a certain number of class types. Next, I want to have a function bar( ?? ) That will accepts a variable number of parameters as well, and be able to verify that the variables are the same number (that's easy) and of the same types (the hard part) as was specified in foo. How can I do that? Edit: to clarify, a call could be: foo (String.class, Int.class); bar ("aaa", 32); // OK! bar (3); // ERROR! bar ("aa" , "bb"); //ERROR! Also, foo and bar are methods of the same class.

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  • Write Java Method Signature with Annotated paramaters with JDT

    - by Scott
    Hi, I am writing an eclipse plug-in which generates code. I am leveraging eclipse jdt to gen out classes, fields, and methods. One of the requirements I have is to generate methods with annotated paramaters... public returnType foo(@someAnnotation int id) { ..... ..... } Does anybody know how to write out the @someAnnotation using JDT? To write out normal parameters in JDT you could do something like the following Signature.createTypeSignature("int", false)

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  • audio processing using java

    - by Sukhhhh
    We have a requirement where we need to convert from .wav file to .mp3 and we are currently using "Tritonus" library to do that . The concern with that library is that requires "installation" of some "dll" files to the class path. I am wondering are there any API's those allow better processing without local installation. And other question is ,having mp3 format files will make it easier to join the files into a single file than having .wav files ?

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  • Sync between ms exchange calendar and Java app

    - by arkadiy
    Hi, we are developing a CRM app which holds customer meeting info. Users have requested that their Outlook calendars should reflect the activity they have booked in the CRM application and vice versa. Is there any solution to achieve this? Preferably not using any plugins or installs on the end user's PC?

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  • Java generic return type

    - by Colby77
    Hi, I'd like to write a method that can accept a type param (or whatever the method can figure out the type from) and return a value of this type so I don't have to cast the return type. Here is a method: public Object doIt(Object param){ if(param instanceof String){ return "string"; }else if(param instanceof Integer){ return 1; }else{ return null; } } When I call this method, and pass in it a String, even if I know the return type will be a String I have to cast the return Object. This is similar to the int param. How shall I write this method to accept a type param, and return this type?

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  • Java - Get a list of all Classes loaded in the JVM

    - by Walter White
    Hi all, I would like to get a list of all the classes loaded in the JVM at a particular point in time. The classes are in a particular package and are accessible via /WEB-INF/classes and not through a jar file in /WEB-INF/lib. How would I get a list of classes? Would I simply get the classpath, list all the files, then look for the names? Walter

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  • Weird Java Math ,10 ^ 1 = 11?

    - by Simon
    For an exercise I was writing a loop that turns a string into an integer without using the built in functions by multiplying each individual value by its numerical position. 75 would be 7*(10 ^ 1) + 5*(10 ^ 0), for example. However, for some reason (10 ^ 1) keeps coming back as 11. Is there some mistake I have made or an explanation for this?

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  • Java - AWT / Swing - handling the Event Descriptor Thread

    - by waitinforatrain
    Hi, I have a question about the 'Event Descriptor Thread'. I have a Main class that is also a JFrame. It initialises the rest of the components in the code, some of them do not involve Swing and some of them do. Is it enough to simply initialise the Main class using the EDT like this?... public static void main(String[] args) { javax.swing.SwingUtilities.invokeLater(new Runnable() { public void run() { new Main(); } }); } This way everything would run on the Event Dispatcher thread.

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  • Java anagram recursion List<List<String>> only storing empty lists<Strings>

    - by Riff Rafffer
    Hi In this recursion method i am trying to find all anagrams and add it to a List but what happens when i run this code is it just returns alot of empty Lists. private List<List<String>> findAnagrams(LetterInventory words, ArrayList<String> anagram, int max, Map<String, LetterInventory> smallDict, int level, List<List<String>> result) { ArrayList<String> solvedWord = new ArrayList<String>(); LetterInventory shell; LetterInventory shell2; if (level < max || max == 0) { Iterator<String> it = smallDict.keySet().iterator(); while (it.hasNext()) { String k = it.next(); shell = new LetterInventory(k); shell2 = words; if (shell2.subtract(shell) != null) { anagram.add(k); shell2 = words.subtract(shell); if (shell2.isEmpty()) { //System.out.println(anagram.toString()); it prints off fine here result.add(anagram); // but doesnt add here } else findAnagrams(shell2, anagram, max, smallDict, level + 1, result); anagram.remove(anagram.size()-1); } } } return results; }

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  • Quick Java question about variables

    - by Spencer
    I'm declaring a variable: private static final String filename = "filename.txt"; First, does the order of private static final matter? If not, is there a standard excepted sequence or convention? Second, the filename in my application is fixed. Is this the best was to store it's value? Thanks, Spencer

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  • Java, LinkedList of Strings. Insert in alphabetical order

    - by user69514
    I have a simple linked list. The node contains a string (value) and an int (count). In the linkedlist when I insert I need to insert the new Node in alphabetical order. If there is a node with the same value in the list, then I simply increment the count of the node. I think I got my method really screwed up. public void addToList(Node node){ //check if list is empty, if so insert at head if(count == 0 ){ head = node; head.setNext(null); count++; } else{ Node temp = head; for(int i=0; i<count; i++){ //if value is greater, insert after if(node.getItem().getValue().compareTo(temp.getItem().getValue()) > 0){ node.setNext(temp.getNext()); temp.setNext(node); } //if value is equal just increment the counter else if(node.getItem().getValue().compareTo(temp.getItem().getValue()) == 0){ temp.getItem().setCount(temp.getItem().getCount() + 1); } //else insert before else{ node.setNext(temp); } } } }

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  • Specify connection timeout in java.nio

    - by miorel
    Using non-blocking I/O, the code for connecting to a remote address looks something like: SocketChannel channel = SelectorProvider.provider().openSocketChannel(); channel.configureBlocking(false); channel.connect(address); The connection process will then have to be finished by invoking finishConnect() on the channel when some selector says the corresponding key isConnectable(). Is there a way to specify the connection timeout when using this idiom?

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  • java - call web service operation - wrong return type

    - by user1639680
    i have a simple web service with one method that returns List<org.company.data.mp> i've created a simple web service client and specified a web service with wsdl. in netbeans i try to call a web service operation: right click, insert code, ... and i pick my web service operation. the code gets inserted but the method's return type is not List<org.company.data.mp> but it is List<org.company.server.mp>! i don't get it.. in the package "server" there is no class called mp! i check the implementation class of my web service - it says the return type is ...data.mp not ...server.mp

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  • Java JFrame method pack() problem

    - by Oliver
    Hi, I have a frame with 4 JPanels and 1 JScrollPane, the 4 panels are in border layout north, east, south, west and the scrollpane in the center. I have been trying to get the pack method for a frame fuctioning but when run you just get the title bar of the window. Any Ideas? Thank you in advance. JFrame conFrame; JPanel panel1; JPanel panel2; JPanel panel3; JPanel panel4; JScrollPane listPane; JList list; Object namesAr[]; ... ... ... namesAr= namesA.toArray(); list = new JList(namesAr); list.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); list.setLayoutOrientation(JList.HORIZONTAL_WRAP); list.setVisibleRowCount(-3); list.addListSelectionListener(this); listPane = new JScrollPane(list); panel1 = new JPanel(); panel2 = new JPanel(); panel3 = new JPanel(); panel4 = new JPanel(); conFrame.setLayout(new BorderLayout()); panel1.setPreferredSize(new Dimension(100, 100)); panel2.setPreferredSize(new Dimension(100, 100)); panel3.setPreferredSize(new Dimension(100, 100)); panel4.setPreferredSize(new Dimension(100, 100)); panel1.setBackground(Color.red); panel2.setBackground(Color.red); panel3.setBackground(Color.red); panel4.setBackground(Color.red); conFrame.pack(); conFrame.add(panel1, BorderLayout.NORTH); conFrame.add(panel2, BorderLayout.EAST); conFrame.add(panel3, BorderLayout.SOUTH); conFrame.add(panel4, BorderLayout.WEST); conFrame.add(listPane, BorderLayout.CENTER); conFrame.setVisible(true);

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  • loop through HashMap Java jsp

    - by blub
    Hello, the related Questions couldn't help me very much. How can i loop through a HashMap in jsp like this example: <% HashMap<String, String> countries = MainUtils.getCountries(l); %> <select name="ccountry" id="ccountry" > <% //HERE I NEED THE LOOP %> </select>*<br/>

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  • generate excel in java

    - by chetan
    I want to generate excel with enabling auto-filter option.For that I have create one template excel file by enabling auto-filter option but when I write something into that template excel file auto-filter option disabled again. Is there any solution to create excel file by enabling auto-filter option.

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