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  • How can I ensure that a Java object (containing cryptographic material) is zeroized?

    - by Jeremy Powell
    My concern is that cryptographic keys and secrets that are managed by the garbage collector may be copied and moved around in memory without zeroization. As a possible solution, is it enough to: public class Key { private char[] key; // ... protected void finalize() throws Throwable { try { for(int k = 0; k < key.length; k++) { key[k] = '\0'; } } catch (Exception e) { //... } finally { super.finalize(); } } // ... }

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  • got a question about Linked-List in java code.

    - by glacier89
    Linked-List: Mirror Consider the following private class for a node of a singly-linked list of integers: private class Node{ public int value; public Node next; } A wrapper-class, called, ListImpl, contains a pointer, called start to the first node of a linked list of Node. Write an instance-method for ListImpl with the signature: public void mirror(); That makes a reversed copy of the linked-list pointed to by start and appends that copy to the end of the list. So, for example the list: start 1 2 3 after a call to mirror, becomes: start 1 2 3 3 2 1 Note: in your answer you do not need to dene the rest of the class for ListImpl just the mirror method.

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  • The Elegant way to handle Cyclic Event in Java ??

    - by dex
    Hi fellows, i think this not a specific problem to me; everybody might have encountered this issue before. To properly illustrate it, here's a simple UI: As you can see, those two spinners are controlling a single variable -- "A". The only difference is that they control it using different views. If i change the top spinner, "A" will be changed and the bottom spinner's value will also be updated accordingly. However, updating the bottom spinner's call (such as setValue) will also trigger another event instructing the top spinner to update based on the bottom spinner's value. Thus creates a bad cycle which can eventually cause a StackOverFlow exception. My previously solution is kinda cumbersome: i placed a guarding boolean to indicate whether the 2nd updating call should be performed. Now i'd like to ask "how can i handle such situation elegantly?" thx

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  • How to upload a directory via Grails or Java ?

    - by fabien-barbier
    What is the best way to upload a directory in grails ? I try this code : def upload = { if(request.method == 'POST') { Iterator itr = request.getFileNames(); while(itr.hasNext()) { MultipartFile file = request.getFile(itr.next()); File destination = new File(file.getOriginalFilename()) if (!file.isEmpty()) { file.transferTo(destination) // success } else { // failure } } response.sendError(200,'Done'); } } Unfortunately, I can only upload file by file. I would like to define my directory, and upload all files directly. Any ideas ?

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  • Can you cast an object to one that implements an interface? (JAVA)

    - by DDP
    Can you cast an object to one that implements an interface? Right now, I'm building a GUI, and I don't want to rewrite the Confirm/Cancel code (A confirmation pop-up) over and over again. So, what I'm trying to do is write a class that gets passed the class it's used in and tells the class whether or not the user pressed Confirm or Cancel. The class always implements a certain interface. Code: class ConfirmFrame extends JFrame implements ActionListener { JButton confirm = new JButton("Confirm"); JButton cancel = new JButton("Cancel"); Object o; public ConfirmFrame(Object o) { // Irrelevant code here add(confirm); add(cancel); this.o = (/*What goes here?*/)o; } public void actionPerformed( ActionEvent evt) { o.actionPerformed(evt); } } I realize that I'm probably over-complicating things, but now that I've run across this, I really want to know if you can cast an object to another object that implements a certain interface.

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  • Why is my program freezing when I use a method? (Java)

    - by user2915567
    When I use a boolean method in the Main body, my program freezes and stops working. I've tried putting the method at different places but the exact same thing happens - it freezes. The method is really simple and well-written, I'm not sure what's causing the problem. P.S. The method is on the bottom of the code. Thanks for your help! Edit: That was a dumb question now that I look at it. Thanks again everyone! public static void main(String[] args) { Scanner keyboard = new Scanner(System.in); int stringNumber = 0; String[] stringArray = new String[10]; for (int i = 0; i <= stringArray.length; i++) { boolean itemExists = false; boolean AddItem = AddItem(); if (AddItem == true) { out.println("\nEnter a string"); String input = keyboard.next(); if (i > 0) { for (int j = 0; j < stringArray.length; j++) { if (input.equalsIgnoreCase(stringArray[j])) { itemExists = true; out.println("Item \"" + input + "\" already exists."); break; } } } if (itemExists == false) { stringArray[stringNumber] = input; out.println("\"" + stringArray[stringNumber] + "\"" + " has been stored.\n"); } else { out.println("Try again."); i--; } PrintArray(stringArray); stringNumber++; } } } // This is the method I was talking about // public static boolean AddItem() { Scanner keyboard = new Scanner(System.in); int input = keyboard.nextInt(); out.println("If you want to add an item, Press 1"); if (input == 1) { return true; } else { out.println("Invalid input."); return false; } }

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  • What Gotchas When Learning C++, If I came from PHP/Java?

    - by silent
    Hi, I need to learn C++ in order to learn building Nokia WRT and or maemo application. I need to know what gotchas and what aspect of C++ that I need/have to learn or focus more. One thing I got in my mind is that C++ doesn't have garbage collector. Therefor, I need to focus on variable type. But, is there any others that really important and I can't ignore it?

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  • why is a minus sign prepended to my biginteger?

    - by kyrogue
    package ewa; import java.io.UnsupportedEncodingException; import java.security.MessageDigest; import java.security.NoSuchAlgorithmException; import java.util.logging.Level; import java.util.logging.Logger; import java.math.BigInteger; /** * * @author Lotus */ public class md5Hash { public static void main(String[] args) throws NoSuchAlgorithmException { String test = "abc"; MessageDigest md = MessageDigest.getInstance("MD5"); try { md.update(test.getBytes("UTF-8")); byte[] result = md.digest(); BigInteger bi = new BigInteger(result); String hex = bi.toString(16); System.out.println("Pringting result"); System.out.println(hex); } catch (UnsupportedEncodingException ex) { Logger.getLogger(md5Hash.class.getName()).log(Level.SEVERE, null, ex); } } } i am testing conversion of byte to hex and when done, the end result has a minus sign on the beginning of the string, why does this happen? i have read the docs and it says it will add a minus sign, however i do not understand it. And will the minus sign affect the hash result? because i am going to implement it to hash password stored on my database

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  • Java: Stopping a thread that has run for too long?

    - by Thomas King
    Say I've got something like this public void run(){ Thread behaviourThread = new Thread(abstractBehaviours[i]); behaviourThread.start(); } And I want to wait until abstractBehaviours[i] run method has either finished or run for 5000 milliseconds. How do I do that? behaviourThread.join(5000) doesn't seem to do that afaik (something is wrong with my code and I've put it down to that). All the abstract abstractBehaviour class is of course Runnable. I don't want to implement it inside each run method as that seems ugly and there are many different behaviours, I'd much rather have it in the calling/executing thread and do it just once. Solutions? First time doing something as threaded as this. Thanks!

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  • Java: I am trying to server a zip file through a link, but the file comes out as being empty

    - by Ankur
    I am trying to server a zip file through a link, but the file comes out as being empty. My app takes a number of files and zips them up, then presents the user with a link to the file so he/she can download it. On the server I can see that the zip file is being created correctly, but when I download it from the server through the normal HTML link provided no data is downloaded i.e. a zip file is created locally but it has file size 0kb. The file names are of the form XPCS.2010-03-09.15.13.42.165.zip - will the dots cause problems?

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  • java - how to split string in to multiple parts?

    - by Ewen
    I have a string that contains a value "firstword second third", and an ArrayList. I want to split the whole string in to by spaces and add the splitted strings in to the ArrayList. For example,"firstword second third" can be split to three separate strings and added three times in to the ArrayList. "1 2 3 4" can be splitted in to 4 strings and added 4 times in to the ArrayList. See the code below: public void separateAndAdd(String notseparated) { for(int i=0;i<canBeSepartedinto(notseparated);i++{ //what should i put here in order to split the string via spaces? thearray.add(separatedstring); } } public int canBeSeparatedinto(String string) //what do i put here to find out the amount of spaces inside the string? return .... } Please leave a comment if you dont get what I mean or I should fix some errors in this post. Thanks for your time!

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  • Java- FileWriter/BufferedWriter - appending to end of a text file?

    - by KP65
    I've done this before once, I'm trying to replicate what I did so far and this is what I've got: try { BufferedWriter writer = new BufferedWriter(new FileWriter("file.P", true)); System.out.println("entered"); if (!(newUserName.isEmpty()) || (newUserPass.isEmpty())){ writer.newLine(); writer.write("hellotest123"); writer.close(); } It seems to find file.P, which is just a txt file, but it doesn't seem to append anything onto it? It enters the code and passes the IF statement fine, but nothing is appended to the text file? I'm slightly stuck!

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  • Are there any new/updated Java web development frameworks to watch for?

    - by predhme
    I know recently Spring 3.0 was released which brought about a nice new set of features and ease of web development with their MVC package. However are there any new frameworks on the horizon and/or new versions of other frameworks that a web developer should have their eyes on? I heard about the Stripes framework, but it seems as though development has stopped. It also seems grails has a new release coming out as well which that looks like it is just an update to support the new features in the latest groovy release.

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  • How do we simplify this kind of code in Java? Something like macros in C?

    - by Terry Li
    public static boolean diagonals(char[][] b, int row, int col, int l) { int counter = 1; // because we start from the current position char charAtPosition = b[row][col]; int numRows = b.length; int numCols = b[0].length; int topleft = 0; int topright = 0; int bottomleft = 0; int bottomright = 0; for (int i=row-1,j=col-1;i>=0 && j>=0;i--,j--) { if (b[i][j]==charAtPosition) { topleft++; } else { break; } } for (int i=row-1,j=col+1;i>=0 && j<=numCols;i--,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } for (int i=row+1,j=col-1;i<=numRows && j>=0;i++,j--) { if (b[i][j]==charAtPosition) { bottomleft++; } else { break; } } for (int i=row+1,j=col+1;i<=numRows && j<=numCols;i++,j++) { if (b[i][j]==charAtPosition) { bottomright++; } else { break; } } return topleft + bottomright + 1 >= l || topright + bottomleft + 1 >= l; //in this case l is 5 } After I was done posting the code above here, I couldn't help but wanted to simplify the code by merging the four pretty much the same loops into one method. Here's the kind of method I want to have: public int countSteps(char horizontal, char vertical) { } Two parameters horizontal and vertical can be either + or - to indicate the four directions to walk in. What I want to see if possible at all is i++; is generalized to i horizontal horizontal; when horizontal taking the value of +. What I don't want to see is if or switch statements, for example: public int countSteps(char horizontal, char vertical) { if (horizontal == '+' && vertical == '-') { for (int i=row-1,j=col+1;i>=0 && j<=numCols;i--,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } } else if (horizontal == '+' && vertical == '+') { for (int i=row+1,j=col+1;i>=0 && j<=numCols;i++,j++) { if (b[i][j]==charAtPosition) { topright++; } else { break; } } } else if () { } else { } } Since it is as tedious as the original one. Note also that the comparing signs for the loop condition i>=0 && j<=numCols; for example, >= && <= have correspondence with the value combination of horizontal and vertical. Sorry for my bad wording, please let me know if anything is not clear.

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  • Java JAX-WS web-service client: how log request & response xml ?

    - by EugeneP
    I created an implementation of LoggingHandler that implements SOAPHandler It should log whenever handleMessage triggers. [ And it is never called in my case ] then : MyService service = new MyService(); MyServicePort port = service.getPortType(); now I try this: BindingProvider bindingProvider = (BindingProvider)port; bindingProvider.getBinding().getHandlerChain().add(new LoggingHandler()); I do not see any request / response xml though. Can you suggest any solution? Maybe there's other way to see output and request xml s ?

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  • java methods and race condition in a jsp/servlets application.

    - by A.S al-shammari
    Hi. Suppose that I have a method called doSomething() and I want to use this method in a multithreaded application (each servlet inherits from HttpServlet).I'm wondering if it is possible that a race condition will occur in the following cases: doSomething() is not staic method and it writes values to a database. doSomething() is static method but it does not write values to a database. what I have noticed that many methods in my application may lead to a race condition or dirty read/write. for example , I have a Poll System , and for each voting operation, a certain method will change a single cell value for that poll as the following: [poll_id | poll_data ] [1 | {choice_1 : 10, choice_2 : 20}] will the JSP/Servlets app solve these issues by itself, or I have to solve all that by myself? Thanks..

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