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  • odd behavior with java collections of parameterized Class objects

    - by Paul
    Ran into some questionable behavior using lists of parameterized Class objects: ArrayList<Class<String>> classList = new ArrayList<Class<String>>(); classList.add(Integer.class); //compile error Class intClass = Integer.class; classList.add(intClass); //legal apparently, as long as intClass is not parameterized Found the same behavior for LinkedList, haven't tried other collections. Is it like this for a reason? Or have I stumbled on something?

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  • Access check on folder in java

    - by Bhaskar
    I'm using the following code to check the access on selected folder. but it's not working. private boolean writeAccess(String path){ try { AccessController.checkPermission(new FilePermission(path, "read,write"));/*,*/ // Has permission return true; } catch (SecurityException e) { // Does not have permission return false; } } wt is prblm in it. and is there any other options to check the existance and access on the folders/directories?

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  • java template design

    - by Sean Nguyen
    Hi, I have this class: public class Converter { private Logger logger = Logger.getLogger(Converter.class); public String convert(String s){ if (s == null) throw new IllegalArgumentException("input can't be null"); logger.debug("Input = " + s); String r = s + "abc"; logger.debug("Output = " + s); return r; } public Integer convert(Integer s){ if (s == null) throw new IllegalArgumentException("input can't be null"); logger.debug("Input = " + s); Integer r = s + 10; logger.debug("Output = " + s); return r; } } The above 2 methods are very similar so I want to create a template to do the similar things and delegate the actual work to the approriate class. But I also want to easily extends this frame work without changing the template. So for example: public class ConverterTemplate { private Logger logger = Logger.getLogger(Converter.class); public Object convert(Object s){ if (s == null) throw new IllegalArgumentException("input can't be null"); logger.debug("Input = " + s); Object r = doConverter(); logger.debug("Output = " + s); return r; } protected abstract Object doConverter(Object arg); } public class MyConverter extends ConverterTemplate { protected String doConverter(String str) { String r = str + "abc"; return r; } protected Integer doConverter(Integer arg) { Integer r = arg + 10; return r; } } But that doesn't work. Can anybody suggest me a better way to do that? I want to achieve 2 goals: 1. A template that is extensible and does all the similar work for me. 2. I ant to minimize the number of extended class. Thanks,

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  • Java: Converting UTF 8 to String

    - by kujawk
    When I run the following program: public static void main(String args[]) throws Exception { byte str[] = {(byte)0xEC, (byte)0x96, (byte)0xB4}; String s = new String(str, "UTF-8"); } on Linux and inspect the value of s in jdb, I correctly get: s = "ì–´" on Windows, I incorrectly get: s = "?" My byte sequence is a valid UTF-8 character in Korean, why would it be producing two very different results?

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  • Confusion in multi dimensional array in Java

    - by Alvin
    Hello, I'm not able to understand the following multi-dimensional code. Could someone please clarify me? int[][] myJaggedArr = new int [][] { new int[] {1,3,5,7,9}, new int[] {0,2,4,6}, new int[] {11,22} }; May I know how it is different from the following code? int[][] myArr = new int [][] { {1,3,5,7,9}, {0,2,4,6}, {11,22} };

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  • Exception and Inheritance in JAVA

    - by user1759950
    Suppose we have this problem public class Father{ public void method1(){...} } public class Child1 extends Father{ public void method1() throws Exception{ super.method1(); ... } } Child1 extends Father and override method1 but given implementation Child1.method1 now throws a exception, this wont compile as override method can't throw new exceptions. What is the best solution? Propagate the required exception to the Father.. to me this is against encapsulation, inheritance and general OOP ( the father potentially throw and exception that will never happen ) Use a RuntimeException instead? This solution wont propagate the Exception to the father but I read In Oracle docs and others sources states class of exceptions should be used when "Client code cannot do anything" this is not that case, this exception will b useful to recover blablabla ( why is wrong to use RuntimeException instead? ) Other.. thanks, Federico

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  • Deferred printing in Java

    - by Bober02
    I have a specific issue with general console printing and I was wondering whether anyone has a solution for it. I am trying to print a dataTable which would look like sth like this: Table ---------------------- Name |Surname | ---------------------- Mike |Mikhailowish| Rafaello|Mirena | and so on. In order to print the border of the bar I need to know what the maximum length of each column value is. I don't want to go through the whole database to find that out and then again to print it. I would rather like to do sth like: System.out.printLater(s); //herejust leave a pointer to a StringBuilder you will build ... s.append("--------"); ... System.out.printAllDeferred(); I understand the above is probably in 99.99999% chances impossible, but perhaps you guys have a clever way of achieving the above?

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  • Java : Singleton class instances in a Web based Application

    - by Preethi Jain
    I have this Singleton class inside a Web Application . public class MyDAO { private static MyDAO instance; private MyDAO() { } public static MyDAO getInstance() { if (instance == null) { instance = new MyDAO(); } return instance; } I will access it this way public void get_Data() { MyDAO dao = MyDAO.getInstance(); } How many Objects of MyDAO class will be created if there are 3 Users accessing the Application ?? Will there be one instance of MyDAO per User ??

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  • Setting the type of a field in a superclass from a subclass (Java)

    - by Ibolit
    Hi. I am writing a project on Google App Engine, within it I have a number of abstract classes that I hope I will be able to use in my future projects, and a number of concrete classes inheriting from them. Among other abstract classes I have an abstract servlet that does user management, and I hava an abstract user. The AbstractUser has all the necessary fields and methods for storing it in the datastore and telling whether the user is registered with my service or not. It does not implement any project specific functionality. The abstract servlet that manages users, refers only to the methods declared in the AbstractUser class, which allows it to generate links for logging in, logging out and registering (for unregistered users). In order to implement the project-specific user functionality I need to subclass the Abstract user. The servlets I use in my project are all indirect descendants from that abstract user management servlet, and the user is a protected field in it, so the descendant servlets can use it as their own field. However, whenever i want to access any project specific method of the concrete user, i need to cast it to that type. i.e. (abstract user managing servlet) ... AbstractUser user = getUser(); ... abstract protected AbstractUser getUser(); (project-specific abstract servlet) @Override protected AbstractUser getUser() { return MyUserFactory.getUser(); } any other project specific servlet: int a = ((ConcreteUser) user).getA(); Well, what i'd like to do is to somehow make the type of “user” in the superclass depend on something in the project-specific abstract class. Is it at all possible? And i don't want to move all the user-management stuff into a project-specific layer, for i would like to have it for my future projects already written :) Thank you for your help.

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  • Memory increases with Java UDP Server

    - by Trevor
    I have a simple UDP server that creates a new thread for processing incoming data. While testing it by sending about 100 packets/second I notice that it's memory usage continues to increase. Is there any leak evident from my code below? Here is the code for the server. public class UDPServer { public static void main(String[] args) { UDPServer server = new UDPServer(15001); server.start(); } private int port; public UDPServer(int port) { this.port = port; } public void start() { try { DatagramSocket ss = new DatagramSocket(this.port); while(true) { byte[] data = new byte[1412]; DatagramPacket receivePacket = new DatagramPacket(data, data.length); ss.receive(receivePacket); new DataHandler(receivePacket.getData()).start(); } } catch (IOException e) { e.printStackTrace(); } } } Here is the code for the new thread that processes the data. For now, the run() method doesn't do anything. public class DataHandler extends Thread { private byte[] data; public DataHandler(byte[] data) { this.data = data; } @Override public void run() { System.out.println("run"); } }

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  • Java Script JQUery

    - by windi
    Hi I am extracting data from an xml file converting it into json and rendering the images which i am retriving to the html file via jtemplate.now i want to user scroller and scroll the images .i can call to the scroller plugin but it is not scrolling throuhg . can any one help me please.

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  • How to append to an array that contains blank spaces - Java

    - by Cameron Townley
    I'm trying to append to a char[] array that contains blank spaces on the end. The char array for example contains the characters 'aaa'. When I append the first time the method functions properly and outputs 'aaabbb'. The initial capacity of the array is set to 80 or multiples of 80. The second time I try and append my output looks like"aaabbb bbb". Any psuedocode would be great.

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  • Convert any object to pretty HTML in java

    - by ripper234
    How can I convert a given object (in a generic way with reflection) to pretty printable HTML? What ready made library do you recommend that does this? I need support for simple nested objects (as long as they don't create loops in the object graph). I tried to convert it to JSON, but DefaultPrettyPrinter is not HTML friendly.

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  • Help using recursion in Java

    - by Mercer
    I have a class Group. In the class I have two fields, idGroup IdGroupGroup. Groups may be part of other groups. My class Group is defined in a HashMap<Integer,Integer>; the key is IdGroupGroup and value is idGroup. I want to search the map for a particular idGroup; can I use recursion to do this?

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  • Problematic tags displaying HTML in Java

    - by Andez
    Hi again, I have the following tag included in my HTML which causes the JEditorPane not to show the HTML output. <META http-equiv="Content-Type" content="text/html; charset=UTF-8"> Not so much a big deal but anyone know why this would happen? Cannot find too much documentation on this - best I came up with was someone having a go a few years ago to see what was supported on retro virus site. At the minute I'm doing a simple find replace on the string which is not good - are there any better ways? I've seen a lot of people saying that RegEx is no good. The code I have used is this._html = this._html.replace( "<META http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\">", ""); Andez

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  • synchronizing reads to a java collection

    - by jeff
    so i want to have an arraylist that stores a series of stock quotes. but i keep track of bid price, ask price and last price for each. of course at any time, the bid ask or last of a given stock can change. i have one thread that updates the prices and one that reads them. i want to make sure that when reading no other thread is updating a price. so i looked at synchronized collection. but that seems to only prevent reading while another thread is adding or deleting an entry to the arraylist. so now i'm onto the wrapper approach: public class Qte_List { private final ArrayList<Qte> the_list; public void UpdateBid(String p_sym, double p_bid){ synchronized (the_list){ Qte q = Qte.FindBySym(the_list, p_sym); q.bid=p_bid;} } public double ReadBid(String p_sym){ synchronized (the_list){ Qte q = Qte.FindBySym(the_list, p_sym); return q.bid;} } so what i want to accomplish with this is only one thread can be doing anything - reading or updating an the_list's contents - at one time. am i approach this right? thanks.

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  • valid xml element in java replaceAll doesnt seem working well

    - by John
    Im trying to create a xml file from a POJO , in which i have a property that stores urls, I have been using the below method to replace all & in the url String to make the xml conform to standards and pass it as an html char entity but the string does not change. public static String forHrefAmpersand(String aURL){ return aURL.replaceAll("&", "&"); } the value might be www.abc.com/controller?a=1&next=showResults I have even tried changing the above method to use "/" as i read replaceAll uses regular expression but replaceAll is not working as exprected, Can anyone tell me what is the mistake im doing ? Thanks in advance

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  • Simple Array in java

    - by user1311590
    I need to create the following in my main method. Create an array of size 100 doubles. write a loop to sotr the number 150.0 - 249.0 in the 100 location. public class Lab6_2 { public static void main(String[] args) { double[] values; values = new double [100]; double i = 0; for(double i = 150.0; i<249.0;i++){ System.out.println(values[99]); } } }

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  • High performance distributed asynchronous RPC in java

    - by unludo
    I would like to do RPC to a list of clients with the following requirements: the server does not know the clients (implies a kind of broker?) and the cleints do not know the server there may be several clients - they share the load to treat the RPC The RPC is asynchronous very fast (round-trip < 1ms) optional : offers a fail-over mechanism. It can be done with underlying tools which are not really intended for that (Hazelcast is an example). What would you use for such requirements? Thanks!

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  • Type casting problem with java for-each loop

    - by pharma_joe
    Hi, I have traced an issue with an application I am developing, it is giving me a type cast exception. Funny thing is it is saying it cannot cast "entities.Movie cannot be cast to entities.Movie"?! movies is an ArrayList. try { movies = getMovies(); } catch (Exception e) { e.printStackTrace(System.out); } finally { try { for (Movie movie : movies) { output.append(" <tr>\n"); output.append(" <td>" + movie.getId() + "</td>"); output.append(" </tr>\n"); } } catch (Exception e) { e.printStackTrace(System.out); } }

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