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  • printStackTrace in java?

    - by Venkats
    I am go through a socket program. In that printStackTrace is caught by the catch block. Actully what it is? catch(IOException ioe) { ioe.printStackTrace(); } I am unaware of it. For what they are used?

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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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  • Add elements to Arraylist and it replaces all previous elements in Java

    - by pie154
    I am adding elements to a ArrayList and it adds the first one correctly but then when I add any subsequent elements it wipes replaces the other elements with the value form the most recently added and adds a new element to the ArrayList. I ran test using arraylist and ints and even another created class and it worked perfectly but soemthing about the custon class i am using here causes problems. The code for the array list is public static void main(String args[]){ List<BasicEvent> list = new ArrayList<BasicEvent>(); list.add(new BasicEvent("Basic", "Door", 9, 4444, new Date(12,04,2010), new Time(12,04,21), 1, 0.98, 0)); list.add(new BasicEvent("Composite", "Door", 125, 4444, new Date(12,04,2010), new Time(12,04,20), 1, 0.98, 1)); list.add(new BasicEvent("Basic", "Door", 105, 88, new Date(12,04,2010), new Time(12,05,23), 1, 0.98, 0)); list.add(new BasicEvent("Basic", "Door", 125, 12, new Date(12,04,2010), new Time(12,05,28), 1, 0.98, 1)); list.add(new BasicEvent("Basic", "Door", 129, 25, new Date(12,04,2010), new Time(12,05,30), 1, 0.98, 0)); list.add(new BasicEvent("Basic", "Door", 125, 63, new Date(12,04,2010), new Time(12,04,20), 1, 0.98, 1)); list.add(new BasicEvent("Basic", "Detect", 127, 9, new Date(12,04,2010), new Time(12,05,29), 1, 0.98, -1)); for(int i=0;i<list.size();i++) {System.out.println("list a poition " + i + " is " + BasicEvent.basicToString(list.get(i)));} And the code for the custom class basicEvent is public class BasicEvent { public static String Level; public static String EType; public static double xPos; public static double yPos; public static Date date; public static Time time; public static double Rlb; public static double Sig; public static int Reserved; public BasicEvent(String L, String E, double X, double Y, Date D, Time T, double R, double S, int Res){ Level = L; EType = E; xPos = X; yPos = Y; date = D; time = T; Rlb = R; Sig = S; Reserved = Res; }; public static String basicToString(BasicEvent bse){ String out = bse.getLevel() + ";" + bse.getEtype() + ";" + bse.getxPos() + ";" + bse.getyPos() + ";" + bse.getDate().dateAsString() + ";" + bse.getTime().timeAsString() + ";" + bse.getRlb() + ";" + bse.getSig() + ";" + bse.getReserved(); return out; }

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  • Java BufferedReader readline blocking?

    - by tgguy
    I want to make an HTTP request and then get the response as sketched here: URLConnection c = new URL("http://foo.com").openConnection(); c.setDoOutput(true); /* write an http request here using a new OutputStreamWriter(c.getOutputStream) */ BufferedReader reader = new BufferedReader(new InputStreamReader(c.getInputStream)); reader.readLine(); But my question is, if the request I send takes a long time before a response is received, what happens in the call reader.readLine() above? Will this process stay running/runnable on the CPU or will it get taken off the CPU and be notified to wake up and run again when there is IO to be read? If it stays on the CPU, what can be done to make it get off and be notified later?

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  • Java multiple connections downloading file

    - by weulerjunior
    Hello friends, I was wanting to add multiple connections in the code below to be able to download files faster. Could someone help me? Thanks in advance. public void run() { RandomAccessFile file = null; InputStream stream = null; try { // Open connection to URL. HttpURLConnection connection = (HttpURLConnection) url.openConnection(); // Specify what portion of file to download. connection.setRequestProperty("Range", "bytes=" + downloaded + "-"); // Connect to server. connection.connect(); // Make sure response code is in the 200 range. if (connection.getResponseCode() / 100 != 2) { error(); } // Check for valid content length. int contentLength = connection.getContentLength(); if (contentLength < 1) { error(); } /* Set the size for this download if it hasn't been already set. */ if (size == -1) { size = contentLength; stateChanged(); } // Open file and seek to the end of it. file = new RandomAccessFile("C:\\"+getFileName(url), "rw"); file.seek(downloaded); stream = connection.getInputStream(); while (status == DOWNLOADING) { /* Size buffer according to how much of the file is left to download. */ byte buffer[]; if (size - downloaded > MAX_BUFFER_SIZE) { buffer = new byte[MAX_BUFFER_SIZE]; } else { buffer = new byte[size - downloaded]; } // Read from server into buffer. int read = stream.read(buffer); if (read == -1) { break; } // Write buffer to file. file.write(buffer, 0, read); downloaded += read; stateChanged(); } /* Change status to complete if this point was reached because downloading has finished. */ if (status == DOWNLOADING) { status = COMPLETE; stateChanged(); } } catch (Exception e) { error(); } finally { // Close file. if (file != null) { try { file.close(); } catch (Exception e) { } } // Close connection to server. if (stream != null) { try { stream.close(); } catch (Exception e) { } } } }

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  • Java webapp: where/how to automatically set each picture's width/height

    - by NoozNooz42
    For several reasons, a lot of "webmaster guides" (like Google and Yahoo!'s webmaster guides/guidelines) repeats several times that it is better to always put the width and height attribute of the img tag. One of the most obvious reason is that the elements in the page won't seem to be "jumping around" to a new location after every picture is loaded (always setting the correct width/height sure gets rid of this behavior). And there are other reasons to follow these guidelines / best practices. So: if we consider that these are indeed good practices if there are a lot of pictures and they are changing often if pictures aren't changing between two .war re-deploy (that is: there's no user-contributed picture) if we don't want to manually edit all these width/height attributes How do we automatically/programmatically serve HTML pages where every img tag have their width/height attribute correctly set as the best practice recommend?

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  • W3C dom api in Java, get child elements by name

    - by Benju
    I just realized that the method Element.getElementsByTagName("someTagName") returns a nodelist of all elements in the document that have a given tagname. What if I just want to get all child elements by tag name? For example... <person> <name>Bob</name> <car> <name>Toyota Corolla</name> </car> </person>

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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 the little console game won't repeat?

    - by Jony Kale
    Okay, what I have so far is: You enter the game, and write "spin" to the console. Program will enter the while loop. In the while loop, if entered int is -1, return to the back (Set console input back to "", and let the user select what game he would like to play). Problem: Instead of going back, and selecting "spin" again, the program exits? Why is it happening? How can I fix this? private static Scanner console = new Scanner(System.in); private static Spin spin = new Spin(); private static String inputS = ""; private static int inputI = 0; private static String[] gamesArray = new String[] {"spin", "tof"}; private static boolean spinWheel = false; private static boolean tof = false; public static void main (String[] args) { if (inputS.equals("")) { System.out.println("Welcome to the system!"); System.out.print("Please select a game: "); inputS = console.nextLine(); } while (inputS.equals("spin")) { System.out.println("Welcome to the spin game! Please write 1 to spin. and -1 to exit back"); inputI = console.nextInt(); switch (inputI) { case 1: break; case -1: inputI = 0; inputS = ""; break; } } }

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  • Mouse event in Java

    - by Harish
    I am trying to move a JComponent say a label over a table.I am tracking this event using MouseMotionListener's mouseDragged method.This method perfectly helps me in tracking the item.Is there a way to track the mouse release after dragging is complete(.ie the dropping event). tktLabel1.addMouseMotionListener(new MouseMotionListener() { public void mouseDragged(MouseEvent arg0) { tktLabel1.setBounds(tktLabel1.getX() + arg0.getX(), tktLabel1.getY() + arg0.getY(), width, height); } public void mouseMoved(MouseEvent arg0) { } });

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  • get particular string using regex java

    - by hussain
    i want to know how to get the string from group of string String j = "<a href=\"/watch?v=4Qx-lBqOqiQ&feature=popular\" onclick=\"\" onmousedown=\"yt.analytics.urchinTracker(\'/Events/Home/PersonalizedHome/POP/Logged_Out');\" ><span class=\"video-thumb video-thumb-220 \" id=\"video-thumb-4Qx-lBqOqiQ-8821469\"><img src=\"http://i1.ytimg.com/vi/4Qx-lBqOqiQ/hqdefault.jpg\" class=\"vimg220\" alt=\"Dog Squirrel Chasing A Squirrel\" title=\"Dog Squirrel Chasing A Squirrel\" onclick=\";yt.www.watch.watch5.IEshenanigans(event, this)\"><span class=\"video-time\"><span>1:08</span></span><span class=\"video-actions\"><button class=\"yt-uix-button-short yt-uix-button yt-uix-button-arrowbutton\" onclick=\"; return false;\" type=\"button\"> <img class=\"yt-uix-button-arrow\" src=\"http://s.ytimg.com/yt/img/pixel-vfl73.gif\" alt=\"\"> hai</a>"; i want to get the string href=\"/watch?v=4Qx-lBqOqiQ&feature=popular\" and src=\"http://i1.ytimg.com/vi/4Qx-lBqOqiQ/hqdefault.jpg\" thanks and advance

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  • How to serialize Java primitives using Jersey REST

    - by Olvagor
    In my application I use Jersey REST to serialize complex objects. This works quite fine. But there are a few method which simply return an int or boolean. Jersey can't handle primitive types (to my knowledge), probably because they're no annotated and Jersey has no default annotation for them. I worked around that by creating complex types like a RestBoolean or RestInteger, which simply hold an int or boolean value and have the appropriate annotations. Isn't there an easier way than writing these container objects?

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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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  • java library for reading RSS and ATOM feeds

    - by Samuel
    I am looking for libraries which can read RSS / ATOM feeds in my J2EE application (based on JBoss Seam). Is Rome the only application there for reading feeds? I am assuming the Seam RSS integration is only for generating RSS feeds and not for reading feeds.

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  • Java 1.5.0_16 corrupted colours when saving jpg image

    - by Coder
    Hi, i have a loaded image from disk (stored as a BufferedImage), which i display correctly on a JPanel but when i try to re-save this image using the command below, the image is saved in a reddish hue. ImageIO.write(image, "jpg", fileName); Note! image is a BufferedImage and fileName is a File object pointing to the filename that will be saved which end in ".jpg". I have read that there were problems with ImageIO methods in earlier JDKs but i'm not on one of those versions as far as i could find. What i am looking for is a way to fix this issue without updating the JDK, however having said that i would still like to know in what JDK this issue was fixed in (if it indeed is still a bug with the JDK i'm using). Thanks.

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  • Example of ==, equals and hashcode in java

    - by Abhishek Jain
    Given this: String s1= new String("abc"); String s2= new String("abc"); String s3 ="abc"; System.out.println(s1==s3); System.out.println(s1==s2); System.out.println(s1.equals(s2)); System.out.println(s1.equals(s3)); System.out.println(s1.hashCode()); System.out.println(s2.hashCode()); System.out.println(s3.hashCode()); Output is: false false true true 96354 96354 96354 Here == is giving false for each object but hashcode for each String object is same. Why is it so?

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  • bounding java generics by 'super' keyword

    - by mohsenof
    Why I can use 'super' just with wildcards and not with type parameters? for example why in Collection interface they've not written toArray method like this interface Collection"<"T{ public "< S super T S[] toArray(S[] a){ } } (sorry, I don't know how to deal with "<")

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  • How to make prevent public key inside jar to be saved using Java code

    - by Abhijith V R
    After signing a jar , we can retrieve the public keys from jar using Certificate[] cert = jarentry.getCertificates(); Once certificate is extracted we can save this to a new keystore as trusted cert. Once this is done , then second user can sign any jar using this certificate , isn't ? I want to distribute content as jars , contents will contain properties files for a application init. I want to make sure that an user is not capable to rebuilding the property files using the certificate he extracted from jarentry. In the code which reads the jar contents i am checking that jar is signed with my certificate only and also checking that jar is not tampered with . But the issue came to my mind that if i am able to extract the cerificate from jar then why don;t a third guy ? Can any one help me in this............

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  • Subqueries on Java GAE Datastore

    - by Dmitry
    I am trying to create a database of users with connection between users (friends list). There are 2 main tables: UserEntity (main field id) and FriendEntity with fields: - initiatorId - id of user who initiated the friendship - friendId - id of user who has been invited. Now I am trying to fetch all friends of one particular user and encountered some problems with using subqueries in JDO here. Logically the query should be something like this: SQL: SELECT * FROM UserEntity WHERE EXISTS (SELECT * FORM FriendEntity WHERE (initiatorId == UserEntity.id && friendId == userId) || (friendId == UserEntity.id && initiatorId == userId)) or SELECT * FROM UserEntity WHERE userId IN (SELECT * FROM FriendEntity WHERE initiatorId == UserEntity.id) OR userId IN (SELECT * FROM FriendEntity WHERE friendId == UserEntity.id) So to replicate the last query in JDOQL, I tried to do the following: Query friendQuery = pm.newQuery(FriendEntity.class); friendQuery.setFilter("initiatorId == uidParam"); friendQuery.setResult("friendId"); Query initiatorQuery = pm.newQuery(FriendEntity.class); initiatorQuery.setFilter("friendId == uidParam"); initiatorQuery.setResult("initiatorId"); Query query = pm.newQuery(UserEntity.class); query.setFilter("initiatorQuery.contains(id) || friendQuery.contains(id)"); query.addSubquery(initiatorQuery, "List initiatorQuery", null, "String uidParam"); query.addSubquery(friendQuery, "List friendQuery", null, "String uidParam"); query.declareParameters("String uidParam"); List<UserEntity> friends = (List<UserEntity>) query.execute(userId); In result I get the following error: Unsupported method while parsing expression. Could anyone help with this query please?

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  • Multiple threads modifying a collection in Java??

    - by posdef
    Hi, The project I am working on requires a whole bunch of queries towards a database. In principle there are two types of queries I am using: read from excel file, check for a couple of parameters and do a query for hits in the database. These hits are then registered as a series of custom classes. Any hit may (and most likely will) occur more than once so this part of the code checks and updates the occurrence in a custom list implementation that extends ArrayList. for each hit found, do a detail query and parse the output, so that the classes created in (I) get detailed info. I figured I would use multiple threads to optimize time-wise. However I can't really come up with a good way to solve the problem that occurs with the collection these items are stored in. To elaborate a little bit; throughout the execution objects are supposed to be modified by both (I) and (II). I deliberately didn't c/p any code, as it would be big chunks of code to make any sense.. I hope it make some sense with the description above. Thanks,

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  • SwingWorker in Java (beginner question)

    - by Malachi
    I am relatively new to multi-threading and want to execute a background task using a Swingworker thread - the method that is called does not actually return anything but I would like to be notified when it has completed. The code I have so far doesn't appear to be working: private void crawl(ActionEvent evt) { try { SwingWorker<Void, Void> crawler = new SwingWorker<Void, Void>() { @Override protected Void doInBackground() throws Exception { Discoverer discover = new Discoverer(); discover.crawl(); return null; } @Override protected void done() { JOptionPane.showMessageDialog(jfThis, "Finished Crawling", "Success", JOptionPane.INFORMATION_MESSAGE); } }; crawler.execute(); } catch (Exception ex) { JOptionPane.showMessageDialog(this, ex.getMessage(), "Exception", JOptionPane.ERROR_MESSAGE); } } Any feedback/advice would be greatly appreciated as multi-threading is a big area of programming that I am weak in.

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