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  • java : how to handle the design when template methods throw exception when overrided method not throw

    - by jiafu
    when coding. try to solve the puzzle: how to design the class/methods when InputStreamDigestComputor throw IOException? It seems we can't use this degisn structure due to the template method throw exception but overrided method not throw it. but if change the overrided method to throw it, will cause other subclass both throw it. So can any good suggestion for this case? abstract class DigestComputor{ String compute(DigestAlgorithm algorithm){ MessageDigest instance; try { instance = MessageDigest.getInstance(algorithm.toString()); updateMessageDigest(instance); return hex(instance.digest()); } catch (NoSuchAlgorithmException e) { LOG.error(e.getMessage(), e); throw new UnsupportedOperationException(e.getMessage(), e); } } abstract void updateMessageDigest(MessageDigest instance); } class ByteBufferDigestComputor extends DigestComputor{ private final ByteBuffer byteBuffer; public ByteBufferDigestComputor(ByteBuffer byteBuffer) { super(); this.byteBuffer = byteBuffer; } @Override void updateMessageDigest(MessageDigest instance) { instance.update(byteBuffer); } } class InputStreamDigestComputor extends DigestComputor{ // this place has error. due to exception. if I change the overrided method to throw it. evey caller will handle the exception. but @Override void updateMessageDigest(MessageDigest instance) { throw new IOException(); } }

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  • Getting the 'external' IP address in Java

    - by Caylem
    Hi I'm not too sure how to go about getting the external IP address of the machine as a computer outside of a network would see it. My following IPAddress class only gets the local IP address of the machine. Any help would be appreciated. Thanks. public class IPAddress { private InetAddress thisIp; private String thisIpAddress; private void setIpAdd(){ try{ InetAddress thisIp = InetAddress.getLocalHost(); thisIpAddress = thisIp.getHostAddress().toString(); } catch(Exception e){} } protected String getIpAddress(){ setIpAdd(); return thisIpAddress; } }

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  • Java convert JSONObject to URL parameter

    - by Alex Ivasyuv
    What is the elegant way to convert JSONObject to URL parameters. For example, JSONObject: {stat: {123456: {x: 1, y: 2}, 123457: {z: 5, y: 2}}}} this should be like: stat[123456][x]=1&stat[123456][y]=2&stat[123457][z]=5&stat[123457][y]=2 of course with escaped symbols, and of course JSON object could be more complicated.. Maybe there already exist some mechanisms for that? Thanks,

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  • Java regex, need help with escape characters

    - by Blankman
    My HTML looks like: <td class="price" valign="top"><font color= "blue">&nbsp;&nbsp;$&nbsp; 5.93&nbsp;</font></td> I tried: String result = ""; Pattern p = Pattern.compile("\"blue\">&nbsp;&nbsp;$&nbsp;(.*)&nbsp;</font></td>"); Matcher m = p.matcher(text); if(m.find()) result = m.group(1).trim(); Doesn't seem to be matching. Am I missing an escape character?

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  • Java Constructor Style (Check parameters aren't null)

    - by Peter
    What are the best practices if you have a class which accepts some parameters but none of them are allowed to be null? The following is obvious but the exception is a little unspecific: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null || two == null) { throw new IllegalArgumentException("Parameters can't be null"); } //... } } Here the exceptions let you know which parameter is null, but the constructor is now pretty ugly: public class SomeClass { public SomeClass(Object one, Object two) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } Here the constructor is neater, but now the constructor code isn't really in the constructor: public class SomeClass { public SomeClass(Object one, Object two) { setOne(one); setTwo(two); } public void setOne(Object one) { if (one == null) { throw new IllegalArgumentException("one can't be null"); } //... } public void setTwo(Object two) { if (two == null) { throw new IllegalArgumentException("two can't be null"); } //... } } Which of these styles is best? Or is there an alternative which is more widely accepted? Cheers, Pete

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  • Java - PriorityQueue vs sorted LinkedList

    - by msr
    Hello, Which implementation is less "heavy": PriorityQueue or a sorted LinkedList (using a Comparator)? I want to have all the items sorted. The insertion will be very frequent and ocasionally I will have to run all the list to make some operations. Thank you!

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  • Java Ugly Rounding Error?

    - by billynomates
    Using series.add(180, 1); produces a perfectly valid chart like this (little red dot at the bottom with some PolarItemRenderer Mods!) but using series.add(3000/(6000/360), 1); produces this beast: I assume it's because somewhere, 6000/360 = 16.6... is getting rounded? How can I stop this happening? Thanks :)

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  • Java Session Like Object

    - by scriptmonster
    I have been developing a project and in this project i have designed my code to do the same job after a specified time interval continuously. The job that wanted to be done has a lot of distinct cycles. The interval is small to execute them normally thus i used threads. Until that point everything is clear for me. To decrease the process and information transaction i wanted to put an session like object that holds the given data and provide it to any thread at anytime. With this object i plan to not query the same configuration information from database at everytime but if it exists on the session take it else query and store on session. I'm not sure how to implement this structure. Regards,

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  • Shift operator in Java bizarre program output

    - by Umesh Kacha
    I came across the following program and it behaving in unexpected manner. public class ShiftProgram { public static void main(String[] args) { int i = 0; while(-1 << i != 0) i++; System.out.println(i); } } If we think about this program output, when it reaches 32 while loop condition should return false and terminate and it should print 32. If you ran this program, it does not print anything but goes into an infinite loop. Any idea whats going on? Thank you in advance.

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  • Read / Write XML file from Java application bundle

    - by Peter
    Hi there! I've got an XML file that is parsed and written in my application. From within my IDE (Eclipse) I simply address it like this: Reading: private String xmlFile = "file.xml"; and then I build the document: doc = sax.build(xmlFile); Writing is done like this: writer = new FileWriter("file.xml"); Runs great so far, but after bundling my application, the file is no longer accessible. What exactly do I have to do to make it accessible from within an application bundle? I'm absolutely not familiar with the classpath or whatever I need for that, so please go easy on me! Thank you very much!

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  • Does Java have a .new operator?

    - by chickeninabiscuit
    I came across this code today whilst reading Accelerated GWT (Gupta) - page 151. public static void getListOfBooks(String category, BookStore bookStore) { serviceInstance.getBooks(category, bookStore.new BookListUpdaterCallback()); } public static void storeOrder(List books, String userName, BookStore bookStore) { serviceInstance.storeOrder(books, userName, bookStore.new StoreOrderCallback()); } What are those new operators doing there? I've never seen such syntax, can anyone explain?

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  • Confusion in RegExp Reluctant quantifier? Java

    - by Dusk
    Hi, Could anyone please tell me the reason of getting an output as: ab for the following RegExp code using Relcutant quantifier? Pattern p = Pattern.compile("abc*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group()); // ab and getting empty indices for the following code? Pattern p = Pattern.compile(".*?"); Matcher m = p.matcher("abcfoo"); while(m.find()) System.out.println(m.group());

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  • assign keys for combo box in java

    - by adesh kumar
    I want to add a JComboBox in Swing that is simple but I want to assign the values for each items in combo. I have the following code JComboBox jc1= new JComboBox(); jc1.addItem("a"); jc1.addItem("b"); jc1.addItem("c"); Now what I want is that when click on combo box it should return 1, 2 and 3 correspondingly instead of a ,b, c. Is there any way to assign the key values for each items in combo box?

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  • Enumeration classes in Java

    - by Crystal
    I have one class that declares an enumeration type as: public enum HOME_LOAN_TERMS {FIFTEEN_YEAR, THIRTY_YEAR}; Is this type usable in another class? I'm basically trying to complete a homework assignment where we have two types of loans, and one loanManager class. When I try to use the HOME_LOAN_TERMS.THIRTY_YEAR in my loanManager class that does not extend or implement the loan class, I get an error saying it 'cannot find symbol HOME_LOAN_TERMS.' So I did not know if my loanManager class needed to implement the two different loan classes. Thanks.

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  • Java - Need help with binary/code string manipulation

    - by ShrimpCrackers
    For a project, I have to convert a binary string into (an array of) bytes and write it out to a file in binary. Say that I have a sentence converted into a code string using a huffman encoding. For example, if the sentence was: "hello" h = 00 e = 01, l = 10, o = 11 Then the string representation would be 0001101011. How would I convert that into a byte? <-- If that question doesn't make sense it's because I know little about bits/byte bitwise shifting and all that has to do with manipulating 1's and 0's.

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  • Java library to partially export a database while respecting referential integrity constraints

    - by Mwanji Ezana
    My production database is several GB's uncompressed and it's getting to be a pain to download and run locally when trying to reproduce a bug or test a feature with real data. I would like to be able to select the specific records that interest me, then have the library figure out what other records are necessary to produce a dataset that respects the databases integrity constraints and finally print it out as a list of insert statements or dump that I can restore. For example: given Author, Blog and Comment tables when I select comments posted after a certain date I should get inserts for the Blog records the comments have foreign keys to and the Author records those Blogs have foreign keys to.

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  • Google App-Engine Java Batch Update

    - by Manjoor
    I need to upload a .csv file and save the records in bigtable. My application successfully parse 200 the records in the csv files and save to table. Here is my code to save the data. for (int i=0;i<lines.length -1;i++) //lines hold total records in csv file { String line = lines[i]; //The record have 3 columns integer,integer,Text if(line.length() > 15) { int n = line.indexOf(","); if (n>0) { int ID = lInteger.parseInt(ine.substring(0,n)); int n1 = line.indexOf(",", n + 2); if(n1 > n) { int Col1 = Integer.parseInt(line.substring(n + 1, n1)); String Col2 = line.substring(n1 + 1); myTable uu = new myTable(); uu.setId(ID); uu.setCol1(MobNo); Text t = new Text(Col2); uu.setCol2(t); PersistenceManager pm = PMF.get().getPersistenceManager(); pm.makePersistent(uu); pm.close(); } } } } But when no of records grow it gives timeout error. The csv file may have upto 800 records. Is it possible to do that in App-Engine? (something like batch update)

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  • java tracing spaghetti code

    - by Amarsh
    Folks, I have just joined this company which has a huge source tree based upon JSP/Servlet and EJB 1.2. No documentation exists. The code has been written over seven years, with a large number of undocumented changes. Are there any tool tah can assist me in tracing the execution? Putting a breakpoint is not helping me much.

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  • Java Swing custom shapes (2D Graphics)

    - by juFo
    I need to draw custom shapes. Now when a user clicks on several points on the panel I create a shape using a polygon. public void mouseClicked(MouseEvent e) { polygon.addPoint(e.getX(), e.getY()); repaint(); } But I don't know if this is the best way to draw custom shapes. It should be possible to edit a drawn shape: resize change its fill color change the stroke color copy/paste it move a single point of the polygon ... I have seen people creating an own class implementing the Shape class and using a GeneralPath. But again I have no idea if this is a good way. Now I can create my own shape with a polygon (or with a GeneralPath) but I have no clue how to attach all the edit functions to my own shape (the edit functions I mean the resize, move, etc from above). I hope somebody could show me a way to do this or maybe write a little bit of code to demonstrate this. Thanks in advance!!

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  • Static Block in Java

    - by Mohit Deshpande
    I was looking over some code the other day and I came across: static { ... } Coming from C++, I had no idea why that was there. Its not an error because the code compiled fine. What is this "static" block of code?

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  • How to keep Java Frame from waiting?

    - by pypmannetjies
    I am writing a genetic algorithm that approximates an image with a polygon. While going through the different generations, I'd like to output the progress to a JFrame. However, it seems like the JFrame waits until the GA's while loop finishes to display something. I don't believe it's a problem like repainting, since it eventually does display everything once the while loop exits. I want to GUI to update dynamically even when the while loop is running. Here is my code: while (some conditions) { //do some other stuff gui.displayPolygon(best); gui.displayFitness(fitness); gui.setVisible(true); } public void displayPolygon(Polygon poly) { BufferedImage bpoly = ImageProcessor.createImageFromPoly(poly); ImageProcessor.displayImage(bpoly, polyPanel); this.setVisible(true); } public static void displayImage(BufferedImage bimg, JPanel panel) { panel.removeAll(); panel.setBounds(0, 0, bimg.getWidth(), bimg.getHeight()); JImagePanel innerPanel = new JImagePanel(bimg, 25, 25); panel.add(innerPanel); innerPanel.setLocation(25, 25); innerPanel.setVisible(true); panel.setVisible(true); }

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