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  • Simplest way of creating java next/previous buttons

    - by Holly
    I know that when creating buttons, like next and previous, that the code can be somewhat long to get those buttons to function. My professor gave us this example to create the next button: private void jbtnNext_Click() { JOptionPane.showMessageDialog(null, "Next" ,"Button Pressed", JOptionPane.INFORMATION_MESSAGE); try { if (rset.next()) { fillTextFields(false); }else{ //Display result in a dialog box JOptionPane.showMessageDialog(null, "Not found"); } } catch (SQLException ex) { ex.printStackTrace(); } } Though, I do not really understand how that short and simple if statement is what makes the next button function. I see that the fillTextFields(false) uses a boolean value and that you need to initialize that boolean value in the beginning of the code I believe. I had put private fillTextFields boolean = false; but this does not seem to be right... I'm just hoping someone could explain it better. Thanks :)

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  • Using interfaces in java..Newb question

    - by Rahul
    Suppose there in an interface Displaceable and a class Circle which implements Displaceable. Displaceable has a method named move() which of course is implemented in Circle. What would happen in the following scenario? Circle a = new Circle(..); Displaceable b = a; b.move() Would the object refer to the Circle's move method?

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  • Search a string in a file and write the matched lines to another file in Java

    - by Geeta
    For searching a string in a file and writing the lines with matched string to another file it takes 15 - 20 mins for a single zip file of 70MB(compressed state). Is there any ways to minimise it. my source code: getting Zip file entries zipFile = new ZipFile(source_file_name); entries = zipFile.entries(); while (entries.hasMoreElements()) { ZipEntry entry = (ZipEntry)entries.nextElement(); if (entry.isDirectory()) { continue; } searchString(Thread.currentThread(),entry.getName(), new BufferedInputStream (zipFile.getInputStream(entry)), Out_File, search_string, stats); } zipFile.close(); Searching String public void searchString(Thread CThread, String Source_File, BufferedInputStream in, File outfile, String search, String stats) throws IOException { int count = 0; int countw = 0; int countl = 0; String s; String[] str; BufferedReader br2 = new BufferedReader(new InputStreamReader(in)); System.out.println(CThread.currentThread()); while ((s = br2.readLine()) != null) { str = s.split(search); count = str.length - 1; countw += count; //word count if (s.contains(search)) { countl++; //line count WriteFile(CThread,s, outfile.toString(), search); } } br2.close(); in.close(); } -------------------------------------------------------------------------------- public void WriteFile(Thread CThread,String line, String out, String search) throws IOException { BufferedWriter bufferedWriter = null; System.out.println("writre thread"+CThread.currentThread()); bufferedWriter = new BufferedWriter(new FileWriter(out, true)); bufferedWriter.write(line); bufferedWriter.newLine(); bufferedWriter.flush(); } Please help me. Its really taking 40 mins for 10 files using threads and 15 - 20 mins for a single file of 70MB after being compressed. Any ways to minimise the time.

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  • base-n series generator for a given number in java,,

    - by Senthil
    I want to create a program for generating the series for the given base-n. , for example if my input is 2,then series shuould be, 00,01,10,11,etc.,(binary) if my input is 10,then series shuould be,1,2,3,4,5,etc.,(decimal) is there any general mechanism to find these numbers so that I can program for base-n.,

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  • Implement dictionary using java

    - by ahmad
    Task Dictionary ADT The dictionary ADT models a searchable collection of key-element entries Multiple items with the same key are allowed Applications: word-definition pairs Dictionary ADT methods: find(k): if the dictionary has an entry with key k, returns it, else, returns null findAll(k): returns an iterator of all entries with key k insert(k, o): inserts and returns the entry (k, o) remove(e): remove the entry e from the dictionary size(), isEmpty() Operation Output Dictionary insert(5,A) (5,A) (5,A) insert(7,B) (7,B) (5,A),(7,B) insert(2,C) (2,C) (5,A),(7,B),(2,C) insert(8,D) (8,D) (5,A),(7,B),(2,C),(8,D) insert(2,E) (2,E) (5,A),(7,B),(2,C),(8,D),(2,E) find(7) (7,B) (5,A),(7,B),(2,C),(8,D),(2,E) find(4) null (5,A),(7,B),(2,C),(8,D),(2,E) find(2) (2,C) (5,A),(7,B),(2,C),(8,D),(2,E) findAll(2) (2,C),(2,E) (5,A),(7,B),(2,C),(8,D),(2,E) size() 5 (5,A),(7,B),(2,C),(8,D),(2,E) remove(find(5)) (5,A) (7,B),(2,C),(8,D),(2,E) find(5) null (7,B),(2,C),(8,D),(2,E) Detailed explanation: NO Specific requirements: please Get it done i need HELP !!!

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  • How to mix two arrays in Java?

    - by roddik
    Hello. I have some String[] arrays, for example: ['a1', 'a2'] ['b1', 'b2', 'b3', 'b4'] ['c1'] How can I mix them, so that I get ['a1', 'b1', 'c1', 'a2', 'b2', 'b3', 'b4'] (0 element of a, then b, c, 1 element of a, b, c and so on)? Thanks

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  • java.math.BigInteger pow(exponent) question

    - by Jan Kraus
    Hi, I did some tests on pow(exponent) method. Unfortunately, my math skills are not strong enough to handle the following problem. I'm using this code: BigInteger.valueOf(2).pow(var); Results: var | time in ms 2000000 | 11450 2500000 | 12471 3000000 | 22379 3500000 | 32147 4000000 | 46270 4500000 | 31459 5000000 | 49922 See? 2,500,000 exponent is calculated almost as fast as 2,000,000. 4,500,000 is calculated much faster then 4,000,000. Why is that? To give you some help, here's the original implementation of BigInteger.pow(exponent): public BigInteger pow(int exponent) { if (exponent < 0) throw new ArithmeticException("Negative exponent"); if (signum==0) return (exponent==0 ? ONE : this); // Perform exponentiation using repeated squaring trick int newSign = (signum<0 && (exponent&1)==1 ? -1 : 1); int[] baseToPow2 = this.mag; int[] result = {1}; while (exponent != 0) { if ((exponent & 1)==1) { result = multiplyToLen(result, result.length, baseToPow2, baseToPow2.length, null); result = trustedStripLeadingZeroInts(result); } if ((exponent >>>= 1) != 0) { baseToPow2 = squareToLen(baseToPow2, baseToPow2.length, null); baseToPow2 = trustedStripLeadingZeroInts(baseToPow2); } } return new BigInteger(result, newSign); }

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  • How would you code an efficient Circular Buffer in Java or C#

    - by Cheeso
    I want a simple class that implements a fixed-size circular buffer. It should be efficient, easy on the eyes, generically typed. EDIT: It need not be MT-capable, for now. I can always add a lock later, it won't be high-concurrency in any case. Methods should be: .Add and I guess .List, where I retrieve all the entries. On second thought, Retrieval I think should be done via an indexer. At any moment I will want to be able to retrieve any element in the buffer by index. But keep in mind that from one moment to the next Element[n] may be different, as the Circular buffer fills up and rolls over. This isn't a stack, it's a circular buffer. Regarding "overflow": I would expect internally there would be an array holding the items, and over time the head and tail of the buffer will rotate around that fixed array. But that should be invisible from the user. There should be no externally-detectable "overflow" event or behavior. This is not a school assignment - it is most commonly going to be used for a MRU cache or a fixed-size transaction or event log.

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  • I have a problem with the following Java code

    - by Sanjeev
    public class b { public static void main(String[] args) { byte b = 1; long l = 127; // b = b + l; // 1 if I try this then it does not compile b += l; // 2 if I try this then it does compile System.out.println(b); } } I am using this code but I have problem: I don't understand why b=b+l; is not compiling but if I write b+=l; then it compiles and runs. Please explain why this happens.

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  • java concurrency assignments

    - by dev
    I am JEE developer, and I want to get skills on concurrency development. Could you provide me some assignments, ideas, or other - just for learning and training concurrency programming? Thanks!

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  • Java: how to use Google's HashBiMap?

    - by HH
    Keys are a file and a word. The file gives all words inside the file. The word gives all files having the word. I am unsure of the domain and co-domain parts. I want K to be of the type <String> and V to be of type <HashSet<FileObject>>. public HashBiMap<K<String>,V<HashSet<FileObject>>> wordToFiles = new HashBiMap<K<String>,V<HashSet<FileObject>>>(); public HashBiMap<K<String>,V<HashSet<FileObject>>> fileToWords = new HashBiMap<K<String>,V<HashSet<FileObject>>>(); Google's HashBiMap.

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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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  • Java ternary operator and boxing Integer/int?

    - by Markus
    I tripped across a really strange NullPointerException the other day caused by an unexpected type-cast in the ternary operator. Given this (useless exemplary) function: Integer getNumber() { return null; } I was expecting the following two code segments to be exactly identical after compilation: Integer number; if (condition) { number = getNumber(); } else { number = 0; } vs. Integer number = (condition) ? getNumber() : 0; . Turns out, if condition is true, the if-statement works fine, while the ternary opration in the second code segment throws a NullPointerException. It seems as though the ternary operation has decided to type-cast both choices to int before auto-boxing the result back into an Integer!?! In fact, if I explicitly cast the 0 to Integer, the exception goes away. In other words: Integer number = (condition) ? getNumber() : 0; is not the same as: Integer number = (condition) ? getNumber() : (Integer) 0; . So, it seems that there is a byte-code difference between the ternary operator and an equivalent if-else-statement (something I didn't expect). Which raises three questions: Why is there a difference? Is this a bug in the ternary implementation or is there a reason for the type cast? Given there is a difference, is the ternary operation more or less performant than an equivalent if-statement (I know, the difference can't be huge, but still)?

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  • Read / write program in java using JChooser

    - by Casper Marcussen
    Hello everyone Didn't want to bother people in here, but since i am under a time pressure, i am desperate to get help. My questions is how to link the file choosen from a JChooser to a file, and how to converte it to stringm being able to display and edit it in a TextArea. i hav ethe GUI set up using swing, but the link between actionListener and the Jchooser is not complete Any help would be much appreciated code: http://pastebin.com/p3fb17Wi

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  • Insert code into a method - Java

    - by DutrowLLC
    Is there a way to automatically insert code into a method? I have the following and I would like to insert the indicated code: public class Person { Set<String> updatedFields = new LinkedHashSet<String>(); String firstName; public String getFirstName(){ return firstName; } boolean isFirstNameChanged = false; // Insert public void setFirstName(String firstName){ if( !isFirstNameChanged ){ // Insert isFirstNameChanged = true; // Insert updatedFields.add("firstName"); // Insert } // Insert this.firstName = firstName; } } I'm also not sure if I can the subset of the method name as a string from inside the method itself as indicated on the line where I add the fieldName as a string into the set of updated fields: updatedFields.add("firstName");. And I'm not sure how to insert fields into a class where I add the boolean field that tracks if the field has been modified or not before (for efficiency to prevent having to manipulate the Set): boolean isFirstNameChanged = false; It seems to most obvious answer to this would be to use code templates inside eclipse, but I'm concerned about having to go back and change the code later.

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  • JNI on Android, how to pass int from c to java

    - by Joaquin
    I have a C function, I simply returns an integer, as follows: JNIEXPORT jint JNICALL Java_org_project_ScreenPosition(JNIEnv* env, jobject thiz){ int i=1; return i; } I call this function in the way of an Activity onCreateContextMenu Android, as follows: public void onCreateContextMenu(ContextMenu menu, View v, ContextMenuInfo menuInfo){ menu.setHeaderTitle("TryMenu"); int a=ScreenPosition(); return; } But all crash

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  • Embeddable database better than SQLite for java

    - by dexter
    I am creating a web application that is accessing a SQLite database in the server. I also have "clients" that updates this same database. As we know SQLite locks the entire database during INSERTs which are done by the clients and the web application is also trying to make some UPDATEs at the same time. So my problem now is about concurrency in database access. I would like to use an embeddable database like SQLite. Any suggestions.

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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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  • Sending an Email Using Java

    - by user217029
    try{ Properties props = new Properties(); props.put("mail.smtp.host", "ipc-smtp.bits-pilani.ac.in"); Session sess = Session.getInstance(props, null); sess.setDebug(true); Message msg = new MimeMessage(sess); InternetAddress addressFrom = new InternetAddress("[email protected]"); msg.setFrom(addressFrom); msg.setRecipient(Message.RecipientType.TO, new InternetAddress("[email protected]")); msg.addHeader("MyHeaderName", "myHeaderValue"); msg.setSubject("Test"); msg.setContent("Yippe", "text/plain"); Transport.send(msg); }catch(Exception exp){ exp.printStackTrace(); } The error is javax.mail.MessagingException: 554 The mail was blocked due to zen-spamhaus RBL action This is my college's smtp server.

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  • How to Create Own HashMap in Java?

    - by Taranfx
    I know about hashing algorithm and hashCode() to convert "key" into an equivalent integer (using some mathematically random expression) that is then compressed and stored into buckets. But can someone point me to an implementation or at least data structure that should be used as baseline? I haven't found it anywhere on the web.

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  • program for calculating metrics in java

    - by senzacionale
    i need to calculate few metrics (CBO, NOC, DAC, LCOM, WMC, RFC and DIT metric). Program is written in jdeveloper and i do not know how to calculate this metrics. Migration to eclipse is not possible becouse code is not compiled. Does anyone know any good program for calculating metrics?

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  • Using java class HttpsURLConnection

    - by KB22
    Hi all, I have a small piece of code which basically impements a HTTP-Client, i.e. it POSTS request and works with re RESPONSE. As long as HTTP is concenerned everthing work well. For some reason I now have to support HTTPS too. So here is briefly what I do in order to get a connection opened: URL url = new URL(serverAddress); HttpsURLConnection httpsConn = (HttpsURLConnection) url.openConnection(); This fails, stating: sun.net.www.protocol.https.HttpsURLConnectionImpl cannot be cast to com.sun.net.ssl.HttpsURLConnection I guess this is kinda trivial, but I just don't get what I'm doing wrong in this one... Googled it, and the code just looks right - not? any ideas are appreciated! thanks, K

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