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  • Java hashcode based on identity

    - by hjfreyer
    The default behavior of Object.hashCode() is to return essentially the "address" of the object so that a.hashCode() == b.hashCode() if and only if a == b. How can I get this behavior in a user-defined class if a superclass already defines hashCode()? For instance: class A { public int hashCode() { return 0; } } class B extends A { public int hashCode() { // Now I want to return a unique hashcode for each object. // In pythonic terms, it'd look something like: return Object.hashCode(this); } } Ideas?

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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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  • Most Elegant Way to write isPrime in java

    - by Anantha Kumaran
    public class Prime { public static boolean isPrime1(int n) { if (n <= 1) { return false; } if (n == 2) { return true; } for (int i = 2; i <= Math.sqrt(n) + 1; i++) { if (n % i == 0) { return false; } } return true; } public static boolean isPrime2(int n) { if (n <= 1) { return false; } if (n == 2) { return true; } if (n % 2 == 0) { return false; } for (int i = 3; i <= Math.sqrt(n) + 1; i = i + 2) { if (n % i == 0) { return false; } } return true; } } public class PrimeTest { public PrimeTest() { } @Test public void testIsPrime() throws IllegalArgumentException, IllegalAccessException, InvocationTargetException { Prime prime = new Prime(); TreeMap<Long, String> methodMap = new TreeMap<Long, String>(); for (Method method : Prime.class.getDeclaredMethods()) { long startTime = System.currentTimeMillis(); int primeCount = 0; for (int i = 0; i < 1000000; i++) { if ((Boolean) method.invoke(prime, i)) { primeCount++; } } long endTime = System.currentTimeMillis(); Assert.assertEquals(method.getName() + " failed ", 78498, primeCount); methodMap.put(endTime - startTime, method.getName()); } for (Entry<Long, String> entry : methodMap.entrySet()) { System.out.println(entry.getValue() + " " + entry.getKey() + " Milli seconds "); } } } I am trying to find the fastest way to check whether the given number is prime or not. This is what is finally came up with. Is there any better way than the second implementation(isPrime2).

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  • What's wrong with my logic (Java syntax)

    - by soda
    I'm trying to make a simple program that picks a random number and takes input from the user. The program should tell the user if the guess was hot (-/+ 5 units) or cold, but I never reach the else condition. Here's the section of code: public static void giveHint (int guess) { int min = guess - 5; int max = guess + 5; if ((guess > min) && (guess < max)) { System.out.println("Hot.."); } else { System.out.println("Cold.."); } }

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  • Require a default constructor in java?

    - by jdc0589
    Is there any way to require that a class have a default (no parameter) constructor, aside from using a reflection check like the following? (the following would work, but it's hacky and reflection is slow) boolean valid = false; for(Constructor<?> c : TParse.class.getConstructors()) { if(c.getParameterTypes().length == 0) { valid = true; break; } } if(!valid) throw new MissingDefaultConstructorException(...);

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  • RSA implementations for Java, alternative to BC

    - by Tom Brito
    The RSA implementation that ships with Bouncy Castle only allows the encrypting of a single block of data. The RSA algorithm is not suited to streaming data and should not be used that way. In a situation like this you should encrypt the data using a randomly generated key and a symmetric cipher, after that you should encrypt the randomly generated key using RSA, and then send the encrypted data and the encrypted random key to the other end where they can reverse the process (ie. decrypt the random key using their RSA private key and then decrypt the data). I can't use the workarond of using symmetric key. So, are there other implementations of RSA than Bouncy Castle?

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  • Are there any libraries for parsing "number expressions" like 1,2-9,33- in Java

    - by mihi
    Hi, I don't think it is hard, just tedious to write: Some small free (as in beer) library where I can put in a String like 1,2-9,33- and it can tell me whether a given number matches that expression. Just like most programs have in their print range dialogs. Special functions for matching odd or even numbers only, or matching every number that is 2 mod 5 (or something like that) would be nice, but not needed. The only operation I have to perform on this list is whether the range contains a given (nonnegative) integer value; more operations like max/min value (if they exist) or an iterator would be nice, of course. What would be needed that it does not occupy lots of RAM if anyone enters 1-10000000 but the only number I will ever query is 12345 :-) (To implement it, I would parse a list into several (min/max/value/mod) pairs, like 1,10,0,1 for 1-10 or 11,33,1,2 for 1-33odd, or 12,62,2,10 for 12-62/10 (i. e. 12, 22, 32, ..., 62) and then check each number for all the intervals. Open intervals by using Integer.MaxValue etc. If there are no libs, any ideas to do it better/more efficient?)

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  • Right method to build a online whiteboard - JAVA

    - by Nikhar Sharma
    I am building a whiteboard, which would have a server(teacher) and clients(students). Teacher would draw something on his side, which will be shown exactly same to the students. I want to know which component i should use to do the drawing? i am currently drawing on JPanel . I want the screen of Server gets copied on the clients, so for that what could be the right method to do this? option1: i save the JPanel as image, and send thru socket, and loads it on the screen of client, also it always saves the background image only, not what the user has drawn onto it. OR option2: both server and client JPanel dimensions are same, so i just send the new coordinates drawn everytime thru socket, with some protocol to understand whether it is rubber or pencil.. Any help would be appreciated.

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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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  • 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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  • replace values in a String from a Hashtable in Java

    - by Adnan
    My string looks like; String values = "I am from UK, and you are from FR"; and my hashtable; Hashtable countries = new Hashtable(); countries.put("United Kingdom", new String("UK")); countries.put("France", new String("FR")); What would be the most effective way to change the values in my string with the values from the hashtable accordingly. These are just 2 values to change, but in my case I will have 100+

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  • Java Matcher groups: Understanding The difference between "(?:X|Y)" and "(?:X)|(?:Y)"

    - by user358795
    Can anyone explain: Why the two patterns used below give different results? (answered below) Why the 2nd example gives a group count of 1 but says the start and end of group 1 is -1? public void testGroups() throws Exception { String TEST_STRING = "After Yes is group 1 End"; { Pattern p; Matcher m; String pattern="(?:Yes|No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } { Pattern p; Matcher m; String pattern="(?:Yes)|(?:No)(.*)End"; p=Pattern.compile(pattern); m=p.matcher(TEST_STRING); boolean f=m.find(); int count=m.groupCount(); int start=m.start(1); int end=m.end(1); System.out.println("Pattern=" + pattern + "\t Found=" + f + " Group count=" + count + " Start of group 1=" + start + " End of group 1=" + end ); } } Which gives the following output: Pattern=(?:Yes|No)(.*)End Found=true Group count=1 Start of group 1=9 End of group 1=21 Pattern=(?:Yes)|(?:No)(.*)End Found=true Group count=1 Start of group 1=-1 End of group 1=-1

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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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  • Java: Embedding Soundbank file in JAR

    - by Pyroclastic
    If I have a soundbank stored in a JAR, how would I load that soundbank into my application using resource loading...? I'm trying to consolidate as much of a MIDI program into the jar file as I can, and the last thing I have to add is the soundbank file I'm using, as users won't have the soundbanks installed. I'm trying to put it into my jar file, and then load it with getResource() in the Class class, but I'm getting an InvalidMidiDataException on a soundbank that I know is valid. Here's the code, it's in the constructor for my synthesizer object: try { synth = MidiSystem.getSynthesizer(); channels = synth.getChannels(); instrument = MidiSystem.getSoundbank(this.getClass().getResource("img/soundbank-mid.gm")).getInstruments(); currentInstrument = instrument[0]; synth.loadInstrument(currentInstrument); synth.open(); } catch (InvalidMidiDataException ex) { System.out.println("FAIL"); instrument = synth.getAvailableInstruments(); currentInstrument = instrument[0]; synth.loadInstrument(currentInstrument); try { synth.open(); } catch (MidiUnavailableException ex1) { Logger.getLogger(MIDISynth.class.getName()).log(Level.SEVERE, null, ex1); } } catch (IOException ex) { Logger.getLogger(MIDISynth.class.getName()).log(Level.SEVERE, null, ex); } catch (MidiUnavailableException ex) { Logger.getLogger(MIDISynth.class.getName()).log(Level.SEVERE, null, ex); }

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  • Implementing Iterable in Java

    - by Artium
    I have the following code public class A extends Iterable<Integer> { ... public Iterator<Integer> iterator() { return new Iterator<Integer>() { A a; public boolean hasNext() { ... } public Integer next() { ... } public void remove(){ ... } }; I would like to initialize the "a" field in the anonymous class with the instance of A that iterator method was called on. Is it possible? Thank you.

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  • Date Comparison using Java

    - by Lakshman
    I have two dates: toDate (user input in MM/dd/yyyy format) currentDate (obtained by new Date()) I need to compare the currentDate with toDate. I have to display a report only when the toDate is equal to or more than currentDate. How can I do that?

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  • How to access files in Java ME

    - by cancelledout
    I want to access the files encircled in this screenshot. What path should I use? This is for my JavaME application. file:///ParseExample/service1.xml doesn't seem to be the right one. http://www.fileden.com/files/2010/5/28/2872707//projectfiles.JPG

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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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  • Beginner Java Question about Integer.parseInt() and casting

    - by happysoul
    so when casting like in the statement below :- int randomNumber=(int) (Math.random()*5) it causes the random no. generated to get converted into an int.. Also there's this method I just came across Integer.parseInt() which does the same ! i.e return an integer Why two different ways to make a value an int ? Also I made a search and it says parseInt() takes string as an argument.. So does this mean that parseInt() is ONLY to convert String into integer ? What about this casting then (int) ?? Can we use this to convert a string to an int too ? sorry if it sounds like a dumb question..I am just confused and trying to understand Help ?

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  • Which Queue implementation to use in Java?

    - by devoured elysium
    I need to use a FIFO structure in my application. It needs to have at most 5 elements. I'd like to have something easy to use (I don't care for concurrency) that implements the Collection interface. I've tried the LinkedList, that seems to come from Queue, but it doesn't seem to allow me to set it's maximum capacity. It feels as if I just want at max 5 elements but try to add 20, it will just keep increasing in size to fit it. I'd like something that'd work the following way: XQueue<Integer> queue = new XQueue<Integer>(5); //where 5 is the maximum number of elements I want in my queue. for (int i = 0; i < 10; ++i) { queue.offer(i); } for (int i = 0; i < 5; ++i) { System.out.println(queue.poll()); } That'd print: 5 6 7 8 9 Thanks

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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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  • Java threads not working correctly with linkedlist

    - by user69514
    Hi I am working on the sleeping barber problem. with the addition of having priority customer when they arrive they go in the front of the line and they are the next ones to get a haircut. I'm using a linkedlist and if I see a priority customer I put him in the beginning of the list, if the customer is not priority he goes to the end of the list. then I call the wantHaircut method getting the first element of the list. my problem is that the customer are being processed in the order they arrive, and the priority customer have to wait. here is the code where it all happens. any ideas what I am doing wrong? thanks public void arrivedBarbershop(Customer c){ if(waiting < numChairs && c.isPriority()){ System.out.println("Customer " + c.getID() + ": is a priority customer - SITTING -"); mutex.up(); customer_list.addFirst(c); } else if(waiting >= numChairs && c.isPriority()){ System.out.println("Customer " + c.getID() + ": is a priority customer - STANDING -"); mutex.up(); customer_list.addFirst(c); } else if(waiting < numChairs && !c.isPriority()){ waiting++; System.out.println("Customer " + c.getID() + ": arrived, sitting in the waiting room"); customer_list.addLast(c); customers.up(); // increment waiting customers } else if(waiting >= numChairs && !c.isPriority()) { System.out.println("Customer " + c.getID() + ": went to another barber because waiting room was full - " + waiting + " waiting"); mutex.up(); } if(!customer_list.isEmpty()){ this.wantHairCut(customer_list.removeFirst()); } } public void wantHairCut(Customer c) { mutex.up(); barber.down(); // waits for being allowed in barber chair System.out.println("Customer " + c.getID() + ": getting haircut"); try { /** haircut takes between 1 and 2 seconds **/ Thread.sleep(Barbershop.randomInt(1, 2) * 1000); } catch (InterruptedException e) { } System.out.println("Barber: finished cutting customer " + c.getID() + "'s hair"); c.gotHaircut = true; cutting.up(); // signals cutting has finished /** customer must pay now **/ this.wantToCashout(c); }

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  • Java Hibernate id auto increment

    - by vinise
    Hy I'v a little problem with hibernate on netbeans. I've a table with an Auto increment id : CREATE TABLE "DVD" ( "DVD_ID" INT not null primary key GENERATED ALWAYS AS IDENTITY (START WITH 1, INCREMENT BY 1), "TITLE" VARCHAR(150), "COM" LONG VARCHAR, "COVER" VARCHAR(150) ); But this auto increment is not properly detected with Reverse Engineering. I get a map file with this : <id name="dvdId" type="int"> <column name="DVD_ID" /> <generator class="assigned" /> </id> i've looked on google and on this site ... foud some stuf but i'm still stuck.. i've tried to add insert="false" update="false" on the map file but i get back : Caused by: org.xml.sax.SAXParseException: Attribute "insert" must be declared for element type "id". Anny help will be pleased Vincent

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