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  • Can Java's random function be zero?

    - by ThirdD3gree
    Just out of curiosity, can Math.random() ever be zero? For example, if I were to have: while (true){ if (Math.random() == 0) return 1; } Would I ever actually get a return of one? There's also rounding error to consider because Math.random() returns a double. I ask because my CS professor stated that random() goes from 0 to 1 inclusive, and I always thought it was exclusive.

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  • java.util.concurrent.ThreadPoolExecutor strange logic

    - by rodrigoap
    Look ath this method of ThreadPoolExcecutor: public void execute(Runnable command) { ... if (runState == RUNNING && workQueue.offer(command)) { if (runState != RUNNING || poolSize == 0) ensureQueuedTaskHandled(command); } ... } It check that runState is RUNNING and then the oposite. As I'm trying to do some tuning on a SEDA like model I wanted to understand the internals of the thread pool. Do you think this code is correct?

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  • Java Reflection Utility

    - by DD
    Is there a utility to get a property which isnt prefixed by get from an object using reflection similar to BeanUtils? e.g. if I specify "hashcode" and I want to get the object.hashcode() value. Thanks.

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  • The best way to assign an immutable instance to a Collection in Java

    - by Ali
    Today I was reading through some Hibernate code and I encounter something interesting. There is a class called CollectionHelper that defines the following constant varibale: public final class CollectionHelper { public static final List EMPTY_LIST = Collections.unmodifiableList( new ArrayList(0 ) ; public static final Collection EMPTY_COLLECTION = Collections.unmodifiableCollection(new ArrayList(0) ); public static final Map EMPTY_MAP = Collections.unmodifiableMap( new HashMap(0) ); They have used these constants to initialize collections with immutable instances. Why they didn't simply use the Collections.EMPTY_LIST for initializing lists? Is there a benefit in using the following method?

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  • java generated excel sorting color mess.

    - by afzal
    I am using jxl api for generating a excel sheet, in which the alternate rows are highlighted, when I sort the contents of a excel and sort manually, the cell background colors messup, usually this is because I am writing the color cell by cell, is there anyway through which i color the alternate rows of the excel while generating it, in such a way that it doesnt effect the sorting of the contents.

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  • Size of Objects in Java Heap w/ Regards to Methods

    - by Eric
    I know about primitives and objects living on the heap, but how does the number of methods effect heap size of the object? For example: public class A { int x; public getX() { return x; } } public class B { int x; public getX() { return x; } public getXString() { return String.valueOf(x); } public doMoreInterestingStuff() { return x * 42; } //etc } When instantiated, both objects live on the heap, both have memory allocated to their primitive x, but is B allocated more heap space due to having more method signatures? Or are those ONLY on the classLoader? In this example its trivial, but when there are 100,000+ of these objects in memory at any given time I imagine it could add up.

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  • get static initialization block to run in a java without loading the class

    - by TP
    I have a few classes as shown here public class TrueFalseQuestion implements Question{ static{ QuestionFactory.registerType("TrueFalse", "Question"); } public TrueFalseQuestion(){} } ... public class QuestionFactory { static final HashMap<String, String > map = new HashMap<String,String>(); public static void registerType(String questionName, String ques ) { map.put(questionName, ques); } } public class FactoryTester { public static void main(String[] args) { System.out.println(QuestionFactory.map.size()); // This prints 0. I want it to print 1 } } How can I change TrueFalseQuestion Type so that the static method is always run so that I get 1 instead of 0 when I run my main method? I do not want any change in the main method. I am actually trying to implement the factory patterns where the subclasses register with the factory but i have simplified the code for this question.

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  • Upload files with java

    - by Marius
    I'd like to upload a few files to a http server. Basically what i need is some sort of a post request to the server with a few parameters and the files. I've seen examples of just uploading files, but didn't find how to also pass additional parameters. So the question would be what's the simplest and free solution of doing this? Does anyone have any file upload examples that i could study? I've been googling for a few hours, but (maybe it's just one of those days) couldn't find exactly what i needed. The best solution would be something that doesn't involve any third party classes or libraries. Thank you

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  • Java Convert ColorSpace of BufferedImage to CS_GRAY without using ConvertColorOp

    - by gmatt
    I know its possible to convert an image to CS_GRAY using public static BufferedImage getGrayBufferedImage(BufferedImage image) { BufferedImageOp op = new ColorConvertOp(ColorSpace .getInstance(ColorSpace.CS_GRAY), null); BufferedImage sourceImgGray = op.filter(image, null); return sourceImgGray; } however, this is a chokepoint of my entire program. I need to do this often, on 800x600 pixel images and takes about 200-300ms for this operation to complete, on average. I know I can do this alot faster by using one for loop to loop through the image data and set it right away. The code above on the other hand constructs a brand new 800x600 BufferedImage that is gray scale. I would rather just transform the image I pass in. Does any one know how to do this with a for loop and given that the image is RGB color space?

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  • Java multi Generic collection parameters complie error

    - by Geln Yang
    Hi, So strange!Please have a look the code first: public class A { } public class B extends A { } public class C extends A { } public class TestMain { public <T extends A> void test(T a, T b) { } public <T extends A> void test(List<T> a, List<T> b) { } public static void main(String[] args) { new TestMain().test(new B(), new C()); new TestMain().test(new ArrayList<B>(), new ArrayList<C>()); } } The statement "new TestMain().test(new ArrayList(), new ArrayList())" get a "Bound mismatch" compile error, while "new TestMain().test(new B(), new C())" is compiled ok. Bound mismatch: The generic method test(T, T) of type TestMain is not applicable for the arguments (ArrayList, ArrayList). The inferred type ArrayList is not a valid substitute for the bounded parameter It seems the type of the second generic List parameter is limited by the Type of the first.Is it a feature or a bug of the compile program? ps, jdk:1.6,IDE:Eclipse 3.5.1

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  • Java synchronized method lock on object, or method?

    - by wuntee
    If I have 2 synchronized methods in the same class, but each accessing different variables, can 2 threads access those 2 methods at the same time? Does the lock occur on the object, or does it get as specific as the variables inside the synchronized method? Example: class x{ private int a; private int b; public synchronized void addA(){ a++; } public synchronized void addB(){ b++; } } Can 2 threads access the same instance of class x performing x.addA() and x.addB() at the same time?

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  • goto statements in java

    - by user238284
    I executed the below code in Eclipse, but the GOTO statements in it is not effective. How to use it? case 2: **outsideloops:** System.out.println("Enter the marks (in 100):"); System.out.println("Subject 1:"); float sub1=Float.parseFloat(br.readLine()); **if(sub1<=101) goto outsideloops;** System.out.println("Subject 2:"); float sub2=Float.parseFloat(br.readLine()); System.out.println("Subject 3:"); float sub3=Float.parseFloat(br.readLine()); System.out.println("The Student is "+stu.average(sub1,sub2,sub3)+ "in the examinations"); break;

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  • java dynamic memory allocation?

    - by JavaUser
    Hi, Why an object initialization using " new " keyword is called as dynamic memory allocation since compile time itself we know the memory needed for that object . Also please explain what happen when u do ClassA object = new ClassA(); in heap and stack . Thx

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  • Java swt treeview popup menu

    - by InsertNickHere
    Hiho, currently I have a working popup menu which appears when I click on a treeview item. But I want to show different popups for different tree view entries. I don't get a idea how to do so... Here is my code for creating the menu: MenuManager menuMgr = new MenuManager("#PopupMenu"); menuMgr.setRemoveAllWhenShown(true); menuMgr.addMenuListener(new IMenuListener() { @Override public void menuAboutToShow(IMenuManager manager) { Action action = new Action() { public void run() { // So something } }; action.setText("Set as working file"); manager.add(action); } }); Menu menu = menuMgr.createContextMenu(getTree()); getTree().setMenu(menu);

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  • JAVA - Download PDF file from Webserver

    - by Augusto Picciani
    I need to download a pdf file from a webserver to my pc and save it locally. I used Httpclient to connect to webserver and get the content body: HttpEntity entity=response.getEntity(); InputStream in=entity.getContent(); String stream = CharStreams.toString(new InputStreamReader(in)); int size=stream.length(); System.out.println("stringa html page LENGTH:"+stream.length()); System.out.println(stream); SaveToFile(stream); Then i save content in a file: //check CRLF (i don't know if i need to to this) String[] fix=stream.split("\r\n"); File file=new File("C:\\Users\\augusto\\Desktop\\progetti web\\test\\test2.pdf"); PrintWriter out = new PrintWriter(new FileWriter(file)); for (int i = 0; i < fix.length; i++) { out.print(fix[i]); out.print("\n"); } out.close(); I also tried to save a String content to file directly: OutputStream out=new FileOutputStream("pathPdfFile"); out.write(stream.getBytes()); out.close(); But the result is always the same: I can open pdf file but i can see white pages only. Does the mistake is around pdf stream and endstream charset encoding? Does pdf content between stream and endStream need to be manipulate in some others way?

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  • TACACS lib for java

    - by guaz
    The only open source TACACS lib I was able to find was Jnetlib http://sourceforge.net/projects/jnetlib But there is not any description about how to use it!! Anyone have used it before?? thanks

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  • Generate UML from java source

    - by Parhs
    Hello. Because i have a big project i must generate the UML for this...Writing UML for 300 classes is overkill... So is there any solution to generate the diagrams for me ? I am using Netbeans.... Thank you for reading

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  • java and threads: very strange behaviour

    - by Derk
    private synchronized Map<Team, StandingRow> calculateStanding() { System.out.println("Calculate standing for group " + getName()); Map<Team, StandingRow> standing = new LinkedHashMap<Team, StandingRow>(); for (Team team : teams) { standing.put(team, new StandingRow(team)); } StandingRow homeTeamRow, awayTeamRow; for (Match match : matches.values()) { homeTeamRow = standing.get(match.getHomeTeam()); awayTeamRow = standing.get(match.getAwayTeam()); System.out.println("Contains key for " + match.getHomeTeam() + ": " + standing.containsKey(match.getHomeTeam())); System.out.println("Contains key for " + match.getAwayTeam() + ": " + standing.containsKey(match.getAwayTeam())); } } This is my code. matches contains 6 elements, but the problem is that after two matches no keys are anymore found in the standing map. The output is for example Contains key for Zuid-Afrika: true Contains key for Mexico: true Contains key for Uruguay: true Contains key for Frankrijk: true Contains key for Zuid-Afrika: false Contains key for Uruguay: false Contains key for Frankrijk: false Contains key for Mexico: false Contains key for Mexico: false Contains key for Uruguay: false Contains key for Frankrijk: false Contains key for Zuid-Afrika: false This is in a threaded environment, but the method is synchronized so I thought that this would not give a problem? I have also a simple unit test for this method and that works well.

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  • Import text file crunching library for Java/Groovy ?

    - by devdude
    In a lot of real life implementations of applications we face the requirement to import some kind of (text) files. Usually we would implement some (hardcoded?) logic to validate the file (eg. proper header, proper number of delimiters, proper date/time value,etc.). Eventually also need to check for the existence of related data in a table (eg. value of field 1 in text file must have an entry in some basic data table). While XML solves this (to some extend) with XSD and DTD, we end up hacking this again and again for proprietary text file formats. Is there any library or framework that allows the creation of templates similar to the xsd approach ? This would make it way more flexible to react on file format changes or implement new formats. Thanks for any hints Sven

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  • Facebook app request in java not working

    - by Arpit Solanki
    I am trying to send a facebook app request to a user through the code below.But it gives an IO Exception and HTTP status code 400 in running.I dont see a any app request being sent to a user on running this. StringBuffer buffer = new StringBuffer(); buffer.append("access_token").append('=').append(this.app_access_token); buffer.append('&').append("message=").append("sent an app request!"); String content = buffer.toString(); try{ URLConnection connection = new URL("https://graph.facebook.com/me/apprequests").openConnection(); connection.setDoOutput(true); connection.setRequestProperty("Content-Type","application/x-www-form-urlencoded"); connection.setRequestProperty("Content-Length",Integer.toString(content.length())); DataOutputStream outs = new DataOutputStream(connection.getOutputStream()); outs.writeBytes(content); outs.flush(); outs.close(); BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream())); String inputLine; while ((inputLine = in.readLine()) != null) { System.out.println(inputLine); } in.close(); } catch(Exception e){ System.out.println(e); }

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  • How to replace characters in a java String?

    - by ManBugra
    I like to replace a certain set of characters of a string with a corresponding replacement character in an efficent way. For example: String sourceCharacters = "šdccŠÐCCžŽ"; String targetCharacters = "sdccSDCCzZ"; String result = replaceChars("Gracišce", sourceCharacters , targetCharacters ); Assert.equals(result,"Gracisce") == true; Is there are more efficient way than to use the replaceAll method of the String class? My first idea was: final String s = "Gracišce"; String sourceCharacters = "šdccŠÐCCžŽ"; String targetCharacters = "sdccSDCCzZ"; // preparation final char[] sourceString = s.toCharArray(); final char result[] = new char[sourceString.length]; final char[] targetCharactersArray = targetCharacters.toCharArray(); // main work for(int i=0,l=sourceString.length;i<l;++i) { final int pos = sourceCharacters.indexOf(sourceString[i]); result[i] = pos!=-1 ? targetCharactersArray[pos] : sourceString[i]; } // result String resultString = new String(result); Any ideas? Btw, the UTF-8 characters are causing the trouble, with US_ASCII it works fine.

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