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  • how random is Math.random() in java across different jvms or different machines

    - by user881480
    I have a large distributed program across many different physical servers, each program spawns many threads, each thread use Math.random() in its operations to draw a piece from many common resource pools. The goal is to utilize the pools evenly across all operations. Sometimes, it doesn't appear so random by looking at a snapshot on a resource pool to see which pieces it's getting at that instant (it might actually be, but it's hard to measure and find out for sure). Is there something that's better than Math.random() and performs just as good (not much worse at least)?

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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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  • What is faster- Java or C# (Or good old C)?

    - by Rexsung
    I'm currently deciding on a platform to build a scientific computational product on, and am deciding on either C#, Java, or plain C with Intels compiler on Core2 Quad CPU's. It's mostly integer arithmetic. My benchmarks so far show Java and C are about on par with each other, and dotNET/C# trails by about 5%- however a number of my coworkers are claiming that dotNET with the right optimizations will beat both of these given enough time for the JIT to do its work. I always assume that the JIT would have done it's job within a few minutes of the app starting (Probably a few seconds in my case, as it's mostly tight loops), so I'm not sure whether to believe them Can anyone shed any light on the situation? Would dotNET beat Java? (Or am I best just sticking with C at this point?). The code is highly multithreaded and data sets are several terabytes in size. Haskell/erlang etc are not options in this case as there is a significant quantity of existing legacy C code that will be ported to the new system, and porting C to Java/C# is a lot simpler than to Haskell or Erlang. (Unless of course these provide a significant speedup). Edit: We are considering moving to C# or Java because they may, in theory, be faster. Every percent we can shave off our processing time saves us tens of thousands of dollars per year. At this point we are just trying to evaluate whether C, Java, or c# would be faster.

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  • Detecting incorrect key using AES/GCM in JAVA

    - by 4r1y4n
    I'm using AES to encrypt/decrypt some files in GCM mode using BouncyCastle. While I'm proving wrong key for decryption there is no exception. How should I check that the key is incorrect? my code is this: SecretKeySpec incorrectKey = new SecretKeySpec(keyBytes, "AES"); IvParameterSpec ivSpec = new IvParameterSpec(ivBytes); Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "BC"); byte[] block = new byte[1048576]; int i; cipher.init(Cipher.DECRYPT_MODE, incorrectKey, ivSpec); BufferedInputStream fis=new BufferedInputStream(new ProgressMonitorInputStream(null,"Decrypting ...",new FileInputStream("file.enc"))); BufferedOutputStream ro=new BufferedOutputStream(new FileOutputStream("file_org")); CipherOutputStream dcOut = new CipherOutputStream(ro, cipher); while ((i = fis.read(block)) != -1) { dcOut.write(block, 0, i); } dcOut.close(); fis.close(); thanks

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  • How to effectively copy an array in java ?

    - by Tony
    The toArray method in ArrayList , Bloch uses both System.arraycopy and Arrays.copyOf to copy an array . public <T> T[] toArray(T[] a) { if (a.length < size) // Make a new array of a's runtime type, but my contents: return (T[]) Arrays.copyOf(elementData, size, a.getClass()); System.arraycopy(elementData, 0, a, 0, size); if (a.length > size) a[size] = null; return a; } How to compare these two copy method , when to use which ? Thanks.

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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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  • How to wrap Java String.format()?

    - by BlinK_
    Hey everyone, I would like to wrap the String.format() method with in my own Logger class. I can't figure a way how to pass arguments from my method to String.format(). public class Logger { public static void format(String format, Object... args) { print(String.format(format, args)); // <-- this gives an error obviously. } public static void print(String s) { System.out.println(s); } }

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  • J2EE fast track (Learning Enterprise Java real fast)

    - by IndexController
    Hello, We just started a new project in J2EE in our office and i am required to participate effectively. I mostly work on web applications and I use PHP/MySql but I also know J2SE and have written couple of standalone applications. I need help and advise on how i can learn J2ee very fast so that i can blend into the project without difficulties. I need help with book & tutorial recommendations and also links to resources. Thank you for your time.

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  • Object Literals In Java?

    - by jjacquay712
    I am learning GWT for web development and came across a piece of code I can't really understand. helloBtn.addClickHandler(new ClickHandler() { public void onClick(ClickEvent event) { Window.alert("Hello!"); } }); If someone could explain to me what it is doing that would be great. Thanks, John

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  • Java Scanner won't follow file

    - by Steve Renyolds
    Trying to tail / parse some log files. Entries start with a date then can span many lines. This works, but does not ever see new entries to file. File inputFile = new File("C:/test.txt"); InputStream is = new FileInputStream(inputFile); InputStream bis = new BufferedInputStream(is); //bis.skip(inputFile.length()); Scanner src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); while (true) { while(src.hasNext()){ System.out.println("[ " + src.next() + " ]"); } } Doesn't seem like Scanner's next() or hasNext() detects new entries to file. Any idea how else I can implement, basically, a tail -f with custom delimiter. ok - using Kelly's advise i'm checking & refreshing the scanner, this works. Thank you !! if anyone has improvement suggestions plz do! File inputFile = new File("C:/test.txt"); InputStream is = new FileInputStream(inputFile); InputStream bis = new BufferedInputStream(is); //bis.skip(inputFile.length()); Scanner src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); while (true) { while(src.hasNext()){ System.out.println("[ " + src.next() + " ]"); } Thread.sleep(50); if(bis.available() > 0){ src = new Scanner(bis); src.useDelimiter("\n2010-05-01 "); } }

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  • Java/Swing: the fast/slow UI binding problem

    - by Jason S
    I need a way to bind UI indicators to rapidly-changing values. I have a class NumberCruncher which does a bunch of heavy processing in a critical non-UI thread, thousands of iterations of a loop per second, and some number of those result in changes to a set of parameters I care about. (think of them as a key-value store) I want to display those at a slower rate in the UI thread; 10-20Hz would be fine. How can I add MVC-style notification so that my NumberCruncher code doesn't need to know about the UI code/binding?

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  • Parsing JSON to XML using net.sf.json (java)

    - by Castanho
    Hi guys, I'm parsing a generic JSON to a XML using net.sf.json. (I'm not using POJO Obj in the conversion) When dealing with vectors I'm receiving: <root> <entry> <Id>1</accountId> <Items> <e> <cost>0.1</cost> <debit>0.1</debit> </e> <e> <cost>0.1</cost> <debit>0.1</debit> </e> </Items> </entry> </root> When the correct for my point of view should be: <root> <entry> <accountId>1</accountId> <Items> <cost>0.1</cost> <debit>0.1</debit> </Items> <Items> <cost>0.2</cost> <debit>0.2</debit> </Items> </entry> </root> Do anyone have used this lib and could help me? Any tips could help! Thanks in advance

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  • Java anonymous class efficiency implications

    - by Po
    Is there any difference in efficiency (e.g. execution time, code size, etc.) between these two ways of doing things? Below are contrived examples that create objects and do nothing, but my actual scenarios may be creating new Threads, Listeners, etc. Assume the following pieces of code happen in a loop so that it might make a difference. Using anonymous objects: void doSomething() { for (/* Assume some loop */) { final Object obj1, obj2; // some free variables IWorker anonymousWorker = new IWorker() { doWork() { // do things that refer to obj1 and obj2 } }; } } Defining a class first: void doSomething() { for (/* Assume some loop */) { Object obj1, obj2; IWorker worker = new Worker(obj1, obj2); } } static class Worker implements IWorker { private Object obj1, obj2; public CustomObject(Object obj1, Object obj2) {/* blah blah */} @Override public void doWork() {} }; Thank you :)

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  • Why does a function that takes IEnumerable<interface> not accept IEnumerable<class>?

    - by Matt Whitfield
    Say, for instance, I have a class: public class MyFoo : IMyBar { ... } Then, I would want to use the following code: List<MyFoo> classList = new List<MyFoo>(); classList.Add(new MyFoo(1)); classList.Add(new MyFoo(2)); classList.Add(new MyFoo(3)); List<IMyBar> interfaceList = new List<IMyBar>(classList); But this produces the error: `Argument '1': cannot convert from 'IEnumerable<MyFoo>' to 'IEnumerable<IMyBar>' Why is this? Since MyFoo implements IMyBar, one would expect that an IEnumerable of MyFoo could be treated as an IEnumerable of IMyBar. A mundane real-world example being producing a list of cars, and then being told that it wasn't a list of vehicles. It's only a minor annoyance, but if anyone can shed some light on this, I would be much obliged.

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  • java serialization and final fields

    - by mdma
    I have an class defining an immutable value type that I now need to serialize. The immutability comes from the final fields which are set in the constructor. I've tried serializing, and it works (surprisingly?) - but I've no idea how. Here's an example of the class public class MyValueType implements Serializable { private final int value; private transient int derivedValue; public MyValueType(int value) { this.value = value; this.derivedValue = derivedValue(value); } // getters etc... } Given that the class doesn't have a no arg constructor, how can it be instantiated and the final field set? (An aside - I noticed this class particularly because IDEA wasn't generating a "no serialVersionUID" inspection warning for this class, yet successfully generated warnings for other classes that I've just made serializable.)

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  • Java - getConstructor() ?

    - by msr
    Hello, I wrote the question as a comment in the code, I think its easier to understand this way. public class Xpto{ protected AbstractClass x; public void foo(){ // AbstractClass y = new ????? Car or Person ????? /* here I need a new object of this.x's type (which could be Car or Person) I know that with x.getClass() I get the x's Class (which will be Car or Person), however Im wondering how can I get and USE it's contructor */ // ... more operations (which depend on y's type) } } public abstract class AbstractClass { } public class Car extends AbstractClass{ } public class Person extends AbstractClass{ }

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  • Java Swing TanleModel fireTableRowsInserted on EDT

    - by Ayman
    I have a TableModel that is populated from a background running thread. I am calling fireTableRowsInserted when data is inserted, which is NOT on the EDT. My question is, do I need to use invokeLater for the fireTableRowsInserted? In other words, is the below correct: public void putData(TableRow row) { // we are not on the EDT here... rows.add(row); fireTableRowsInserted(rows.size()-1, rows.size()-1); }

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  • Static variables in Java for a test oObject creator

    - by stevebot
    Hey, I have something like the following TestObjectCreator{ private static Person person; private static Company company; static { person = new Person() person.setName("Joe"); company = new Company(); company.setName("Apple"); } public Person createTestPerson(){ return person; } public Person createTestCompany(){ return company; } } By applying static{} what am I gaining? I assume the objects are singletons as a result. However, if I did the following: Person person = TestObjectCreator.createTestPerson(); person.setName("Jill"); Person person2 = TestObjectCreator.createTestPerson(); would person2 be named Jill or Joe?

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  • Networking multiple computers to one brain in Java

    - by Morpheous
    Hello, I was wondering which libraries or API's would be useful in this. what im aiming for is to be able to type a command into a prompt and then specify which computer(out of all of them that are networked together) to execute that command on. the second part is i want to be able to see that command execute and the result on the computer that was specified. for example if i enter "firefox www.google.com, desktop2" i want to be able to see the window open on the monitor of that computer. Do you understand what im trying to do? any help is appreciated. Thanks, Morpheous

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  • java source code doubt

    - by abson
    this compiles class ex1 { public int show() { try { int a=10/10; return 10;} catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally");} System.out.println("hello"); return 20; } } on the other hand this doesn't class ex15 { public int show() { try { int a=10/0; return 10;} catch(ArithmeticException e) { System.out.println(e); } finally { System.out.println("Finally"); return 40;} System.out.println("hello"); return 20; } } why is it so?

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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 : HTTP POST Request

    - by SpunkerBaba
    I have to do a http post request to a web-service for authenticating the user with username and password. The Web-service guy gave me following information to construct HTTP Post request. POST /login/dologin HTTP/1.1 Host: webservice.companyname.com Content-Type: application/x-www-form-urlencoded Content-Length: 48 id=username&num=password&remember=on&output=xml The XML Response that i will be getting is <?xml version="1.0" encoding="ISO-8859-1"?> <login> <message><![CDATA[]]></message> <status><![CDATA[true]]></status> <Rlo><![CDATA[Username]]></Rlo> <Rsc><![CDATA[9L99PK1KGKSkfMbcsxvkF0S0UoldJ0SU]]></Rsc> <Rm><![CDATA[b59031b85bb127661105765722cd3531==AO1YjN5QDM5ITM]]></Rm> <Rl><![CDATA[[email protected]]]></Rl> <uid><![CDATA[3539145]]></uid> <Rmu><![CDATA[f8e8917f7964d4cc7c4c4226f060e3ea]]></Rmu> </login> This is what i am doing HttpPost postRequest = new HttpPost(urlString); How do i construct the rest of the parameters?

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