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• How to create an adhoc network between laptops in java?

  - by Muaz

  Hello, I want to create an adhoc between labtops were they will communicate using wireless communication. I will use java for this but still I do not know how to start.. I think I'll have to use sockets for the connections right? How will a laptop notice other laptops in its local network or the other way around? Do i need a server to handle the communication between laptops? Another thing, how to broadcast a message from one laptop to other laptops in the network? Please reply as soon as you can. Any help will be appreciated. Thanks in advance.

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• How to get the first non-null value in Java?

  - by froadie

  Is there a Java equivalent of SQL's COALESCE function? That is, is there any way to return the first non-null value of several variables? e.g. Double a = null; Double b = 4.4; Double c = null; I want to somehow have a statement that will return the first non-null value of a, b, and c - in this case, it would return b, or 4.4. (Something like the sql method - return COALESCE(a,b,c)). I know that I can do it explicitly with something like: return a != null ? a : (b != null ? b : c) But I wondered if there was any built-in, accepted function to accomplish this.

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• When should I write my own Look and Feel for Java Swing instead of customizing one?

  - by Jonas

  I have used a few different Look and Feels for Java Swing, but I don't really like anyone to 100% so I often end up with customizing it a lot. Sometimes I am thinking about if it is a better idea to write my own LaF (by extending an existing one), but I don't really know. For the moment, I mostly use Nimbus, but I change all colors (to darker ones) and rewrite the appearance of some components, like sliders and scrollbars. I also mostly customize all tables and I am thinking about to change the look of a few other components. When is it recommended to create a new Look-and-Feel instead of customizing one? What are the pros and cons? I.e. customize Nimbus or create a new one by extending Nimbus? Related article: Creating a Custom Look and Feel (old)

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• How should I handle searching through byte arrays in Java?

  - by Zombies

  Preliminary: I am writting my own httpclient in Java. I am trying to parse out the contents of chunked encoding. Here is my dilema: Since I am trying to parse out chunked http transfer encoding with a gzip payload there is a mix of ascii and binary. I can't just take the http resp content and convert it to a string and make use of StringUtils since the binary data can easily contain nil characters. So what I need to do is some basic things for parsing out each chunk and its chunk length (as per chunked transfer/HTTP/1.1 spec). Are there any helpful ways of searching through byte arrays of binary/part ascii data for certain patterns (like a CR LF) (instead of just a single byte) ? Or must I write the for loops for this?

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• How to deploy a Java Swing application with an embedded JavaDB database?

  - by Jonas

  I have implemented an Java Swing application that uses an embedded JavaDB database. The database need to be stored somewhere and the database tables need to be created at the first run. What is the preferred way to do these procedures? Should I always create the database in the local directory, and first check if the database file exist, and if it doesn't exist let the user create the tables (or at least show a message that the tables will be created). Or should I let the user choose a path? but then I have to save the path somewhere. Should I save the path with Preferences.systemRoot();, and check if that variable is set on startup? If the user choses a path and save it in the Preferences, can I get any problems with user permissions? or should it be safe wherever the user store the database? Or how do I handle this? Any other suggestions for this procedure?

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• Is there a Java equivalent for Ruby on Rails "url_for"?

  - by Oren Ben-Kiki

  I have written something like this pretty easily in C# (string GetUrl(new { controller = "foo", action = "bar", baz = "fnord" }), based on the existing capabilities of the XmlRouteCollection class provided by the ASP.NET MVC framework (why it isn't there out of the box is beyond me; the additional required code was trivial). I am now faced with a JSP project, and I need the same ability: centralize the logic for generating all URLs in one place, based on a list of routing rules. Is there some code somewhere I could reuse/adapt to do this in Java? It seems like a common enough requirement, but google proved surprisingly unhelpful in finding something like this.

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• Strange Java Coding??? Class in class???

  - by poeschlorn

  Hi guys, I got a question about Java coding in general... In some sample codes there are methods and classes declared WITHIN other methods and/or classes.... I've never heard/red about this...what effect does this kind of programming have? Wouldn't it be better to write down classes in a seperate file and methods side by side and not within each other (like every book tells you)? What are the advantages and disadvantages of this kind of programming? Here's an example of what I mean: Handler mHandler = new Handler() { public void handleMessage(android.os.Message msg) { TextView textView = (TextView) findViewById(R.id.description); textView.setText(mRoad.mName + " " + mRoad.mDescription); MapOverlay mapOverlay = new MapOverlay(mRoad, mapView); List<Overlay> listOfOverlays = mapView.getOverlays(); listOfOverlays.clear(); listOfOverlays.add(mapOverlay); mapView.invalidate(); }; };

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• How do I get the median/mode/range of a column in SQL using Java?

  - by Derek

  I have to get the median, mode and range of test scores from one column in a table but I am unsure how to go about doing that. When you connect to the database using java, you are normally returned a ResultSet that you can make a table or something out of but how do you get particular numbers or digits? Is there an SQL command to get the median/mode/range or will I have to calculate this myself, and how do you pull out numbers from the table in order to be able to calculate the mode/median/range? Thanks.

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• Does Java Mac OSX native look and feel respect UIManager font changes?

  - by Erik Lickerman

  I have a java applet and the only look and feel that works properly is the native mac one. I wanted to make the fonts a bit larger and tried using the standard UIManager methods UIManager.put("Label.font", new Font("Georgia", Font.PLAIN, 18)); This produces no change. It does not throw an exception, of course. Does anyone know if the native mac look and feel ignores these? I know there are specific ways to make controls different sizes on mac but these only seem to make them smaller. You cannot make the controls larger than regular.

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• How do I get Java to parse and format a date/time with the same time zone? I keep getting the local timezone

  - by fishtoprecords

  My application keeps all Java Date's in UTC. Parsing them is easy, but when I print them out, the display shows the computer's local time zone, and I want to show it as UTC. Example code: String sample = "271210 200157 UTC"; SimpleDateFormat dfmt = new SimpleDateFormat("ddMMyy HHmmss Z"); Date result = dfmt.parse(sample); System.out.printf("%tc\n", result); the result is Mon Dec 27 15:01:57 EST 2010 What I want is Mon Dec 27 20:01:57 UTC 2010 Clearly I have to set some Locale and TimeZone values, but I don't see where to put them. Thanks Pat

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• How can I pass a javaScript function to a Java Method to act as a callback (Rhino)

  - by Dan Howard

  Hi everyone, Basically I'm trying to pass a javaScript function to a Java method to act as a callback to the script. I can do it - sort of - but the object I receive is a sun.org.mozilla.javascript.internal.InterpretedFunction and I don't see a way to invoke it. Any ideas? Here's what I have so far: var someNumber = 0; function start() { // log is just an log4j instance added to the Bindings log.info("started...."); someNumber = 20; // Test is a unit test object with this method on it (taking Object as a param). test.callFromRhino(junk); } function junk() { log.info("called back " + someNumber); }

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• Java - How to find that the user has changed the configuration file?

  - by Yatendra Goel

  I am developing a Java Desktop Application. This app needs a configuration to be started. For this, I want to supply a defaultConfig.properties or defaultConfig.xml file with the application so that If user doesn't select any configuration, then the application will start with the help of defaultConfig file. But I am afraid of my application crash if the user accidentally edit the defaultConfig file. So Is there any mechanism through which I can check before the start of the application that whether the config file has changed or not. How other applications (out in the market) deal with this type of situation in which their application depends on a configuration file? If the user edited the config file accidentally or intentionally, then the application won't run in future unless he re-installs the application.

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• Need help in translating code from C to Java.

  - by Vuntic

  From this article. Here's the code: float InvSqrt(float x){ // line 0 float xhalf = 0.5f * x; int i = *(int*)&x; // store floating-point bits in integer i = 0x5f3759d5 - (i >> 1); // initial guess for Newton's method x = *(float*)&i; // convert new bits into float x = x*(1.5f - xhalf*x*x); // One round of Newton's method return x; } ...I can't even tell if that's C or C++. [okay apparently it's C, thanks] Could someone translate it to Java for me, please? It's (only, I hope) lines 2 and 4 that are confusing me.

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• The Java interface doesn't declare any exception. How to manage checked exception of the implementat

  - by Frór

  Let's say I have the following Java interface that I may not modify: public interface MyInterface { public void doSomething(); } And now the class implementing it is like this: class MyImplementation implements MyInterface { public void doSomething() { try { // read file } catch (IOException e) { // what to do? } } } I can't recover from not reading the file. A subclass of RuntimeException can clearly help me, but I'm not sure if it's the right thing to do: the problem is that that exception would then not be documented in the class and a user of the class would possibly get that exception an know nothing about solving this. What can I do?

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• in java, which is better - three arrays of booleans or 1 array of bytes?

  - by joe_shmoe

  I know the question sounds silly, but consider this: I have an array of items and a labelling algorithm. at any point the item is in one of three states. The current version holds these states in a byte array, where 0, 1 and 2 represent the three states. alternatively, I could have three arrays of boolean - one for each state. which is better (consumes less memory) depends on how jvm (sun's version) stores the arrays - is a boolean represented by 1 bit? (p.s. don't start with all that "this is not the way OO/Java works" - I know, but here performance comes in front. plus the algorithm is simple and perfectly readable even in such form). Thanks a lot

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• Location of various javax.xml.* packages within the Java 6 SDK.

  - by celestialorb

  Alright, so recently I was using Notepad++ for all of my programming needs, but I've started using Eclipse for larger-scale Java projects now. I decided to pick up an old project of mine which used various classes within the "javax.xml.*" namespaces. When I was compiling and running the program with Notepad++ it worked just fine, however Eclipse can't seem to find these packages. My question is this, since I obviously have the classes somewhere within my current installation of JDK 6 (since I had no problems when using Notepad++), where can I find the location of the .JAR file(s) that include these namespaces/classes so that I can add them to my Eclipse project? Thanks for any help you can give me! Regards, celestialorb Also, if you're curious about the specific packages I'm looking for they are: javax.xml.soap.* javax.xml.transform.* Thanks again!

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• How do you encrypt data between client and server running in Flash and Java?

  - by ArmlessJohn

  We have a multiclient system where the client is written in Flash and the server is written in Java. Currently, communication is done in Flash by usage of flash.net.Socket and the protocol is written in JSON. The server uses a custom port to receive connections and then proceed to talk with each client. As expected, data is sent and received on both fronts as raw bytes, which are then decoded as needed. We would like to encrypt the communication between clients and server. I have some basic understanding about public/private key encryption, but I do not know what is the best way to exchange keys or what libraries are available (on both languages) to do this. What would be the best strategy to attack this problem and where should I start looking for libraries/methods to implement this encryption?

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• How do I create an ant builder file (build.xml) for an existing Java project?

  - by Amir Rachum

  Hi all, I am working on an Java assignment for a software design course in my university. It's not really complicated and it includes some classes, interfaces and jUnit test cases. We we're now told we should supply a build.xml file as an input for an ant builder. I have never heard of or used ant before. I also saw Eclipse supports it. My question is - What does build.xml does? How does Eclipse builds my project and why not do the same instead of using ant? And most important - how to create this file with Eclipse? Thanks.

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• Java or Python distributed compute job (on a student budget)?

  - by midget_sadhu

  I have a large dataset (c. 40G) that I want to use for some NLP (largely embarrassingly parallel) over a couple of computers in the lab, to which i do not have root access, and only 1G of user space. I experimented with hadoop, but of course this was dead in the water-- the data is stored on an external usb hard drive, and i cant load it on to the dfs because of the 1G user space cap. I have been looking into a couple of python based options (as I'd rather use NLTK instead of Java's lingpipe if I can help it), and it seems distributed compute options look like: Ipython DISCO After my hadoop experience, i am trying to make sure i try and make an informed choice -- any help on what might be more appropriate would be greatly appreciated. Amazon's EC2 etc not really an option, as i have next to no budget.

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• Java data structure to use with Hibernate to store unknown number of parameters?

  - by Lunikon

  Following problem: I want to render a news stream of short messages based on localized texts. In various places of these messages I have to insert parameters to "customize" them. I guess you know what I mean ;) My question probably falls into the "Which is the best style to do it?" category: How would you store these parameters (they may be Strings and Numbers that need to be formatted according to Locale) in the database? I'm using Hibernate to do the ORM and I can think of the following solutions: build a combined String and save it as such (ugly and hard to maintain I think) do some kind of fancy normalization and and make every parameter a single row on the database (clean I guess, but a performance nightmare) Put the params into an Array, Map or other Java data structure and save it in binary format (probably causes a lot of overhead size-wise) I tend towards option #3 but I'm afraid that it might be to costly in terms of size in the database. What do you think?

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• How to adapt a SOAP Service to REST in java?

  - by Norbert Hartl

  I need to integrate some services that are external and that are offered as SOAP Services. I don't like to use SOAP inside our system for a few reasons. I think from a pragmatic point of view it should be fairly easy to adapt SOAP to REST. This is not a SOAP vs. REST question! I'm just trying to collect java libraries, code, howtos etc. to accomplish this. Due the difference in its nature I don't expect a ready made solution. Just a couple of hints for tools and such to get going.

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• how to split string with some seperator but without removing that seperator in Java?

  - by sag

  Hi, I m facing problem in splitting string. Actually i want to split a string with some seperator but without loosing that seperator. when we use somestring.split(String seperator) method in java it splits the string but removes the seperator part from string.It should not happen. I want result like below: Example::string1="Ram-sita-laxman"; seperator="-"; string1.split(seperator); output : [Ram, sita, laxman] but i want the result like :[Ram, -sita, -laxman] is there a way to get output like this?

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• What is the optimal number of threads for performing IO operations in java?

  - by marc

  In Goetz's "Java Concurrency in Practice", in a footnote on page 101, he writes "For computational problems like this that do not I/O and access no shared data, Ncpu or Ncpu+1 threads yield optimal throughput; more threads do not help, and may in fact degrade performance..." My question is, when performing I/O operations such as file writing, file reading, file deleting, etc, are there guidelines for the number of threads to use to achieve maximum performance? I understand this will be just a guide number, since disk speeds and a host of other factors play into this. Still, I'm wondering: can 20 threads write 1000 separate files to disk faster than 4 threads can on a 4-cpu machine?

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• What's the easiest way for a Java Swing client to consumer a webservice?

  - by Stephane Grenier

  I have a Java Swing application client that I want to use to consume certain webservices, but I want to make it as painless as possible to code (because really all I want is the info). I do understand that whatever solution is used will need to stub the POJO's too. If you'd like to give a demo, that would be great, or if you can point to a tutorial that would also be really appreciated. I did look at Axis, including the more recent Axis2, but it's a bit more complex than I was hoping (aka. I have to learn something). At least just for some quick prototype testing and not real development, more for the sake of just saying I can, is there something or a tutorial out there?

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• How do I configure NetBeans to only step through Java code that I've written.

  - by blissapp

  Am I missing something? I'm delighted that all that code is there showing how the generic collections work etc. However when I want to simply walk my code I'm forever finding myself going deeper into Java's own library code than I care to. Is it possible to simply disable that when stepping code - I want to treat all of that stuff as a Black Box, code stepping is just for stuff I've written. And you know what, now I've got that capability, is it possible to wrap up my own code that way too so that I can step just the bits I'm most interested in? And if i can't easily in netbeans, is it possible in eclipse? thanks

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