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  • Java creation of new set too slow

    - by Mgccl
    I have this program where it have some recursive function similar to this: lambda(HashSet<Integer> s){ for(int i=0;i<w;i++){ HashSet<Integer> p = (HashSet) s.clone(); p.addAll(get_next_set()); lambda(p); } } What I'm doing is union every set with the set s. And run lambda on each one of the union. I run a profiler and found the c.clone() operation took 100% of the time of my code. Are there any way to speed this up considerably?

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  • java Database framework comparison

    - by user293655
    Hi, I want to create an application that synchronize a database to multiple databases(various type of databases). I'm looking for a framework that suitable to do this. I was looking for something just get the Object of the data (like a resultset) then copy that object to the destination database. Or comparing between 2 data. Any ideas? Thanks,

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  • Java io ugly try-finally block

    - by Tom Brito
    Is there a not so ugly way of treat the close() exception to close both streams then: InputStream in = new FileInputStream(inputFileName); OutputStream out = new FileOutputStream(outputFileName); try { copy(in, out); } finally { try { in.close(); } catch (Exception e) { try { // event if in.close fails, need to close the out out.close(); } catch (Exception e2) {} throw e; // and throw the 'in' exception } out.close(); }

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  • Call a method of subclass in Java

    - by eyecreate
    If I have a base class Base thing = null; of which there is a subclass class Subclass extends Base and I instigate it as thing = new Subclass how would I call a method that is specifically in Subclass, but not in Base? ex. Base has only method() Subclass has method() and specialMethod() the method specialMethod() is the one I want to call.

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  • Searching a 2D array for a range of values in java

    - by Paige O
    I have a 2^n size int array and I want to check if an element exists that is greater than 0. If the element exists, I want to divide the array by 4 and check if the coordinates of the found element are in the 1st, 2nd, 3rd or 4th quadrant of the array. For example, logically if the element exists in the first quadrant it would look something like this: If array[][] 0 && the row of that coordinate is in the range 0-(grid.length/2-1) && the column of that coordinate is in the range 0-(grid.length/2-1) then do something. I'm really not sure how to check the row and column index of the found element and store those coordinates to use in my if statement. Help!

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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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  • `return value' from Constructor Exception in Java?

    - by Lajos Nagy
    Take a look that the following code snippet: A a = null try { a = new A(); } finally { a.foo(); // What happens at this point? } Suppose A's constructor throws a runtime exception. At the marked line, am I always guaranteed to get a NullPointerException, or foo() will get invoked on a half constructed instance?

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  • How do I display java.lang.* object allocations in Eclipse profiler?

    - by Martin Wickman
    I am profiling an application using the Eclipse profiler. I am particularly interested in number of allocated object instances of classes from java.lang (for instance java.lang.String or java.util.HashMap). I also want to know stuff like number of calls to String.equals() etc. I use the "Object Allocations" tab and I shows all classes in my application and a count. It also shows all int[], byte[], long[] etc, but there is no mention of any standard java classes. For instance, this silly code: public static void main(String[] args) { Object obj[] = new Object[1000]; for (int i = 0; i < 1000; i++) { obj[i] = new StringBuffer("foo" + i); } System.out.println (obj[30]); } Shows up in the Object Allocations tab as 7 byte[]s, 4 char[]s and 2 int[]s. It doesn't matter if I use 1000 or 1 iterations. It seems the profiler simply ignores everything that is in any of the java.* packages. The same applies to Execution Statistics as well. Any idea how to display instances of java.* in the Eclipse Profiler?

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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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  • 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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  • Getting specific values with regex [JAVA, ANDROID]

    - by David
    I need to knowingly isolate each row of the vcard and get its value. For instance, I want to get "5555" from X-CUSTOMFIELD. So far, my thoughts are: "X-CUSTOMFIELD;\d+" I have been looking at some tutorials and I am a little confused with what function to use? What would my regex above return? Would it give me the whole line or just the numerical part (5555)? I was thinking I i get the whole row, I can use substring to get the digits? BEGIN:VCARD VERSION:2.1 N:Last;First; FN:First Last TEL;HOME;VOICE:111111 TEL;MOBILE;VOICE:222222 X-CUSTOMFIELD;5555 END:VCARD

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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 - Make an object collection friendly

    - by DutrowLLC
    If an object holds a unique primary key, what interfaces does it need to implement in order to be collection friendly especially in terms of being efficiently sortable, hashable, etc...? If the primary key is a string, how are these interfaces best implemented? Thanks!

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  • asking the container to notify your application whenever a session is about to timeout in Java

    - by user136101
    Which method(s) can be used to ask the container to notify your application whenever a session is about to timeout?(choose all that apply) A. HttpSessionListener.sessionDestroyed -- correct B. HttpSessionBindingListener.valueBound C. HttpSessionBindingListener.valueUnbound -- correct this is kind of round-about but if you have an attribute class this is a way to be informed of a timeout D. HttpSessionBindingEvent.sessionDestroyed -- no such method E. HttpSessionAttributeListener.attributeRemoved -- removing an attribute isn’t tightly associated with a session timeout F. HttpSessionActivationListener.sessionWillPassivate -- session passivation is different than timeout I agree with option A. 1) But C is doubtful How can value unbound be tightly coupled with session timeout.It is just the callback method when an attribute gets removed. 2) and if C is correct, E should also be correct. HttpSessionAttributeListener is just a class that wants to know when any type of attribute has been added, removed, or replaced in a session. It is implemented by any class. HttpSessionBindingListener exists so that the attribute itself can find out when it has been added to or removed from a session and the attribute class must implement this interface to achieve it. Any ideas…

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  • Incorrect sizing of a JPanel in a JScrollPane In Java 1.5

    - by Coder
    Hi, I am making an image loading component which consists of a JPanel containing a JScrollPane, which in turn contains another JPanel. What this component does is allows images to be dropped on top of it, after which point the image is loaded and the inner most JPanel is set to the size of the image dropped. This in turn causes the scroll bars to show up and the user can scroll the image. This all works fine. The problem comes in when i try to auto-shrink the image to the maximum visible area in the outer JPanel. In this case i do a uniform scale of the image to be less than or equal to the width and height of the outer JPanel. What happens now is that both the horizontal and vertical scroll bars show up indicating the the inner JPanel is bigger than the visible area (which should not be the case). I verified that the image is scale to the proper dimensions(ie. the maximum width and height is respected). I also verified that if i decrease the maximum height by 3 pixels, then no scroll bars appear. What i believe the problem is, is that panel.getWidth() and panel.getHeight() don't actually return the visible area (maximum area) that sub components can take up. Ie. there is likely some more width and height taken up by the border around the JPanel or something like that. My question is, how do i get around this problem. Functionally all i want is to determine the maximum size a JPanel can be in a JScrollPane, then set the panel to that size and paint an image over top of it and be assured that the scroll bars of the scroll pane will not show up. Right now the scroll bars are set to AS_NEEDED. Thanks!

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  • export a JOGL applet and embedd into a html page

    - by nkint
    hi guys it is some time that i'm testing opengl with java and JOGL. now i have good result and i wanto to pubblish it on web. but i have some problem. i'm in eclipse, and i'm testing an Applet with JOGL. first of all i have this run time error (but the program works correctly): java.lang.IllegalArgumentException: adding a window to a container at java.awt.Container.checkNotAWindow(Container.java:431) at java.awt.Container.addImpl(Container.java:1039) at java.awt.Container.add(Container.java:365) at AppletHelloWorld.init(AppletHelloWorld.java:30) at sun.applet.AppletPanel.run(AppletPanel.java:424) at java.lang.Thread.run(Thread.java:619) then i found this incredibly clear page and i do what is said, i open html with the browser, the libs are downloaded but it stops at "Starting applet AppletHelloWorld" that is the name i gave to my applet. mayebe i miss something like main function or exporting well the jar? this is my main code: public class AppletHelloWorld extends Applet { public static void main(String[] args) { JFrame fr=new JFrame(); fr.setBounds(0,0,1015,600); fr.add(new AppletHelloWorld()); fr.setVisible(true); } public void init() { setLayout(null); MyJOGLProject canvas = new MyJOGLProject(); //MyJOGLProject extends JFrame canvas.run(); Container c = new Container(); c.add(canvas); add(c); } //....

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  • Compile error in java application using netbeans - linked project

    - by Malachi
    I have a project which has shared functionality between three other projects and have linked these to existing projects as I normally would using the add project functionality of the libraries folder. This all used to work however when I started up Netbeans yesterday it just wasn't working as in the other projects won't compile even though the projects are linked. It can recognise the packages - just the actual classes themselves were not recognised. I have checked the dist folder of the shared project and the Shared.jar file exists. Any suggestions?

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  • java: speed up reading foreign characters

    - by Yang
    My current code needs to read foreign characters from the web, currently my solution works but it is very slow, since it read char by char using InputStreamReader. Is there anyway to speed it up and also get the job done? // Pull content stream from response HttpEntity entity = response.getEntity(); InputStream inputStream = entity.getContent(); StringBuilder contents = new StringBuilder(); int ch; InputStreamReader isr = new InputStreamReader(inputStream, "gb2312"); // FileInputStream file = new InputStream(is); while( (ch = isr.read()) != -1) contents.append((char)ch); String encode = isr.getEncoding(); return contents.toString();

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  • Java: Ignoring escapes when parsing XML

    - by Personman
    I'm using a DocumentBuilder to parse XML files. However, the specification for the project requires that within text nodes, strings like " and < be returned literally, and not turned into the corresponding ASCII values. A previous similar question, http://stackoverflow.com/questions/1979785/read-escaped-quote-as-escaped-quote-from-xml, received one answer that seems to be specific to Apache, and another that appears to simply not not do what it says it does. I'd love to be proven wrong on either count, however :) For reference, here is some code: file = new File(fileName); DocBderFac = DocumentBuilderFactory.newInstance(); DocBder = DocBderFac.newDocumentBuilder(); doc = DocBder.parse(file); NodeList textElmntLst = doc.getElementsByTagName(text); Element textElmnt = (Element) textElmntLst.item(0); NodeList txts = textElmnt.getChildNodes(); String txt = ((Node) txts.item(0)).getNodeValue(); System.out.println(txt); I would like that println() to produce things like &quot;3&gt;2&quot; instead of "3>2" which is what currently happens. Thanks!

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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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  • 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 apache commons library source license question

    - by llm
    I want to use functionality from a certain method in apache commons StringUtils. I currently do not have the option of just using the library as one would normally do. I found the source for the method I need and my question is: am I free (legally) to use this code (just a method out of the library) or do I have to use the entire library? If its ok, what kind of attribution would I need in my code, if any? Thanks.

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