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  • Issue with WatchService in java 7

    - by user972590
    I'm using jdk7's WatchService API for monitoring the folder on file system.I'm sending a new file through email to that folder, when the file comes into that folder i m triggering the ENTRY_CRATE option. its working fine. But the issue is its generating two events of ENTRY_CREATE instead of one event which i'm invoking. BELOW IS THE CODE: Path dir = Paths.get(/var/mail); WatchService watcher = dir.getFileSystem().newWatchService(); dir.register(watcher, StandardWatchEventKinds.ENTRY_CREATE); System.out.println("waiting for new file"); WatchKey watckKey = watcher.take(); List<WatchEvent<?>> events = watckKey.pollEvents(); System.out.println(events.size()); for(WatchEvent<?> event : events){ if(event.kind() == StandardWatchEventKinds.ENTRY_CREATE){ String fileCreated=event.context().toString().trim(); } } In the above code I'm gettng the events size as 2. Can any one please help me in finding out the reason why i'm getting two events.

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  • Covariant return types in Java enums

    - by Kelvin Chung
    As mentioned in another question on this site, something like this is not legal: public enum MyEnum { FOO { public Integer doSomething() { return (Integer) super.doSomething(); } }, BAR { public String doSomething() { return (String) super.doSomething(); } }; public Object doSomething(); } This is due to covariant return types apparently not working on enum constants (again breaking the illusion that enum constants are singleton subclasses of the enum type...) So, how about we add a bit of generics: is this legal? public enum MyEnum2 { FOO { public Class<Integer> doSomething() { return Integer.class; } }, BAR { public Class<String> doSomething() { return String.class; } }; public Class<?> doSomething(); } Here, all three return Class objects, yet the individual constants are "more specific" than the enum type as a whole...

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  • Adapting pseudocode to java implementation for finding the longest word in a trie

    - by user1766888
    Referring to this question I asked: How to find the longest word in a trie? I'm having trouble implementing the pseudocode given in the answer. findLongest(trie): //first do a BFS and find the "last node" queue <- [] queue.add(trie.root) last <- nil map <- empty map while (not queue.empty()): curr <- queue.pop() for each son of curr: queue.add(son) map.put(son,curr) //marking curr as the parent of son last <- curr //in here, last indicate the leaf of the longest word //Now, go up the trie and find the actual path/string curr <- last str = "" while (curr != nil): str = curr + str //we go from end to start curr = map.get(curr) return str This is what I have for my method public static String longestWord (DTN d) { Queue<DTN> holding = new ArrayQueue<DTN>(); holding.add(d); DTN last = null; Map<DTN,DTN> test = new ArrayMap<DTN,DTN>(); DTN curr; while (!holding.isEmpty()) { curr = holding.remove(); for (Map.Entry<String, DTN> e : curr.children.entries()) { holding.add(curr.children.get(e)); test.put(curr.children.get(e), curr); } last = curr; } curr = last; String str = ""; while (curr != null) { str = curr + str; curr = test.get(curr); } return str; } I'm getting a NullPointerException at: for (Map.Entry<String, DTN> e : curr.children.entries()) How can I find and fix the cause of the NullPointerException of the method so that it returns the longest word in a trie?

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  • Extracting user-friendly exception details in Java

    - by Jon
    I've got a J2EE web application that I'm working on and when an exception occurs, I'd like to get some basic details about the exception and log it. The message that I'm logging should be pretty basic, something that might mean something to the people running the web server(s). Would using e.getMessage() be the best thing to log? Thanks.

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  • Strange Java Socket Behavior (Connects, but Doesn't Send)

    - by Donald Campbell
    I have a fairly complex project that boils down to a simple Client / Server communicating through object streams. Everything works flawlessly for two consecutive connections (I connect once, work, disconnect, then connect again, work, and disconnect). The client connects, does its business, and then closes. The server successfully closes both the object output stream and the socket, with no IO errors. When I try to connect a third time, the connection appears to go through (the ServerSocket.accept() method goes through and an ObjectOutputStream is successfully created). No data is passed, however. The inputStream.readUnshared() method simply blocks. I have taken the following memory precautions: When it comes time to close the sockets, all running threads are stopped, and all objects are nulled out. After every writeUnshared() method call, the ObjectOutputBuffer is flushed and reset. Has anyone encountered a similar problem, or does anyone have any suggestions? I'm afraid my project is rather large, and so copying code is problematic. The project boils down to this: SERVER MAIN ServerSocket serverSocket = new ServerSocket(port); while (true) { new WorkThread(serverSocket.accept()).start(); } WORK THREAD (SERVER) public void run() { ObjectInputBuffer inputBuffer = new ObjectInputBuffer(new BufferedInputStream(socket.getInputStream())); while (running) { try { Object myObject = inputBuffer.readUnshared(); // do work is not specified in this sample doWork(myObject); } catch (IOException e) { running = false; } } try { inputBuffer.close(); socket.close(); } catch (Exception e) { System.out.println("Could not close."); } } CLIENT public Client() { Object myObject; Socket mySocket = new Socket(address, port); try { ObjectOutputBuffer output = new ObjectOutputBuffer(new BufferedOutputStream(mySocket.getOutputStream())); output.reset(); output.flush(); } catch (Exception e) { System.out.println("Could not get an input."); mySocket.close(); return; } // get object data is not specified in this sample. it simply returns a serializable object myObject = getObjectData(); while (myObject != null) { try { output.writeUnshared(myObject); output.reset(); output.flush(); } catch (Exception e) { e.printStackTrace(); break; } // catch } // while try { output.close(); socket.close(); } catch (Exception e) { System.out.println("Could not close."); } } Thank you to everyone who may be able to help!

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  • performing auditing in java with sql server DB - before and/or after do not get audited

    - by Domingos
    When auditing, sometimes the before value does not get audited, other times the after value does not get audited, other times both values do not get audited at all. After researching, I found out that only values from a specific codes table get audited. the code was: compareCodesTableInteger(audit, int, int, objectBefore, objectAfter, stringDescription, stringCodesTable); I then changed it to: compareCodesTableInteger(audit, int, int, objectBefore, objectAfter, stringDescription, booleanCheck ? stringCodesTableIfTrue : stringCodesTableIfFalse); Description: if objectBefore AND objectAfter are both from stringCodesTableIfTrue OR from stringCodesTableIfFalse, auditing takes place as expected. The problem is: most of the times, objectBefore is from stringCodesTableIfTrue, and objectAfter is from stringCodesTableIfFalse, or vice-versa. In this scenario auditing fails. How do I go around this? Please assist

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  • DB Interface Design Optimization: Is it better to optimise for Fewer requests of smaller data size?

    - by Overflow
    The prevailing wisdom in webservices/web requests in general is to design your api such that you use as few requests as possible, and that each request returns therefore as much data as is needed In database design, the accepted wisdom is to design your queries to minimise size over the network, as opposed to minimizing the number of queries. They are both remote calls, so what gives?

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  • Java: Reflection against casting when you know superclass

    - by Ema
    I don't know exactly how to define my doubt so please be patient if the question has already been asked. Let's say I have to dinamically instantiate an object. This object will surely be instance of a subclass of a known, immutable class A. I can obtain dinamically the specific implementation class. Would it be better to use reflection exactly as if I didn't know anything about the target class, or would it be preferrable/possible to do something like: A obj = (Class.forName("com.package.Sub-A")) new A(); where Sub-A extends A ? The purpose would be to avoid reflection overhead times... Thank you in advance.

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  • What is the use of reflection in Java/C# etc

    - by zengr
    I was just curious, why should we use reflection in the first place? // Without reflection Foo foo = new Foo(); foo.hello(); // With reflection Class cls = Class.forName("Foo"); Object foo = cls.newInstance(); Method method = cls.getMethod("hello", null); method.invoke(foo, null); We can simply create an object and call the class's method, but why do the same using forName, newInstance and getMthod functions? To make everything dynamic?

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  • Revalidate and repaint - Java Swing

    - by bosra
    I have a JPanel that I am adding JLabel's to. I then want to remove all the JLabels and add some new ones. So I do the following: panel.removeAll();panel.repaint(); panel.add(new JLabel("Add something new"); panel.revalidate(); This works fine. My problem arises when I start a new thread after this like: panel.removeAll();panel.repaint(); (1)panel.add(new JLabel("Add something new"); panel.revalidate(); //new thread to start - this thread creates new JLabels that should appear under (1) firstProducer.start(); try { firstProducer.join(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Then the output from the original JLabels is still visible. I have read that the revalidate process is a long running task and hence the firstProducer thread is getting started while the revalidation is going on and a conflict is arising. What is the best way to deal with this?

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  • Reading lines of data from text files using java

    - by razshan
    I have a text file with x amount of lines. each line holds a integer number. When the user clicks a button, an action is performed via actionlistener where it should list all the values as displayed on the text file. However, right now I have linenum set to 10 implying I already told the code that just work with 10 lines of the text file. So, if my text file has only 3 rows/lines of data...it will list those lines and for rest of the other 7 lines, it will spit out "null". I recall there is a way to use ellipsis to let the program know that you don't know the exact value but at the end it calculates it based on the given information. Where my given information will the number of lines with numbers(data). Below is part of the code. private class thehandler implements ActionListener{ public void actionPerformed(ActionEvent event){ BufferedReader inputFile=null; try { FileReader freader =new FileReader("Data.txt"); inputFile = new BufferedReader(freader); String MAP = ""; int linenum=10; while(linenum > 0) { linenum=linenum-1; MAP = inputFile.readLine();//read the next line until the specfic line is found System.out.println(MAP); } } catch( Exception y ) { y.printStackTrace(); } }}

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  • Java-Recursion: When does statements after a recursive method call executes

    - by Ruru Morlano
    When are statements after the method call itself going to execute? private void inorderHelper(TreeNode node) { if ( node==null ) return; inorderHelper(node.leftNode); System.out.printf("%d", node.data); inorderHelper(node.rigthNode); } All I can see is that the line of codes inorderHelper(node.leftNode) will continue to iterate until node == null and the method terminates immediately before node.data is printed. I think that I didn't get well recursion but all examples I can find doesn't have statements after the recursive call. All I want to know is when are statements like System.out.printf("%d",node.data) going to execute before the method return?

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  • Singleton & Multithreading in Java

    - by vivek jagtap
    What is the preferred way to work with Singleton class in multithreaded environment? Suppose if I have 3 thread, and all they try to access getInstance() method of singleton class at the same time - What would happen if no synchronization is maintained? Is it good practice to use synchronized getInstance() method or use synchronized block inside getInstance(). Please advise if there is any other way out.

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  • java increase xmx dynamically at runtime

    - by Tomer
    Hi, I have a jvm server in my machine, now I want to have 2 apservers of mine sitting in same machine, however I want the standby one to have a really low amount of memory allocated with xmx because its passive, one the main server (active) goes down I want to allocate more memory to my passive server which is already up without restarting it (I have have them both having too much xmx - note they would consume memory at startup and I cant allow possibility of outOfMemory). So I want passive - low xmx once active goes down I want my passive to receive much more xmx. is there a way for me to achieve that. Thanks

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  • Java regex skipping matches

    - by Mihail Burduja
    I have some text; I want to extract pairs of words that are not separated by punctuation. Thi is the code: //n-grams Pattern p = Pattern.compile("[a-z]+"); if (n == 2) { p = Pattern.compile("[a-z]+ [a-z]+"); } if (n == 3) { p = Pattern.compile("[a-z]+ [a-z]+ [a-z]+"); } Matcher m = p.matcher(text.toLowerCase()); ArrayList<String> result = new ArrayList<String>(); while (m.find()) { String temporary = m.group(); System.out.println(temporary); result.add(temporary); } The problem is that it skips some matches. For example "My name is James", for n = 3, must match "my name is" and "name is james", but instead it matches just the first. Is there a way to solve this?

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  • Dynamic, reflective SignalHandler in Java

    - by pilcrow
    How do I install signal handling logic iff sun.misc.Signal is available? Background First generation of my code looked something like this: class MyApp { public static void main(String[] args) { ... Signal.handle(term_sig, new SignalHandler() { public void handle(Signal sig) { ... } }); ... } } I believe I understand how to reflectively test for and use signal handlers -- Class.forName("sun.misc.Signal"), reflectively call Signal.handle, and so forth. My impulse was simply to instantiate another anonymous inner class with the dynamically obtained SignalHandler class, but I think that's just wishful syntax.

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  • Java String object creation

    - by Ajay
    Hi, 1) What is difference in thers two statements: String s1 = "abc"; and String s1 = new String("abc") 2) as i am not using new in first statement, how string object will be created Thanks

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  • java multiple operations depending on the type of the object passed

    - by mixm
    assuming i create a method which is passed an object, and that method would perform an action depending on the object passed. how should i identify the object? i thought of using the class name to identify the object, but may be impractical since i could easily change the class name of objects, and generate headaches during future development. am i right?

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  • Help with float numbers in Java

    - by Alvin
    Hi, Could anyone please me why the output of the following programme is not " different different"? public static void main(String[] args) { float f1=3.2f; float f2=6.5f; if(f1==3.2) System.out.println("same"); else System.out.println("different"); if(f2==6.5) System.out.println("same"); else System.out.println("different"); } o/p :different same

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  • A very strange problem -> CSS file not detected .Java web application

    - by Nitesh Panchal
    Hello, If i browse my site using http://localhost:8080/abc/Login/index.jsf, everything works fine. But if browse it using simply http://localhost:8080/abc, the page is shown but all its images and css files are missing. What can be the problem? I have this in my web.xml :- <form-login-config> <form-login-page>/Login/index.jsf</form-login-page> <form-error-page>/Login/index.jsf</form-error-page> </form-login-config> Probably, images are not getting referenced correctly. Can anybody help me? I have referenced css file as follows :- <link href="./Css/MainStyleSheet.css" rel="stylesheet" type="text/css" /> where Css is folder in Login

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  • delete item from array in java

    - by davit-datuashvili
    hello can anybody tell me what is wrong here? i want delete item from array but it shows me error ArrayIndexOutBound exception public class delete{ public static void main(String[]args){ int i; //delete item from array int k[]=new int[]{77,99,44,11,00,55,66,33,10}; //delete 55 int searchkey=55; int nums=k.length; for ( i=0;i<nums;i++) if (k[i]==searchkey) break; for (int t=i;t<nums;t++) k[t]=k[t+1]; nums--; for (int m=0;m<nums;m++){ System.out.println(k[m]); } } }

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