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  • Shallow Copy in Java

    - by Vilius
    Hello there! I already know, what a shallow copy is, but I'm not able to impliment it. Here's a short example. public class Shallow { String name; int number; public Shallow (String name, int number) { this.name = name; this.number = number; } } Test the implementation ... public class ShallowTest { public static void main (String[] args) { Shallow shallow = new Shallow("Shallow", 123); Shallow shallowClone = new Shallow(shallow); shallowClone.name = 'Peter'; shallowClone.number = 321; System.out.println(shallow.name + " - " + shallow.number); } } As I purpose, just the reference of the non primitive datatype String would be copied, so that by calling "shallowClone.name = 'Peter';" I would also change the name of "shallow". Am I right? But somehow, it just does not want to work ....

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  • Class unloading in java

    - by java_geek
    When a classloader is garbage collected, are the classes loaded by it unloaded? When the JVM is running is verbose mode, all the loaded classes are o/p. Similarly will the JVM log when it unloads a class? I wrote a custom class loader to test this, but could not see any verbose log for unloading of the classes. CustomClassLoader loader = new CustomClassLoader(new URL[]{}, CustomClassLoader.class.getClassLoader()); loader.addURL("D:\workspace\ClassLoaderTest\implementation.jar"); Class c = null; try { c = Class.forName("Horse",false,loader); if (c != null) { try { Animal animal = (Animal)c.newInstance(); animal.eat(); } catch(Exception ex) { ex.printStackTrace(); } } } catch(Exception e) { e.printStackTrace(); } loader = null; byte[] b = new byte[58*1024*1024]; System.gc(); ClassLoadingMXBean clBean = ManagementFactory.getClassLoadingMXBean(); System.out.println("Number of classes currently loaded " + clBean.getLoadedClassCount()); System.out.println("Number of classes loaded totally " + clBean.getTotalLoadedClassCount()); System.out.println("Number of classes unloaded " + clBean.getUnloadedClassCount()); Even the ClassLoadingMXBean gives number of unloaded classes as 0. How can i know that a class is unloaded when the class loader is GCed?

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  • using regular expression in Java

    - by Mrityunjay
    Hi, i need to check a string that should contain only ABCDEFG characters, in any sequence and with only 7 characters. Please let me know the correct way of using regular expression. as corrently i am using String abs = "ABPID"; if(!Pattern.matches("[[ABCDEFG]", abs)) System.out.println("Error"); i am using the following code which works when i use the String abcdefg but for other cases it fails. please help me out.

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  • Create java sandbox based on security policies

    - by argos
    I need to create environment to run potentially untrusted code. Program allowed to connect to preconfigured address:port and nothing else (even read the system time). I have compiled the class whitelist. I'd searched similar questions, but found only template that based on SecurityManager which AFAIK is deprecated. Can anybody give me a simple sample how to run code in sandbox based on security policies and AccessController?

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  • How to synchronize java code

    - by Milan
    I have the next code: Process p = Runtime.getRuntime().exec(args); and I want my program to wait for the Runtime.getRuntime().exec(args); to finish cause it last 2-3sec and then to continue. Ideas?

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  • Sending files from server to client in Java

    - by Lee Jacobson
    Hi, I'm trying to find a way to send files of different file types from a server to a client. I have this code on the server to put the file into a byte array: File file = new File(resourceLocation); byte[] b = new byte[(int) file.length()]; FileInputStream fileInputStream; try { fileInputStream = new FileInputStream(file); try { fileInputStream.read(b); } catch (IOException ex) { System.out.println("Error, Can't read from file"); } for (int i = 0; i < b.length; i++) { fileData += (char)b[i]; } } catch (FileNotFoundException e) { System.out.println("Error, File Not Found."); } I then send fileData as a string to the client. This works fine for txt files but when it comes to images I find that although it creates the file fine with the data in, the image won't open. I'm not sure if I'm even going about this the right way. Thanks for the help.

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  • Java logger that automatically determines caller's class name

    - by alex
    public static Logger getLogger() { final Throwable t = new Throwable(); final StackTraceElement methodCaller = t.getStackTrace()[1]; final Logger logger = Logger.getLogger(methodCaller.getClassName()); logger.setLevel(ResourceManager.LOGLEVEL); return logger; } This method would return a logger that knows the class it's logging for. Any ideas against it?

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  • Sudoku Recursion Issue (Java)

    - by SkylineAddict
    I'm having an issue with creating a random Sudoku grid. I tried modifying a recursive pattern that I used to solve the puzzle. The puzzle itself is a two dimensional integer array. This is what I have (By the way, the method doesn't only randomize the first row. I had an idea to randomize the first row, then just decided to do the whole grid): public boolean randomizeFirstRow(int row, int col){ Random rGen = new Random(); if(row == 9){ return true; } else{ boolean res; for(int ndx = rGen.nextInt() + 1; ndx <= 9;){ //Input values into the boxes sGrid[row][col] = ndx; //Then test to see if the value is valid if(this.isRowValid(row, sGrid) && this.isColumnValid(col, sGrid) && this.isQuadrantValid(row, col, sGrid)){ // grid valid, move to the next cell if(col + 1 < 9){ res = randomizeFirstRow(row, col+1); } else{ res = randomizeFirstRow( row+1, 0); } //If the value inputed is valid, restart loop if(res == true){ return true; } } } } //If no value can be put in, set value to 0 to prevent program counting to 9 setGridValue(row, col, 0); //Return to previous method in stack return false; } This results in an ArrayIndexOutOfBoundsException with a ridiculously high or low number (+- 100,000). I've tried to see how far it goes into the method, and it never goes beyond this line: if(this.isRowValid(row, sGrid) && this.isColumnValid(col, sGrid) && this.isQuadrantValid(row, col, sGrid)) I don't understand how the array index goes so high. Can anyone help me out?

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  • Regex help -- cleaning up whitespace -- Java

    - by FarmBoy
    I'm trying to view the text of HTML files in a reasonable way. After I remove all of the markup and retain only the visible text, I obtain a String that looks something like this: \n\n\n\n \n\n\n \n\n \n Title here \n\n\n \n\n \n\n Menu Item 1 \n\n \n\n Menu Item 2 \n\n\n \n\n you get the point. I would like to use String.replaceAll(String regex, String regex) to replace any whitespace substring that contains more than two occurances of \n with "\n\n". Any ideas?

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  • How to solve following issue in java?

    - by lakshmi
    Im getting following error while running the query. org.hibernate.hql.ast.QuerySyntaxException: expecting CLOSE, found 'LIMIT' near line 1, column 194 [from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' and gpsdate in (select id.gpsdate from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' ORDER BY id.gpsdate DESC LIMIT 1 ) and gpsstatus='true'] This is my Query.Please give the suggession what is the mistake in this query? data=session.createQuery[from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' and gpsdate in (select id.gpsdate from com.claystone.db.Gpsdata where id.mobileunitid = '2090818044' ORDER BY id.gpsdate DESC LIMIT 1 ) and gpsstatus='true']

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  • Timeout with GAE Java

    - by user242153
    Hi, I am having some issues with an app I have deployed on GAE. Specifically, I am intermittently running into the DeadlineExceededException where the server is not responding within the 30 seconds required. What is odd is that the code is not overly complex, it should run in milliseconds. My guess is that the delay is in dealing with the persistence manager and accessing the datastore. 2 questions: 1) What is the best way to track where all of the CPU time on the server is being used up? Log files do not seem helpful and to make things more complicated the code runs very fast when I am running it locally 2) Any tips / best practices in dealing with the 30 second exception? What are the biggest drivers of this? Datastore? HTTP requests / responses? Thanks

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  • Java: getInputMap(WHEN_IN_FOCUSED_WINDOW) from within JInternalFrame

    - by gerardlouw
    I have a component inside a JInternalFrame which needs to perform actions when keys are pressed within the JInternalFrame's parenting window. Using InputMap/ActionMap would be ideal, but the getInputMap(WHEN_IN_FOCUSED_WINDOW) of the component returns an InputMap that treats the JInternalFrame as the "focused window", rather than its parenting window. Any solutions or ideas?

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  • Java Runtime.freeMemory() returning bizarre results when adding more objects

    - by Sotirios Delimanolis
    For whatever reason, I wanted to see how many objects I could create and populate a LinkedList with. I used Runtime.getRuntime().freeMemory() to get the approximation of free memory in my JVM. I wrote this: public static void main(String[] arg) { Scanner kb = new Scanner(System.in); List<Long> mem = new LinkedList<Long>(); while (true) { System.out.println("Max memory: " + Runtime.getRuntime().maxMemory() + ". Available memory: " + Runtime.getRuntime().freeMemory() + " bytes. Press enter to use more."); String s = kb.nextLine(); if (s.equals("m")) for (int i = 0; i < 1000000; i++) { mem.add(new Long((new Random()).nextLong())); } } } If I write in m, the app adds a million Long objects to the list. You would think the more objects (to which we have references, so can't be gc'ed), the less free memory. Running the code: Max memory: 1897725952. Available memory: 127257696 bytes. m Max memory: 1897725952. Available memory: 108426520 bytes. m Max memory: 1897725952. Available memory: 139873296 bytes. m Max memory: 1897725952. Available memory: 210632232 bytes. m Max memory: 1897725952. Available memory: 137268792 bytes. m Max memory: 1897725952. Available memory: 239504784 bytes. m Max memory: 1897725952. Available memory: 169507792 bytes. m Max memory: 1897725952. Available memory: 259686128 bytes. m Max memory: 1897725952. Available memory: 189293488 bytes. m Max memory: 1897725952. Available memory: 387686544 bytes. The available memory fluctuates. How does this happen? Is the GC cleaning up other things (what other things are there on the heap to really clean up?), is the freeMemory() method returning an approximation that's way off? Am I missing something or am I crazy?

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