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  • Close resources before exiting JFrame and TCP communication in Java

    - by Oz Molaim
    1. I'm writing a chat based application on TCP communication. I'm using NetBeans and I want to add functionality to the default EXIT_ON_CLOSE when exiting JFrame. The reason of course is because I want to clean resources and end threads safely. How can I call a method that clear resources and only then close the JFrame safely and end the process. 2. I need to implement the server side. The server has List/HashMap/Queue of 'Socket' with their chat nick-names. Is there any simple design pattern to do it correctly because I don't want to re-invent the wheel. thanks.

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  • Java - Circular Garbage Collection

    - by aloh
    A <- B <- C <- D <- A... // A is firstNode, D is lastNode if ( length == 1 ) { firstNode = null; lastNode = null; firstNode.next = null; firstNode.prev = null; } else { Node secondNode = firstNode.next; Node secondToLast = lastNode.prev; firstNode.next = null; firstNode.prev = null; lastNode.next = null; lastNode.prev = null; secondNode.prev = null; secondToLast.next = null; firstNode = null; lastNode = null; } That should send everything in between as candidates for garbage collection, I hope?

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  • Show users a list of unique items on Java Google App Engine

    - by James
    I've been going round in circles with what must be a very simple challenge but I want to do it the most efficient way from the start. So, I've watched Brett Slatkin's Google IO videos (2008 & 2009) about building scalable apps including http://www.youtube.com/watch?v=AgaL6NGpkB8 and read the docs but as a n00b, I'm still not sure. I'm trying to build an app on GAEJ similar to the original 'hotornot' where a user is presented with an item which they rate. Once they rate it, they are presented with another one which they haven't seen before. My question is this; is it most efficient to do a query up front to grab x items (say 100) and put them in a list (stored in memcache?) or is it better to simply make a query for a new item after each rating. To keep track of the items a user has seen, I'm planning to keep those items' keys in a list property of the user's entity. Does that sound sensible? I've really got myself confused about this so any help would be much appreciated.

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  • how to generate a random String? in java

    - by chandra wibowo
    hi everyone, i have an object called Student, and it has studentName, studentId, studentAddress, etc. for the studentId, i have to generate random string consist of seven numeric charaters, eg. studentId = getRandomId(); studentId = "1234567" <-- from the random generator. and i have to make sure that there is no duplicate id. thanks in advance

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  • JAVA Inheritance Generics and Casting.

    - by James Moore
    Hello, I have two classes which both extends Example. public class ClassA extends Example { public ClassA() { super("a", "class"); } .... } public class ClassB extends Example { public ClassB() { super("b", "class"); } .... } public class Example () { public String get(String x, String y) { return "Hello"; } } So thats all very well. So suppose we have another class called ExampleManager. With example manager I want to use a generic type and consequently return that generic type. e.g. public class ExampleManager<T extends Example> { public T getExample() { return new T("example","example"); // So what exactly goes here? } } So where I am returning my generic type how do i get this to actually work correctly and cast Example as either classA or classB? Many Thanks

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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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  • Java generics: Illegal forward reference

    - by Arian
    Given a generic interface interface Foo<A, B> { } I want to write an implementation that requires A to be a subclass of B. So I want to do class Bar<A, B super A> implements Foo<A, B> { } // --> Syntax error or class Bar<A extends B, B> implements Foo<A, B> { } // --> illegal forward reference But the only solution that seems to work is this: class Bar<B, A extends B> implements Foo<A, B> { } which is kind of ugly, because it reverses the order of the generic parameters. Are there any solutions or workarounds to this problem?

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  • Cast element in Java For Each statement

    - by Carl Summers
    Is it possible (or even advisable) to cast the element retrieved from a for each statement in the statement itself? I do know that each element in list will be of type . I.E.: List<BaseType> list = DAO.getList(); for(<SubType> element : list){ // Cannot convert from element type <BaseType> to <SubType> ... } rather than: List <BaseType> list = DAO.getList(); for(<BaseType> el : list){ <SubType> element = (<SubType>)el; ... }

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  • Java Enum List from Class

    - by DD
    How do I go from a Class object to a list of enums generically? i.e. public static <T extends Enum> List<T> getList(Class<T> clazz) I cant find a way to get to the values() method

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  • generation of random numbers in java

    - by S.PRATHIBA
    Hi all, I want to create 30 tables which consists of the following fields.For example, Service_ID Service_Type consumer_feedback 75 Computing 1 35 Printer 0 33 Printer -1 3 rows in set (0.00 sec) mysql select * from consumer2; Service_ID Service_Type consumer_feedback 42 data 0 75 computing 0 mysql select * from consumer3; Service_ID Service_Type consumer_feedback 43 data -1 41 data 1 72 computing -1 As you can infer from the above tables, i am getting the feedback values.I have generated these consumer_feedback values,Service_ID,Service_Type using the concept of random numbers .I have used the funtion int min1=31;//printer int max1=35;//the values are generated if the Service_Type is printer. int provider1 = (int) (Math.random() * (max1 - min1 + 1) ) + min1; int min2=41;//data int max2 =45 int provider2 = (int) (Math.random() * (max2 - min2 + 1) ) + min2; int min3=71;//computing int max3=75; int provider3 = (int) (Math.random() * (max3 - min3 + 1) ) + min3; int min5 = -1;//feedback values int max5 =1; int feedback = (int) (Math.random() * (max5 - min5 + 1) ) + min5; I need the Service_Types to be distributed uniformly in all the 30 tables.Similarly I need feedback value of 1 to be generated many times other than 0 and -1.Please Help me.

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  • java.sql.SQLException: Parameter index out of range (3 > number of parameters, which is 2)

    - by sam
    @WebMethod(operationName = "SearchOR") public SearchOR getSearchOR (@WebParam(name = "comp") String comp, @WebParam(name = "name") String name) { //TODO write your implementation code here: SearchOR ack = null; try{ String simpleProc = "{ call getuser_info_or(?,?)}"; CallableStatement cs = con.prepareCall(simpleProc); cs.setString(1, comp); cs.setString(2, name); ResultSet rs = cs.executeQuery(); System.out.print("2"); /* int i = 0, j = 0; if (rs.last()) { i = rs.getRow(); ack = new SearchOR[i]; rs.beforeFirst(); }*/ while (rs.next()) { // ack[j] = new SearchOR(rs.getString(1), rs.getString(2)); // j++; ve.add(rs.getString(1)); ve.add(rs.getString(2)); }}catch ( Exception e) { e.printStackTrace(); System.out.print(e); } return ack; } I am getting error at portion i have made bold.It is pointing to that location.My Query is here: DELIMITER $$ DROP PROCEDURE IF EXISTS discoverdb.getuser_info_or$$ MySQL returned an empty result set (i.e. zero rows). CREATE PROCEDURE discoverdb.getuser_info_or ( IN comp VARCHAR(100), IN name VARCHAR(100), OUT Login VARCHAR(100), OUT email VARCHAR(100) ) BEGIN SELECT sLogin, sEmail INTO Login, email FROM ad_user WHERE company = comp OR sName=name; END $$ MySQL returned an empty result set (i.e. zero rows). DELIMITER ;

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  • How to combine array list string in java ?

    - by tiendv
    I have some arraylist string with keyword inside like that ! A windows is arraylist string with keyword is bold Struct of window : 9 words before + keyword + 9 words after You can see some window overlaping How to i combine that arraylist to receive like that : Thanks

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  • Java xsd validation of xml without namespace

    - by Darkflare
    Hi, I want to validate an xml file against an xsd schema. The xml files root element does not have any namespace or xsi details. It has no attributes so just . I have tried the following code from http://www.ibm.com/developerworks/xml/library/x-javaxmlvalidapi.html with no luck as I receive cvc-elt.1: Cannot find the declaration of element 'root' SchemaFactory factory = SchemaFactory.newInstance("http://www.w3.org/2001/XMLSchema"); File schemaFile = new File("schema.xsd"); Schema xsdScheme = factory.newSchema(schemaFile); Validator validator = xsdScheme.newValidator(); Source source = new StreamSource(xmlfile); validator.validate(source); The xml validates fine with the namespace headers included etc (added via xmlspy), but I would have thought the xml namespace could be declared without having to manually edit the source file?

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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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  • system out output for double numbers in a java program

    - by Nikunj Chauhan
    I have a program where I am generating two double numbers by adding several input prices from a file based on a condition. String str; double one = 0.00; double two = 0.00; BufferedReader in = new BufferedReader(new FileReader(myFile)); while((str = in.readLine()) != null){ if(str.charAt(21) == '1'){ one += Double.parseDouble(str.substring(38, 49) + "." + str.substring(49, 51)); } else{ two += Double.parseDouble(str.substring(38, 49) + "." + str.substring(49, 51)); } } in.close(); System.out.println("One: " + one); System.out.println("Two: " + two); The output is like: One: 2773554.02 Two: 6.302505836000001E7 Question: None of the input have more then two decimals in them. The way one and two are getting calculated exactly same. Then why the output format is like this. What I am expecting is: One: 2773554.02 Two: 63025058.36 Why the printing is in two different formats ? I want to write the outputs again to a file and thus there must be only two digits after decimal.

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