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  • How to enforce unique field value in java Google App Engine

    - by supercobra
    Hello there, I am try to find out how to enforce uniqueness in fields other than the unique id. Example: @PersistenceCapable(identityType = IdentityType.APPLICATION) public class User implements IsSerializable { @PrimaryKey @Persistent(valueStrategy = IdGeneratorStrategy.IDENTITY) private Long id; @Persistent private String name; @Persistent private String email; // <= I want this to be unique as well } In the example above, how can I enforce uniqueness of the email value across the database? Daniel

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  • Java syntax of +

    - by Pindatjuh
    Why is the following syntax correct: x = y+++y; (Where it means y++ + y or y + ++y which both mean y * 2 + 1) But this is not valid syntax: x = y+++++y; (Which should mean y++ + ++y, which must mean y and increase y and then add ++y which increases y thus y * 2 + 2) Is there a reason for this?

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  • Java scanner - taking specific part of line

    - by user1290213
    Hi ive got a log file containing trace routes and pings. Ive seperated these by using if(scanner.nextLine().startsWith("64 bytes"){} so i can work with just the pings for now. All im interested in from the ping is time=XX example data line = 64 bytes from ziva.zarnet.ac.zw (209.88.89.132): icmp_seq=119 ttl=46 time=199 ms I have been reading other peoples similar questions and im not sure how to apply to mine. I literally need just the number as i will be putting them into a csv file so i can make a graph of the data.

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  • java multiple connections between server and one client

    - by user1507128
    I'm trying to make like a skype-instant messager, my idea for it is to have one server which handles multiple connections for the clients. What I now have is a friend list etc, but now I want to create Threads both for server and client to handle a conversation. The problem is that I need multiple connections between a server and one client for every conversation(I think). but i dont think it's possible. Does someone have another way for doing this or maybe a way to make multiple connections between the server and a client? Thanks for helping me out PS: English is not my main language so please excuse me for my grammar.

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  • Executing in java code an external program that takes arguments

    - by rmaster
    Process p; String line; String path; String[] params = new String [3]; params[0] = "D:\\prog.exe"; params[1] = picA+".jpg"; params[2] = picB+".jpg"; try { p = Runtime.getRuntime().exec(params); BufferedReader input = new BufferedReader (new InputStreamReader(p.getInputStream())); while ((line = input.readLine()) != null) System.out.println(line); input.close(); } catch (IOException e) {System.out.println(" procccess not read"+e);} i don't get any error, just nothing in cmd.exe prog.exe is working fine What to improve in order to make this code working?

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  • Read an invalid cookie with Java (jsp)?

    - by jsumners
    I have a cookie that is formatted like partA:partB. The colon is not escaped in any fashion. I need to read this cookie in a JSP script, and request.getCookies() is only returning partA. I can't change the cookie because it is used in multiple applications, and fixing the cookie would break production code. Any ideas how I can read the full value of this cookie?

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  • Time not entered in mysql ? Java

    - by Nitesh Panchal
    Hello, I have a datetime field in mysql table and i am using JPA for persisting data but only date goes in database. Time always shows 00:00:00. What should i do? I am not doing any manipulation with Date. All i do is to assign new Date() to a variable and store it in database. What am i doing wrong?

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  • pls give reason why this java program always comes to the else part

    - by Anbu
    public class Test { public static void main(String[] args){ if (5.0 5) // (5.0<5) for both case it is going to else System.out.println("5.0 is greater than 5"); else System.out.println("else part always comes here"); /another sample/ if (5.0 == 5) System.out.println("equals"); else System.out.println("not equal"); } } can any one explain the first "if statement" why it always come to else part

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  • java random percentages

    - by erw
    I need to generate n percentages (integers between 0 and 100) such that the sum of all n numbers adds up to 100. If I just do nextInt() n times, each time ensuring that the parameter is 100 minus the previously accumulated sum, then my percentages are biased (i.e. the first generated number will usually be largest etc.). How do I do this in an unbiased way?

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  • Java generics: actual class as a generic parameter.

    - by user554916
    What do I write instead of "TheClass" to make this work? Or is there an alternative way to do it (possibly without making WithName and WithAge generic)? class Item { NeigborList<TheClass> neighbors; } class WithName extends Item { // here I want neighbors to be a NeighborList<WithName> String name; void someMethod() { System.out.println(neighbors.nearestTo(this).name); } } class WithAge extends Item { // here I want neighbors to be a NeighborList<WithAge> int age; void someOtherMethod() { System.out.println(neighbors.nearestTo(this).age); } }

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  • concurrentmodificationexception hashmap in java

    - by chetan
    I write following code but when this run it generate concurrentmodificationexception if( attendancePolicy.getType().equals( AttendanceConstants.EMPLOYEE_ATTENDANCE_POLICY ) ) { synchronized( attendancePolicy.getListEmployee() ) { for( EmployeeAttendancePolicy employeeAttendancePolicy : attendancePolicy.getListEmployee() ) { employeeInfo = employeeInfoSessionBeanLocal.findEmployeeInfoEntityByEmployeeInfoId( employeeAttendancePolicy.getEmployeeId() ); if( employeeInfo != null ) { employeeAttendancePolicy.setEmpName( employeeInfo.getFirstName() + " " + employeeInfo.getMiddleName() + " " + employeeInfo.getLastName() ); company = companySessionBeanLocal.findCompanyById( employeeInfo.getCompanyId() ); employeeAttendancePolicy.setCompanyName( company.getName() ); department = departmentSessionBeanLocal.findDepartmentEntityByDepartmentId( employeeInfo.getDepartmentId() ); employeeAttendancePolicy.setDepartmentName( department.getName() ); } else { attendancePolicy.getListEmployee().remove( employeeAttendancePolicy ); } } } }

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  • Pass off execution to different/specific thread in Java

    - by Mike
    I have about 4 threads. One thread keeps checking some data that the other thread is updating. The others are doing some processing in the background. All have been started at this point. My question is when the checking thread sees that the data has not been updated yet I currently sleep for a little bit but is there any way for me to tell the system to back to executing the thread that does the updating? That or is there any way I can put something like a listener on the data(a String) and once its updated an event will fire that will do what it needs to do? I tried using yield() and it seemed to just keep returning to the thread I called yield() from. Thanks

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  • Get file full path in java

    - by c0mrade
    When I pass File file to a method I'm trying to get its full path like file.getAbsolutePath(); I always get the same result no matter which one I use either absolute or canonical path PATH_TO_MY_WORKSPACE/projectName/filename and it is not there, how can I get exact location of the file? Thank you

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  • Java Map question

    - by user552961
    I have one Map that contains some names and numbers Map<String,Integer> abc = new TreeMap<String,Integer>(); It works fine. I can put some values in it but when I call it in different class it gives me wrong order. For example: I putted abc.put("a",1); abc.put("b",5); abc.put("c",3); some time it returns the order (b,a,c) and some time (a,c,b). What is wrong with it? Is there any step that I am missing when I call this map?

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  • Java Wicket - Calling javascript ( JQuery ) before AJAX

    - by user1428051
    I got this thing i'm trying to solve: I got a ListView created using Wicket ( 1.5 ) with a lot of elements and a scroll. When new items are available, the user is asked if he would like to refresh the list via a message backed by an AjaxLink: public void onClick(AjaxRequestTarget ajaxTarget) { /* do something ... */ ajaxTarget.addComponent(_list); } So on click the list gets reloaded and the scroll position is reset to zero. Is there any way i can call JavaScript before the list reloads the save the scroll position? (I know how to get/save the scroll position ( .scrollTop() ) , i just don't know how to call a function right before AJAX ).

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  • Passing a class ("Country.class") as an argument in Java

    - by Coronatus
    I'm trying to make a method that takes an argument of Country.class, User.class etc, and returns argument.count(). All the possible classes that I would give to this method extend from Model and have the method count(). My code: private static long <T> countModel(Model<T> clazz) { return clazz.count(); } Called by: renderArgs.put("countryCount", countModel(Country.class)); However this just doesn't work at all. How do I do this, please?

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  • Java ThreadPool for multiple identical tasks

    - by tdimmig
    I have 1 thread who sole job is to grab DatagramPackets off of a socket and stick them in a buffer. Another thread works out of that buffer, processing the DatagramPackets. I'd like to have a pool of threads working out of that buffer. I had thought to use a fixed thread pool to do this. To do so, do I need to create the pool, then submit enough runnables for execution to fill it up? I had hoped for a way to say "this is the thread/runnable that I want you to execute, this is how many I want running, GO!". Is there such a method of doing this? Is something other than a fixed thread pool better suited?

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  • Searching in a TreeMap (Java)

    - by Kronen
    I need to do a search in a map of maps and return the keys this element belong. I think this implementation is very slow, can you help me to optimize it?. I need to use TreeSet and I can't use contains because they use compareTo, and equals/compareTo pair are implemented in an incompatible way and I can't change that. (sorry my bad english) Map m = new TreeSet(); public String getKeys(Element element) { for(Entry e : m.entrySet()) { mapSubKey = e.getValue(); for(Entry e2 : mapSubKey.entrySet()) { setElements = e2.getValue(); for(Element elem : setElements) if(elem.equals(element)) return "Key: " + e.getKey() + " SubKey: " + e2.getKey(); } } }

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  • Java interface 'interview'-style problem

    - by Codenotguru
    Problem/Task: Write an interface with one method and two classes that implement this interface. Now write a main method with an array that holds an instance of each class. Using a for-each loop, invoke the method upon each item. Is this an interview question? (I'm not sure if the author meant to post this as a question or was looking for an answer to the above.)

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  • Java using generics with lists and interfaces

    - by MirroredFate
    Ok, so here is my problem: I have a list containing interfaces - List<Interface> a - and a list of interfaces that extend that interface: List<SubInterface> b. I want to set a = b. I do not wish to use addAll() or anything that will cost more memory as what I am doing is already very cost-intensive. I literally need to be able to say a = b. I have tried List<? extends Interface> a, but then I cannot add Interfaces to the list a, only the SubInterfaces. Any suggestions? EDIT I want to be able to do something like this: List<SubRecord> records = new ArrayList<SubRecord>(); //add things to records recordKeeper.myList = records; The class RecordKeeper is the one that contains the list of Interfaces (NOT subInterfaces) public class RecordKeeper{ public List<Record> myList; }

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  • Why fill() and copy() of Collections in java is implemented this way

    - by Priyank Doshi
    According to javadoc... Collections.fill() is written as below : public static <T> void fill(List<? super T> list, T obj) { int size = list.size(); if (size < FILL_THRESHOLD || list instanceof RandomAccess) { for (int i=0; i<size; i++) list.set(i, obj); } else { ListIterator<? super T> itr = list.listIterator(); for (int i=0; i<size; i++) { itr.next(); itr.set(obj); } } } Its easy to understand why they didn't use listIterator for if (size < FILL_THRESHOLD || list instanceof RandomAccess) condition as of RandomAccess. But whats the use of size < FILL_THRESHOLD in above? I mean is there any significant performance benefit over using iterator for size>=FILL_THRESHOLD and not for size < FILL_THRESHOLD ? I see the same approach for Collections.copy() also : public static <T> void copy(List<? super T> dest, List<? extends T> src) { int srcSize = src.size(); if (srcSize > dest.size()) throw new IndexOutOfBoundsException("Source does not fit in dest"); if (srcSize < COPY_THRESHOLD || (src instanceof RandomAccess && dest instanceof RandomAccess)) { for (int i=0; i<srcSize; i++) dest.set(i, src.get(i)); } else { ListIterator<? super T> di=dest.listIterator(); ListIterator<? extends T> si=src.listIterator(); for (int i=0; i<srcSize; i++) { di.next(); di.set(si.next()); } } } FYI: private static final int FILL_THRESHOLD = 25; private static final int COPY_THRESHOLD = 10;

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