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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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• Interview question: about Java serialization and singletons

  - by subhashis

  In an interview the interviewer asked me the following question: is it possible to serialize a singleton object? I said yes, but in which scenario should we serialize a singleton? And is it possible to design a class whose object can not be serialized?

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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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• 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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• 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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• 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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• API for neural networks with Java

  - by LxZv

  I´ve been searching for it and I found Encog and Neuroph but I don´t know if any about them... I've to do a final project and I need a litle feedback from humans, sometimes google is not enough XD

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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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• 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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• 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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• 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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• Create a java executable with Eclipse

  - by Micah

  This is a totally newbie question. I'm running Eclipse on Ubuntu. I created a test project that I want to compile to an executable (whataver the linux equivalent is of a Windows .exe file). Here's the contents of my program: public class MyTest { public static void main(String[] args) { System.out.println("You passed in: " + args[0]); } } I want to know how to compile it and then how to execute it from the command line. 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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• Catching screen prints in Java

  - by Amir Rachum

  There's a class I'm working with that has a display() function that prints some information to the screen. I am not allowed to change it. Is there a way to "catch" the string it prints to the screen externally?

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• why 2.1/1000 = 0.0021000000000000003 in java?

  - by Vivart

  double value = 2.1/1000; System.out.println(value); why o/p is 0.0021000000000000003

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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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• how to get a byte[] representation from a IP in String form in Java

  - by Manuel

  Suppose I have the IP stored in a String: String ip = "192.168.2.1" and I want to get the byte array with the four ints. How can I do it? Thanks!

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• Simple Java web application on Tomcat

  - by EugeneP

  If we only need to graphically authorize a user, view a few tables representation (from database), ability to change data in the database visually what tools to use to write such a web application that will run on Tomcat? What framework allows to do that in the most straightforward, easy-to-manage and elegant way?

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• Should I use the java.net or org.apache.http library for HTTP in my Java application?

  - by soneff

  What should I know about the trade-offs between these two HTTP libraries?

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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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• 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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• ByteArrayOutputStream to PrintWriter (Java Servlet)

  - by Thomas

  Writing generated PDF (ByteArrayOutputStream) in a Servlet to PrintWriter. I am desperately looking for a way to write a generated PDF file to the response PrintWriter. Since a Filter up the hierarchy chain has already called response.getWriter() I can't get response.getOutputStream(). I do have a ByteArrayOutputStream where I generated the PDF into. Now all I need is a way to output the content of this ByteArrayOutputStream to the PrintWriter. If anyone could give me a helping hand would be very much appreciated!

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• Java - Count words in two documents

  - by user552961

  Good Morning - it is school assignment, I am not asking for any source code (if you can provide any pesudo code it would be awesome). Here is the problem :( I have to create a term frequency table. It is not pure TF, I just need to count the words and write down. I know basic steps to do it 1 - extract all terms (I can do it with file reader) 2 - remove repeating terms (I can do it with TreeMap) The output of 2nd step would be Niga, ponga, dinga, bitlo, etc. 3 - Now I have to see if there is any word in current file from above terms or not, if yes then I will count. Now this is my problem, I stucked on step 3 :( I have some idea how to count words with TreeMap (treemap.containskey etc.) but it would be global count not local count for each file :( Any pseudo code?

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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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