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  • Java Variable Initialization

    - by Samuel Brainard
    Here's a piece of code I wrote. public class cube { private int length; private int breadth; private int height; private int volume; private int density; private int weight; public cube(int l,int b,int h, int d) { length=l; breadth=b; height=h; density=d; } public void volmeShow(){ volume=length*breadth*height; System.out.println("The Volume of the cube is "+this.volume); So if I implement the above cube class like this, public class cubeApp { public static void main(String[] args){ cube mycube = new cube(5,6,9,2); mycube.volumeShow(); I get an output that tells me Volume is 270. But I get an output that says Volume is 0 if I define the volume variable like this: public class cube { private int length; private int breadth; private int height; private int volume=length*breadth*height; private int density; private int weight; public cube(int l,int b,int h, int d) { length=l; breadth=b; height=h; density=d; } public void volmeShow(){ System.out.println("The Volume of the cube is "+this.volume); Can somebody please explain why this is happening? Thanks, Samuel.

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  • String Index Out Of Bound Exception error

    - by Fd Fehfhd
    Im not really sure why a am getting this error. But here is my code it is meant to test palindromes disregarding punctuation. So here is my code import java.util.Scanner; public class PalindromeTester { public static void main(String [] args) { Scanner kb = new Scanner(System.in); String txt = ""; int left; int right; int cntr = 0; do { System.out.println("Enter a word, phrase, or sentence (blank line to stop):"); txt = kb.nextLine(); txt = txt.toLowerCase(); char yP; String noP = ""; for (int i = 0; i < txt.length(); i++) { yP = txt.charAt(i); if (Character.isLetterOrDigit(txt.charAt(yP))) { noP += yP; } } txt = noP; left = 0; right = txt.length() -1; while (txt.charAt(left) == txt.charAt(right) && right > left) { left++; right--; } if (left > right) { System.out.println("Palindrome"); cntr++; } else { System.out.println("Not a palindrome"); } } while (!txt.equals("")); System.out.println("You found " + cntr + " palindromes. Thank you for using palindromeTester."); } } And if i test it and then i put enter so it will tell me how many palindromes you found the error i am getting is javav.lang.StringIndexOutOfBoundException : String index out of range 0 at PalindromeTester.main(PalindromeTester.java:38) and line 28 is while (txt.charAt(left) == txt.charAt(right) && right > left) Thanks for the help in advance

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  • Doesn't this defeat the whole purpose of having read-only properties?

    - by flockofcode
    I know how to use properties and I understand that they implicitly call underlying get and set accessors, depending on whether we are writing to or reading from a property. static void Main(string[] args) { A a = new A(); (a.b).i = 100; } class A { private B _b = new B(); public B b { get { return _b; } } } class B { public int i; } What code (a.b).i = 100; essentially does is that first property’s get accessor returns a reference to an object _b, and once we have this reference, we are able to access _b’s members and change their values. Thus, in our example, having read only property only prevents outside code from changing the value of a reference variable _b, but it doesn’t prevent outside code from accessing _b’s members. So it seems that property can only detect whether we are trying to read from or write to a variable ( in our case variable _b ) located on the stack, while it’s not able to detect whether we’re trying to also write to members of an object to which the variable on the stack ( assuming this variable is of reference type ) points to. a) But doesn’t that defeat the whole purpose of having read-only properties? Wouldn’t it be more effective if properties had the ability to also detect whether we’re trying to access members of an object returned by get accessor( assuming backing field is of a reference type )? thank you

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  • Celery Received unregistered task of type (run example)

    - by Echeg
    I'm trying to run example from Celery documentation. I run: celeryd --loglevel=INFO /usr/local/lib/python2.7/dist-packages/celery/loaders/default.py:64: NotConfigured: No 'celeryconfig' module found! Please make sure it exists and is available to Python. "is available to Python." % (configname, ))) [2012-03-19 04:26:34,899: WARNING/MainProcess] -------------- celery@ubuntu v2.5.1 ---- **** ----- --- * *** * -- [Configuration] -- * - **** --- . broker: amqp://guest@localhost:5672// - ** ---------- . loader: celery.loaders.default.Loader - ** ---------- . logfile: [stderr]@INFO - ** ---------- . concurrency: 4 - ** ---------- . events: OFF - *** --- * --- . beat: OFF -- ******* ---- --- ***** ----- [Queues] -------------- . celery: exchange:celery (direct) binding:celery tasks.py: # -*- coding: utf-8 -*- from celery.task import task @task def add(x, y): return x + y run_task.py: # -*- coding: utf-8 -*- from tasks import add result = add.delay(4, 4) print (result) print (result.ready()) print (result.get()) In same folder celeryconfig.py: CELERY_IMPORTS = ("tasks", ) CELERY_RESULT_BACKEND = "amqp" BROKER_URL = "amqp://guest:guest@localhost:5672//" CELERY_TASK_RESULT_EXPIRES = 300 When I run "run_task.py": on python console eb503f77-b5fc-44e2-ac0b-91ce6ddbf153 False errors on celeryd server [2012-03-19 04:34:14,913: ERROR/MainProcess] Received unregistered task of type 'tasks.add'. The message has been ignored and discarded. Did you remember to import the module containing this task? Or maybe you are using relative imports? Please see http://bit.ly/gLye1c for more information. The full contents of the message body was: {'retries': 0, 'task': 'tasks.add', 'utc': False, 'args': (4, 4), 'expires': None, 'eta': None, 'kwargs': {}, 'id': '841bc21f-8124-436b-92f1-e3b62cafdfe7'} Traceback (most recent call last): File "/usr/local/lib/python2.7/dist-packages/celery/worker/consumer.py", line 444, in receive_message self.strategies[name](message, body, message.ack_log_error) KeyError: 'tasks.add' Please explain what's the problem.

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  • Generics in a bidirectional association

    - by Verhoevenv
    Let's say I have two classes A and B, with B a subtype of A. This is only part of a richer type hierarchy, obviously, but I don't think that's relevant. Assume A is the root of the hierarchy. There is a collection class C that keeps track of a list of A's. However, I want to make C generic, so that it is possible to make an instance that only keeps B's and won't accept A's. class A(val c: C[A]) { c.addEntry(this) } class B(c: C[A]) extends A(c) class C[T <: A]{ val entries = new ArrayBuffer[T]() def addEntry(e: T) { entries += e } } object Generic { def main(args : Array[String]) { val c = new C[B]() new B(c) } } The code above obviously give the error 'type mismatch: found C[B], required C[A]' on the new B(c) line. I'm not sure how this can be fixed. It's not possible to make C covariant in T (like C[+T <: A]) because the ArrayBuffer is non-variantly typed in T. It's not possible to make the constructor of B require a C[B] because C can't be covariant. Am I barking up the wrong tree here? I'm a complete Scala newbie, so any ideas and tips might be helpful. Thank you! EDIT: Basically, what I'd like to have is that the compiler accepts both val c = new C[B]() new B(c) and val c = new C[A]() new B(c) but would reject val c = new C[B]() new A(c) It's probably possible to relax the typing of the ArrayBuffer in C to be A instead of T, and thus in the addEntry method as well, if that helps.

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  • Is there a jQuery Equivalent of YUI 2 Custom Event Publish/Subscribe Event Model?

    - by Abe
    Hello! I learned how to develop in Javascript using the YUI 2 library and was wondering if there is a jQuery equivalent of Custom Events (http://developer.yahoo.com/yui/event/#customevent) Specifically, I want to be able to define custom events without having to attach the listeners initially. In YUI, I would create a page class and declare different custom events that can be subscribed to. Below is some example code to demonstrate what I want to do, but with jQuery function ListPage() { var me = this; this.initEvent = new YAHOO.util.CustomEvent("initEvent"); this.init = function() { // initialize events, DOM, etc this.initEvent.fire(me); } } In application Javascript, I would then like to subscribe to the initEvent. var page = new ListPage(); page.initEvent.subscribe( function (type, args) { // do stuff here } ); page.init(); Are there any tutorials/examples of something this in jQuery? I understand I can do something similar using bind() and trigger(), but the impression I get is I have to pass in the event handler when I call bind(). Is it possible in jQuery to create the custom event, but pass in the event handler later? I hope my question makes sense. thanks!

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  • implementing interface

    - by 1ace1
    hello guys so i have this assignment that i need to implement interface to go over an ArrayList and sort it (ascending or descnding).I dont want "the" answer i just need some suggestions on my approach and why i get this error Exception in thread "main" java.lang.ClassCastException: Week7.Check cannot be cast to java.lang.Comparable at java.util.Arrays.mergeSort(Unknown Source) at java.util.Arrays.sort(Unknown Source) at java.util.Collections.sort(Unknown Source) at Week7.TestCheck.main(TestCheck.java:18) This is how i did it: comparable had one method called public int compairTo(Object o) public class Check implements comparable { private Integer checkNumber; public Check(Integer newCheckNumber) { setCheckNumber(newCheckNumber); } public String toString() { return getCheckNumber().toString(); } public void setCheckNumber(Integer checkNumber) { this.checkNumber = checkNumber; } public Integer getCheckNumber() { return checkNumber; } @Override public int compairTo(Object o) { Check compair = (Check)o; int result = 0; if (this.getCheckNumber() > compair.getCheckNumber()) result = 1; else if(this.getCheckNumber() < compair.getCheckNumber()) result = -1; return result; } } in my main i had this import java.util.ArrayList; import java.util.Collections; public class TestCheck { public static void main(String[] args) { ArrayList checkList = new ArrayList(); checkList.add(new Check(445)); checkList.add(new Check(101)); checkList.add(new Check(110)); checkList.add(new Check(553)); checkList.add(new Check(123)); Collections.sort(checkList); for (int i =0; i < checkList.size(); i++){ System.out.println(checkList.get(i)); } } }

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  • question about siftdown operation on heap

    - by davit-datuashvili
    i have following pseudo code which execute siftdown operation on heap array suppose is x void siftdown(int n) pre heap(2,n) && n>=0 post heap(1,n) i=1; loop /*invariant heap(1,n) except perhaps between i and it's (0,1,or 2) children*/ c=2*i; if (c>n) break; // c is left child of i if (c+1)<=n /* c+1 is rigth child of i if (x[c+1]<x[c]) c++ /* c is lesser child of i if (x[i]<=x[c]) break; swap(c,i) i=c; i have wrote following code is it correct? public class siftdown{ public static void main(String[]args){ int c; int n=9; int a[]=new int[]{19,100,17,2,7,3,36,1,25}; int i=1; while (i<n){ c=2*i; if (c>n) break; //c is the left child of i if (c+1<=n) //c+1 ir rigth child of i if (a[c+1]<a[c]) c++; if (a[i]<=a[c]) break; int t=a[c]; a[c]=a[i]; a[i]=t; i=c; } for (int j=0;j<a.length;j++){ System.out.println(a[j]); } } } // result is 19 2 17 1 7 3 36 100 25

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  • Memory increases with Java UDP Server

    - by Trevor
    I have a simple UDP server that creates a new thread for processing incoming data. While testing it by sending about 100 packets/second I notice that it's memory usage continues to increase. Is there any leak evident from my code below? Here is the code for the server. public class UDPServer { public static void main(String[] args) { UDPServer server = new UDPServer(15001); server.start(); } private int port; public UDPServer(int port) { this.port = port; } public void start() { try { DatagramSocket ss = new DatagramSocket(this.port); while(true) { byte[] data = new byte[1412]; DatagramPacket receivePacket = new DatagramPacket(data, data.length); ss.receive(receivePacket); new DataHandler(receivePacket.getData()).start(); } } catch (IOException e) { e.printStackTrace(); } } } Here is the code for the new thread that processes the data. For now, the run() method doesn't do anything. public class DataHandler extends Thread { private byte[] data; public DataHandler(byte[] data) { this.data = data; } @Override public void run() { System.out.println("run"); } }

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  • binary quicksort

    - by davit-datuashvili
    hi i want implement Binary quicksort algorithm from robert sedgewick book it looks like this public class quickb{ public static final int bitsword=32; public static void quicksortB(int a[],int l,int r,int d){ int i=l; int j=r-1; if (r<=l || d>bitsword) return ; while (j!=i) { while (digit(a[i],d)==0 && (i<j)) i++; while (digit(a[j],d)==1 && (j>i)) j++; int t=a[i]; a[i]=a[j]; a[j]=t; } if (digit(a[r-1],d)== 0) j++; quicksortB(a,l,j-1,d+1); quicksortB(a,j,r,d+1); } public static void main(String[]args){ int a[]=new int[]{4,7,3,9,8,2}; quicksortB(a,0,a.length-1,0); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } } public static int digit(int m,int d){ return (m>>d)&1; } } but it show me error: java.lang.ArrayIndexOutOfBoundsException: 6 at quickb.quicksortB(quickb.java:13) at quickb.main(quickb.java:32) what is wrong?

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  • call function inside a nested jquery plugin

    - by tchoesang
    There are many topics related to my question and i have been through most of them, but i haven't got it right. The closest post to my question is the following: http://stackoverflow.com/questions/1042072/how-to-call-functions-that-are-nested-inside-a-jquery-plugin Below is the jquery plugin i am using. On resize, the element sizes are recalculated. I am now trying to call the function resizeBind() from outside of the jquery plugin and it gives me error I tried the following combinations to call the function $.fn.splitter().resizeBind() $.fn.splitter.resizeBind() Any ideas, where i am getting wrong? ;(function($){ $.fn.splitter = function(args){ //Other functions ...... $(window).bind("resize", function(){ resizeBind(); }); function resizeBind(){ var top = splitter.offset().top; var wh = $(window).height(); var ww = $(window).width(); var sh = 0; // scrollbar height if (ww <0 && !jQuery.browser.msie ) sh = 17; var footer = parseInt($("#footer").css("height")) || 26; splitter.css("height", wh-top-footer-sh+"px"); $("#tabsRight").css("height", splitter.height()-30+"px"); $(".contentTabs").css("height", splitter.height()-70+"px"); } return this.each(function() { }); }; })(jQuery);

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  • Threads syncronization with ThreadPoolExecutor

    - by justme1
    I'm trying to implement some logic when I create main(father) thread witch executes several other threads. Then it waits for some condition which child threads creates. After condition is meet the father executes some more child threads. The problem that when I use wait/notify I have java.lang.IllegalMonitorStateException exception. Here is the code: public class MyExecutor { final static ArrayBlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(10); final static ExecutorService svc = Executors.newFixedThreadPool(1); static final ThreadPoolExecutor threadPool = new ThreadPoolExecutor(5, 8, 10, TimeUnit.SECONDS, queue); public static void main(String[] args) throws InterruptedException { final MyExecutor me = new MyExecutor(); svc.execute(new Runnable() { public void run() { try { System.out.println("Main Thread"); me.execute(threadPool, 1); System.out.println("Main Thread waiting"); wait(); System.out.println("Main Thread notified"); me.execute(threadPool, 2); Thread.sleep(100); threadPool.shutdown(); threadPool.awaitTermination(20000, TimeUnit.SECONDS); } catch (InterruptedException e) { e.printStackTrace(); } } }); svc.shutdown(); svc.awaitTermination(10000, TimeUnit.SECONDS); System.out.println("Main Thread finished"); } public void execute(ThreadPoolExecutor tpe, final int id) { tpe.execute(new Runnable() { public void run() { try { System.out.println("Child Thread " + id); Thread.sleep(2000); System.out.println("Child Thread " + id + " finished"); notify(); } catch (InterruptedException e) { e.printStackTrace(); } } }); } } When I comment wait and notify line I have the following output: Main Thread Main Thread waiting Main Thread notified Child Thread 1 Child Thread 2 Child Thread 1 finished Child Thread 2 finished Main Thread finished

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  • Top n items in a List ( including duplicates )

    - by Krishnan
    Trying to find an efficient way to obtain the top N items in a very large list, possibly containing duplicates. I first tried sorting & slicing, which works. But this seems unnnecessary. You shouldn't need to sort a very large list if you just want the top 20 members. So I wrote a recursive routine which builds the top-n list. This also works, but is very much slower than the non-recursive one! Question: Which is my second routine (elite2) so much slower than elite, and how do I make it faster ? My code is attached below. Thanks. import scala.collection.SeqView import scala.math.min object X { def elite(s: SeqView[Int, List[Int]], k:Int):List[Int] = { s.sorted.reverse.force.slice(0,min(k,s.size)) } def elite2(s: SeqView[Int, List[Int]], k:Int, s2:List[Int]=Nil):List[Int] = { if( k == 0 || s.size == 0) s2.reverse else { val m = s.max val parts = s.force.partition(_==m) val whole = if( parts._1.size > 1) parts._1.tail:::parts._2 else parts._2 elite2( whole.view, k-1, m::s2 ) } } def main(args:Array[String]) = { val N = 1000000/3 val x = List(N to 1 by -1).flatten.map(x=>List(x,x,x)).flatten.view println(elite2(x,20)) println(elite(x,20)) } }

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  • Problem with Java Scanner sc.nextLine();

    - by Jonathan B
    Hi, sry about my english :) Im new to Java programming and i have a problem with Scanner. I need to read an Int, show some stuff and then read a string so i use sc.nextInt(); show my stuff showMenu(); and then try to read a string palabra=sc.nextLine(); Some one told me i need to use a sc.nextLine(); after sc.nextInt(); but i dont understand why do you have to do it :( Here is my code: public static void main(String[] args) { // TODO code application logic here Scanner sc = new Scanner(System.in); int respuesta = 1; showMenu(); respuesta = sc.nextInt(); sc.nextLine(); //Why is this line necessary for second scan to work? switch (respuesta){ case 1: System.out.println("=== Palindromo ==="); String palabra = sc.nextLine(); if (esPalindromo(palabra) == true) System.out.println("Es Palindromo"); else System.out.println("No es Palindromo"); break; } } Ty so much for your time and Help :D

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  • For each loop not reading in the last item

    - by Gandalf StormCrow
    I'm trying to read in a multi line string then split it then print it .. here is the string : 1T1b5T!1T2b1T1b2T!1T1b1T2b2T!1T3b1T1b1T!3T3b1T!1T3b1T1b1T!5T1*1T 11X21b1X 4X1b1X When I split the string with ! I get this without the last line string : 1T1b5T 1T1b5T1T2b1T1b2T 1T2b1T1b2T1T1b1T2b2T 1T1b1T2b2T1T3b1T1b1T 1T3b1T1b1T3T3b1T 3T3b1T1T3b1T1b1T 1T3b1T1b1T5T1*1T 5T1*1T11X21b1X 11X21b1X Here is my code : import java.io.BufferedInputStream; import java.util.Scanner; public class Main { public static void main(String args[]) { Scanner stdin = new Scanner(new BufferedInputStream(System.in)); while (stdin.hasNext()) { for (String line : stdin.next().split("!")) { System.out.println(line); for (int i = 0; i < line.length(); i++) { System.out.print(line.charAt(i)); } } } } } Where did I make the mistake, why is not reading in the last line? After I read in all lines properly I should go trough each line if I encounter number I should print the next char the n times the number I just read, but that is long way ahead first I need help with this. Thank you

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  • Get class instance by class name string

    - by VDVLeon
    Hi all, I noticed the function Object.factory(char[] className) in D. But it does not work like I hoped it would work; it does not work ;) An example: import std.stdio; class TestClass { override string toString() { return typeof(this).stringof; // TestClass } }; void main(string[] args) { auto i = Object.factory("TestClass"); if (i is null) { writeln("Class not found"); } else { writeln("Class string: " ~ i); } } I think this should result in the message: "Class string: TestClass" but it says "Class not found". Does anybody know why this happens and how I could fix it ? Or do I need to make my own class factory. For example by make a class with a static array Object[string] classes; with class instances. When I want a new instance I do this: auto i = (className in classes); if (i is null) { return null; } return i.classinfo.create();

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  • Dispose, when is it called?

    - by Snake
    Consider the following code: namespace DisposeTest { using System; class Program { static void Main(string[] args) { Console.WriteLine("Calling Test"); Test(); Console.WriteLine("Call to Test done"); } static void Test() { DisposeImplementation di = new DisposeImplementation(); } } internal class DisposeImplementation : IDisposable { ~DisposeImplementation() { Console.WriteLine("~ in DisposeImplementation instance called"); } public void Dispose() { Console.WriteLine("Dispose in DisposeImplementation instance called"); } } } The Dispose just never get's called, even if I put a wait loop after the Test(); invocation. So that quite sucks. I want to write a class that is straightforward and very easy to use, to make sure that every possible resource is cleaned up. I don't want to put that responsibilty to the user of my class. Possible solution: use using, or call Dispose myself(basicly the same). Can I force the user to use a using? Or can I force the dispose to be called? Calling GC.Collect(); after Test(); doesn't work either. Putting di to null doesn't invoke Dispose either. The Deconstructor DOES work, so the object get's deconstructed when it exits Test()

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  • Overlaying several CLR reference fields with each other in explicit struct?

    - by thr
    Edit: I'm well aware of that this works very well with value types, my specific question is about using this for reference types. I've been tinkering around with structs in .NET/C#, and I just found out that you can do this: using System; using System.Runtime.InteropServices; namespace ConsoleApplication1 { class Foo { } class Bar { } [StructLayout(LayoutKind.Explicit)] struct Overlaid { [FieldOffset(0)] public object AsObject; [FieldOffset(0)] public Foo AsFoo; [FieldOffset(0)] public Bar AsBar; } class Program { static void Main(string[] args) { var overlaid = new Overlaid(); overlaid.AsObject = new Bar(); Console.WriteLine(overlaid.AsBar); overlaid.AsObject = new Foo(); Console.WriteLine(overlaid.AsFoo); Console.ReadLine(); } } } Basically circumventing having to do dynamic casting during runtime by using a struct that has an explicit field layout and then accessing the object inside as it's correct type. Now my question is: Can this lead to memory leaks somehow, or any other undefined behavior inside the CLR? Or is this a fully supported convention that is usable without any issues? I'm aware that this is one of the darker corners of the CLR, and that this technique is only a viable option in very few specific cases.

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  • how to find by date from timestamp column in JPA criteria

    - by Kre Toni
    I want to find a record by date. In entity and database table datatype is timestamp. I used Oracle database. @Entity public class Request implements Serializable { @Id private String id; @Version private long version; @Temporal(TemporalType.TIMESTAMP) @Column(name = "CREATION_DATE") private Date creationDate; public Request() { } public Request(String id, Date creationDate) { setId(id); setCreationDate(creationDate); } public String getId() { return id; } public void setId(String id) { this.id = id; } public long getVersion() { return version; } public void setVersion(long version) { this.version = version; } public Date getCreationDate() { return creationDate; } public void setCreationDate(Date creationDate) { this.creationDate = creationDate; } } in mian method public static void main(String[] args) { RequestTestCase requestTestCase = new RequestTestCase(); EntityManager em = Persistence.createEntityManagerFactory("Criteria").createEntityManager(); em.getTransaction().begin(); em.persist(new Request("005",new Date())); em.getTransaction().commit(); Query q = em.createQuery("SELECT r FROM Request r WHERE r.creationDate = :creationDate",Request.class); q.setParameter("creationDate",new GregorianCalendar(2012,12,5).getTime()); Request r = (Request)q.getSingleResult(); System.out.println(r.getCreationDate()); } in oracle database record is ID CREATION_DATE VERSION 006 05-DEC-12 05.34.39.200000 PM 1 Exception is Exception in thread "main" javax.persistence.NoResultException: getSingleResult() did not retrieve any entities. at org.eclipse.persistence.internal.jpa.EJBQueryImpl.throwNoResultException(EJBQueryImpl.java:1246) at org.eclipse.persistence.internal.jpa.EJBQueryImpl.getSingleResult(EJBQueryImpl.java:750) at com.ktrsn.RequestTestCase.main(RequestTestCase.java:29)

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  • What else I must do allow my method to handle any type of objects

    - by NewHelpNeeder
    So to allow any type object I must use generics in my code. I have rewrote this method to do so, but then when I create an object, for example Milk, it won't let me pass it to my method. Ether there's something wrong with my generic revision, or Milk object I created is not good. How should I pass my object correctly and add it to linked list? This is a method that causes error when I insert an item: public void insertFirst(T dd) // insert at front of list { Link newLink = new Link(dd); // make new link if( isEmpty() ) // if empty list, last = newLink; // newLink <-- last else first.previous = newLink; // newLink <-- old first newLink.next = first; // newLink --> old first first = newLink; // first --> newLink } This is my class I try to insert into linked list: class Milk { String brand; double size; double price; Milk(String a, double b, double c) { brand = a; size = b; price = c; } } This is test method to insert the data: public static void main(String[] args) { // make a new list DoublyLinkedList theList = new DoublyLinkedList(); // this causes: // The method insertFirst(Comparable) in the type DoublyLinkedList is not applicable for the arguments (Milk) theList.insertFirst(new Milk("brand", 1, 2)); // insert at front theList.displayForward(); // display list forward theList.displayBackward(); // display list backward } // end main() } // end class DoublyLinkedApp Declarations: class Link<T extends Comparable<T>> {} class DoublyLinkedList<T extends Comparable<T>> {}

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  • Synchronize JTextFields Values by PropertyChangeListener

    - by gt_ebuddy
    I want to copy the value of a jTextField - TXTFLD1 to another jTextField -TXTFLD2 when the value at TXTFLD1 changes. I choose propertychangelistener because i cannot detect when the value at TXTFLD1 is changed, Because it is changed by some external code which i cannot modify now. The test code is as follows : public class TxtFldSync extends JFrame { private JButton BTN1 = null; private JTextField TXTFLD1 = null; private JTextField TXTFLD2 = null; public static void main(String[] args) { TxtFldSync thisClass = new TxtFldSync(); thisClass.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); thisClass.setVisible(true); } public TxtFldSync() { super(); this.setSize(300, 200); BTN1 = new JButton(); BTN1.setBounds(new Rectangle(178, 38, 67, 17)); TXTFLD1 = new JTextField(); TXTFLD1.setBounds(new Rectangle(32, 42, 83, 20)); TXTFLD2 = new JTextField(); TXTFLD2.setBounds(new Rectangle(30, 78, 83, 20)); //listeners TXTFLD1.addPropertyChangeListener("value", new PropertyChangeListener() { @Override public void propertyChange(PropertyChangeEvent arg0) { TXTFLD2.setText(TXTFLD1.getText()+"set by change listener"); //this doesnot work why ? } }); BTN1.addActionListener( new ActionListener() { @Override public void actionPerformed(ActionEvent arg0) { TXTFLD1.setText("Action Performed"); //i what to set same value to TXTFLD2 using property change listener } }); this.setContentPane(new Container()); this.getContentPane().add(BTN1); this.getContentPane().add(TXTFLD1); this.getContentPane().add(TXTFLD2); } } Why the property change listener is not working. What are the other alternatives solution for this problem?

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  • Weird behaviour with Scanner#nextFloat

    - by James P.
    Running the following in Eclipse initially caused Scanner to not recognize carriage returns in the console effectively blocking further input: price = sc.nextFloat(); Adding this line before the code causes Scanner to accept 0,23 (french notation) as a float: Locale.setDefault(Locale.US); This is most probably due to regional settings in Windows XP Pro. When the code is run again 0,23 is still accepted and entering 0.23 causes it to throw a java.util.InputMismatchException. Any explanation as to why this is happening? Also is there a workaround or should I just use Float#parseFloat? Edit: import java.util.Locale; import java.util.Scanner; public class NexFloatTest { public static void main(String[] args) { //Locale.setDefault(Locale.US); //Locale.setDefault(Locale.FRANCE); // Gives fr_BE on this system System.out.println(Locale.getDefault()); float price; String uSDecimal = "0.23"; String frenchDecimal = "0,23"; Scanner sc = new Scanner(uSDecimal); try{ price = sc.nextFloat(); System.out.println(price); } catch (java.util.InputMismatchException e){ e.printStackTrace(); } try{ sc = new Scanner(frenchDecimal); price = sc.nextFloat(); System.out.println(price); } catch (java.util.InputMismatchException e){ e.printStackTrace(); } String title = null; System.out.print("Enter title:"); try{ title = sc.nextLine(); // This line is skippe } catch(java.util.NoSuchElementException e ){ e.printStackTrace(); } System.out.print(title); } }

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  • Strange behavior when overloading methods in Java

    - by Sep
    I came across this weird (in my opinion) behavior today. Take this simple Test class: public class Test { public static void main(String[] args) { Test t = new Test(); t.run(); } private void run() { List<Object> list = new ArrayList<Object>(); list.add(new Object()); list.add(new Object()); method(list); } public void method(Object o) { System.out.println("Object"); } public void method(List<Object> o) { System.out.println("List of Objects"); } } It behaves the way you expect, printing "List of Objects". But if you change the following three lines: List<String> list = new ArrayList<String>(); list.add(""); list.add(""); you will get "Object" instead. I tried this a few other ways and got the same result. Is this a bug or is it a normal behavior? And if it is normal, can someone explain why? Thanks.

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  • When calling a static method on parent class, can the parent class deduce the type on the child (C#)

    - by Matt
    Suppose we have 2 classes, Child, and the class from which it inherits, Parent. class Parent { public static void MyFunction(){} } class Child : Parent { } Is it possible to determine in the parent class how the method was called? Because we can call it two ways: Parent.MyFunction(); Child.MyFunction(); My current approach was trying to use: MethodInfo.GetCurrentMethod().ReflectedType; // and MethodInfo.GetCurrentMethod().DeclaringType; But both appear to return the Parent type. If you are wondering what, exactly I am trying to accomplish (and why I am violating the basic OOP rule that the parent shouldn't have to know anything about the child), the short of it is this (let me know if you want the long version): I have a Model structure representing some of our data that persists to the database. All of these models inherit from an abstract Parent. This parent implements a couple of events, such as SaveEvent, DeleteEvent, etc. We want to be able to subscribe to events specific to the type. So, even though the event is in the parent, I want to be able to do: Child.SaveEvent += new EventHandler((sender, args) => {}); I have everything in place, where the event is actually backed by a dictionary of event handlers, hashed by type. The last thing I need to get working is correctly detecting the Child type, when doing Child.SaveEvent. I know I can implement the event in each child class (even forcing it through use of abstract), but it would be nice to keep it all in the parent, which is the class actually firing the events (since it implements the common save/delete/change functionality).

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  • How to create a String Array and link it to a Grade array

    - by user1861544
    I have a project that I need to create 2 Arrays, one to hold Student Names and one to hold Student Scores. The user inputs the size of the array, and the array needs to be sorted using BubbleSort (putting the high scores at the top). I have started the project, created the first array for scores, I have successfully done bubble sort and sorted the grades. Now I can't figure out how to make an array for Names, and once I do how do I make the names array correspond to the Grades array BubbleSort? Here is the code I have so far. import java.util.Scanner; public class Grades { public static void main(String[]args){ { Scanner UserIn = new Scanner(System.in); System.out.print( "How many students are there? " ); int[]GradeArray = new int[UserIn.nextInt()]; for( int i=0 ; i<GradeArray.length ; i++ ) { System.out.print( "Enter Grade for Student " + (i+1) + ": " ); GradeArray[i] = UserIn.nextInt(); } bubbleSort(GradeArray); for( int i : GradeArray ) System.out.println( i ); System.out.println(); } } private static void bubbleSort(int[]GradeArray){ int n = GradeArray.length; int temp = 0; String temp2; for(int i=0; i<n; i++){ for(int j=1; j<(n-i);j++){ if(GradeArray[j-1]<GradeArray[j]){ //swap temp=GradeArray[j-1]; GradeArray[j-1]=GradeArray[j]; GradeArray[j]=temp; } } } } } Also how do I change the grades to Double? I started with Int and when I try to change everything to double I get an error saying "Found Double, expected Int".

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