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  • How to create a true singleton in java?

    - by rjoshi
    I am facing a problem with my singleton when used across multiple class loaders. E.g Singleton accessed by multiple EJBs. Is there any way to create a singleton which has only one instance across all class loader? I am looking for pure java solution either using custom class loader or some other way.

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  • Eclipse Javadoc tooltip help doesn't show classes' supertypes and interfaces

    - by Pooria
    I'm talking about the tooltip that pops up when you hover your mouse over a class in your source (which also helps with intellisense and auto completion), which describes what a class/method/etc does. I find it very annoying that it doesn't show what superclass the class (being described) extends or what interfaces it implements. Is there a way to make eclipse show the additional information?

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  • No improvement in speed when using Ehcache with Hibernate

    - by paddydub
    I'm getting no improvement in speed when using Ehcache with Hibernate Here are the results I get when i run the test below. The test is reading 80 Stop objects and then the same 80 Stop objects again using the cache. On the second read it is hitting the cache, but there is no improvement in speed. Any idea's on what I'm doing wrong? Speed Test: First Read: Reading stops 1-80 : 288ms Second Read: Reading stops 1-80 : 275ms Cache Info: elementsInMemory: 79 elementsInMemoryStore: 79 elementsInDiskStore: 0 JunitCacheTest public class JunitCacheTest extends TestCase { static Cache stopCache; public void testCache() { ApplicationContext context = new ClassPathXmlApplicationContext("beans-hibernate.xml"); StopDao stopDao = (StopDao) context.getBean("stopDao"); CacheManager manager = new CacheManager(); stopCache = (Cache) manager.getCache("ie.dataStructure.Stop.Stop"); //First Read for (int i=1; i<80;i++) { Stop toStop = stopDao.findById(i); } //Second Read for (int i=1; i<80;i++) { Stop toStop = stopDao.findById(i); } System.out.println("elementsInMemory " + stopCache.getSize()); System.out.println("elementsInMemoryStore " + stopCache.getMemoryStoreSize()); System.out.println("elementsInDiskStore " + stopCache.getDiskStoreSize()); } public static Cache getStopCache() { return stopCache; } } HibernateStopDao @Repository("stopDao") public class HibernateStopDao implements StopDao { private SessionFactory sessionFactory; @Transactional(readOnly = true) public Stop findById(int stopId) { Cache stopCache = JunitCacheTest.getStopCache(); Element cacheResult = stopCache.get(stopId); if (cacheResult != null){ return (Stop) cacheResult.getValue(); } else{ Stop result =(Stop) sessionFactory.getCurrentSession().get(Stop.class, stopId); Element element = new Element(result.getStopID(),result); stopCache.put(element); return result; } } } ehcache.xml <cache name="ie.dataStructure.Stop.Stop" maxElementsInMemory="1000" eternal="false" timeToIdleSeconds="5200" timeToLiveSeconds="5200" overflowToDisk="true"> </cache> stop.hbm.xml <class name="ie.dataStructure.Stop.Stop" table="stops" catalog="hibernate3" mutable="false" > <cache usage="read-only"/> <comment></comment> <id name="stopID" type="int"> <column name="STOPID" /> <generator class="assigned" /> </id> <property name="coordinateID" type="int"> <column name="COORDINATEID" not-null="true"> <comment></comment> </column> </property> <property name="routeID" type="int"> <column name="ROUTEID" not-null="true"> <comment></comment> </column> </property> </class> Stop public class Stop implements Comparable<Stop>, Serializable { private static final long serialVersionUID = 7823769092342311103L; private Integer stopID; private int routeID; private int coordinateID; }

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  • How to implement jsf validator?

    - by Krishna
    HI, I want to know how to implement Validator in JSF. What is the advantages of declaring the validator-id. When it will be called in the life cycle?. I have implemented the following code. Please find out what is wrong in the code. I am not seeing it called anywhere in the life cycle. <?xml version="1.0"?> <!DOCTYPE faces-config PUBLIC "-//Sun Microsystems, Inc.//DTD JavaServer Faces Config 1.1//EN" "http://java.sun.com/dtd/web-facesconfig_1_1.dtd"> <faces-config> <lifecycle> <phase-listener>javabeat.net.jsf.JsfPhaseListener</phase-listener> </lifecycle> <validator> <validator-id>JsfValidator</validator-id> <validator-class>javabeat.net.jsf.JsfValidator</validator-class> </validator> <managed-bean> <managed-bean-name>jsfBean</managed-bean-name> <managed-bean-class>javabeat.net.beans.ManagedBean</managed-bean-class> <managed-bean-scope>request</managed-bean-scope> </managed-bean> <navigation-rule> <navigation-case> <from-outcome>success</from-outcome> <to-view-id>success.jsp</to-view-id> </navigation-case> </navigation-rule> </faces-config> public class JsfValidator implements Validator { public JsfValidator() { System.out.println("Inside JsfValidator Constructor"); } @Override public void validate(FacesContext facesContext, UIComponent uiComponent, Object object) throws ValidatorException { System.out.println("Inside Validator"); } }

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  • how to model a follower stream in appengine?

    - by molicule
    I am trying to design tables to buildout a follower relationship. Say I have a stream of 140char records that have user, hashtag and other text. Users follow other users, and can also follow hashtags. I am outlining the way I've designed this below, but there are two limitaions in my design. I was wondering if others had smarter ways to accomplish the same goal. The issues with this are The list of followers is copied in for each record If a new follower is added or one removed, 'all' the records have to be updated. The code class HashtagFollowers(db.Model): """ This table contains the followers for each hashtag """ hashtag = db.StringProperty() followers = db.StringListProperty() class UserFollowers(db.Model): """ This table contains the followers for each user """ username = db.StringProperty() followers = db.StringListProperty() class stream(db.Model): """ This table contains the data stream """ username = db.StringProperty() hashtag = db.StringProperty() text = db.TextProperty() def save(self): """ On each save all the followers for each hashtag and user are added into a another table with this record as the parent """ super(stream, self).save() hfs = HashtagFollowers.all().filter("hashtag =", self.hashtag).fetch(10) for hf in hfs: sh = streamHashtags(parent=self, followers=hf.followers) sh.save() ufs = UserFollowers.all().filter("username =", self.username).fetch(10) for uf in ufs: uh = streamUsers(parent=self, followers=uf.followers) uh.save() class streamHashtags(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() class streamUsers(db.Model): """ The stream record is the parent of this record """ followers = db.StringListProperty() Now, to get the stream of followed hastags indexes = db.GqlQuery("""SELECT __key__ from streamHashtags where followers = 'myusername'""") keys = [k,parent() for k in indexes[offset:numresults]] return db.get(keys) Is there a smarter way to do this?

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  • Hibernate @Transactional not starting transaction

    - by rhinds
    I have a web app using Hibernate, and I am attempting to persist some data, but it is failing to persist within a Transaction despite using the @Transactional annotation. My service class is as follows: @Service("profileService") public class ProfileService { private EntityManager entityManager; @Autowired private AccountService accountService; @Autowired private ProfileDAOImpl profileDao; @PersistenceContext public void setEntityManager(EntityManager em) { this.entityManager = em; } @Transactional public void addConnectionToAccount(SocialConnection sc) { entityManager.persist(sc); } } The addConnectionToAccount() method is being called from another Spring bean in a normal method, and the ProfileService class is currently being injected there: public class HibernateConnectionRepository implements ConnectionRepository { @Inject private ProfileService profileService; @Override @Transactional public void addConnection(SocialConnection sc) { try { profileService.addConnectionToAccount(accountId, sc); } catch (Exception e) { e.printStackTrace(); } } I tried putting the @Transactional annotation on the calling method in the vain hope that it might make a difference but nothing. Previously I have experienced problems like this its been because the object being persisted does not satisfy table restrictions (such as non-nullable columns as null) or because the method is being called from within the same class and the calling method is not Transactional, but neither of those are the case here.. Any ideas? it just fails silently, the logs are as follows: 2012-03-26 22:25:04,702 [http-bio-8085-exec-9] DEBUG com.mchange.v2.resourcepool.BasicResourcePool - trace com.mchange.v2.resourcepool.BasicResourcePool@1bc25c8 [managed: 3, unused: 2, excluded: 0] (e.g. com.mchange.v2.c3p0.impl.NewPooledConnection@e5b006) 2012-03-26 22:25:04,710 [http-bio-8085-exec-9] DEBUG org.hibernate.SQL - select SEQ_COUNT from SEQUENCE where SEQ_NAME = 'PO_SEQ' for update 2012-03-26 22:25:04,711 [http-bio-8085-exec-9] DEBUG org.hibernate.SQL - update SEQUENCE set SEQ_COUNT = ? where SEQ_COUNT = ? and SEQ_NAME = 'PO_SEQ' 2012-03-26 22:25:04,723 [http-bio-8085-exec-9] DEBUG com.mchange.v2.resourcepool.BasicResourcePool - trace com.mchange.v2.resourcepool.BasicResourcePool@1bc25c8 [managed: 3, unused: 2, excluded: 0] (e.g. com.mchange.v2.c3p0.impl.NewPooledConnection@e5b006) 2012-03-26 22:25:04,723 [http-bio-8085-exec-9] DEBUG org.hibernate.event.internal.AbstractSaveEventListener - Generated identifier: 2200, using strategy: org.hibernate.id.MultipleHiLoPerTableGenerator UPDATE Also wanted to mention that the HibernateConnectionRepository bean is not annotated and is actually being configured in an @Configuration class (if this makes any difference? not used @Configuration classes much). The method to create the bean is as follows: @Bean @Scope(value = "request", proxyMode = ScopedProxyMode.INTERFACES) public ConnectionRepository connectionRepository() { Authentication authentication = SecurityContextHolder.getContext().getAuthentication(); if (authentication == null) { throw new IllegalStateException("Unable to get a ConnectionRepository: no user signed in"); } ApplicationUser user = (ApplicationUser) authentication.getPrincipal(); return usersConnectionRepository().createConnectionRepository(String.valueOf(user.getAccountId())); } The bean is scoped to the logged in user, but may also be created multiple times for each user..

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  • how to transform xml with xslt preserving <br /> and not preserve other tags in a text

    - by liysd
    This question is quite similar to this one. Except that I want to preserve only <br /> and some <img> tags (with class="visible"). I.e from: <example> <text> Some text with <br /> and <img src="source" /> then text .... <img class="visible" src="source" /> </text> </example> To have: <div class="example"> <p>Some text with <br /> and then text .... <img class="visible" src="source" /></p> </div>

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  • Using pointers, references, handles to generic datatypes, as generic and flexible as possible

    - by Patrick
    In my application I have lots of different data types, e.g. Car, Bicycle, Person, ... (they're actually other data types, but this is just for the example). Since I also have quite some 'generic' code in my application, and the application was originally written in C, pointers to Car, Bicycle, Person, ... are often passed as void-pointers to these generic modules, together with an identification of the type, like this: Car myCar; ShowNiceDialog ((void *)&myCar, DATATYPE_CAR); The 'ShowNiceDialog' method now uses meta-information (functions that map DATATYPE_CAR to interfaces to get the actual data out of Car) to get information of the car, based on the given data type. That way, the generic logic only has to be written once, and not every time again for every new data type. Of course, in C++ you could make this much easier by using a common root class, like this class RootClass { public: string getName() const = 0; }; class Car : public RootClass { ... }; void ShowNiceDialog (RootClass *root); The problem is that in some cases, we don't want to store the data type in a class, but in a totally different format to save memory. In some cases we have hundreds of millions of instances that we need to manage in the application, and we don't want to make a full class for every instance. Suppose we have a data type with 2 characteristics: A quantity (double, 8 bytes) A boolean (1 byte) Although we only need 9 bytes to store this information, putting it in a class means that we need at least 16 bytes (because of the padding), and with the v-pointer we possibly even need 24 bytes. For hundreds of millions of instances, every byte counts (I have a 64-bit variant of the application and in some cases it needs 6 GB of memory). The void-pointer approach has the advantage that we can almost encode anything in a void-pointer and decide how to use it if we want information from it (use it as a real pointer, as an index, ...), but at the cost of type-safety. Templated solutions don't help since the generic logic forms quite a big part of the application, and we don't want to templatize all this. Additionally, the data model can be extended at run time, which also means that templates won't help. Are there better (and type-safer) ways to handle this than a void-pointer? Any references to frameworks, whitepapers, research material regarding this?

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  • Changing the HTML of CKEditor form elements (in the dialog window)

    - by Kenny Meyers
    I'm trying to modify the HTML of the dialog boxes in CKEditor. The HTML inside each of those boxes is an absolute nightmare, and even worse, the source code is compressed and it's unclear what the path of execution is. I want to take something like this: <div class="cke_dialog_ui_select" id="44_uiElement" role="presentation"><label style="" for="42_select" id="43_label" class="cke_dialog_ui_labeled_label">Link Type</label><div role="presentation" class="cke_dialog_ui_labeled_content"><select aria-labelledby="43_label" class="cke_dialog_ui_input_select" id="42_select"><option value="url"> URL</option><option value="anchor"> Link to anchor in the text</option><option value="email"> E-mail</option></select></div></div> and turn it into something more legible and easier to style, removing one of the divs. These are for the Image and Anchor dialog boxes (Modal dialogues) respectively. Thanks for your help.

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  • Why are types found on an imported namepace but not on a fully qualified namespace after retargeting the framework?

    - by Paul Ferguson
    We've just re-targeted a VB.NET project from .Net 2.0 to 3.5. Various framework types are now missing from our project. Wherever the type is referenced using a fully qualified namespace it's missing. If the relevant namespace is imported for the type; it's found. For example, this doesn't find the type Object, with compiler error "System.Object is not defined.": Public Class Foo Inherits System.Object End Class However, this works ok: Imports System Public Class Foo Inherits [Object] End Class I've already tried re-opening the solution with no success.

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  • java: "downcasting" to new object / opposite of slicing

    - by rhavin
    Sorry, i really dont know how to make a headline for that question; maybe there is a name for what im trying to do that i dont know, but i can explain it with some code: Guess you have a class that unfortunately neither has a copy-constructor nor a public static copy method. class A { private int i; // <- private, cant access String x; // <- even worse: cant access unless in same pkg! /* … other stuff, ctor, etc. … */ public A clone() { A a = new A(); a.i = i; a.x = x; return x; } } Guess further, there is some function that returns an object of that class: public static A someFn(x,y,z); Now the problem: I want to derive from that class to add some functionality. Unfortunately, i neither have a sizeof in java nor a cc or static copy method. So when i do a class B extends A { protected w; public B clone() { /* as usual */ } } then i can clone my B and get a new one, but how can i convert the returned A from someFn() into a B. Is there anyway to do the opposite of slicing in java? if i clone it, it's still an A, and i cant copy it field by field. This is all simple in c++, but how to do this in Java?

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  • Error with html post form in internet explorer

    - by Ron
    I have a html form which posts to a php script. It works fine in chrome and firefox but not in IE. I have ran a test on W3C but can not find any errors that relate to the form. My code is: <form class="formular" id="formular" method="post" action="script/contact.php"> <fieldset> <label> <span>Name : </span> <input type="text" class="validate['required','length[3,-1]','nodigit'] text-input" name="Name" /> </label> <label> <span>Email address : </span> <input type="text" class="validate['required','email'] text-input" name="email" /> </label> </fieldset> <div class="button"> <input type="submit" value="Contact" class="submit" /> </div> </form> Thanks in advance

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  • Addind link with existin href.

    - by Dom
    Hello gurus, Im trying to create link inside my list tag that will have href inherited from link that already exists in this list tag. Don't know how much sense does it makes, but i have this: <ul> <li><a href="page1.html">Support</a></li> <li><a href="page2.html">Products</a></li> <li><a href="page3.html">Management</a></li> <li><a href="page4.html">Others</a></li> </ul> and I need soothing like this: <ul> <li> <a href="page1.html">Support</a> <div class="slideLink"><a href="page1.html">Click Here</a></div> </li> <li> <a href="page2.html">Products</a> <div class="slideLink"><a href="page2.html">Click Here</a></div> </li> <li> <a href="page3.html">Management</a> <div class="slideLink"><a href="page3.html">Click Here</a></div> </li> <li> <a href="page4.html">Others</a> <div class="slideLink"><a href="page4.html">Click Here</a></div> </li> </ul> So far I have managed to add div with class and link within it with "click here" text, but i don't have a clue how to grab link href and add it to my new link. $('ul li a').each(function(){ $(this).after("<div class='slideLink'><a href=" + Link + ">Read more</div>"); }); Thank you for your help in advance. Best Regards Dom

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  • Resuming execution of code after exception is thrown and caught

    - by dotnetdev
    Hi, How is it possible to resume code execution after an exception is thrown? For exampel, take the following code: namespace ConsoleApplication1 { class Test { public void s() { throw new NotSupportedException(); string @class = "" ; Console.WriteLine(@class); Console.ReadLine(); } } class Program { static void Main(string[] args) { try { new Test().s(); } catch (ArgumentException x) { } catch (Exception ex) { } } } } After catching the exception when stepping through, the program will stop running. How can I still carry on execution? Thanks

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  • With NHibernate, how can I add a child object when updating a parent object?

    - by BMZ
    I have a simple Parent/Child relationship between a Person object and an Address object. The Person object exists in the DB. After doing a Get on the Person, I add a new Address object to the Address sub-object list of the parent, and do some other updates to the Person object. Finally, I do an Update on the Person object. With a SQL trace window, I can see the update to the Person object to the Person table and the Insert of the Address record to the Address table. The issue is that, after the update is performed, the AddressId (primary key on the Address object) is still set to 0, which is what it defaults to when you first initialize the Address object. I have verified that when I do an Add, this value is set correctly. Is this a known issue when trying to add sub-objects as part of an NHibernate UPDATE? Sample code and mapping files are below Thanks <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"> <class name="BusinessEntities.Wellness.Person,BusinessEntities.Wellness" table="Person" lazy="true" dynamic-insert="true" dynamic-update="false"> <id name="Personid" column="PersonID" type="int"> <generator class="native" /> </id> <version type="binary" generated="always" name="RecordVersion" column="`RecordVersion`"/> <property type="int" not-null="true" name="Customerid" column="`CustomerID`" /> <property type="AnsiString" not-null="true" length="9" name="Ssn" column="`SSN`" /> <property type="AnsiString" not-null="true" length="30" name="FirstName" column="`FirstName`" /> <property type="AnsiString" not-null="true" length="35" name="LastName" column="`LastName`" /> <property type="AnsiString" length="1" name="MiddleInitial" column="`MiddleInitial`" /> <property type="DateTime" name="DateOfBirth" column="`DateOfBirth`" /> <bag name="PersonAddresses" inverse="true" lazy="true" cascade="all"> <key column="PersonID" /> <one-to-many class="BusinessEntities.Wellness.PersonAddress,BusinessEntities.Wellness" / </bag> </class> </hibernate-mapping> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"> <class name="BusinessEntities.Wellness.PersonAddress,BusinessEntities.Wellness" table="PersonAddress" lazy="true" dynamic-insert="true" dynamic-update="false"> <id name="PersonAddressId" column="PersonAddressID" type="int"> <generator class="native" /> </id> <version type="binary" generated="always" name="RecordVersion" column="`RecordVersion`" /> <property type="AnsiString" not-null="true" length="1" name="AddressTypeid" column="`AddressTypeID`" /> <property type="AnsiString" not-null="true" length="60" name="AddressLine1" column="`AddressLine1`" /> <property type="AnsiString" length="60" name="AddressLine2" column="`AddressLine2`" /> <property type="AnsiString" length="60" name="City" column="`City`" /> <property type="AnsiString" length="2" name="UsStateId" column="`USStateID`" /> <property type="AnsiString" length="5" name="UsPostalCodeId" column="`USPostalCodeID`" /> <many-to-one name="Person" cascade="none" column="PersonID" /> </class> </hibernate-mapping> Person newPerson = new Person(); newPerson.PersonName = "John Doe"; newPerson.SSN = "111111111"; newPerson.CreatedBy = "RJC"; newPerson.CreatedDate = DateTime.Today; personDao.AddPerson(newPerson); Person updatePerson = personDao.GetPerson(newPerson.PersonId); updatePerson.PersonAddresses = new List<PersonAddress>(); PersonAddress addr = new PersonAddress(); addr.AddressLine1 = "1 Main St"; addr.City = "Boston"; addr.State = "MA"; addr.Zip = "12345"; updatePerson.PersonAddresses.Add(addr); personDao.UpdatePerson(updatePerson); int addressID = updatePerson.PersonAddresses[0].AddressId;

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  • How to return a value when destroying/cleaning-up an object instance

    - by Mridang Agarwalla
    When I initiate a class in Python, I give it some values. I then call method in the class which does something. Here's a snippet: class TestClass(): def __init__(self): self.counter = 0 def doSomething(self): self.counter = self.counter + 1 print 'Hiya' if __name__ == "__main__": obj = TestClass() obj.doSomething() obj.doSomething() obj.doSomething() print obj.counter As you can see, everytime I call the doSomething method, it prints some text and increments an internal variable i.e. counter. When I initiate the class, i set the counter variable to 0. When I destroy the object, I'd like to return the internal counter variable. What would be a good way of doing this? I wanted to know if there were other ways apart from doing stuff like: accessing the variable directly. Like obj.counter. creating a method like getCounter. Thanks.

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  • Python decorator question

    - by nsharish
    decorator 1: def dec(f): def wrap(obj, *args, **kwargs): f(obj, *args,**kwargs) return wrap decorator 2: class dec: def __init__(self, f): self.f = f def __call__(self, obj, *args, **kwargs): self.f(obj, *args, **kwargs) A sample class, class Test: @dec def disp(self, *args, **kwargs): print(*args,**kwargs) The follwing code works with decorator 1 but not with decorator 2. a = Test() a.disp("Message") I dont understand why decorator 2 is not working here. Can someone help me with this?

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  • Javascript and VERY LONG string

    - by StealthRT
    Hey all, i am having problems with the below code: function showTableData() { var tableArray; var x = 0; var theHTML; for (i = 0; i < 7032; i++) { if (x = 0) { theHTML = '<tr>' + '<th scope="row" class="spec">' + partNum[i] + '</th>' + '<td>' + Msrp[i] + '</td>' + '<td>' + blah[i] + '</td>' + '<td>' + blahs[i] + '</td>' + '</tr>' + theHTML; x++; }else{ theHTML = '<tr>' + '<th scope="row" class="specalt">' + partNum[i] + '</th>' + '<td class="alt">' + Msrp[i] + '</td>' + '<td class="alt">' + blah[i] + '</td>' + '<td class="alt">' + blahs[i] + '</td>' + '</tr>' + theHTML; x--; } } theHTML = '<table id="mytable" cellspacing="0">' + '<tr>' + '<th scope="col" abbr="Configurations" class="nobg">Part Number</th>' + '<th scope="col" abbr="Dual 1.8">Msrp Price</th>' + '<th scope="col" abbr="Dual 2">blahs Price</th>' + '<th scope="col" abbr="Dual 2.5">Low Price</th>' + '</tr>' + theHTML + '</table>'; $('#example').append(theHTML); } </script> <div id="example"> </div> The problem being that the $('#example').append(theHTML); never executes (or shows on the page). I think its because the string is soooooo long! It has over 7,000 items in the array so im not sure if thats the reason or if its something else? Any help would be great! Thanks! David

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  • Eclipse outline of Prototype javascript classes

    - by Rob Agar
    Is there a way to show the structure of a javascript class declared using Prototype's Class.create function in the Eclipse outline view? The declarations look like: var Foo = Class.create({ bar: function() { ... }, baz: function() { ... }, }); At the moment all I get is "Foo:". (A google search turned up http://marketplace.eclipse.org/content/prototypewtp, but the link to the plugin homepage is dead)

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  • Which design pattern is most appropriate?

    - by Anon
    Hello, I want to create a class that can use one of four algorithms (and the algorithm to use is only known at run-time). I was thinking that the Strategy design pattern sounds appropriate, but my problem is that each algorithm requires slightly different parameters. Would it be a bad design to use strategy, but pass in the relevant parameters into the constructor?. Here is an example (for simplicity, let's say there are only two possible algorithms) ... class Foo { private: // At run-time the correct algorithm is used, e.g. a = new Algorithm1(1); AlgorithmInterface* a; }; class AlgorithmInterface { public: virtual void DoSomething = 0; }; class Algorithm1 : public AlgorithmInterface { public: Algorithm1( int i ) : value(i) {} virtual void DoSomething(){ // Does something with int value }; int value; }; class Algorithm2 : public AlgorithmInterface { public: Algorithm2( bool b ) : value(b) {} virtual void DoSomething(){ // Do something with bool value }; bool value; };

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  • C# Virtual method call in constructor - how to refactor?

    - by Cristi Diaconescu
    I have an abstract class for database-agnostic cursor actions. Derived from that, there are classes that implement the abstract methods for handling database-specific stuff. The problem is, the base class ctor needs to call an abstract method - when the ctor is called, it needs to initialize the database-specific cursor. I know why this shouldn't be done, I don't need that explanation! This is my first implementation, that obviously doesn't work - it's the textbook "wrong way" of doing it. The overridden method accesses a field from the derived class, which is not yet instantiated: public abstract class CursorReader { private readonly int m_rowCount; protected CursorReader() { m_rowCount = CreateCursor(sqlCmd); //virtual call ! } protected abstract int CreateCursor(string sqlCmd); } public class SqlCursorReader : CursorReader { private SqlConnection m_sqlConnection; public SqlCursorReader(string sqlCmd, SqlConnection sqlConnection) { m_sqlConnection = sqlConnection; //field initialized here } protected override int CreateCursor(string sqlCmd) { //uses not-yet-initialized member *m_sqlConnection* //so this throws a NullReferenceException var cursor = new CustomCursor(sqlCmd, m_sqlConnection); return cursor.Count(); } } I will follow up with an answer on my attempts to fix this...

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  • Error while including j2ssh in a j2me midlet

    - by Farhan
    I obtained an evaluation license for j2ssh maverick, downloaded the library and included the j2me jar into my project. But i get the following error when i try to run/build the project (in netbeans, using WTK 3.0) Error preverifying class com.maverick.events.J2SSHEventMessages VERIFIER ERROR com/maverick/events/J2SSHEventMessages.class$(Ljava/lang/String;)Ljava/lang/Class;: Cannot find class java/lang/NoClassDefFoundError I get the same error when i use eclipse (error in preverifying stage). Any pointers ? There are more than one NoClassDefFoundErrors in the preverifying stage. Am i using the wrong .jar file ?

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  • How to save to Django Model that Have Mulitple Foreign Keys Fields

    - by Spikie
    I have Models for business Apps class staff_name(models.Model): TITLE_CHOICES = ( ('Mr', 'Mr'), ('Miss', 'Miss'), ( 'Mrs', 'Mrs'), ( 'chief', 'chief'), ) titlename = models.CharField(max_length=10,choices=TITLE_CHOICES) firstname = models.CharField(max_length=150) surname = models.CharField(max_length=150) date = models.DateTimeField(auto_now=True) class meta: ordering = ["date"] get_latest_by = "date" class inventory_transaction(models.Model): stock_in = models.DecimalField(blank=True, null=True,max_digits=8, decimal_places=2) stock_out = models.DecimalField(blank=True,null=True,max_digits=8, decimal_places=2) Number_container = models.ForeignKey(container_identity) staffs = models.ForeignKey(staff_name) goods_details = models.ForeignKey(departments) balance = models.DecimalField(max_digits=8, decimal_places=2) date = models.DateTimeField(auto_now=True) What i want to accomplish is check if the staff have made entry to the table before if yes add the value for the stock in plus (last) balance field and assign to balance if no just assign stock in value to balance field and save these are my codes These are my codes: try: s = staffname.staffs_set.all().order_by("-date").latest() # staffname is the instant of the class model staff_name e = s.staffs_set.create(stockin=vdataz,balance=s.balance + vdataz ) # e is the instant of the class model inventory_transaction e.save e.staffs.add(s) e.from_container.add(containersno) e.goods_details.add(department) except ObjectDoesNotExist: e = staff_name.objects.create(stockin=vdataz,balance=vdataz ) e.save e.staffs.add(staffname) e.from_container.add(containersno) e.goods_details.add(department) I will really appreciate a solution Thanks I hope it make more sense now. iam on online if you need more explanation just ask in the comment.Thank you for your help

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