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  • How to synchronize static method in java.

    - by Summer_More_More_Tea
    Hi there: I come up with this question when implementing singleton pattern in Java. Even though the example listed blow is not my real code, yet very similar to the original one. public class ConnectionFactory{ private static ConnectionFactory instance; public static synchronized ConnectionFactory getInstance(){ if( instance == null ){ instance = new ConnectionFactory(); } return instance; } private ConnectionFactory(){ // private constructor implementation } } Because I'm not quite sure about the behavior of a static synchronized method, I get some suggestion from google -- do not have (or as less as possible) multiple static synchronized methods in the same class. I guess when implementing static synchronized method, a lock belongs to Class object is used so that multiple static synchronized methods may degrade performance of the system. Am I right? or JVM use other mechanism to implement static synchronized method? What's the best practice if I have to implement multiple static synchronized methods in a class? Thank you all! Kind regards!

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  • Does C++ have a static polymorphism implementation of interface that does not use vtable?

    - by gilbertc
    Does C++ have a proper implementation of interface that does not use vtable? for example class BaseInterface{ public: virtual void func() const = 0; } class BaseInterfaceImpl:public BaseInterface{ public: void func(){ std::cout<<"called."<<endl; } } BaseInterface* obj = new BaseInterfaceImpl(); obj->func(); the call to func at the last line goes to vtable to find the func ptr of BaseInterfaceImpl::func, but is there any C++ way to do that directly as the BaseInterfaceImpl is not subclassed from any other class besides the pure interface class BaseInterface? Thanks. Gil.

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  • python list/dict property best practice

    - by jterrace
    I have a class object that stores some properties that are lists of other objects. Each of the items in the list has an identifier that can be accessed with the id property. I'd like to be able to read and write from these lists but also be able to access a dictionary keyed by their identifier. Let me illustrate with an example: class Child(object): def __init__(self, id, name): self.id = id self.name = name class Teacher(object): def __init__(self, id, name): self.id = id self.name = name class Classroom(object): def __init__(self, children, teachers): self.children = children self.teachers = teachers classroom = Classroom([Child('389','pete')], [Teacher('829','bob')]) This is a silly example, but it illustrates what I'm trying to do. I'd like to be able to interact with the classroom object like this: #access like a list print classroom.children[0] #append like it's a list classroom.children.append(Child('2344','joe')) #delete from like it's a list classroom.children.pop(0) But I'd also like to be able to access it like it's a dictionary, and the dictionary should be automatically updated when I modify the list: #access like a dict print classroom.childrenById['389'] I realize I could just make it a dict, but I want to avoid code like this: classroom.childrendict[child.id] = child I also might have several of these properties, so I don't want to add functions like addChild, which feels very un-pythonic anyway. Is there a way to somehow subclass dict and/or list and provide all of these functions easily with my class's properties? I'd also like to avoid as much code as possible.

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  • XCode enum woes

    - by Raconteur
    Hi gang, I thought I had this sorted, but I am still missing something. Very simply, I have a Settings class that hold a DAO (sitting on a plist). I want to have a couple of enums for the settings for convenience and readability, such as GamePlayType and DifficultyLevel. Right now I am defining them in the Settings.h file above the @interface line as such: typedef enum { EASY, NORMAL, HARD } DifficultyLevel; and typedef enum { SET_NUMBER_OF_MOVES, TO_COMPLETION } GamePlayType; If I access them from within the Settings class like: - (int)gridSizeForLOD { switch ([self difficultyLevel]) { case EASY: return GRID_SIZE_EASY; case NORMAL: return GRID_SIZE_NORMAL; case HARD: return GRID_SIZE_HARD; default: return GRID_SIZE_NORMAL; } } everything is fine. But, if I try to access them outside of the Settings class, let's say in my main view controller class, like this: if (([settings gameType] == SET_NUMBER_OF_MOVES) && (numMoves == [settings numMovesForLOD])) { [self showLoseScreen]; } I get errors (like EXC_BAD_ACCESS) or the condition always fails. Am I doing something incorrectly? Also, I should point out that I have this code for the call to gameType (which lives in the Settings class): - (GamePlayType)gameType { return [dao gameType]; } and the DAO implements gameType like this: - (int)gameType { return (settingsContent != nil) ? [[settingsContent objectForKey:@"Game Type"] intValue] : 0; } I know I have the DAO returning an int instead of a GamePlayType, but A) the problem I am describing arose there when I tried to use the "proper" data type, and B) I did not think it would matter since the enum is just a bunch of named ints, right? Any help, greatly appreciated. I really want to understand this thoroughly, and something is eluding me... Cheers, Chris

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  • Must parameter of assignment operator be reference?

    - by Tim
    When overloading assignment operator of a class in C++, must its parameter be reference? For example, class MyClass { public: ... MyClass & operator=(const MyClass &rhs); ... } Can it be class MyClass { public: ... MyClass & operator=(const MyClass rhs); ... } ? Thanks!

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  • How do I get 2-way data binding to work for nested asp.net Repeater controls

    - by jimblanchard
    I have the following (trimmed) markup: <asp:Repeater ID="CostCategoryRepeater" runat="server"> <ItemTemplate> <div class="costCategory"> <asp:Repeater ID="CostRepeater" runat="server" DataSource='<%# Eval("Costs")%>'> <ItemTemplate> <tr class="oddCostRows"> <td class="costItemTextRight"><span><%# Eval("Variance", "{0:c0}")%></span></td> <td class="costItemTextRight"><input id="SupplementAmount" class="costEntryRight" type="text" value='<%# Bind("SupplementAmount")%>' runat="server" /></td> </tr> </ItemTemplate> </asp:Repeater> </div> </ItemTemplate> </asp:Repeater> The outer repeater's DataSource is set in the code-beside. I've snipped them, but there are Eval statements that wire up to the properties in the outer Repeater. Anyway, one of the fields in the inner Repeater needs to be a Bind instead of an Eval, as I want to get the values that the user types in. The SupplementAmount input element correctly receives it's value when the page loads, but on the other side, when I inspect the contents of the Costs List when the form posts back, the changes the user made aren't present. Thanks.

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  • Examine one particular call and ignore the rest

    - by lulalala
    I have a Currency class and want to update its rates. The following is the spec of an update class I plan to write: describe WebCrawlers::Currency::FeedParser do let(:gbp){ double('GBP').as_null_object } let(:usd){ double('USD').as_null_object } describe '#perform' do before do Currency.stub(:find_by_name).with('GBP').and_return( gbp ) Currency.stub(:find_by_name).with('USD').and_return( usd ) end it 'should update GBP rate' do gbp.should_receive(:update_attributes).with(rate_to_usd:0.63114) subject.perform end it 'should not update USD rate' do usd.should_not_receive(:update_attributes) subject.perform end end end and it works find if I only update GBP in my actual class: class WebCrawlers::Currency::FeedParser def perform Currency.find_by_name('GBP').update_attributes(rate_to_usd: 0.63114) end end However once I start updating other currencies like 'CAD', Rspec complains <Currency> received :find_by_name with unexpected arguments expected: ("USD") got: ("CAD") Why is this the case? Instead of NOT expecting USD, it says it is. And in the future there will be lots of currencies to update, but I don't want to test and stub each one of them. How can I resolve this issue?

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  • help with generating models from database for many to many in doctrine

    - by ajsie
    im using doctrine and i have set up some test tables to be generated into models: I want a many-to-many relationship models (3 tables converted into 3 models) (things are simplified to make the point clear) mysql tables: user: id INT // primary key name VARCHAR group: id INT // primary key name VARCHAR user_group: user_id INT // primary and foreign key to user.id group_id INT // primary and foreign key to group.id i thought that it would generate these models (from the documentation): // User.php class User extends Doctrine_Record { public function setTableDefinition() { $this->hasColumn('id'); $this->hasColumn('name); } public function setUp() { $this->hasMany('Group as Groups', array( 'refClass' => 'UserGroup', 'local' => 'user_id', 'foreign' => 'group_id' ) ); } } // Group.php class Group extends Doctrine_Record { public function setTableDefinition() { $this->hasColumn('id'); $this->hasColumn('name); } public function setUp() { $this->hasMany('User as Users', array( 'refClass' => 'UserGroup', 'local' => 'group_id', 'foreign' => 'user_id' ) ); } } // UserGroup.php class UserGroup extends Doctrine_Record { public function setTableDefinition() { $this->hasColumn('user_id') ); $this->hasColumn('group_id') ); } } but it generated this: // User.php abstract class BaseUser extends Doctrine_Record { public function setTableDefinition() { $this->hasColumn('id'); $this->hasColumn('name'); } public function setUp() { $this->hasMany('UserGroup', array( 'local' => 'id', 'foreign' => 'user_id')); } } // Group.php abstract class BaseGroup extends Doctrine_Record { public function setTableDefinition() { $this->hasColumn('id'); $this->hasColumn('name'); } public function setUp() { $this->hasMany('UserGroup', array( 'local' => 'id', 'foreign' => 'group_id')); } } // UserGroup.php abstract class BaseUserGroup extends Doctrine_Record { public function setTableDefinition() { $this->hasColumn('user_id'); $this->hasColumn('group_id'); } public function setUp() { $this->hasOne('User', array( 'local' => 'user_id', 'foreign' => 'id')); $this->hasOne('Group', array( 'local' => 'group_id', 'foreign' => 'id')); } } as you can see, there is no 'refClass' in the 'User' and 'Group' models pointing to the 'UserGroup'. the 'UserGroup' table in this case is just another table from Doctrine's perspective not a reference table. I've checked my table definitions in mysql. They are correct. user_group has 2 columns (primary keys and foreign keys), each one pointing to the primary key in either User or Group. But i want the standard many-to-many relationship models in Doctrine models. I'd appreciate some help. I have struggled to figure it out for a half day now. What is wrong? Thanks!

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  • Example of contravariance

    - by Misha
    I am thinking of the following example to illustrate why contravariance is useful. Let's consider a GUI framework with Widgets, Events, and Event Listeners. abstract class Event; class KeyEvent extends Event class MouseEvent extends Event trait EventListener[-Event] { def listen(e:Event) } Let Widgets define the following methods: def addKeyEventListener(listener:EventListener[KeyEvent]) def addMouseEventListener(listener:EventListener[MouseEvent]) These methods accept only "specific" event listeners, which is fine. However I would like to define also "kitchen-sink" listeners, which listen to all events, and pass such listeners to the "add listener" methods above. For instance, I would like to define LogEventListener to log all incoming events class LogEventListener extends EventListener[Event] { def listen(e:Event) { log(event) } } Since the trait EventListener is contravariant in Event we can pass LogEventListener to all those "add listener" methods without losing their type safety. Does it make sense ?

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  • Formatting Field Declarations in Eclipse

    - by geeko
    Greetings Overflowers, Problem: public abstract class Filter { private long id; protected String expression; } how can I align fields automatically in Eclipse, such in: public abstract class Filter { private long id; protected String expression; } Note the space before long, thank you ! UPDATE: I cannot find a customization option to align types of class members (e.g.: long and String) under Eclipse formatter options. Yes, there is one to align names of class members (e.g.: id and expression) but not their types. Please, take a lock at this issue in my examples above. Any solution ?

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  • Extending existing data structure in Scala.

    - by Lukasz Lew
    I have a normal tree defined in Scala. sealed abstract class Tree case class Node (...) extends Tree case class Leaf (...) extends Tree Now I want to add a member variable to all nodes and leaves in the tree. Is it possible with extend keyword or do I have to modify the tree classes by adding [T]?

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  • ASP.NET MVC4: How do I keep from having multiple identical results in my lookup tables

    - by sehummel
    I'm new to ASP.NET so this may be an easy question. I'm seeding my database with several rows of dummy data. Here is one of my rows: new Software { Title = "Microsoft Office", Version = "2012", SerialNumber = "12346231434543", Platform = "PC", Notes = "Macs really rock!", PurchaseDate = "2011-12-04", Suite = true, SubscriptionEndDate = null, SeatCount = 0, SoftwareTypes = new List<SoftwareType> { new SoftwareType { Type="Suite" }}, Locations = new List<Location> { new Location { LocationName = "Paradise" }}, Publishers = new List<SoftwarePublisher> { new SoftwarePublisher { Publisher = "Microsoft" }}} But when I do this, a new row is created for each location, with the LocationName being set in each row like this. We only have two locations. How do I get it to create a LocationID property for the Software class and in my Locations class. Here is my Location class: public class Location { public int Id { get; set; } [Required] [StringLength(20)] public string LocationName { get; set; } public virtual Software Software { get; set; } } I have this line in my Software class to reference this table: public virtual List<Location> Locations { get; set; } Again, what I want when I am done is a Locations table with two entries, and a LocationID field in my Software table. How do I do this?

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  • Forget late static binding, I need late static __FILE__ ...

    - by bobthecow
    I'm looking for the get_called_class() equivalent for __FILE__ ... Maybe something like get_included_file()? I have a set of classes which would like to know what directory they exist in. Something like this: <?php class A { protected $baseDir; public function __construct() { $this->baseDir = dirname(__FILE__); } public function getBaseDir() { return $this->baseDir; } } ?> And in some other file, in some other folder... <?php class B extends A { // ... } class C extends B { // ... } $a = new A; echo $a->getBaseDir(); $b = new B; echo $b->getBaseDir(); $c = new C; echo $c->getBaseDir(); // Annnd... all three return the same base directory. ?> Now, I could do something ghetto, like adding $this->baseDir = dirname(__FILE__) to each and every extending class, but that seems a bit... ghetto. After all, we're talking about PHP 5.3, right? Isn't this supposed to be the future? Is there another way to get the path to the file where a class was declared?

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  • Django admin: how do I add an unrelated model field to a model change/add page?

    - by NP
    I have the following models: class Foo(models.Model): field1 = models.IntegerField() ... class Bar(models.Model): field1 = models.IntegerField() ... class Foo_bar(models.Model): foo = models.ForeignKey(Foo) bar = models.ForeignKey(Bar) ... In the admin, I want it so that in the Foo change/add page, you can specify a Bar object, and on save I want to create a Foo_bar object to represent the relationship. How can I do this through customizing the Admin site/ModelAdmins? Thanks.

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  • How to override the attr_protected?

    - by KandadaBoggu
    I have STI implementation as follows: class Automobile < ActiveRecord::Base end class Car < Automobile end class Truck < Automobile end class User < ActiveRecord::Base has_many :automobiles accepts_nested_attributes_for :automobiles end I am creating a list of automobiles for a user. For each automobile, the UI sets the type field and the properties associated with the automobile.While form submission, the type field is ignored as it is a protected attribute. How do I work around this issue? Is there a declarative way to unprotect a protected attribute?

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  • Help decoding MSDN Dynamic Data Article

    - by davemackey
    I'm trying to run through this msdn article: http://msdn.microsoft.com/en-us/library/dd723645.aspx One of the steps is: In the class file for the page, change the base class from UserControl to EntityTemplateUserControl. Nowhere is it made clear what page is being referenced. Can someone help me? I don't see any relevant class in the pages I have, so I assumed maybe they were talking about the ascx and didn't really mean page, but I'm not seeing an option there either.

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  • Compare Properties automatically

    - by juergen d
    I want to get the names of all properties that changed for matching objects. I have these (simplified) classes: public enum PersonType { Student, Professor, Employee } class Person { public string Name { get; set; } public PersonType Type { get; set; } } class Student : Person { public string MatriculationNumber { get; set; } } class Subject { public string Name { get; set; } public int WeeklyHours { get; set; } } class Professor : Person { public List<Subject> Subjects { get; set; } } Now I want to get the objects where the Property values differ: List<Person> oldPersonList = ... List<Person> newPersonList = ... List<Difference> = GetDifferences(oldPersonList, newPersonList); public List<Difference> GetDifferences(List<Person> oldP, List<Person> newP) { //how to check the properties without casting and checking //for each type and individual property?? //can this be done with Reflection even in Lists?? } In the end I would like to have a list of Differences like this: class Difference { public List<string> ChangedProperties { get; set; } public Person NewPerson { get; set; } public Person OldPerson { get; set; } } The ChangedProperties should contain the name of the changed properties.

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  • What are the different methods for injecting cross-cutting concerns?

    - by Stacy Vicknair
    What are the different methods for injecting cross-cutting concerns into a class so that I can minimize the coupling of the classes involved while keeping the code testable (TDD or otherwise)? For example, consider if I have a class that requires both logging functionality and centralized exception management. Should I use DIP and inject both required concerns via an interface into the class that requires them? Should I use a service locater that I pass to each class that will require some cross cutting functionality? Is there a different solution altogether? Am I asking the wrong question entirely?

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  • How to get parameters out of an ascx back to the main aspx page

    - by Hallaghan
    I've got an aspx page that renders an ascx page with filtering capabilities. Inside the ascx page, parameters are passed as follows: <tr> <td class="label">Plataforma</td> <td class="field lookup"><%= Html.Lookup("s.Site", null, Url, "Sites") %></td> </tr> <tr> <td class="label">Data</td> <td class="field date"><%= Html.TextBox("s.Date", DateTime.Today.ToString("yyyy-MM-dd")) %></td> </tr> I need to be able to get those parameters on the main aspx page, because they are needed for an action that is called there. How could I access these parameters?

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  • Problem accessing base member in derived constructor

    - by LeopardSkinPillBoxHat
    Given the following classes: class Foo { struct BarBC { protected: BarBC(uint32_t aKey) : mKey(aKey) mOtherKey(0) public: const uint32_t mKey; const uint32_t mOtherKey; }; struct Bar : public BarBC { Bar(uint32_t aKey, uint32_t aOtherKey) : BarBC(aKey), mOtherKey(aOtherKey) // Compile error here }; }; I am getting a compilation error at the point indicated: error: class `Foo::Bar' does not have any field named `mOtherKey'. Can anyone explain this? I suspect it's a syntactical problem due to my Bar class being defined within the Foo class, but can't seem to find a way around it. This is simple public inheritance, so mOtherKey should be accessible from the Bar constructor. Right? Or is it something to do with the fact that mOtherKey is const and I have already initialised it to 0 in the BarBC constructor?

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  • How to call a generic method with an anonymous type involving generics?

    - by Alex Black
    I've got this code that works: def testTypeSpecialization = { class Foo[T] def add[T](obj: Foo[T]): Foo[T] = obj def addInt[X <% Foo[Int]](obj: X): X = { add(obj) obj } val foo = addInt(new Foo[Int] { def someMethod: String = "Hello world" }) assert(true) } But, I'd like to write it like this: def testTypeSpecialization = { class Foo[T] def add[X, T <% Foo[X](obj: T): T = obj val foo = add(new Foo[Int] { def someMethod: String = "Hello world" }) assert(true) } This second one fails to compile: no implicit argument matching parameter type (Foo[Int]{ ... }) = Foo[Nothing] was found. Basically: I'd like to create a new anonymous class/instance on the fly (e.g. new Foo[Int] { ... } ), and pass it into an "add" method which will add it to a list, and then return it The key thing here is that the variable from "val foo = " I'd like its type to be the anonymous class, not Foo[Int], since it adds methods (someMethod in this example) Any ideas? I think the 2nd one fails because the type Int is being erased. I can apparently 'hint' the compiler like this: def testTypeSpecialization = { class Foo[T] def add[X, T <% Foo[X]](dummy: X, obj: T): T = obj val foo = add(2, new Foo[Int] { def someMethod: String = "Hello world" }) assert(true) }

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  • How could I implement a fuzzy time date replacer using Knockout?

    - by rball
    I'd like to implement what this plugin does using jQuery: https://github.com/rmm5t/jquery-timeago A short description of that plugin: This will turn all abbr elements with a class of timeago and an ISO 8601 timestamp in the title (conforming to the datetime design pattern microformat): <abbr class="timeago" title="2011-12-17T09:24:17Z">December 17, 2011</abbr> Into something like this: <abbr class="timeago" title="December 17, 2011">about 1 day ago</abbr> Except using knockout my markup looks like this: <abbr data-bind="attr: { title: Posted }" class="timeago"></abbr> I think something isn't synced up because nothing is happening even if I put the call to timeago within the viewmodel itself. I'm guessing I need a subscriber that's attached to the observable "Posted" but I'm not sure how to set that up.

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  • Toggle jQuery-UI widgets

    - by cf_PhillipSenn
    I have: <div class="ui-widget"> <div class="ui-widget-header"> <span class="ui-icon ui-icon-circle-triangle-n">My Menu</span> </div> <ul class="ui-widget-content"> <li>Menu Item 1</li> <li>Menu Item 2</li> <li>Menu Item 3</li> </ul> </div> My jQuery is: $('.ui-widget-header').click(function() { $('.ui-widget-header+ul').toggle('slow'); }); Q: How do I toggle classes between ui-icon-circle-triangle-n and ui-icon-circle-triangle-s as the user clicks on .ui-widget-header?

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  • How to use interfaces in exception handling

    - by vikp
    Hi, I'm working on the exception handling layer for my application. I have read few articles on interfaces and generics. I have used inheritance before quite a lot and I'm comfortable with in that area. I have a very brief design that I'm going to implement: public interface IMyExceptionLogger { public void LogException(); // Helper methods for writing into files,db, xml } I'm slightly confused what I should be doing next. public class FooClass: IMyExceptionLogger { // Fields // Constructors } Should I implement LogException() method within FooClass? If yes, than I'm struggling to see how I'm better of using an interface instead of the concrete class... I have a variety of classes that will make a use of that interface, but I don't want to write an implementation of that interface within each class. In the same time If I implement an interface in one class, and then use that class in different layers of the application I will be still using concrete classes instead of interfaces, which is a bad OO design... I hope this makes sense. Any feedback and suggestions are welcome. Please notice that I'm not interested in using net4log or its competitors because I'm doing this to learn. Thank you Edit: Wrote some more code. So I will implement variety of loggers with this interface, i.e. DBExceptionLogger, CSVExceptionLogger, XMLExceptionLogger etc. Than I will still end up with concrete classes that I will have to use in different layers of my application.

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  • Hibernate NamingStrategy implementation that maintains state between calls

    - by Robert Petermeier
    Hi, I'm working on a project where we use Hibernate and JBoss 5.1. We need our entity classes to be mapped to Oracle tables that follow a certain naming convention. I'd like to avoid having to specify each table and column name in annotations. Therefore, I'm currently considering implementing a custom implementation of org.hibernate.cfg.NamingStrategy. The SQL naming conventions require the name of columns to have a suffix that is equivalent to a prefix of the table name. If there is a table "T100_RESOURCE", the ID column would have to be named "RES_ID_T100". In order to implement this in a NamingStrategy, the implementation would have to maintain state, i.e. the current class name it is creating the mappings for. It would rely on Hibernate to always call classToTableName() before propertyToColumnName() and to determine all column names by calling propertyToColumnName() before the next call to classToTableName() Is it safe to do that or are there situations where Hibernate will mix things up? I am not thinking of problems through multiple threads here (which can be solved by keeping the last class name in a ThreadLocal) but also of Hibernate deliberately calling this out of order in certain circumstances. For example Hibernate asking for mappings of three properties of class A, then one of class B, then again more attributes of class A.

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