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  • When is @uncheckedVariance needed in Scala, and why is it used in GenericTraversableTemplate?

    - by retronym
    @uncheckedVariance can be used to bridge the gap between Scala's declaration site variance annotations and Java's invariant generics. scala import java.util.Comparator import java.util.Comparator scala trait Foo[T] extends Comparator[T] defined trait Foo scala trait Foo[-T] extends Comparator[T] :5: error: contravariant type T occurs in invariant position in type [-T]java.lang.Object with java.util.Comparator[T] of trait Foo trait Foo[-T] extends Comparator[T] ^ scala import annotation.unchecked._ import annotation.unchecked._ scala trait Foo[-T] extends Comparator[T @uncheckedVariance] defined trait Foo This says that java.util.Comparator is naturally contra-variant, that is the type parameter T appears in parameters and never in a return type. Which begs the question, why is it also used in the Scala collections library: trait GenericTraversableTemplate[+A, +CC[X] <: Traversable[X]] extends HasNewBuilder[A, CC[A] @uncheckedVariance] What are the valid uses for this annotation?

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  • Accessing type-parameter of a type-parameter

    - by itemState
    i would like to access, in a trait, the type-parameter of a type-parameter of that trait. without adding this "second-order" type-parameter as another "first-order" parameter to the trait. the following illustrates this problem: sealed trait A; sealed trait A1 extends A; sealed trait A2 extends A trait B[ ASpecific <: A ] { type ASpec = ASpecific } trait D[ ASpecific <: A ] extends B[ ASpecific ] trait C[ +BSpecific <: B[ _ <: A ]] { def unaryOp : C[ D[ BSpecific#ASpec ]] } def test( c: C[ B[ A1 ]]) : C[ D[ A1 ]] = c.unaryOp the test fails to compile because apparently, the c.unaryOp has a result of type C[D[A]] and not C[D[A1]], indicating that ASpec is merely a shortcut for _ <: A and does not refer to the specific type parameter. the two-type-parameter solution is simple: sealed trait A; sealed trait A1 extends A; sealed trait A2 extends A trait B[ ASpecific <: A ] trait D[ ASpecific <: A ] extends B[ ASpecific ] trait C[ ASpecific <: A, +BSpecific <: B[ ASpecific ]] { def unaryOp : C[ ASpecific, D[ ASpecific ]] } def test( c: C[ A1, B[ A1 ]]) : C[ A1, D[ A1 ]] = c.unaryOp but i don't understand why i need to clutter my source with this second, obviously redundant, parameter. is there no way to retrieve it from trait B?

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  • What would be different in Java if Enum declaration didn't have the recursive part

    - by atamur
    Please see http://stackoverflow.com/questions/211143/java-enum-definition and http://stackoverflow.com/questions/3061759/why-in-java-enum-is-declared-as-enume-extends-enume for general discussion. Here I would like to learn what exactly would be broken (not typesafe anymore, or requiring additional casts etc) if Enum class was defined as public class Enum<E extends Enum> I'm using this code for testing my ideas: interface MyComparable<T> { int myCompare(T o); } class MyEnum<E extends MyEnum> implements MyComparable<E> { public int myCompare(E o) { return -1; } } class FirstEnum extends MyEnum<FirstEnum> {} class SecondEnum extends MyEnum<SecondEnum> {} With it I wasn't able to find any benefits in this exact case. PS. the fact that I'm not allowed to do class ThirdEnum extends MyEnum<SecondEnum> {} when MyEnum is defined with recursion is a) not relevant, because with real enums you are not allowed to do that just because you can't extend enum yourself b) not true - pls try it in a compiler and see that it in fact is able to compile w/o any errors PPS. I'm more and more inclined to believe that the correct answer here would be "nothing would change if you remove the recursive part" - but I just can't believe that.

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  • Overloading generic implicit conversions

    - by raichoo
    Hi I'm having a little scala (version 2.8.0RC1) problem with implicit conversions. Whenever importing more than one implicit conversion the first one gets shadowed. Here is the code where the problem shows up: // containers class Maybe[T] case class Nothing[T]() extends Maybe[T] case class Just[T](value: T) extends Maybe[T] case class Value[T](value: T) trait Monad[C[_]] { def >>=[A, B](a: C[A], f: A => C[B]): C[B] def pure[A](a: A): C[A] } // implicit converter trait Extender[C[_]] { class Wrapper[A](c: C[A]) { def >>=[B](f: A => C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, f) } def >>[B](b: C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, { (x: A) => b } ) } } implicit def extendToMonad[A](c: C[A]) = new Wrapper[A](c) } // instance maybe object maybemonad extends Extender[Maybe] { implicit object MaybeMonad extends Monad[Maybe] { override def >>=[A, B](a: Maybe[A], f: A => Maybe[B]): Maybe[B] = { a match { case Just(x) => f(x) case Nothing() => Nothing() } } override def pure[A](a: A): Maybe[A] = Just(a) } } // instance value object identitymonad extends Extender[Value] { implicit object IdentityMonad extends Monad[Value] { override def >>=[A, B](a: Value[A], f: A => Value[B]): Value[B] = { a match { case Value(x) => f(x) } } override def pure[A](a: A): Value[A] = Value(a) } } import maybemonad._ //import identitymonad._ object Main { def main(args: Array[String]): Unit = { println(Just(1) >>= { (x: Int) => MaybeMonad.pure(x) }) } } When uncommenting the second import statement everything goes wrong since the first "extendToMonad" is shadowed. However, this one works: object Main { implicit def foo(a: Int) = new { def foobar(): Unit = { println("Foobar") } } implicit def foo(a: String) = new { def foobar(): Unit = { println(a) } } def main(args: Array[String]): Unit = { 1 foobar() "bla" foobar() } } So, where is the catch? What am I missing? Regards, raichoo

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  • Java Generic Type and Reflection

    - by Tom Tucker
    I have some tricky generic type problem involving reflection. Here's the code. public @interface MyConstraint { Class<? extends MyConstraintValidator<?>> validatedBy(); } public interface MyConstraintValidator<T extends Annotation> { void initialize(T annotation); } /** @param annotation is annotated with MyConstraint. */ public void run(Annotation annotation) { Class<? extends MyConstraintValidator<? extends Annotation>> validatorClass = annotation.annotationType().getAnnotation(MyConstraint.class).validatedBy(); validatorClass.newInstance().initialize(annotation) // will not compile! } The run() method above will not compile because of the following error. The method initialize(capture#10-of ? extends Annotation) in the type MyConstraintValidator<capture#10-of ? extends Annotation> is not applicable for the arguments (Annotation) If I remove the wild cards, then it compiles and works fine. What would be the propert way to declare the type parameter for the vairable validatorClass? Thanks.

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  • How can I make a universal construction more efficient?

    - by VF1
    A "universal construction" is a wrapper class for a sequential object that enables it to be linearized (a strong consistency condition for concurrent objects). For instance, here's an adapted wait-free construction, in Java, from [1], which presumes the existence of a wait-free queue that satisfies the interface WFQ (which only requires one-time consensus between threads) and assumes a Sequential interface: public interface WFQ<T> // "FIFO" iteration { int enqueue(T t); // returns the sequence number of t Iterable<T> iterateUntil(int max); // iterates until sequence max } public interface Sequential { // Apply an invocation (method + arguments) // and get a response (return value + state) Response apply(Invocation i); } public interface Factory<T> { T generate(); } // generate new default object public interface Universal extends Sequential {} public class SlowUniversal implements Universal { Factory<? extends Sequential> generator; WFQ<Invocation> wfq = new WFQ<Invocation>(); Universal(Factory<? extends Sequential> g) { generator = g; } public Response apply(Invocation i) { int max = wfq.enqueue(i); Sequential s = generator.generate(); for(Invocation invoc : wfq.iterateUntil(max)) s.apply(invoc); return s.apply(i); } } This implementation isn't very satisfying, however, since it presumes determinism of a Sequential and is really slow. I attempted to add memory recycling: public interface WFQD<T> extends WFQ<T> { T dequeue(int n); } // dequeues only when n is the tail, else assists other threads public interface CopyableSequential extends Sequential { CopyableSequential copy(); } public class RecyclingUniversal implements Universal { WFQD<CopyableSequential> wfqd = new WFQD<CopyableSequential>(); Universal(CopyableSequential init) { wfqd.enqueue(init); } public Response apply(Invocation i) { int max = wfqd.enqueue(i); CopyableSequential cs = null; int ctr = max; for(CopyableSequential csq : wfq.iterateUntil(max)) if(--max == 0) cs = csq.copy(); wfqd.dequeue(max); return cs.apply(i); } } Here are my specific questions regarding the extension: Does my implementation create a linearizable multi-threaded version of a CopyableSequential? Is it possible extend memory recycling without extending the interface (perhaps my new methods trivialize the problem)? My implementation only reduces memory when a thread returns, so can this be strengthened? [1] provided an implementation for WFQ<T>, not WFQD<T> - one does exist, though, correct? [1] Herlihy and Shavit, The Art of Multiprocessor Programming.

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  • Make a controller a superclass in MVC design pattern

    - by Nikola
    I am really confused how to handle this. I have: model.Outsider model.SubContractor (which extends Outsider) Basically, Outsider would mean Supplier, but SubContractor is not a Supplier itself so I had to divide it somehow. I used to have model.Outsider (super class of the two bellow) model.Supplier model.SubContractor But Supplier didn't have any unique fields so I have removed it (Was this correct?) So, continuing, I have db layer which has: db.DBOutsider db.DBSubContractor (which again extends the top one) And I have no place to put my Supplier methods. I can do that in DBOutsider, but then DBSubContractor (which extends DBOutsider) would get unnecessary methods. Do I create a DBSupplier even though there is no such class in the model layer? Then again, going to controller layer. It is the same situation as db layer. I have OutsiderController and SubContractorController (which extends the first one) (is this correct in first place? to have an extended controller?). But I have no place to put the methods which are concerned with Supplier and if I put them in the OutsiderController the SubContractorController would recieve unneccessary methods. At the moment I am going for the extra DBSupplier and SupplierController classes, but I have no idea if this is the correct way. Basically what perplexes me is the "empty" Supplier. Since it is supposed to be an Outsider but has no extra methods or fields, should there be an empty class?

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  • Changing State in PlayerControler from PlayerInput

    - by Jeremy Talus
    In my player input I wanna change the the "State" of my player controller but I have some trouble to do it my player input is declared like that : class ResistancePlayerInput extends PlayerInput within ResistancePlayerController config(ResistancePlayerInput); and in my playerControler I have that : class ResistancePlayerController extends GamePlayerController; var name PreviousState; DefaultProperties { CameraClass = class 'ResistanceCamera' //Telling the player controller to use your custom camera script InputClass = class'ResistanceGame.ResistancePlayerInput' DefaultFOV = 90.f //Telling the player controller what the default field of view (FOV) should be } simulated event PostBeginPlay() { Super.PostBeginPlay(); } auto state Walking { event BeginState(name PreviousStateName) { Pawn.GroundSpeed = 200; `log("Player Walking"); } } state Running extends Walking { event BeginState(name PreviousStateName) { Pawn.GroundSpeed = 350; `log("Player Running"); } } state Sprinting extends Walking { event BeginState(name PreviousStateName) { Pawn.GroundSpeed = 800; `log("Player Sprinting"); } } I have tried to use PCOwner.GotoState(); and ResistancePlayerController(PCOwner).GotoState(); but won't work. I have also tried a simple GotoState, and nothing happen how can I call GotoState for the PC Class from my player input ?

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  • Repository query conditions, dependencies and DRY

    - by vFragosop
    To keep it simple, let's suppose an application which has Accounts and Users. Each account may have any number of users. There's also 3 consumers of UserRepository: An admin interface which may list all users Public front-end which may list all users An account authenticated API which should only list it's own users Assuming UserRepository is something like this: class UsersRepository extends DatabaseAbstraction { private function query() { return $this->database()->select('users.*'); } public function getAll() { return $this->query()->exec(); } // IMPORTANT: // Tons of other methods for searching, filtering, // joining of other tables, ordering and such... } Keeping in mind the comment above, and the necessity to abstract user querying conditions, How should I handle querying of users filtering by account_id? I can picture three possible roads: 1. Should I create an AccountUsersRepository? class AccountUsersRepository extends UserRepository { public function __construct(Account $account) { $this->account = $account; } private function query() { return parent::query() ->where('account_id', '=', $this->account->id); } } This has the advantage of reducing the duplication of UsersRepository methods, but doesn't quite fit into anything I've read about DDD so far (I'm rookie by the way) 2. Should I put it as a method on AccountsRepository? class AccountsRepository extends DatabaseAbstraction { public function getAccountUsers(Account $account) { return $this->database() ->select('users.*') ->where('account_id', '=', $account->id) ->exec(); } } This requires the duplication of all UserRepository methods and may need another UserQuery layer, that implements those querying logic on chainable way. 3. Should I query UserRepository from within my account entity? class Account extends Entity { public function getUsers() { return UserRepository::findByAccountId($this->id); } } This feels more like an aggregate root for me, but introduces dependency of UserRepository on Account entity, which may violate a few principles. 4. Or am I missing the point completely? Maybe there's an even better solution? Footnotes: Besides permissions being a Service concern, in my understanding, they shouldn't implement SQL query but leave that to repositories since those may not even be SQL driven.

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  • PHP MVC Framework Structure

    - by bigstylee
    I am sorry about the amount of code here. I have tried to show enough for understanding while avoiding confusion (I hope). I have included a second copy of the code at Pastebin. (The code does execute without error/notice/warning.) I am currently creating a Content Management System while trying to implement the idea of Model View Controller. I have only recently come across the concept of MVC (within the last week) and trying to implement this into my current project. One of the features of the CMS is dynamic/customisable menu areas and each feature will be represented by a controller. Therefore there will be multiple versions of the Controller Class, each with specific extended functionality. I have looked at a number of tutorials and read some open source solutions to the MVC Framework. I am now trying to create a lightweight solution for my specific requirements. I am not interested in backwards compatibility, I am using PHP 5.3. An advantage of the Base class is not having to use global and can directly access any loaded class using $this->Obj['ClassName']->property/function();. Hoping to get some feedback using the basic structure outlined (with performance in mind). Specifically; a) Have I understood/implemented the concept of MVC correctly? b) Have I understood/implemented Object Orientated techniques with PHP 5 correctly? c) Should the class propertise of Base be static? d) Improvements? Thank you very much in advance! <?php /* A "Super Class" that creates/stores all object instances */ class Base { public static $Obj = array(); // Not sure this is the correct use of the "static" keyword? public static $var; static public function load_class($directory, $class) { echo count(self::$Obj)."\n"; // This does show the array is getting updated and not creating a new array :) if (!isset(self::$Obj[$class]) && !is_object(self::$Obj[$class])) //dont want to load it twice { /* Locate and include the class file based upon name ($class) */ return self::$Obj[$class] = new $class(); } return TRUE; } } /* Loads general configuration objects into the "Super Class" */ class Libraries extends Base { public function __construct(){ $this->load_class('library', 'Database'); $this->load_class('library', 'Session'); self::$var = 'Hello World!'; //testing visibility /* Other general funciton classes */ } } class Database extends Base { /* Connects to the the database and executes all queries */ public function query(){} } class Session extends Base { /* Implements Sessions in database (read/write) */ } /* General functionality of controllers */ abstract class Controller extends Base { protected function load_model($class, $method) { /* Locate and include the model file */ $this->load_class('model', $class); call_user_func(array(self::$Obj[$class], $method)); } protected function load_view($name) { /* Locate and include the view file */ #include('views/'.$name.'.php'); } } abstract class View extends Base { /* ... */ } abstract class Model extends Base { /* ... */ } class News extends Controller { public function index() { /* Displays the 5 most recent News articles and displays with Content Area */ $this->load_model('NewsModel', 'index'); $this->load_view('news', 'index'); echo $this->var; } public function menu() { /* Displays the News Title of the 5 most recent News articles and displays within the Menu Area */ $this->load_model('news/index'); $this->load_view('news/index'); } } class ChatBox extends Controller { /* ... */ } /* Lots of different features extending the controller/view/model class depending upon request and layout */ class NewsModel extends Model { public function index() { echo $this->var; self::$Obj['Database']->query(/*SELECT 5 most recent news articles*/); } public function menu() { /* ... */ } } $Libraries = new Libraries; $controller = 'News'; // Would be determined from Query String $method = 'index'; // Would be determined from Query String $Content = $Libraries->load_class('controller', $controller); //create the controller for the specific page if (in_array($method, get_class_methods($Content))) { call_user_func(array($Content, $method)); } else { die('Bad Request'. $method); } $Content::$var = 'Goodbye World'; echo $Libraries::$var . ' - ' . $Content::$var; ?> /* Ouput */ 0 1 2 3 Goodbye World! - Goodbye World

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  • Question about casting a class in Java with generics

    - by Florian F
    In Java 6 Class<? extends ArrayList<?>> a = ArrayList.class; gives and error, but Class<? extends ArrayList<?>> b = (Class<? extends ArrayList<?>>)ArrayList.class; gives a warning. Why is (a) an error? What is it, that Java needs to do in the assignment, if not the cast shown in (b)? And why isn't ArrayList compatible with ArrayList? I know one is "raw" and the other is "generic", but what is it you can do with an ArrayList and not with an ArrayList, or the other way around?

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  • How can I access bitmaps created in another activity?

    - by user22241
    I am currently loading my game bitmaps when the user presses 'start' in my animated splash screen activity (the first / launch activity) and the app progresses from my this activity to the main game activity, This is causing choppy animation in the splashscreen while it loads/creates the bitmaps for the new activity. I've been told that I should load all my bitmaps in one go at the very beginning. However, I can't work out how to do this - could anyone please point me in the right direction? I have 2 activities, a splash screen and the main game. Each consist of a class that extends activity and a class that extends SurfaceView (with an inner class for the rendering / logic updating). So, for example at the moment I am creating my bitmaps in the constructor of my SurfaceView class like so: public class OptionsScreen extends SurfaceView implements SurfaceHolder.Callback { //Create variables here public OptionsScreen(Context context) { Create bitmaps here } public void intialise(){ //This method is called from onCreate() of corresponding application context // Create scaled bitmaps here (from bitmaps previously created) }

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  • Separating Db from business with Inherited classes using multiple views

    - by catalinux
    I have a software that has a car model that will be used in different views (listing, ads, detail page, carousel, up sell widget,etc). class CarModel extends DbModel{ } I look for a "nice way" (a combination of flexible, easy to maintain,etc) to have this used in views. I'm thinking at two different ways Having object views for each context CarViewBase{ var car;// of type CarModel function constructor(args){ //will instantienta internal variable car based on args } function getThumb(){ } function getTitle(){ } } CarListingView extends CarViewBase{ function getListing(){ } } CarAdsView extends CarViewBase{ //the busines rule changes for ads widget function getThumb(){ } } Extending directly the CarModel The challenges comes when My Car Model might need an abstract factory. Let's say I have a field on my car object that states the type of the car : a truck, or a bike, or van. How would affect that my object view? Let's say that getTitle() rule would be different for each type of it. How would you do it?

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  • Roles / Profiles / Perspectives in NetBeans IDE 7.1

    - by Geertjan
    With a check out of main-silver from yesterday, I'm able to use the brand new "role" attribute in @TopComponent.Registration, as you can see below, in the bit in bold: @ConvertAsProperties(dtd = "-//org.role.demo.ui//Admin//EN", autostore = false) @TopComponent.Description(preferredID = "AdminTopComponent", //iconBase="SET/PATH/TO/ICON/HERE", persistenceType = TopComponent.PERSISTENCE_ALWAYS) @TopComponent.Registration(mode = "editor", openAtStartup = true, role="admin") public final class AdminTopComponent extends TopComponent { And here's a window for general users of the application, with the "role" attribute set to "user": @ConvertAsProperties(dtd = "-//org.role.demo.ui//User//EN", autostore = false) @TopComponent.Description(preferredID = "UserTopComponent", //iconBase="SET/PATH/TO/ICON/HERE", persistenceType = TopComponent.PERSISTENCE_ALWAYS) @TopComponent.Registration(mode = "explorer", openAtStartup = true, role="user") public final class UserTopComponent extends TopComponent { So, I have two windows. One is assigned to the "admin" role, the other to the "user" role. In the "ModuleInstall" class, I add a "WindowSystemListener" and set "user" as the application's role: public class Installer extends ModuleInstall implements WindowSystemListener { @Override public void restored() { WindowManager.getDefault().addWindowSystemListener(this); } @Override public void beforeLoad(WindowSystemEvent event) { WindowManager.getDefault().setRole("user"); WindowManager.getDefault().removeWindowSystemListener(this); } @Override public void afterLoad(WindowSystemEvent event) { } @Override public void beforeSave(WindowSystemEvent event) { } @Override public void afterSave(WindowSystemEvent event) { } } So, when the application starts, the "UserTopComponent" is shown, not the "AdminTopComponent". Next, I have two Actions, for switching between the two roles, as shown below: @ActionID(category = "Window", id = "org.role.demo.ui.SwitchToAdminAction") @ActionRegistration(displayName = "#CTL_SwitchToAdminAction") @ActionReferences({ @ActionReference(path = "Menu/Window", position = 250) }) @Messages("CTL_SwitchToAdminAction=Switch To Admin") public final class SwitchToAdminAction extends AbstractAction { @Override public void actionPerformed(ActionEvent e) { WindowManager.getDefault().setRole("admin"); } @Override public boolean isEnabled() { return !WindowManager.getDefault().getRole().equals("admin"); } } @ActionID(category = "Window", id = "org.role.demo.ui.SwitchToUserAction") @ActionRegistration(displayName = "#CTL_SwitchToUserAction") @ActionReferences({ @ActionReference(path = "Menu/Window", position = 250) }) @Messages("CTL_SwitchToUserAction=Switch To User") public final class SwitchToUserAction extends AbstractAction { @Override public void actionPerformed(ActionEvent e) { WindowManager.getDefault().setRole("user"); } @Override public boolean isEnabled() { return !WindowManager.getDefault().getRole().equals("user"); } } When I select one of the above actions, the role changes, and the other window is shown. I could, of course, add a Login dialog to the "SwitchToAdminAction", so that authentication is required in order to switch to the "admin" role. Now, let's say I am now in the "user" role. So, the "UserTopComponent" shown above is now opened. I decide to also open another window, the Properties window, as below... ...and, when I am in the "admin" role, when the "AdminTopComponent" is open, I decide to also open the Output window, as below... Now, when I switch from one role to the other, the additional window/s I opened will also be opened, together with the explicit members of the currently selected role. And, the main window position and size are also persisted across roles. When I look in the "build" folder of my project in development, I see two different Windows2Local folders, one per role, automatically created by the fact that there is something to be persisted for a particular role, e.g., when a switch to a different role is done: And, with that, we now clearly have roles/profiles/perspectives in NetBeans Platform applications from NetBeans Platform 7.1 onwards.

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  • Scala: How to combine parser combinators from different objects

    - by eed3si9n
    Given a family of objects that implement parser combinators, how do I combine the parsers? Since Parsers.Parser is an inner class, and in Scala inner classes are bound to the outer object, the story becomes slightly complicated. Here's an example that attempts to combine two parsers from different objects. import scala.util.parsing.combinator._ class BinaryParser extends JavaTokenParsers { def anyrep: Parser[Any] = rep(any) def any: Parser[Any] = zero | one def zero: Parser[Any] = "0" def one: Parser[Any] = "1" } object LongChainParser extends BinaryParser { def parser1: Parser[Any] = zero~zero~one~one } object ShortChainParser extends BinaryParser { def parser2: Parser[Any] = zero~zero } object ExampleParser extends BinaryParser { def parser: Parser[Any] = (LongChainParser.parser1 ||| ShortChainParser.parser2) ~ anyrep def main(args: Array[String]) { println(parseAll(parser, args(0) )) } } This results to the following error: <console>:11: error: type mismatch; found : ShortChainParser.Parser[Any] required: LongChainParser.Parser[?] def parser: Parser[Any] = (LongChainParser.parser1 ||| ShortChainParser.parser2) ~ anyrep I've found the solution to this problem already, but since it was brought up recently on scala-user ML (Problem injecting one parser into another), it's probably worth putting it here too.

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  • Abstract Base Class or Class?

    - by Mohit Deshpande
    For my semester project, my team and I are supposed to make a .jar file (library, not runnable) that contains a game development framework and demonstrate the concepts of OOP. Its supposed to be a FRAMEWORK and another team is supposed to use our framework and vice-versa. So I want to know how we should start. We thought of several approaches: 1. Start with a plain class public class Enemy { public Enemy(int x, int y, int health, int attack, ...) { ... } ... } public class UserDefinedClass extends Enemy { ... } 2. Start with an abstract class that user-defined enemies have to inherit abstract members public abstract class Enemy { public Enemy(int x, int y, int health, int attack, ...) { ... } public abstract void draw(); public abstract void destroy(); ... } public class UserDefinedClass extends Enemy { ... public void draw() { ... } public void destroy() { ... } } 3. Create a super ABC (Abstract Base Class) that ALL inherit from public abstract class VectorEntity { ... } public abstract class Enemy extends VectorEntity { ... } public class Player extends VectorEntity { ... } public class UserDefinedClass extends Enemy { ... } Which should I use? Or is there a better way?

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  • How to use objetcs as modules/functors in Scala?

    - by Jeff
    Hi. I want to use object instances as modules/functors, more or less as shown below: abstract class Lattice[E] extends Set[E] { val minimum: E val maximum: E def meet(x: E, y: E): E def join(x: E, y: E): E def neg(x: E): E } class Calculus[E](val lat: Lattice[E]) { abstract class Expr case class Var(name: String) extends Expr {...} case class Val(value: E) extends Expr {...} case class Neg(e1: Expr) extends Expr {...} case class Cnj(e1: Expr, e2: Expr) extends Expr {...} case class Dsj(e1: Expr, e2: Expr) extends Expr {...} } So that I can create a different calculus instance for each lattice (the operations I will perform need the information of which are the maximum and minimum values of the lattice). I want to be able to mix expressions of the same calculus but not be allowed to mix expressions of different ones. So far, so good. I can create my calculus instances, but problem is that I can not write functions in other classes that manipulate them. For example, I am trying to create a parser to read expressions from a file and return them; I also was trying to write an random expression generator to use in my tests with ScalaCheck. Turns out that every time a function generates an Expr object I can't use it outside the function. Even if I create the Calculus instance and pass it as an argument to the function that will in turn generate the Expr objects, the return of the function is not recognized as being of the same type of the objects created outside the function. Maybe my english is not clear enough, let me try a toy example of what I would like to do (not the real ScalaCheck generator, but close enough). def genRndExpr[E](c: Calculus[E], level: Int): Calculus[E]#Expr = { if (level > MAX_LEVEL) { val select = util.Random.nextInt(2) select match { case 0 => genRndVar(c) case 1 => genRndVal(c) } } else { val select = util.Random.nextInt(3) select match { case 0 => new c.Neg(genRndExpr(c, level+1)) case 1 => new c.Dsj(genRndExpr(c, level+1), genRndExpr(c, level+1)) case 2 => new c.Cnj(genRndExpr(c, level+1), genRndExpr(c, level+1)) } } } Now, if I try to compile the above code I get lots of error: type mismatch; found : plg.mvfml.Calculus[E]#Expr required: c.Expr case 0 = new c.Neg(genRndExpr(c, level+1)) And the same happens if I try to do something like: val boolCalc = new Calculus(Bool) val e1: boolCalc.Expr = genRndExpr(boolCalc) Please note that the generator itself is not of concern, but I will need to do similar things (i.e. create and manipulate calculus instance expressions) a lot on the rest of the system. Am I doing something wrong? Is it possible to do what I want to do? Help on this matter is highly needed and appreciated. Thanks a lot in advance.

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  • Niewbie OutOfMemory problem

    - by Nick
    So I am trying to create a producer/consumer type scala app. The LoopControl just sends a message to the MessageReceiver continoually. The MessageReceiver then delegates work to the MessageCreatorActor (whose work is to check a map for an object, and if not found create one and start it up). Each MessageActor created by this MessageCreatorActor is associated with an Id. Eventually this is where I want to do business logic. But I run out of memory after 15 minutes. Any help is appreciated import scala.actors.Actor import java.util.HashMap; import scala.actors.Actor._ case object LoopControl case object MessageReceiver case object MessageActor case object MessageActorCreator class MessageReceiver(msg: String) extends Actor { var messageActorMap = new HashMap[String, MessageActor] val messageCreatorActor = new MessageActorCreator(null, null) def act() { messageCreatorActor.start loop { react { case MessageActor(messageId) = if (msg.length() 0) { var messageActor = messageActorMap.get(messageId); if(messageActor == null) { messageCreatorActor ! MessageActorCreator(messageId, messageActorMap) }else { messageActor ! MessageActor } } } } } } case class MessageActorCreator(msg:String, messageActorMap: HashMap[String, MessageActor]) extends Actor { def act() { loop { react { case MessageActorCreator(messageId, messageActorMap) = if(messageId != null ) { var messageActor = new MessageActor(messageId); messageActorMap.put(messageId, messageActor) println(messageActorMap) messageActor.start messageActor ! MessageActor } } } } } class LoopControl(messageReceiver:MessageReceiver) extends Actor { var count : Int = 0; def act() { while (true) { messageReceiver ! MessageActor ("00-122-0X95-FEC0" + count) //Thread.sleep(100) count = count +1; if(count 5) { count = 0; } } } } case class MessageActor(msg: String) extends Actor { def act() { loop { react { case MessageActor = println() println("MessageActor: Got something- " + msg) } } } } object messages extends Application { val messageReceiver = new MessageReceiver("bootstrap") val loopControl = new LoopControl(messageReceiver) messageReceiver.start loopControl.start }

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  • How to register a custom type in Hibernate using org.springframework.orm.hibernate4.LocalSessionFactoryBean

    - by Luis
    I'm migrating from hibernate 3 to hibernate 4, In hibernate 3 the way I was registering a custom type was: public class AnnotationSessionFactoryBean extends org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean { private Collection<? extends BasicType> customTypes; public Collection<? extends BasicType> getCustomTypes() { return customTypes; } public void setCustomTypes(Collection<? extends BasicType> customTypes) { this.customTypes = customTypes; } @Override protected Configuration newConfiguration() throws HibernateException { Configuration configuration = super.newConfiguration(); if (CollectionUtils.hasEntries(customTypes)) { for (BasicType customType:customTypes) { configuration.registerTypeOverride(customType); } } return configuration; }} I'm now trying to do the same operation but using hibernate 4, my question is how is the best way to do this? since I dont have access do change configuration when using "org.springframework.orm.hibernate4.LocalSessionFactoryBean" instead of "org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean". Thanks

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  • GWT CssResource Customization

    - by Eric Landry
    I'm writing a GWT widget using UIBinder and MVP. The widget's default styles are defined in TheWidgetView.ui.xml: <ui:style type="com.widgetlib.spinner.display.TheWidgetView.MyStyle"> .textbox { border: 1px solid #red; } .important { font-weight: bold; } </ui:style> The widget's CssResource interface is defined in TheWidgetView.java: public class TheWidgetView extends HorizontalPanel implements TheWidgetPresenter.Display { // ... some code @UiField MyStyle style; public interface MyStyle extends CssResource { String textbox(); String important(); } // ... more code } I'd like the consumer of this widget to be able to customize part of the widget's styles and to have this in their MyExample.ui.xml: <ui:style type="com.consumer.MyExample.MyStyle"> .textbox { border: 2px solid #black; } </ui:style> And this be their MyExample.java: public class MyExample extends Composite { // ... some code @UiField MyStyle style; interface MyStyle extends TheWidgetView.MyStyle{ String textbox(); } // ... more code } Is there a way that my widget can have default styles, but that the consumer of the widget can override one of them? When an interface extends TheWidgetView.MyStyle, the of the widget consumer needs to define all the styles listed in that parent interface. I've seen some widget libraries have the widget's constructor take in a ClientBundle as parameter, which I suppose could apply to CssResource. Although, I'm not sure how I'd pass in this style object in a constructor invoked by UIBinder. Thanks much in advance!

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  • Question concerning SCJP-6 exam

    - by abatishchev
    While preparing for the SCJP-6 exam I faced with a difficult issue. I can’t find answer by myself. Please, answer for the question and give short comments: abstract class A<K> extends Number> { // insert code here } public abstract <K> A<? extends Number> useMe(A<? super K> k); public abstract <K> A<? super Number> useMe(A<? extends K> k); public abstract <K> A<K> useMe(A<K> k); public abstract <V extends K> A<V> useMe(A<V> k); public abstract <V super K> A<V> useMe(A<V> k); public abstract <V extends Character> A<? super V> useMe(A<K> k); public abstract <V super Character> A<? super V> useMe(A<K> k); Which method can be inserted in a placeholder above? P.S. I tried to look on the specification. Those one was not helpful for me.

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  • Creating circular generic references

    - by M. Jessup
    I am writing an application to do some distributed calculations in a peer to peer network. In defining the network I have two class the P2PNetwork and P2PClient. I want these to be generic and so have the definitions of: P2PNetwork<T extends P2PClient<? extends P2PNetwork<T>>> P2PClient<T extends P2PNetwork<? extends T>> with P2PClient defining a method of setNetwork(T network). What I am hoping to describe with this code is: A P2PNetwork is constituted of clients of a certain type A P2PClient may only belong to a network whose clients consist of the same type as this client (the circular-reference) This seems correct to me but if I try to create a non-generic version such as MyP2PClient<MyP2PNetwork<? extends MyP2PClient>> myClient; and other variants I receive numerous errors from the compiler. So my questions are as follows: Is a generic circular reference even possible (I have never seen anything explicitly forbidding it)? Is the above generic definition a correct definition of such a circular relationship? If it is valid, is it the "correct" way to describe such a relationship (i.e. is there another valid definition, which is stylistically preferred)? How would I properly define a non-generic instance of a Client and Server given the proper generic definition?

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  • Extending Controller

    - by MakDotGNU
    Hi, I'm very new to Kohana and I'm trying to make a project in kohana 2.x, in my previous projects i had created a Base controller which used to extends Controller. and all other controller to Base_Controller. in Kohana I'm facing the problem. here is my structure. class Base_Controller extends Template_Controller class Home_Controller extends Base_Controller both these Controllers are in application/controller folder Fatal error: Class 'Base_Controller' not found in /home/myadav/public_html/innteract/innteract/controllers/home.php on line 2

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  • Extending the IndexController with a BaseController in Zend

    - by BillA
    I'm trying to extend my controllers with a global base controller as such: class BaseController extends Zend_Controller_Action { // common controller actions public function listAction() { // do stuff } } class IndexController extends BaseController { // index controller specific actions } class LoginController extends BaseController { // login controller specific actions } But I get this error: PHP Fatal error: Class 'BaseController' not found in /var/www/Zend/project/application/controllers/IndexController.php on line 3 Any ideas on how to get Zend to "see" this controller?

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