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  • Can't declare an abstract method private....

    - by Zombies
    I want to do this, yet I can't. Here is my scenario and rational. I have an abstract class for test cases that has an abstract method called test(). The test() method is to be defined by the subclass; it is to be implemented with logic for a certain application, such as CRMAppTestCase extends CompanyTestCase. I don't want the test() method to be invoked directly, I want the super class to call the test() method while the sub class can call a method which calls this (and does other work too, such as setting a current date-time right before the test is executed for example). Example code: public abstract class CompanyTestCase { //I wish this would compile, but it cannot be declared private private abstract void test(); public TestCaseResult performTest() { //do some work which must be done and should be invoked whenever //this method is called (it would be improper to expect the caller // to perform initialization) TestCaseResult result = new TestCaseResult(); result.setBeginTime(new Date()); long time = System.currentTimeMillis(); test(); //invoke test logic result.setDuration(System.currentTimeMillis() - time); return result; } } Then to extend this.... public class CRMAppTestCase extends CompanyTestCase { public void test() { //test logic here } } Then to call it.... TestCaseResult result = new CRMAppTestCase().performTest();

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  • C#&ndash;Using a delegate to raise an event from one class to another

    - by Bill Osuch
    Even though this may be a relatively common task for many people, I’ve had to show it to enough new developers that I figured I’d immortalize it… MSDN says “Events enable a class or object to notify other classes or objects when something of interest occurs. The class that sends (or raises) the event is called the publisher and the classes that receive (or handle) the event are called subscribers.” Any time you add a button to a Windows Form or Web app, you can subscribe to the OnClick event, and you can also create your own event handlers to pass events between classes. Here I’ll show you how to raise an event from a separate class to a console application (or Windows Form). First, create a console app project (you could create a Windows Form, but this is easier for this demo). Add a class file called MyEvent.cs (it doesn’t really need to be a separate file, this is just for clarity) with the following code: public delegate void MyHandler1(object sender, MyEvent e); public class MyEvent : EventArgs {     public string message; } Your event can have whatever public properties you like; here we’re just got a single string. Next, add a class file called WorkerDLL.cs; this will simulate the class that would be doing all the work in the project. Add the following code: class WorkerDLL {     public event MyHandler1 Event1;     public WorkerDLL()     {     }     public void DoWork()     {         FireEvent("From Worker: Step 1");         FireEvent("From Worker: Step 5");         FireEvent("From Worker: Step 10");     }     private void FireEvent(string message)     {         MyEvent e1 = new MyEvent();         e1.message = message;         if (Event1 != null)         {             Event1(this, e1);         }         e1 = null;     } } Notice that the FireEvent method creates an instance of the MyEvent class and passes it to the Event1 handler (which we’ll create in just a second). Finally, add the following code to Program.cs: static void Main(string[] args) {     Program p = new Program(args); } public Program(string[] args) {     Console.WriteLine("From Console: Creating DLL");     WorkerDLL wd = new WorkerDLL();     Console.WriteLine("From Console: Wiring up event handler");     WireEventHandlers(wd);     Console.WriteLine("From Console: Doing the work");     wd.DoWork();     Console.WriteLine("From Console: Done - press any key to finish.");     Console.ReadLine(); } private void WireEventHandlers(WorkerDLL wd) {     MyHandler1 handler = new MyHandler1(OnHandler1);     wd.Event1 += handler; } public void OnHandler1(object sender, MyEvent e) {     Console.WriteLine(e.message); } The OnHandler1 method is called any time the event handler “hears” an event matching the specified signature – you could have it log to a file, write to a database, etc. Run the app in debug mode and you should see output like this: You can distinctly see which lines were written by the console application itself (Program.cs) and which were written by the worker class (WorkerDLL.cs). Technorati Tags: Csharp

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  • Series of abstract classes and NHibernate

    - by Chris Cowdery-Corvan
    Hello, and first off thanks for your time to look at this. For a research project I'm working on, I have a somewhat complex design (which I've been given) to persist to a database via NHibernate. Here's an example of the class hierarchy: TransitStrategy, TransportationCompany and TransportationLocation are all abstract classes. The XML configuration I have is presently: <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Vacationizer" namespace="Vacationizer.Domain.Transit"> <class name="TransitStrategy"> <id name="TransitStrategyId"> <generator class="guid" /> </id> <property name="Restrictions" /> <joined-subclass name="Flight" table="Flight_TransitStrategy"> <key column="TransitStrategyId" /> <property name="DepartingAirport" /> <property name="ArrivingAirport" /> <property name="Airline" /> <property name="FlightNumber" /> <property name="FlightArrivalTime" /> <property name="FlightDepartureTime" /> </joined-subclass> <joined-subclass name="RentalCar" table="RentalCar_TransitStrategy"> <key column="TransitStrategyId" /> <property name="RentalCarBranch" /> <property name="CarMake" /> <property name="CarModel" /> <property name="CarYear" /> <property name="CarColor" /> <property name="RentalBegins" /> <property name="RentalEnds" /> </joined-subclass> </class> <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Vacationizer" namespace="Vacationizer.Domain.Transit"> <class name="TransportationCompany"> <id name="TransportationCompanyId"> <generator class="guid" /> </id> <property name="Name" /> <property name="Reviews" /> <property name="Website" /> <property name="Photo" /> <joined-subclass name="Airline" table="Airline_TransportationCompany"> <key column="TransportationLocationId" /> </joined-subclass> <joined-subclass name="RentalCarAgency" table="RentalCarAgency_TransportationCompany"> <key column="TransportationLocationId" /> </joined-subclass> </class> <?xml version="1.0" encoding="utf-8" ?> <hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="Vacationizer" namespace="Vacationizer.Domain.Transit"> <class name="TransportationLocation"> <id name="TransportationLocationId"> <generator class="guid" /> </id> <property name="Name" /> <property name="Image" /> <property name="Geolocation" /> <property name="Reviews" /> <!-- <property name="HoursOpen" />--> <property name="PhoneNumber" /> <property name="FaxNumber" /> <joined-subclass name="Airport" table="Airport_TransportationLocation"> <key column="TransportationLocationId" /> <property name="AirportCode" /> <property name="Website" /> </joined-subclass> <joined-subclass name="RentalCarBranch" table="RentalCarBranch_TransportationLocation"> <key column="TransitStrategyId" /> <property name="Agency" /> </joined-subclass> </class> However, whenever I try to use this schema I get this error/stack trace: ------ Test started: Assembly: Vacationizer.Tests.dll ------ TestCase 'M:Vacationizer.Tests.VacationRepository_Fixture.TestFixtureSetUp' failed: Could not compile the mapping document: Vacationizer.Mappings.TransitStrategy.hbm.xml NHibernate.MappingException: Could not compile the mapping document: Vacationizer.Mappings.TransitStrategy.hbm.xml ---> NHibernate.MappingException: Problem trying to set property type by reflection ---> NHibernate.MappingException: class Vacationizer.Domain.Transit.RentalCar, Vacationizer, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null not found while looking for property: RentalCarBranch ---> NHibernate.PropertyNotFoundException: Could not find a getter for property 'RentalCarBranch' in class 'Vacationizer.Domain.Transit.RentalCar' at NHibernate.Properties.BasicPropertyAccessor.GetGetter(Type type, String propertyName) at NHibernate.Util.ReflectHelper.ReflectedPropertyClass(String className, String name, String accessorName) --- End of inner exception stack trace --- at NHibernate.Util.ReflectHelper.ReflectedPropertyClass(String className, String name, String accessorName) at NHibernate.Mapping.SimpleValue.SetTypeUsingReflection(String className, String propertyName, String accesorName) --- End of inner exception stack trace --- at NHibernate.Mapping.SimpleValue.SetTypeUsingReflection(String className, String propertyName, String accesorName) at NHibernate.Cfg.XmlHbmBinding.ClassBinder.CreateProperty(IValue value, String propertyName, String className, XmlNode subnode, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.ClassBinder.PropertiesFromXML(XmlNode node, PersistentClass model, IDictionary`2 inheritedMetas, UniqueKey uniqueKey, Boolean mutable, Boolean nullable, Boolean naturalId) at NHibernate.Cfg.XmlHbmBinding.JoinedSubclassBinder.HandleJoinedSubclass(PersistentClass model, XmlNode subnode, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.ClassBinder.PropertiesFromXML(XmlNode node, PersistentClass model, IDictionary`2 inheritedMetas, UniqueKey uniqueKey, Boolean mutable, Boolean nullable, Boolean naturalId) at NHibernate.Cfg.XmlHbmBinding.RootClassBinder.Bind(XmlNode node, HbmClass classSchema, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.MappingRootBinder.AddRootClasses(XmlNode parentNode, IDictionary`2 inheritedMetas) at NHibernate.Cfg.XmlHbmBinding.MappingRootBinder.Bind(XmlNode node) at NHibernate.Cfg.Configuration.AddValidatedDocument(NamedXmlDocument doc) --- End of inner exception stack trace --- at NHibernate.Cfg.Configuration.LogAndThrow(Exception exception) at NHibernate.Cfg.Configuration.AddValidatedDocument(NamedXmlDocument doc) at NHibernate.Cfg.Configuration.ProcessMappingsQueue() at NHibernate.Cfg.Configuration.AddDocumentThroughQueue(NamedXmlDocument document) at NHibernate.Cfg.Configuration.AddXmlReader(XmlReader hbmReader, String name) at NHibernate.Cfg.Configuration.AddInputStream(Stream xmlInputStream, String name) at NHibernate.Cfg.Configuration.AddResource(String path, Assembly assembly) at NHibernate.Cfg.Configuration.AddAssembly(Assembly assembly) at NHibernate.Cfg.Configuration.AddAssembly(String assemblyName) at NHibernate.Cfg.Configuration.DoConfigure(IHibernateConfiguration hc) at NHibernate.Cfg.Configuration.Configure() VacationRepository_Fixture.cs(24,0): at Vacationizer.Tests.VacationRepository_Fixture.TestFixtureSetUp() 0 passed, 1 failed, 0 skipped, took 8.38 seconds (Ad hoc). Any ideas on how I can implement this differently? Thanks very much!

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  • How to get table cells evenly spaced?

    - by DaveDev
    I'm trying to create a page with a number of static html tables on them. What do I need to do to get them to display each column the same size as each other column in the table? The HTML is as follows: <span class="Emphasis">Interest rates</span><br /> <table cellpadding="0px" cellspacing="0px" class="PerformanceTable"> <tr><th class="TableHeader"></th><th class="TableHeader">Current rate as at 31 March 2010</th><th class="TableHeader">31 December 2009</th><th class="TableHeader">31 March 2009</th></tr> <tr class="TableRow"><td>Index1</td><td class="PerformanceCell">1.00%</td><td>1.00%</td><td>1.50%</td></tr> <tr class="TableRow"><td>index2</td><td class="PerformanceCell">0.50%</td><td>0.50%</td><td>0.50%</td></tr> <tr class="TableRow"><td>index3</td><td class="PerformanceCell">0.25%</td><td>0.25%</td><td>0.25%</td></tr> </table> <span>Source: Bt</span><br /><br /> <span class="Emphasis">Stock markets</span><br /> <table cellpadding="0px" cellspacing="0px" class="PerformanceTable"> <tr><th class="TableHeader"></th><th class="TableHeader">As at 31 March 2010</th><th class="TableHeader">1 month change</th><th class="TableHeader">QTD change</th><th class="TableHeader">12 months change</th></tr> <tr class="TableRow"><td>index1</td><td class="PerformanceCell">1169.43</td><td class="PerformanceCell">5.88%</td><td class="PerformanceCell">4.87%</td><td class="PerformanceCell">46.57%</td></tr> <tr class="TableRow"><td>index2</td><td class="PerformanceCell">1958.34</td><td class="PerformanceCell">7.68%</td><td class="PerformanceCell">5.27%</td><td class="PerformanceCell">58.31%</td></tr> <tr class="TableRow"><td>index3</td><td class="PerformanceCell">5679.64</td><td class="PerformanceCell">6.07%</td><td class="PerformanceCell">4.93%</td><td class="PerformanceCell">44.66%</td></tr> <tr class="TableRow"><td>index4</td><td class="PerformanceCell">2943.92</td><td class="PerformanceCell">8.30%</td><td class="PerformanceCell">-0.98%</td><td class="PerformanceCell">44.52%</td></tr> <tr class="TableRow"><td>index5</td><td class="PerformanceCell">978.81</td><td class="PerformanceCell">9.47%</td><td class="PerformanceCell">7.85%</td><td class="PerformanceCell">26.52%</td></tr> <tr class="TableRow"><td>index6</td><td class="PerformanceCell">3177.77</td><td class="PerformanceCell">10.58%</td><td class="PerformanceCell">6.82%</td><td class="PerformanceCell">44.84%</td></tr> </table> <span>Source: B</span><br /><br /> I'm also open to suggestion on how to tidy this up, if there are any? :-)

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  • How do i use findAll method with a class in Doctrine?

    - by terrani
    Hi, I am a little bit confused with Doctrine class. I created a class and its base class in Doctrine. The class's name is User. so..I created an object of class User. $oUser = new User(); when I try to use findAll method, it does not work. I found the following code on the doctrine documentation. Doctrine_Core::getTable('User')-findAll(); I don't understand why i need to call getTable to use findAll method when I have User class. Am I missing something?

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  • Passing an instantiated class to concrete class derived by Castle Windsor

    - by Tr1stan
    I have a system that I'm using to test some new architecture. I have the following setup (In MVC2 .Net - C Sharp): View < Controller < Service < Repository < DB I'm using Castle Windsor as my DI (IoC) controller, and this is working just fine in both the Service and Repo layers. However, I'm now at a point where I would like to pass an Entity Framework (DatabaseNameEntity) to the constructor to the Service, and then to the Repo, so that I have something similar to a Unit of Work pattern per request (This feels like what I'm trying to achieve anyway) - and I'm having trouble working out how this can be done using Castle Windsor. Am I going off on a silly tangent? Any pointers appreciated.

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  • ZipArchive php Class, would this be the best approach??

    - by SoLoGHoST
    Ok, just wondering on the versions of PHP that this class is built into. And if they are built into all platforms (OS's). I'm wanting an approach to search through a zip file and place files using file_put_contents in different filepaths within the webroot. In any case, I'm familiar with how to do this with the ZipArchive class, but I'm wondering if using this class would be a good solution and support MOST, if not ALL servers?? I mean, I'd rather not use a method that requires the Server to have it installed. I'm looking for a solution to this that will support at least MOST servers without having to install the class... Thanks :) Also, I'd like to support opening tar.gz and/or .tgz files if possible, but I don't think the ZipArchive class supports this, but perhaps a different built-in php class does??

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  • ZipArchive php Class - Is it built-in to PHP?

    - by SoLoGHoST
    Ok, just wondering on the versions of PHP that this class is built into. And if they are built into all platforms (OS's). I'm wanting an approach to search through a zip file and place files using file_put_contents in different filepaths within the webroot. In any case, I'm familiar with how to do this with the ZipArchive class, but I'm wondering if using this class would be a good solution and support MOST, if not ALL servers?? I mean, I'd rather not use a method that requires the Server to have it installed. I'm looking for a solution to this that will support at least MOST servers without having to install the class... Thanks :) Also, I'd like to support opening tar.gz and/or .tgz files if possible, but I don't think the ZipArchive class supports this, but perhaps a different built-in php class does??

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  • abstract class in C++

    - by Alexander
    I have a derived derived class from an abstract class. The code is below. I have a FishTank class which is derived from an Aquarium and Aquarium is derived from item. My question is that should I put the definition of virtual int minWidth() const = 0; in aquarium again or is the code below sufficient? class Item{ public: virtual int minWidth() const = 0; }; class Aquarium{ public: virtual int calWidth() = 0; // Pure virtual function. }; class FishTank : public Aquarium{ public: FishTank(int base1, int base2, int height); ~FishTank(); int calWidth(); int minWidth(); };

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  • Java class Class<T> and static method Class.forName() drive me crazy.

    - by matt
    Hi, this code doesn't compile. i'm wandering what i am doing wrong: private static Importable getRightInstance(String s) throws Exception { Class<Importable> c = Class.forName(s); Importable i = c.newInstance(); return i; } where Importable is an interface and the string s is the name of an implementing class. The compiler says: ./Importer.java:33: incompatible types found : java.lang.Class<capture#964 of ?> required: java.lang.Class<Importable> Class<Importable> c = Class.forName(format(s)); thanks for any help!

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  • how to specify which child class this object belong to after retrieving from a hashmap?

    - by chandra wibowo
    hi everyone, i have a parent class called Course, and two child class PostgradCourse and UndergradCourse. i have a hashmap HashMap courses; i store all the postgradCourse and undergradCourse objects in the hashmap. i want to retrieve an undergradCourse object from the hashmap using the key. Course course = courses.get(courseCode); then i want to call a method in the UndergradCourse class, setUnits() method course.setUnits(); but the compiler say cannot find symbol- method setUnit() im pretty sure the problem is the compiler is looking for a method setUnit() in the Course class instead of UndergradCourse class i did this but its not working UndergradCourse course = courses.get(courseCode); results in incompatible type so how can i retrieve undergradCourse object from the hashmap as an undergradCourse object instead of course object? so then i can call a method inside the child class thanks in advance

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  • How to extend abstract Entity class in RIA Services

    - by Calanus
    I want to add a bool variable and property to the base Entity class in my RIA services project so that it is available throughout all the entity objects but seem unable to work out how to do this. I know that adding properties to actual entities themselves is easy using .shared.cs and partial classes but adding such properties to the Entity class using similar methods doesn't work. For example, the following code doesn't work namespace System.ServiceModel.DomainServices.Client { public abstract partial class Entity { private bool auditRequired; public bool AuditRequired { get { return auditRequired; } set { auditRequired = value; } } } } All that happens is that the existing Entity class gets totally overriden rather than extending the Entity class. How do I extend the base Entity class so that functionality is available thoughout all derived entity classes?

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  • Why isn't this simple test class's method inherited in Ruby?

    - by Kevin Bannister
    Consider this very simple logging class: class MockLog def self.log_stub_method(*args) args.each do |a| define_method "#{a}" do |msg| t = Time.now.strftime("%Y-%m-%d %H:%M:%S") $stderr.puts "[#{a.upcase}] \u00bb [#{t}] #{msg}" end end end log_stub_method :fatal, :error, :warn, :info, :debug end Let's add logging to all our classes: class Module def has_logging() class_eval { @log = MockLog.new def log self.class.instance_variable_get :@log end } end end Now, why doesn't this work? class Foo has_logging end Foo.new.log.nil? # => false, as expected class Bar < Foo end Bar.new.log.nil? # => true?! Why wasn't the `log` method inherited?

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  • app_label in an abstract Django model

    - by rayan
    Hi all, I'm trying to get an abstract model working in Django and I hit a brick wall trying to set the related_name per the recommendation here: http://docs.djangoproject.com/en/dev/topics/db/models/#be-careful-with-related-name This is what my abstract model looks like: class CommonModel(models.Model): created_on = models.DateTimeField(editable=False) creared_by = models.ForeignKey(User, related_name="%(app_label)s_%(class)s_created", editable=False) updated_on = models.DateTimeField(editable=False) updated_by = models.ForeignKey(User, related_name="%(app_label)s_%(class)s_updated", editable=False) def save(self): if not self.id: self.created_on = datetime.now() self.created_by = user.id self.updated_on = datetime.now() self.updated_by = user.id super(CommonModel, self).save() class Meta: abstract = True My common model is in [project_root]/models.py. It is the parent object of this model, which is located in an app called Feedback [project_root]/feedback/models.py: from django.db import models from mediasharks.models import CommonModel class Feedback(CommonModel): message = models.CharField(max_length=255) request_uri = models.CharField(max_length=255) domain = models.CharField(max_length=255) feedback_type = models.IntegerField() Basically I'm trying to set up a common model so that I'll always be able to tell when and by whom database entries were created. When I run "python manage.py validate" I get this error message: KeyError: 'app_label' Am I missing something here?

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  • c# 3.5 class List<int> class initialisation

    - by josephj1989
    I can initialize a List like new List{1,2,3,4,5}; However List does not have a constructor which accepts a single parameter. So I tried to run this through the debugger and it seems to be calling the Add method. So how does the compiler know which method to invoke to add each individual element. This may be a silly question but I am a bit confused. Thanks

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  • I want to be able to derive from a class internally, but disallow class in other assemblies to derive from the class

    - by Rokke
    Hej I have the following setup: Assembly 1 public abstract class XX<T> : XX where T: YY { } public abstract class XX {} Assembly 2 public class ZZ : YY {} public class ZZFriend : XX<ZZ> {} I use this feature in reflection when in YY: public class YY { public Type FindFriend { return GetType().Assembly.GetTypes().FirstOrDefault( t => t.BaseType != null && t.BaseType.IsGenericType && typeof(XX).IsAssignableFrom(t) && t.BaseType.GetGenericArguments().FirstOrDefault() == GetType()); } } I would like do disallow inheritance of the non generic class XX like: public class ZZFriend: XX {} Alternatively, I need a method like (that can be used in the reflection in YY.FindFrind()): public Type F(Type t) { return GetTypeThatIsGeneric(XX, Type genericTypeParameter); } That can be used in YY as: Typeof(XX<ZZ) == F(typeof(GetType()) Hope that makes sense... Thanks in advance Søren Rokkedal

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  • Abstract class get parameter from implementing subclass?

    - by soren.qvist
    I'm wondering if there is way to do this without breaking encapsulation, I want the abstract class to rely on parameters defined in the implementing subclass. Like so: public abstract class Parent { private int size; private List<String> someList; public Parent() { size = getSize(); someList = new ArrayList<String>(size); } public abstract int getSize(); } public class Child extends Parent { @Override public int getSize() { return 5; } } Is this ugly? Is there a better way? And perhaps more importantly, is this even a good idea?

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  • any way to simplify this with a form of dynamic class instantiation?

    - by gnychis
    I have several child classes that extend a parent class, forced to have a uniform constructor. I have a queue which keeps a list of these classes, which must extend MergeHeuristic. The code that I currently have looks like the following: Class<? extends MergeHeuristic> heuristicRequest = _heuristicQueue.pop(); MergeHeuristic heuristic = null; if(heuristicRequest == AdjacentMACs.class) heuristic = new AdjacentMACs(_parent); if(heuristicRequest == SimilarInterfaceNames.class) heuristic = new SimilarInterfaceNames(_parent); if(heuristicRequest == SameMAC.class) heuristic = new SameMAC(_parent); Is there any way to simplify that to dynamically instantiate the class, something along the lines of: heuristic = new heuristicRequest.somethingSpecial(); That would flatten that block of if statements.

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  • Call subclass constructor from abstract class in Java

    - by Joel
    public abstract class Parent { private Parent peer; public Parent() { peer = new ??????("to call overloaded constructor"); } public Parent(String someString) { } } public class Child1 extends parent { } public class Child2 extends parent { } When I construct an instance of Child1, I want a "peer" to automatically be constructed which is also of type Child1, and be stored in the peer property. Likewise for Child2, with a peer of type Child2. The problem is, on the assignment of the peer property in the parent class. I can't construct a new Child class by calling new Child1() because then it wouldn't work for Child2. How can I do this? Is there a keyword that I can use that would refer to the child class? Something like new self()?

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  • A Reusable Builder Class for Ruby Testing

    - by Liam McLennan
    My last post was about a class for building test data objects in C#. This post describes the same tool, but implemented in Ruby. The C# version was written first but I originally came up with the solution in my head using Ruby, and then I translated it to C#. The Ruby version was easier to write and is easier to use thanks to Ruby’s dynamic nature making generics unnecessary.  Here are my example domain classes: class Person attr_accessor :name, :age def initialize(name, age) @name = name @age = age end end class Property attr_accessor :street, :manager def initialize(street, manager) @street = street @manager = manager end end and the test class showing what the builder does: class Test_Builder < Test::Unit::TestCase def setup @build = Builder.new @build.configure({ Property => lambda { Property.new '127 Creek St', @build.a(Person) }, Person => lambda { Person.new 'Liam', 26 } }) end def test_create assert_not_nil @build end def test_can_get_a_person @person = @build.a(Person) assert_not_nil @person assert_equal 'Liam', @person.name assert_equal 26, @person.age end def test_can_get_a_modified_person @person = @build.a Person do |person| person.age = 999 end assert_not_nil @person assert_equal 'Liam', @person.name assert_equal 999, @person.age end def test_can_get_a_different_type_that_depends_on_a_type_that_has_not_been_configured_yet @my_place = @build.a(Property) assert_not_nil @my_place assert_equal '127 Creek St', @my_place.street assert_equal @build.a(Person).name, @my_place.manager.name end end Finally, the implementation of Builder: class Builder # defaults is a hash of Class => creation lambda def configure defaults @defaults = defaults end def a(klass) temp = @defaults[klass].call() yield temp if block_given? temp end end

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  • Strategies for invoking subclass methods on generic objects

    - by Brad Patton
    I've run into this issue in a number of places and have solved it a bunch of different ways but looking for other solutions or opinions on how to address. The scenario is when you have a collection of objects all based off of the same superclass but you want to perform certain actions based only on instances of some of the subclasses. One contrived example of this might be an HTML document made up of elements. You could have a superclass named HTMLELement and subclasses of Headings, Paragraphs, Images, Comments, etc. To invoke a common action across all of the objects you declare a virtual method in the superclass and specific implementations in all of the subclasses. So to render the document you could loop all of the different objects in the document and call a common Render() method on each instance. It's the case where again using the same generic objects in the collection I want to perform different actions for instances of specific subclass (or set of subclasses). For example (an remember this is just an example) when iterating over the collection, elements with external links need to be downloaded (e.g. JS, CSS, images) and some might require additional parsing (JS, CSS). What's the best way to handle those special cases. Some of the strategies I've used or seen used include: Virtual methods in the base class. So in the base class you have a virtual LoadExternalContent() method that does nothing and then override it in the specific subclasses that need to implement it. The benefit being that in the calling code there is no object testing you send the same message to each object and let most of them ignore it. Two downsides that I can think of. First it can make the base class very cluttered with methods that have nothing to do with most of the hierarchy. Second it assumes all of the work can be done in the called method and doesn't handle the case where there might be additional context specific actions in the calling code (i.e. you want to do something in the UI and not the model). Have methods on the class to uniquely identify the objects. This could include methods like ClassName() which return a string with the class name or other return values like enums or booleans (IsImage()). The benefit is that the calling code can use if or switch statements to filter objects to perform class specific actions. The downside is that for every new class you need to implement these methods and can look cluttered. Also performance could be less than some of the other options. Use language features to identify objects. This includes reflection and language operators to identify the objects. For example in C# there is the is operator that returns true if the instance matches the specified class. The benefit is no additional code to implement in your object hierarchy. The only downside seems to be the lack of using something like a switch statement and the fact that your calling code is a little more cluttered. Are there other strategies I am missing? Thoughts on best approaches?

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  • In Search Data Structure And Algorithm Project Title Based on Topic

    - by Salehin Suhaimi
    As the title says, my lecturer gave me a project that i needed to finish in 3 weeks before final semester exams. So i thought i will start now. The requirement is to "build a simple program that has GUI based on all the chapter that we've learned." But i got stuck on WHAT program should i build. Any idea a program that is related to this chapter i've learned? Any input will help. list, array list, linked list, vectors, stacks, Queues, ADT, Hashing, Binary Search Tree, AVL Tree, That's about all i can remember. Any idea where can i start looking?

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  • Python class representation under the hood

    - by decentralised
    OK, here is a simple Python class: class AddSomething(object): __metaclass__ = MyMetaClass x = 10 def __init__(self, a): self.a = a def add(self, a, b): return a + b We have specified a metaclass, and that means we could write something like this: class MyMetaClass(type): def __init__(cls, name, bases, cdict): # do something with the class Now, the cdict holds a representation of AddSomething: AddSomething = type('AddSomething', (object,), {'x' : 10, '__init__': __init__, 'add': add}) So my question is simple, are all Python classes represented in this second format internally? If not, how are they represented? EDIT - Python 2.7

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  • Do first-class methods exist?

    - by gdhoward
    Okay, I know first-class functions are cool, closures even better, etc. But is there any language with first-class methods? In my mind, I see a first-class method as an "object" that has both a function pointer and a pointer to a specific instance of the class/object, but the implementation doesn't matter. I just want to know if there is any language that uses them. And as a bonus, how were they implemented?

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