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  • Inheritance or identifier

    - by Lina
    Hi! Does anyone here have opinions about when to user inheritance and when to use an identifier instead? Inheritance example: class Animal { public int Name { get; set; } } class Dog : Animal {} class Cat : Animal {} Identifier example: class Animal { public int Name { get; set; } public AnimalType { get; set; } } In what situations should i prefer which solution and what are the pros and cons for them? /Lina

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  • Linq to SQL inheritance and Table per Class - approach needed for multiple roles

    - by Ash Machine
    I am using L2S and an inheritance model for mapping Persons against certain roles. Guy Burstein's excellent blog post explains how to accomplish this: http://blogs.microsoft.co.il/blogs/bursteg/archive/2007/10/01/linq-to-sql-inheritance.aspx However, I have a specific case where a Person has multiple roles. For example 'Jane Doe' is a Contact and a Programmer. In this model, she would need two rows in the People table, one as Contact (PersonType = 1) and one as Programmer (PersonType = 3). If she changes her last name, and that update happens in her role as Contact, I would need to change all instances of 'Jane Doe' to reflect the name change everywhere. What sort of best approach (improved data structure) could be used to change last name within all roles? Finally, I am hoping to avoid overriding each general form update events to include all instances, but that may be the only way. Any suggestions or approaches appreciated.

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  • Table per subclass inheritance relationship: How to query against the Parent class without loading a

    - by Arthur Ronald F D Garcia
    Suppose a Table per subclass inheritance relationship which can be described bellow (From wikibooks.org - see here) Notice Parent class is not abstract @Entity @Inheritance(strategy=InheritanceType.JOINED) public class Project { @Id private long id; // Other properties } @Entity @Table(name="LARGEPROJECT") public class LargeProject extends Project { private BigDecimal budget; } @Entity @Table(name="SMALLPROJECT") public class SmallProject extends Project { } I have a scenario where i just need to retrieve the Parent class. Because of performance issues, What should i do to run a HQL query in order to retrieve the Parent class and just the Parent class without loading any subclass ???

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  • Alternatives to multiple inheritance for my architecture (NPCs in a Realtime Strategy game)?

    - by Brettetete
    Coding isn't that hard actually. The hard part is to write code that makes sense, is readable and understandable. So I want to get a better developer and create some solid architecture. So I want to do create an architecture for NPCs in a video-game. It is a Realtime Strategy game like Starcraft, Age of Empires, Command & Conquers, etc etc.. So I'll have different kinds of NPCs. A NPC can have one to many abilities (methods) of these: Build(), Farm() and Attack(). Examples: Worker can Build() and Farm() Warrior can Attack() Citizen can Build(), Farm() and Attack() Fisherman can Farm() and Attack() I hope everything is clear so far. So now I do have my NPC Types and their abilities. But lets come to the technical / programmatical aspect. What would be a good programmatic architecture for my different kinds of NPCs? Okay I could have a base class. Actually I think this is a good way to stick with the DRY principle. So I can have methods like WalkTo(x,y) in my base class since every NPC will be able to move. But now lets come to the real problem. Where do I implement my abilities? (remember: Build(), Farm() and Attack()) Since the abilities will consists of the same logic it would be annoying / break DRY principle to implement them for each NPC (Worker,Warrior, ..). Okay I could implement the abilities within the base class. This would require some kind of logic that verifies if a NPC can use ability X. IsBuilder, CanBuild, .. I think it is clear what I want to express. But I don't feel very well with this idea. This sounds like a bloated base class with too much functionality. I do use C# as programming language. So multiple inheritance isn't an opinion here. Means: Having extra base classes like Fisherman : Farmer, Attacker won't work.

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  • Scala: Mixing traits with private fields

    - by Vilius Normantas
    It's not much of a question, it's rather my excitement that it's possible at all! I wrote this little example just to prove the opposite - I expected either a compiler error or one of the values (111 or 222, I wasn't sure). scala> trait T1 { private val v = 111; def getValueT1 = v } scala> trait T2 { private val v = 222; def getValueT2 = v } scala> class T12 extends T1 with T2 scala> val t = new T12 scala> t.getValueT1 res9: Int = 111 scala> t.getValueT2 res10: Int = 222 Why doesn't the v get overridden? Off course this works only as long as vs are private, but still.

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  • C++ inheritance: scoping and visibility of members

    - by Poiuyt
    Can you explain why this is not allowed, #include <stdio.h> class B { private: int a; public: int a; }; int main() { return 0; } while this is? #include <stdio.h> class A { public: int a; }; class B : public A{ private: int a; }; int main() { return 0; } In both the cases, we have one public and one private variable named a in class B. edited now!

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  • C++ inheritance doubt

    - by Poiuyt
    Can you explain why this is not allowed, #include <stdio.h> class B { private: int a; public: int a; }; int main() { return 0; } while this is? #include <stdio.h> class A { public: int a; }; class B : public A{ private: int a; }; int main() { return 0; } In both the cases, we have one public and one private variable named a in class B.

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  • C++ Exceptions and Inheritance from std::exception

    - by fbrereto
    Given this sample code: #include <iostream> #include <stdexcept> class my_exception_t : std::exception { public: explicit my_exception_t() { } virtual const char* what() const throw() { return "Hello, world!"; } }; int main() { try { throw my_exception_t(); } catch (const std::exception& error) { std::cerr << "Exception: " << error.what() << std::endl; } catch (...) { std::cerr << "Exception: unknown" << std::endl; } return 0; } I get the following output: Exception: unknown Yet simply making the inheritance of my_exception_t from std::exception public, I get the following output: Exception: Hello, world! Could someone please explain to me why the type of inheritance matters in this case? Bonus points for a reference in the standard.

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  • How does virtual inheritance solve the diamond problem?

    - by cambr
    class A { public: void eat(){ cout<<"A";} }; class B: virtual public A { public: void eat(){ cout<<"B";} }; class C: virtual public A { public: void eat(){ cout<<"C";} }; class D: public B,C { public: void eat(){ cout<<"D";} }; int main(){ A *a = new D(); a->eat(); } I understand the diamond problem, and above piece of code does not have that problem. How exatly does virtual inheritance solve the problem? What I understand: When I say A *a = new D();, the compiler wants to know if an object of type D can be assigned to a pointer of type A, but it has two paths that it can follow, but cannot decide by itself. So, how does virtual inheritance resolve the issue (help compiler take the decision)?

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  • Active Record two belongs_to calls or single table inheritance

    - by ethyreal
    In linking a sports event to two teams, at first this seemed to make sense: events - id:integer - integer:home_team_id - integer:away_team_id teams - integer:id - string:name However I am troubled by how I would link that up in the active record model: class Event belongs_to :home_team, :class_name => 'Team', :foreign_key => "home_team_id" belongs_to :away_team, :class_name => 'Team', :foreign_key => "away_team_id" end Is that the best solution? In an answer to a similar question I was pointed to single table inheritance, and then later found polymorphic associations. Neither of which seemed to fit this association. Perhaps I am looking at this wrong, but I see no need to subclass a team into home and away teams since the distinction is only in where the game is played. If I did go with single table inheritance I wouldn't want each team to belong_to an event so would this work? # app/models/event.rb class Event < ActiveRecord::Base belongs_to :home_team belongs_to :away_team end # app/models/team.rb class Team < ActiveRecord::Base has_many :teams end # app/models/home_team.rb class HomeTeam < Team end # app/models/away_team.rb class AwayTeam < Team end I thought also about a has_many through association but that seems two much as I will only ever need two teams, but those two teams don't belong to any one event. event_teams - integer:event_id - integer:team_id - boolean:is_home Is there a cleaner more semantic way for making these associations in active record? or is one of these solutions the best choice? Thanks

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  • Inheritance of closure objects and overriding of methods

    - by bobikk
    I need to extend a class, which is encapsulated in a closure. This base class is following: var PageController = (function(){ // private static variable var _current_view; return function(request, new_view) { ... // priveleged public function, which has access to the _current_view this.execute = function() { alert("PageController::execute"); } } })(); Inheritance is realised using the following function: function extend(subClass, superClass){ var F = function(){ }; F.prototype = superClass.prototype; subClass.prototype = new F(); subClass.prototype.constructor = subClass; subClass.superclass = superClass.prototype; StartController.cache = ''; if (superClass.prototype.constructor == Object.prototype.constructor) { superClass.prototype.constructor = superClass; } } I subclass the PageController: var StartController = function(request){ // calling the constructor of the super class StartController.superclass.constructor.call(this, request, 'start-view'); } // extending the objects extend(StartController, PageController); // overriding the PageController::execute StartController.prototype.execute = function() { alert('StartController::execute'); } Inheritance is working. I can call every PageController's method from StartController's instance. However, method overriding doesn't work: var startCont = new StartController(); startCont.execute(); alerts "PageController::execute". How should I override this method?

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  • @PrePersist with entity inheritance

    - by gerry
    I'm having some problems with inheritance and the @PrePersist annotation. My source code looks like the following: _the 'base' class with the annotated updateDates() method: @javax.persistence.Entity @Inheritance(strategy = InheritanceType.TABLE_PER_CLASS) public class Base implements Serializable{ ... @Id @GeneratedValue protected Long id; ... @Column(nullable=false) @Temporal(TemporalType.TIMESTAMP) private Date creationDate; @Column(nullable=false) @Temporal(TemporalType.TIMESTAMP) private Date lastModificationDate; ... public Date getCreationDate() { return creationDate; } public void setCreationDate(Date creationDate) { this.creationDate = creationDate; } public Date getLastModificationDate() { return lastModificationDate; } public void setLastModificationDate(Date lastModificationDate) { this.lastModificationDate = lastModificationDate; } ... @PrePersist protected void updateDates() { if (creationDate == null) { creationDate = new Date(); } lastModificationDate = new Date(); } } _ now the 'Child' class that should inherit all methods "and annotations" from the base class: @javax.persistence.Entity @NamedQueries({ @NamedQuery(name=Sensor.QUERY_FIND_ALL, query="SELECT s FROM Sensor s") }) public class Sensor extends Entity { ... // additional attributes @Column(nullable=false) protected String value; ... // additional getters, setters ... } If I store/persist instances of the Base class to the database, everything works fine. The dates are getting updated. But now, if I want to persist a child instance, the database throws the following exception: MySQLIntegrityConstraintViolationException: Column 'CREATIONDATE' cannot be null So, in my opinion, this is caused because in Child the method "@PrePersist protected void updateDates()" is not called/invoked before persisting the instances to the database. What is wrong with my code?

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  • Programming exercises in Java inheritance for intern

    - by Tenner
    I work for a small software development team, working primarily in Java, for a very large company. Our new intern showed up sight-unseen (not uncommon in my company). He has some C++ experience but no Java. Worse, he's never worked with inheritance in C++. Our code has a great deal of abstraction and a heavy reliance on inheritance. We need to get him up to speed as quickly as possible. Of course the rest of the team is busy, and so we can't take the time out of our day to teach a one-student 200-level CS course. Instead, I'd like to give him an actual programming project to work on which highlights how classes, interfaces, method overrides, etc. work. I've had him look at Project Euler, but most of the solutions end up being procedural, and not object-oriented programs. Do any of you have any somewhat-straightforward (and relatively quick) projects which you would give to an intern in this situation? Or, any recent (or current) students have a school project they'd be willing to share? Anyone else had this experience?

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  • Rails Model inheritance in forms

    - by Tiago
    I'm doing a reporting system for my app. I created a model ReportKind for example, but as I can report a lot of stuff, I wanted to make different groups of report kinds. Since they share a lot of behavior, I'm trying to use inheritance. So I have the main model: model ReportKind << ActiveRecord::Base end and created for example: model UserReportKind << ReportKind end In my table report_kinds I've the type column, and until here its all working. My problem is in the forms/controllers. When I do a ReportKind.new, my form is build with the '*report_kind*' prefix. If a get a UserReportKind, even through a ReportKind.find, the form will build the 'user_report_kind' prefix. This mess everything in the controllers, since sometimes I'll have params[:report_kind], sometimes params[:user_report_kind], and so on for every other inheritance I made. Is there anyway to force it to aways use the 'report_kind' prefix? Also I had to force the attribute 'type' in the controller, because it didn't get the value direct from the form, is there a pretty way to do this? Routing was another problem, since it was trying to build routes based in the inherited models names. I overcome that by adding the other models in routes pointing to the same controller.

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  • Asp.net mvc inheritance controllers

    - by Ris90
    Hi, I'm studing asp.net mvc and in my test project I have some problems with inheritance: In my model I use inheritanse in few entities: public class Employee:Entity { /* few public properties */ } It is the base class. And descendants: public class RecruitmentOfficeEmployee: Employee { public virtual RecruitmentOffice AssignedOnRecruitmentOffice { get; set; } } public class ResearchInstituteEmployee: Employee { public virtual ResearchInstitute AssignedOnResearchInstitute { get; set; } } I want to implement a simple CRUD operations to every descedant. What is the better way to inplement controllers and views in descendants: - One controller per every descendant; - Controller inheritance; - Generic controller; - Generic methods in one controller. Or maybe there is an another way? My ORM is NHibernate, I have a generic base repository and every repository is its descedant. Using generic controller, I think, is the best way, but in it I will use only generic base repository and extensibility of the system will be not very good. Please, help the newbie)

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  • Problem understanding Inheritance

    - by dhruvbird
    I've been racking my brains over inheritance for a while now, but am still not completely able to get around it. For example, the other day I was thinking about relating an Infallible Human and a Fallible Human. Let's first define the two: Infallible Human: A human that can never make a mistake. It's do_task() method will never throw an exception Fallible Human: A human that will occasionally make a mistakes. It's do_task() method may occasionally throw a ErrorProcessingRequest Exception The question was: IS an infallible human A fallible human OR IS a fallible human AN infallible human? The very nice answer I received was in the form of a question (I love these since it gives me rules to answer future questions I may have). "Can you pass an infallible human where a fallible human is expected OR can you pass a fallible human where an infallible human is expected?" It seems apparent that you can pass an infallible human where a fallible human is expected, but not the other way around. I guess that answered my question. However, it still feels funny saying "An infallible human is a fallible human". Does anyone else feel queasy when they say it? It almost feels as if speaking out inheritance trees is like reading out statements from propositional calculus in plain English (the if/then implication connectives don't mean the same as that in spoken English). Does anyone else feel the same?

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  • XCode project complains about missing files if a linked framework contains private headers

    - by darklight
    My Problem is this: My framework contains public and private headers - the public headers import private headers in the framework My app that links against this framework imports public headers Now when I compile it, XCode complains about missing files (the private headers that are indirectly imported via the frameworks public headers). I read somewhere on stackoverflow that I should do this: "In the public header file use @class to include other interfaces and use #import in the implementation file (.m)." I find this solution pretty unsatisfying - you have to use it for circular dependencies, too. Is there any better way to keep my headers private?

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  • Copy constructor using private attributes

    - by Pedro Magueija
    Hello all, My first question here so be gentle. I would like arguments for the following code: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.name = e.name; // accessing a private attribute of an instance this.age = e.age; } ... } I believe this breaks the modularity of the instance passed to the copy construct. This is what I believe to be correct: public class Example { private String name; private int age; ... // copy constructor here public Example(Example e) { this.setName(e.getName()); this.setAge(e.getAge()); } ... } A friend has exposed a valid point of view, saying that in the copy construct we should create the object as fast as possible. And adding getter/setter methods would result in unnecessary overhead. I stand on a crossroad. Can you shed some light?

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  • Ruby module_function, invoking module's private method, invoked in class method style on module shows error

    - by Jignesh
    test_module.rb module MyModule def module_func_a puts "module_func_a invoked" private_b end module_function :module_func_a private def private_b puts "private_b invoked" end end class MyClass include MyModule def test_module module_func_a end end Invoking module function from class c = MyClass.new c.test_module Output 1: $ ruby test_module.rb module_func_a invoked private_b invoked Invoking module function on module in class method style ma = MyModule.module_func_a Output 2: module_func_a invoked test_module.rb:5:in `module_func_a': undefined local variable or method `private_b' for MyModule:Module (NameError) from test_module.rb:31 As can be seen from the Output 1 and Output 2 when including the module in a class, no issue occurs when a module's private method gets invoked from a module function while in case when directly invoking the module function on the module in class method style the module's private method, invoked from module function, is not found. Can anybody make me understand the reason behind above behavior and whether invoking module function (which in turn invokes module's private method) on module in class method style is possible or not? If possible, then what rectifications are required in my code to do the same? Thanks, Jignesh

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  • initializing properties with private sets in .Net

    - by Martin Neal
    public class Foo { public string Name { get; private set;} // <-- Because set is private, } void Main() { var bar = new Foo {Name = "baz"}; // <-- This doesn't compile /*The property or indexer 'UserQuery.Foo.Name' cannot be used in this context because the set accessor is inaccessible*/ using (DataContext dc = new DataContext(Connection)) { // yet the following line works. **How**? IEnumerable<Foo> qux = dc.ExecuteQuery<Foo>( "SELECT Name FROM Customer"); } foreach (q in qux) Console.WriteLine(q); } I have just been using the private modifier because it works and kept me from being stupid with my code, but now that I need to create a new Foo, I've just removed the private modifier from my property. I'm just really curious, why does the ExecuteQuery into an IEnumerable of Foo's work?

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  • Calling private event handler from outside class

    - by Azodious
    i've two classes. One class (say A) takes a textbox in c'tor. and registers TextChanged event with private event-handler method. 2nd class (say B) creates the object of class A by providing a textbox. how to invoke the private event handler of class A from class B? it also registers the MouseClick event. is there any way to invoke private eventhandlers?

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  • Why C# does not support multiple inheritance?

    - by Jalpesh P. Vadgama
    Yesterday, One of my friend Dharmendra ask me that why C# does not support multiple inheritance. This is question most of the people ask every time. So I thought it will be good to write a blog post about it. So why it does not support multiple inheritance? I tried to dig into the problem and I have found the some of good links from C# team from Microsoft for why it’s not supported in it. Following is a link for it. http://blogs.msdn.com/b/csharpfaq/archive/2004/03/07/85562.aspx Also, I was giving some of the example to my friend Dharmendra where multiple inheritance can be a problem.The problem is called the diamond problem. Let me explain a bit. If you have class that is inherited from the more then one classes and If two classes have same signature function then for child class object, It is impossible to call specific parent class method. Here is the link that explains more about diamond problem. http://en.wikipedia.org/wiki/Diamond_problem Now of some of people could ask me then why its supporting same implementation with the interfaces. But for interface you can call that method explicitly that this is the method for the first interface and this the method for second interface. This is not possible with multiple inheritance. Following is a example how we can implement the multiple interface to a class and call the explicit method for particular interface. Multiple Inheritance in C# That’s it. Hope you like it. Stay tuned for more update..Till then happy programming.

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  • Javascript Inheritance Part 2

    - by PhubarBaz
    A while back I wrote about Javascript inheritance, trying to figure out the best and easiest way to do it (http://geekswithblogs.net/PhubarBaz/archive/2010/07/08/javascript-inheritance.aspx). That was 2 years ago and I've learned a lot since then. But only recently have I decided to just leave classical inheritance behind and embrace prototypal inheritance. For most of us, we were trained in classical inheritance, using class hierarchies in a typed language. Unfortunately Javascript doesn't follow that model. It is both classless and typeless, which is hard to fathom for someone who's been using classes the last 20 years. For the last two or three years since I've got into Javascript I've been trying to find the best way to force it into the class model without much success. It's clunky and verbose and hard to understand. I think my biggest problem was that it felt so wrong to add or change object members at run time. Every time I did it I felt like I needed a shower. That's the 20 years of classical inheritance in me. Finally I decided to embrace change and do something different. I decided to use the factory pattern to build objects instead of trying to use inheritance. Javascript was made for the factory pattern because of the way you can construct objects at runtime. In the factory pattern you have a factory function that you call and tell it to give you a certain type of object back. The factory function takes care of constructing the object to your specification. Here's an example. Say we want to have some shape objects and they have common attributes like id and area that we want to depend on in other parts of your application. So first thing to do is create a factory object and give it a factory method to create an abstract shape object. The factory method builds the object then returns it. var shapeFactory = { getShape: function(id){ var shape = { id: id, area: function() { throw "Not implemented"; } }; return shape; }}; Now we can add another factory method to get a rectangle. It calls the getShape() method first and then adds an implementation to it. getRectangle: function(id, width, height){ var rect = this.getShape(id); rect.width = width; rect.height = height; rect.area = function() { return this.width * this.height; }; return rect;} That's pretty simple right? No worrying about hooking up prototypes and calling base constructors or any of that crap I used to do. Now let's create a factory method to get a cuboid (rectangular cube). The cuboid object will extend the rectangle object. To get the area we will call into the base object's area method and then multiply that by the depth. getCuboid: function(id, width, height, depth){ var cuboid = this.getRectangle(id, width, height); cuboid.depth = depth; var baseArea = cuboid.area; cuboid.area = function() { var a = baseArea.call(this); return a * this.depth; } return cuboid;} See how we called the area method in the base object? First we save it off in a variable then we implement our own area method and use call() to call the base function. For me this is a lot cleaner and easier than trying to emulate class hierarchies in Javascript.

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