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  • Constructors from extended class in Java

    - by Crystal
    I'm having some trouble with a hw assignment. In one assignment, we had to create a Person class. Mine was: public class Person { String firstName; String lastName; String telephone; String email; public Person() { firstName = ""; lastName = ""; telephone = ""; email = ""; } public Person(String firstName) { this.firstName = firstName; } public Person(String firstName, String lastName, String telephone, String email) { this.firstName = firstName; this.lastName = lastName; this.telephone = telephone; this.email = email; } public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } public String getTelephone() { return telephone; } public void setTelephone(String telephone) { this.telephone = telephone; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } public boolean equals(Object otherObject) { // a quick test to see if the objects are identical if (this == otherObject) { return true; } // must return false if the explicit parameter is null if (otherObject == null) { return false; } if (!(otherObject instanceof Person)) { return false; } Person other = (Person) otherObject; return firstName.equals(other.firstName) && lastName.equals(other.lastName) && telephone.equals(other.telephone) && email.equals(other.email); } public int hashCode() { return 7 * firstName.hashCode() + 11 * lastName.hashCode() + 13 * telephone.hashCode() + 15 * email.hashCode(); } public String toString() { return getClass().getName() + "[firstName = " + firstName + '\n' + "lastName = " + lastName + '\n' + "telephone = " + telephone + '\n' + "email = " + email + "]"; } } Now we have to extend that class and use that class in our constructor. The function protoype is: public CarLoan(Person client, double vehiclePrice, double downPayment, double salesTax, double interestRate, CAR_LOAN_TERMS length) I'm confused on how I use the Person constructor from the superclass. I cannot necessarily do super(client); in my constructor which is what the book did with some primitive types in their example. Not sure what the correct thing to do is... Any thoughts? Thanks!

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  • Implement two functions with the same name but different, non-covariant return types due to multiple abstract base classes

    - by user1508167
    If I have two abstract classes defining a pure virtual function with the same name, but different, non-covariant return types, how can I derive from these and define an implementation for both their functions? #include <iostream> class ITestA { public: virtual ~ITestA() {}; virtual float test() =0; }; class ITestB { public: virtual ~ITestB() {}; virtual bool test() =0; }; class C : public ITestA, public ITestB { public: /* Somehow implement ITestA::test and ITestB::test */ }; int main() { ITestA *a = new C(); std::cout << a->test() << std::endl; // should print a float, like "3.14" ITestB *b = dynamic_cast<ITestB *>(a); if (b) { std::cout << b->test() << std::endl; // should print "1" or "0" } delete(a); return 0; } As long as I don't call C::test() directly there's nothing ambiguous, so I think that it should work somehow and I guess I just didn't find the right notation yet. Or is this impossible, if so: Why?

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  • templated class : accessing derived normal-class methods

    - by user1019129
    I have something like this : class Container1 { public: method1() { ... } } class Container2 { public: method1() { ... } } template<class C = Container1> class X : public C { public: using C::method1(); ..... X(string& str) : C(str) {}; X& other_method() { method1(); ...; } } My question is why I have to use "using C::method1()", to be able to access the method.. Most of answers I found is for the case where templated-class inhering templated-class. Normally they mention using "this-", but this does not seem to work in this case. Can I do something else shorter... Also I'm suspecting the other error I'm getting is related to the same problem : no match call for (X<Container1>) (<std::string&>)

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  • How do I inherit abstract unit tests in Ruby?

    - by Graeme Moss
    I have two unit tests that should share a lot of common tests with slightly different setup methods. If I write something like class Abstract < Test::Unit::TestCase def setup @field = create end def test_1 ... end end class Concrete1 < Abstract def create SomeClass1.new end end class Concrete2 < Abstract def create SomeClass2.new end end then Concrete1 does not seem to inherit the tests from Abstract. Or at least I cannot get them to run in eclipse. If I choose "Run all TestCases" for the file that contains Concrete1 then Abstract is run even though I do not want it to be. If I specify Concrete1 then it does not run any tests at all! If I specify test_1 in Concrete1 then it complains it cannot find it ("uncaught throw :invalid_test (ArgumentError)"). I'm new to Ruby. What am I missing here?

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  • Is there any difference these two pieces of code?

    - by Poiuyt
    #include<stdio.h> class A {public: int a; }; class B: public A {private: int a;}; int main(){ B b; printf("%d", b.a); return 0; } #include<stdio.h> class A {public: int a; }; class B: private A {}; int main(){ B b; printf("%d", b.a); return 0; } I ask because I get different errors: error: 'int B::a' is private error: 'int A::a' is inaccessible Apart from what the errors might reveal, is there any difference at all in the behaviour of these two pieces of code?

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  • Javascript: Inherit method from base class and return the subclass's private variable

    - by marisbest2
    I have the following BaseClass defined: function BaseClass (arg1,arg2,arg3) { //constructor code here then - var privateVar = 7500; this.getPrivateVar = function() { return privateVar; }; } I want to have the following subclass which allows changing privateVar like so: function SubClass (arg1,arg2,arg3,privateVar) { //constructor code here then - var privateVar = privateVar; } SubClass.prototype = new BaseClass(); Now I want SubClass to inherit the getPrivateVar method. However, when I try this, it always returns 7500 which is the value in the BaseClass and not the value of privateVar. In other words, is it possible to inherit a BaseClass's public methods but have any references in them refer to the SubClass's properties? And how would I do that?

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  • base pointer to derived class

    - by Jay
    Suppose there are Base class and Derived class. Base *A = new Base; Here A is a pointer point to Base class, and new constructs one that A points to. I also saw Base *B = new Derived; How to explain this? B is a pointer to Base Class, and a Derived class constructed and pointed by B? If there is a function derived from Base class, say, Virtual void f(), and it's been overridden in Derived class, then B->f() will invoke which version of the function? version in Base class, or version that overridden in Derived Class. What if there is a new function void g()in Derived, is B->g() going to invoke this function properly? One more is, is int *a = new double; or int *a = new int; legal?

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  • Java : Using parent class method to access child class variable

    - by Jayant
    I have the following scenario : public class A { private int x = 5; public void print() { System.out.println(x); } } public class B extends A { private int x = 10; /*public void print() { System.out.println(x); }*/ public static void main(String[] args) { B b = new B(); b.print(); } } On executing the code, the output is : 5. How to access the child class(B's) variable(x) via the parent class method? Could this be done without overriding the print() method (i.e. uncommenting it in B)? [This is important because on overriding we will have to rewrite the whole code for the print() method again]

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  • Force the use of interface instead of concrete implementation in declaration (.NET)

    - by gammelgul
    In C++, you can do the following: class base_class { public: virtual void do_something() = 0; }; class derived_class : public base_class { private: virtual void do_something() { std::cout << "do_something() called"; } }; The derived_class overrides the method do_something() and makes it private. The effect is, that the only way to call this method is like this: base_class *object = new derived_class(); object->do_something(); If you declare the object as of type derived_class, you can't call the method because it's private: derived_class *object = new derived_class(); object->do_something(); // --> error C2248: '::derived_class::do_something' : cannot access private member declared in class '::derived_class' I think this is quite nice, because if you create an abstract class that is used as an interface, you can make sure that nobody accidentally declares a field as the concrete type, but always uses the interface class. Since in C# / .NET in general, you aren't allowed to narrow the access from public to private when overriding a method, is there a way to achieve a similar effect here?

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  • Similar Sub-Classes

    - by praks5432
    Lets say I have a class A that is fairly simple like this - public class A{ private int randomField = 0; protected int key; protected double dmg; } Now I want to write a number of sub-classes that inherit the protected fields and only differ based on the initial values that are assigned to those fields - for example, if I wrote two subclasses B and C, the only difference between those two sub-classes would be that the values key and dmg would have different values. They would share a method, set, which would be exactly the same, in that it would affect the same variable. I find when I'm writing these sub-classes I'm repeating myself, as I just change the constructor to set different initial values to key and dmg, and simply copy and paste the set method. Is there a 'good' way to do this?

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  • error - inherited class field undeclared according to g++

    - by infoholic_anonymous
    I have a code that has the following logic. g++ gives me the error that I have not declared n in my iterator2. What could be wrong? template <typename T> class List{ template <typename TT> class Node; Node<T> *head; /* (...) */ template <bool D> class iterator1{ protected: Node<T> n; public: iterator1( Node<T> *nn ) { n = nn } /* (...) */ }; template <bool D> class iterator2 : public iterator1<D>{ public: iterator2( Node<T> *nn ) : iterator1<D>( nn ) {} void fun( Node<T> *nn ) { n = nn; } /* (...) */ }; }; EDIT : I attach the actual header file. iterator1 would be iterable_frame and iterator2 - switchable_frame. #ifndef LST_H #define LST_H template <typename T> class List { public: template <typename TT> class Node; private: Node<T> *head; public: List() { head = new Node<T>; } ~List() { empty_list(); delete head; } List( const List &l ); inline bool is_empty() const { return head->next[0] == head; } void empty_list(); template <bool DIM> class iterable_frame { protected: Node<T> *head; Node<T> **caret; public: iterable_frame( const List &l ) { head = *(caret = &l.head); } iterable_frame( const iterable_frame &i ) { head = *(caret = i.caret); } ~iterable_frame() {} /* (...) - a few methods follow */ template <bool _DIM> friend class supervised_frame; }; template <bool DIM> class switchable_frame : public iterable_frame<DIM> { Node<T> *main_head; public: switchable_frame( const List& l ) : iterable_frame<DIM>(l) { main_head = head; } inline bool next_frame() { caret = &head->next[!DIM]; head = *caret; return head != main_head; } }; template <bool DIM> class supervised_frame { iterable_frame<DIM> sentinels; iterable_frame<DIM> cells; public: supervised_frame( const List &l ) : sentinels(l), cells(l) {} ~supervised_frame() {} /* (...) - a few methods follow */ }; template <typename TT> class Node { unsigned index[2]; TT num; Node<TT> *next[2]; public: Node( unsigned x = 0, unsigned y = 0 ) { index[0]=x; index[1]=y; next[0] = this; next[1] = this; } Node( unsigned x, unsigned y, TT d ) { index[0]=x; index[1]=y; num=d; next[0] = this; next[1] = this; } Node( const Node &n ) { index[0] = n.index[0]; index[1] = n.index[1]; num = n.num; next[0] = next[1] = this; } ~Node() {} friend class List; }; }; #include "List.cpp" #endif the exact error log is the following: In file included from main.cpp:1: List.h: In member function ‘bool List<T>::switchable_frame<DIM>::next_frame()’: List.h:77: error: ‘caret’ was not declared in this scope

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  • How to access base (super) class in Delphi?

    - by Niyoko Yuliawan
    In C# i can access base class by base keyword, and in java i can access it by super keyword. How to do that in delphi? suppose I have following code: type TForm3 = class(TForm) private procedure _setCaption(Value:String); public property Caption:string write _setCaption; //adding override here gives error end; implementation procedure TForm3._setCaption(Value: String); begin Self.Caption := Value; //it gives stack overflow end;

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  • Friendly way to override `const`-overloaded member function?

    - by xtofl
    Given a base class class A { int i; public: int& f(){ return i;} const int& f() const { return i;} }; And a sub class class ConstA : private A { public: const int& f() const { return A::f(); } }; Is there a wrist-friendly way to access the ConstA::f method on a non-const variable? ConstA ca; int i = ca.f(); // compile error: int& A::f() is not accessible since A is privately inherited int j = static_cast<const ConstA&>(ca).f(); // this works, but it hurts a little... Or is it so ugly since hiding A::f generally is a bad idea, violating the Liskov Substitution Principle: any subclass of A must at least be capable of all A's functionality? void set( A& a, int i ) { a.f() = i; } class ConstA2 : public A { private: int& f(){ return A::f(); } }; ConstA2 ca2; set( ca2, 1 ); (Note: this question popped up while thinking about this question)

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  • Remove .img css from prepended div

    - by Ivan Schrecklich
    OK as the title says I've got a div which is prepended and dynamically loaded. The problem I have is that I can't split the css on this one as it parses also whole strings. The usage is like that: I've got a @username somewhere in the string. If the user hovers it a div with informations will get prepended to the current username. Now there is the problem that I've allowed users to post images in this text also. As the autolinker is flexible it doesn't know the image sizes and restrictions and I want to leave it like that! So I define css classes which look like that: .minpost img{ max-height: 30px; max-width: 30px; } Of course I don't need to mention that this attribute is also inherited by the prepended div. And that I don't want to! nifty little tricks like !important won't work for me. So I am asking you guys. If you need further informations just ask?!

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  • Use of .apply() with 'new' operator. Is this possible?

    - by Premasagar
    In JavaScript, I want to create an object instance (via the new operator), but pass an arbitrary number of arguments to the constructor. Is this possible? What I want to do is something like this (but the code below does not work): function Something(){ // init stuff } function createSomething(){ return new Something.apply(null, arguments); } var s = createSomething(a,b,c); // 's' is an instance of Something The Answer From the responses here, it became clear that there's no in-built way to call .apply() with the new operator. However, people suggested a number of really interesting solutions to the problem. My preferred solution was this one from Matthew Crumley (I've modified it to pass the arguments property): var createSomething = (function() { function F(args) { return Something.apply(this, args); } F.prototype = Something.prototype; return function() { return new F(arguments); } })();

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  • Is context inheritance, as shown by Head First Design Patterns' Duck example, irrelevant to strategy pattern?

    - by Korey Hinton
    In Head First Design Patterns it teaches the strategy pattern by using a Duck example where different subclasses of Duck can be assigned a particular behavior at runtime. From my understanding the purpose of the strategy pattern is to change an object's behavior at runtime. Emphasis on "an" meaning one. Could I further simplify this example by just having a Duck class (no derived classes)? Then when implementing one duck object it can be assigned different behaviors based on certain circumstances that aren't dependent on its own object type. For example: FlyBehavior changes based on the weather or QuackBehavior changes based on the time of day or how hungry a duck is. Would my example above constitute the strategy pattern as well? Is context inheritance (Duck) irrelevant to the strategy pattern or is that the reason for the strategy pattern? Here is the UML diagram from the Head First book:

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  • An alternative to multiple inheritance when creating an abstraction layer?

    - by sebf
    In my project I am creating an abstraction layer for some APIs. The purpose of the layer is to make multi-platform easier, and also to simplify the APIs to the feature set that I need while also providing some functionality, the implementation of which will be unique to each platform. At the moment, I have implemented it by defining and abstract class, which has methods which creates objects that implement interfaces. The abstract class and these interfaces define the capabilities of my abstraction layer. The implementation of these in my layer should of course be arbitrary from the POV view of my application, but I have done it, for my first API, by creating chains of subclasses which add more specific functionality as the features of the APIs they expose become less generic. An example would probably demonstrate this better: //The interface as seen by the application interface IGenericResource { byte[] GetSomeData(); } interface ISpecificResourceOne : IGenericResource { int SomePropertyOfResourceOne {get;} } interface ISpecificResourceTwo : IGenericResource { string SomePropertyOfResourceTwo {get;} } public abstract class MyLayer { ISpecificResourceOne CreateResourceOne(); ISpecificResourceTwo CreateResourceTwo(); void UseResourceOne(ISpecificResourceOne one); void UseResourceTwo(ISpecificResourceTwo two); } //The layer as created in my library public class LowLevelResource : IGenericResource { byte[] GetSomeData() {} } public class ResourceOne : LowLevelResource, ISpecificResourceOne { int SomePropertyOfResourceOne {get{}} } public class ResourceTwo : ResourceOne, ISpecificResourceTwo { string SomePropertyOfResourceTwo {get {}} } public partial class Implementation : MyLayer { override UseResourceOne(ISpecificResourceOne one) { DoStuff((ResourceOne)one); } } As can be seen, I am essentially trying to have two inheritance chains on the same object, but of course I can't do this so I simulate the second version with interfaces. The thing is though, I don't like using interfaces for this; it seems wrong, in my mind an interface defines a contract, any class that implements that interface should be able to be used where that interface is used but here that is clearly not the case because the interfaces are being used to allow an object from the layer to masquerade as something else, without the application needing to have access to its definition. What technique would allow me to define a comprehensive, intuitive collection of objects for an abstraction layer, while their implementation remains independent? (Language is C#)

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  • Can somebody link me to some code where there is a fantastic or a nice use of Inheritance

    - by Soham
    I strongly believe that, reading code and reading good code is key to great programming. If not one of the many. I had been facing some problems in visualizing and having a "feel" of using inheritance to better my code architecture. Can somebody give me some link to good code to emulate, where folks have used inheritance in an absolute "kung-fooey ruthless" manner [in a good way]

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  • Is there anyway to stop automatic DataContext inheritance in Silverlight?

    - by Ant
    Is there anyway to stop automatic DataContext inheritance in Silverlight? I Set my DataContext on my parent UserControl in code. As a result all the xaml bindings inside the UserControl try to bind to the new DataConext they get (through the automatic DataContext Inheritance). The DataContext's for the children elements (actually they are children of children of children) of the UserControl is something I need to set in the UserControl's code... I don't want them being all smart because they end up binding to the wrong data object! :-)

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  • How do I create self-relationships in polymorphic inheritance in Elixir and Pylons?

    - by Turukawa
    I am new to programming and am following the example in the Pylons documentation on creating a Wiki. The database I want to link to the wiki was created with Elixir so I rewrote the Wiki database schema and have continued from there. In the wiki there is a requirement for a Navigation table which is inherited by Pages and Sections. A section can have many pages, while a page can only have one section. In addition, each sibling node can be chain-referenced to each other. So: Nav has "section" (OneToMany) and "before" (OneToOne - to reference preceeding node) Page has "section" (ManyToOne - many pages in one section) and inherits "before" Section inherits all from Nav The code I've written looks like this: class Nav(Entity): using_options(inheritance='multi') name = Field(Unicode(30), default=u'Untitled Node') path = Field(Unicode(255), default=u'') section = OneToMany('Page', inverse='section') after = OneToOne('Nav', inverse='before') before = OneToMany('Nav', inverse='after') class Page(Nav): using_options(inheritance='multi') content = Field(UnicodeText, nullable=False) posted = Field(DateTime, default=now()) title = Field(Unicode(255), default=u'Untitled Page') heading = Field(Unicode(255)) tags = ManyToMany('Tag') comments = OneToMany('Comment') section = ManyToOne('Nav', inverse='section') class Section(Nav): using_options(inheritance='multi') Errors received on this: sqlalchemy.exc.OperationalError: (OperationalError) table nav has no column named aftr_id u'INSERT INTO nav (name, path, aftr_id, row_type) VALUES (?, ?, ?, ?)' I've also tried: before = ManyToMany('Nav', inverse='before') on Nav in the hopes this might break the problem, but also not. The original SQLAlchemy code from the tutorial for these declarations is as follows: nav_table = schema.Table('nav', meta.metadata, schema.Column('id', types.Integer(), schema.Sequence('nav_id_seq', optional=True), primary_key=True), schema.Column('name', types.Unicode(255), default=u'Untitled Node'), schema.Column('path', types.Unicode(255), default=u''), schema.Column('section', types.Integer(), schema.ForeignKey('nav.id')), schema.Column('before', types.Integer(), default=None), schema.Column('type', types.String(30), nullable=False) ) page_table = schema.Table('page', meta.metadata, schema.Column('id', types.Integer, schema.ForeignKey('nav.id'), primary_key=True), schema.Column('content', types.Text(), nullable=False), schema.Column('posted', types.DateTime(), default=now), schema.Column('title', types.Unicode(255), default=u'Untitled Page'), schema.Column('heading', types.Unicode(255)), ) section_table = sa.Table('section', meta.metadata, schema.Column('id', types.Integer, schema.ForeignKey('nav.id'), primary_key=True), ) orm.mapper(Nav, nav_table, polymorphic_on=nav_table.c.type, polymorphic_identity='nav') orm.mapper(Section, section_table, inherits=Nav, polymorphic_identity='section') orm.mapper(Page, page_table, inherits=Nav, polymorphic_identity='page', properties={ 'comments':orm.relation(Comment, backref='page', cascade='all'), 'tags':orm.relation(Tag, secondary=pagetag_table) }) Any help is much appreciated.

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  • multiple inheritence in OOPS

    - by user145610
    Hi, Im confused about OOPS feature esp about multiple inheritance. Is OOPS allows Multiple Inheritance. Is Multiple Inheritance is a feature of OOPS. If Multiple Inheritance is feature then languages like C#,VB.NET,java etc doesn't support multiple inheritance.But those languages are considered as strongly supported OOPS language. Can anyone address this question

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  • Is it possible to apply inheritance to a Singleton class?

    - by Bragaadeesh
    Hi, Today I faced one question in interview. Is it possible to apply inheritance concept on Singleton Classes. I said since the constructor is private, we cannot extend that Singleton class (can someone please validate this). Next thing he asked me is to apply inheritance on that Singleton class. So, I made the Singleton's constructor as protected thinking that child's constructor also has be protected. But I was wrong the child can have a modifier either equal to or higher than that. So, I asked him to give a real world example on such a case. He was not able to give me one and said that I cant ask questions and wanted me to tell whether this scenario is possible or not. I went kind of blank. My question here is, Is this possible? Even if its possible, what is the use of it? What real world scenario would demand such a use. Thanks

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