I usually make a base class abstract to give the signal this is a base class - you cannot instantiate me! even if there are no abstract methods in it. Furthermore, I always make the base class constructor protected, although there's no real functional need to do that - I just want to make another point that this is a base class - you ca...
Hi all, I recently fumbled into a problem with an API and an implementation where the following type of code appeared: The API is an abstract class: public abstract class A { public A sum(A a) { System.out.println("A.sum(A) called"); return null; } } The implementation is a simple class: public class B extends A { public B s...
Let's see if I can explain myself, I have this models: class BillHeader(models.Model): number = models.CharField(_('Bill number'), max_length=10, unique=True, \ default=__number) client = models.ForeignKey(ClienteYProveedor, verbose_name=_('Client')) date = models.DateTimeField(_('Date'), default=datetime.now) def _...
I need to implement a listener in JavaScript by anonymous subclass of an existing abstract base class, defined like this: public class Speaker { public static abstract class MyListener { private String name; public MyListener(final String name) { this.name = name; } public abstract boolean listen(final String words); } }...
I thought that if a C# array held reference types it would simply hold references to each of the objects, however the code below tells me otherwise. It appears as if the array is holding a reference to an object of which I thought was set to be garbage collected. I feel like i'm missing something fundamental here. Can anyone tell me w...
We cant instantiate an abstract class.Then what is the necessity of having constructors in abstract class.Please give me some examples? ...
Hi, Is calling Class.getInstance() equivalent to new Class()? I know the constructor is called for the latter, but what about getInstance? Thanks. ...
I have following code. And I need to hide one function of the interface. interface IOne { int FunctionOne(); } interface ITwo { double FunctionTwo(); } interface IInterfaceToImplement : IOne, ITwo { void AFunctionToImplement(); } public abstract MyBaseClass : TheVeryHeavyBaseClass<T, IInterfaceToImplement>, IInterfaceToIm...
I have decided to start doing small coding projects on my own that focus on code quality instead of code quantity and have a question about the use of abstract classes. Now I know the differences between abstract classes and interfaces with the biggest one (I think) being that interface allow you to only define methods that need to be i...
I have the following classes, Base and Derived and when I compile the compiler complains that it cannot create an instance of DLog because it is abstract. Can someone tell me how I can fix this error? I'm guessing it's because not both pure virtual functions are not implemented in the Derived. class Logger { public: virtual void ...
Here is the simple php code <? abstract class A{ abstract public function a($x); } class B extends A{ public function a($x) { echo $x; } } $q = new B; $q->a(10); ?> which gives: PHP Fatal error: Cannot call abstract method A::a() but changing the name of the function to something else than "a" works. So what is really happening ...
I'm having an issue with inheritance between 2 classes and a single normal class. Here is an example of what I have: Abstract ClassA function get_name(); Abstract ClassB extends ClassA ClassC extends ClassB Now, when I create an object of ClassC, I can't access the get_name() function. I'm not sure what I'm doing wrong here. ...
In django, I would like to reference the class whose method is being called, where the method itself is implemented in its abstract ancestor. class AbstractFather(models.Model): class Meta: abstract = True def my_method(self): # >>> Here <<< class Child(AbstractFather): pass I'm looking to do something lik...
Hi, I'm trying to write a ruby class that works similarly to rails activerecord model in the way that attributes are handled: class Person attr_accessor :name, :age # init with Person.new(:name => 'John', :age => 30) def initialize(attributes={}) attributes.each { |key, val| send("#{key}=", val) if respond_to?("#{key}=") } ...
Of course, the following doesn't work in Java (no abstract static methods)... public abstract class Animal { public abstract static Animal getInstance(byte[] b); } public class Dog extends Animal { @Override public static Dog getInstance(byte[] b) { // Woof. return new Dog(...); } } public class Cat ext...
I wasn't completely sure how to phrase what I wanted to ask in the title so I'll try to clarify it better in what follows. For C++ software library developers, what abstract interfaces do you find yourselves rewriting often between projects/jobs? For instance, I would imagine that it is fairly common practice for different projects to ...
In the following example, the class Derived implements the abstract method method from class Main. But I can't think of a reason to fill in the method body in the abstract Derived class' implementation. Surely I should only implement abstract methods within real classes. So how can I avoid doing it? What else can I do? abstract class ...
I have created an abstract base class Animal which has public virtual abstract method makeSound(). I created a subclass Cow which implements Animal.makeSound() as you would expect (you know... "moo"). And I have a Farm class which holds a private member variable std::vector<Animal*> animals. In one of the Farm methods I iterate over a...
Say we have a class inheriting from two base classes (multiple inheritance). Base class A is abstract, declaring a pure virtual function foo, the other base class B declares and implements a function foo of the very same signature. struct A { virtual void foo(int i) = 0; }; struct B { virtual void foo(int i) {} }; struct C : publi...
I realize that in most cases, it's preferred in Python to just access attributes directly, since there's no real concept of encapsulation like there is in Java and the like. However, I'm wondering if there aren't any exceptions, particularly with abstract classes that have disparate implementations. Let's say I'm writing a bunch of abst...