Questions tagged [inheritance]
Inheritance is the system in object oriented programming that allows objects to support operations defined by anterior types without having to provide their own definition. It is the major vector for polymorphism in object-oriented programming.
inheritance
42,717
questions
3234
votes
7
answers
2.8m
views
Understanding Python super() with __init__() methods [duplicate]
Why is super() used?
Is there a difference between using Base.__init__ and super().__init__?
class Base(object):
def __init__(self):
print "Base created"
class ChildA(...
- 51.9k
1994
votes
36
answers
495k
views
Prefer composition over inheritance?
Why prefer composition instead of inheritance? What trade-offs are there for each approach? And the converse question: when should I choose inheritance instead of composition?
- 351k
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votes
10
answers
1.4m
views
Calling the base constructor in C#
If I inherit from a base class and want to pass something from the constructor of the inherited class to the constructor of the base class, how do I do that?
For example, if I inherit from the ...
- 115k
1727
votes
29
answers
253k
views
Why not inherit from List<T>?
When planning out my programs, I often start with a chain of thought like so:
A football team is just a list of football players. Therefore, I should represent it with:
var football_team = new ...
- 26.2k
1693
votes
6
answers
449k
views
Why do Python classes inherit object?
Why does the following class declaration inherit from object?
class MyClass(object):
...
- 17.8k
1561
votes
8
answers
894k
views
What are the differences between type() and isinstance()? [duplicate]
What are the differences between these two code snippets?
Using type:
import types
if type(a) is types.DictType:
do_something()
if type(b) in types.StringTypes:
do_something_else()
Using ...
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1262
votes
17
answers
783k
views
What is the difference between public, private, and protected inheritance?
What is the difference between public, private, and protected inheritance in C++?
user106599
1051
votes
3
answers
157k
views
What are the nuances of scope prototypal / prototypical inheritance in AngularJS?
The API Reference Scope page says:
A scope can inherit from a parent scope.
The Developer Guide Scope page says:
A scope (prototypically) inherits properties from its parent scope.
So, does a ...
- 364k
919
votes
17
answers
270k
views
910
votes
19
answers
141k
views
Is List<Dog> a subclass of List<Animal>? Why are Java generics not implicitly polymorphic?
I'm a bit confused about how Java generics handle inheritance / polymorphism.
Assume the following hierarchy -
Animal (Parent)
Dog - Cat (Children)
So suppose I have a method doSomething(List<...
- 82k
898
votes
17
answers
612k
views
How do you declare an interface in C++?
How do I setup a class that represents an interface? Is this just an abstract base class?
- 21.1k
868
votes
10
answers
1.1m
views
What are the rules for calling the base class constructor?
What are the C++ rules for calling the base class constructor from a derived class?
For example, I know in Java, you must do it as the first line of the subclass constructor (and if you don't, an ...
- 117k
822
votes
19
answers
1.3m
views
Implements vs extends: When to use? What's the difference?
Please explain in an easy to understand language or a link to some article.
- 11.2k
817
votes
16
answers
934k
views
How do I call a parent class's method from a child class in Python?
When creating a simple object hierarchy in Python, I'd like to be able to invoke methods of the parent class from a derived class. In Perl and Java, there is a keyword for this (super). In Perl, I ...
- 10k
795
votes
9
answers
992k
views
How to call a parent class function from derived class function?
How do I call the parent function from a derived class using C++? For example, I have a class called parent, and a class called child which is derived from parent. Within
each class there is a print ...
- 12.6k
754
votes
11
answers
303k
views
What does 'super' do in Python? - difference between super().__init__() and explicit superclass __init__()
What's the difference between:
class Child(SomeBaseClass):
def __init__(self):
super(Child, self).__init__()
and:
class Child(SomeBaseClass):
def __init__(self):
SomeBaseClass....
- 7,551
616
votes
14
answers
853k
views
How to determine an object's class?
If class B and class C extend class A and I have an object of type B or C, how can I determine of which type it is an instance?
- 32.7k
571
votes
5
answers
244k
views
Ruby: kind_of? vs. instance_of? vs. is_a?
What is the difference? When should I use which? Why are there so many of them?
- 227k
546
votes
25
answers
432k
views
When to use an interface instead of an abstract class and vice versa?
This may be a generic OOP question. I wanted to do a generic comparison between an interface and an abstract class on the basis of their usage.
When would one want to use an interface and when would ...
- 15.6k
542
votes
31
answers
480k
views
How should I have explained the difference between an Interface and an Abstract class? [closed]
In one of my interviews, I have been asked to explain the difference between an Interface and an Abstract class.
Here's my response:
Methods of a Java interface are implicitly abstract
and ...
- 6,872
519
votes
7
answers
408k
views
How to invoke the super constructor in Python?
class A:
def __init__(self):
print("world")
class B(A):
def __init__(self):
print("hello")
B() # output: hello
In all other languages I've worked with the super constructor ...
- 60.1k
483
votes
36
answers
85k
views
Use of .apply() with 'new' operator. Is this possible?
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 (...
- 16.1k
460
votes
13
answers
301k
views
Is it possible to make abstract classes in Python?
How can I make a class or method abstract in Python?
I tried redefining __new__() like so:
class F:
def __new__(cls):
raise Exception("Unable to create an instance of abstract class %...
user1632861
436
votes
6
answers
402k
views
Including another class in SCSS
I have this in my SCSS file:
.class-a{
display: inline-block;
//some other properties
&:hover{
color: darken(#FFFFFF, 10%);
}
}
.class-b{
//Inherite class-a here
//some ...
- 33k
405
votes
8
answers
149k
views
What's wrong with overridable method calls in constructors?
I have a Wicket page class that sets the page title depending on the result of an abstract method.
public abstract class BasicPage extends WebPage {
public BasicPage() {
add(new Label("...
- 91.3k
365
votes
15
answers
244k
views
Extend data class in Kotlin
Data classes seem to be the replacement to the old-fashioned POJOs in Java. It is quite expectable that these classes would allow for inheritance, but I can see no convenient way to extend a data ...
- 4,392
364
votes
11
answers
199k
views
Calling parent class __init__ with multiple inheritance, what's the right way?
Say I have a multiple inheritance scenario:
class A(object):
# code for A here
class B(object):
# code for B here
class C(A, B):
def __init__(self):
# What's the right code to ...
- 18.4k
356
votes
7
answers
110k
views
Explicitly calling a default method in Java
Java 8 introduces default methods to provide the ability to extend interfaces without the need to modify existing implementations.
I wonder if it's possible to explicitly invoke the default ...
- 46k
330
votes
8
answers
392k
views
Inheriting constructors
Why does this code:
class A
{
public:
explicit A(int x) {}
};
class B: public A
{
};
int main(void)
{
B *b = new B(5);
delete b;
}
Result in these errors:
main.cpp: In ...
- 14k
330
votes
7
answers
162k
views
How can you represent inheritance in a database? [closed]
I'm thinking about how to represent a complex structure in a SQL Server database.
Consider an application that needs to store details of a family of objects, which share some attributes, but have ...
- 3,505
322
votes
6
answers
134k
views
JSP tricks to make templating easier?
At work I've been tasked with turning a bunch of HTML files into a simple JSP project. It's really all static, no serverside logic to program. I should mention I'm completely new to Java. JSP files ...
- 4,100
317
votes
15
answers
63k
views
Why is it necessary to set the prototype constructor?
In the section about inheritance in the MDN article Introduction to Object Oriented Javascript, I noticed they set the prototype.constructor:
// correct the constructor pointer because it points to ...
- 6,019
306
votes
6
answers
354k
views
Abstract methods in Python [duplicate]
I am having trouble in using inheritance with Python. While the concept seems too easy for me in Java yet up till now I have been unable to understand in Python which is surprising to me at least.
I ...
user506710
298
votes
5
answers
86k
views
Benefits of prototypal inheritance over classical?
So I finally stopped dragging my feet all these years and decided to learn JavaScript “properly”. One of the most head-scratching elements of the languages design is its implementation of inheritance....
- 10.1k
298
votes
3
answers
180k
views
Chain-calling parent initialisers in python [duplicate]
Consider this - a base class A, class B inheriting from A, class C inheriting from B. What is a generic way to call a parent class initialiser in an initialiser? If this still sounds too vague, here's ...
- 10.1k
290
votes
8
answers
412k
views
How to define custom exception class in Java, the easiest way?
I'm trying to define my own exception class the easiest way, and this is what I'm getting:
public class MyException extends Exception {}
public class Foo {
public bar() throws MyException {
...
- 104k
288
votes
21
answers
277k
views
Do subclasses inherit private fields?
This is an interview question.
Does subclasses inherit private
fields?
I answered "No", because we can't access them using the "normal OOP way". But the interviewer thinks that they are ...
- 15.7k
285
votes
8
answers
69k
views
What does it mean that Javascript is a prototype based language?
One of the major advantages with Javascript is said to be that it is a prototype based language.
But what does it mean that Javascript is prototype based, and why is that an advantage?
- 9,166
284
votes
14
answers
128k
views
Difference between new and override
Wondering what the difference is between the following:
Case 1: Base Class
public void DoIt();
Case 1: Inherited class
public new void DoIt();
Case 2: Base Class
public virtual void DoIt();
...
- 64.8k
272
votes
14
answers
165k
views
In Python, how do I indicate I'm overriding a method?
In Java, for example, the @Override annotation not only provides compile-time checking of an override but makes for excellent self-documenting code.
I'm just looking for documentation (although if ...
- 5,426
271
votes
6
answers
184k
views
How to "perfectly" override a dict?
How can I make as "perfect" a subclass of dict as possible? The end goal is to have a simple dict in which the keys are lowercase.
It would seem that there should be some tiny set of primitives I can ...
- 28.4k
269
votes
15
answers
319k
views
How do I get a PHP class constructor to call its parent's parent's constructor?
I need to have a class constructor in PHP call its parent's parent's (grandparent?) constructor without calling the parent constructor.
// main class that everything inherits
class Grandpa
{
...
- 4,293
268
votes
11
answers
298k
views
Maven project version inheritance - do I have to specify the parent version?
I have two projects: Parent project: A, Sub project: B
A/pom.xml:
<groupId>com.dummy.bla</groupId>
<artifactId>parent</artifactId>
<version>0.1-SNAPSHOT</version>
...
- 12.6k
266
votes
3
answers
33k
views
Why do I have to access template base class members through the this pointer?
If the classes below were not templates I could simply have x in the derived class. However, with the code below, I have to use this->x. Why?
template <typename T>
class base {
protected:
...
- 57.8k
258
votes
13
answers
28k
views
Do I really have a car in my garage? [duplicate]
I'm a newbie to Java programming, trying to get the hang of OOP.
So I built this abstract class:
public abstract class Vehicle{....}
and 2 subclasses:
public class Car extends Vehicle{....}
public ...
- 1,550
251
votes
17
answers
264k
views
Difference between Inheritance and Composition
Are Composition and Inheritance the same?
If I want to implement the composition pattern, how can I do that in Java?
- 15.8k
251
votes
15
answers
150k
views
Convert List<DerivedClass> to List<BaseClass>
While we can inherit from base class/interface, why can't we declare a List<>
using same class/interface?
interface A
{ }
class B : A
{ }
class C : B
{ }
class Test
{
static void Main(...
- 21.8k
251
votes
6
answers
239k
views
249
votes
8
answers
101k
views
Why is it not possible to extend annotations in Java?
I don't understand why there is no inheritance in Java annotations, just as Java classes. I think it would be very useful.
For example: I want to know if a given annotation is a validator. With ...
- 20.2k
248
votes
13
answers
180k
views
Why can't I inherit static classes?
I have several classes that do not really need any state. From the organizational point of view, I would like to put them into hierarchy.
But it seems I can't declare inheritance for static classes.
...
- 30.8k