Upcasting permits an object of a subclass type to be treated as an object of any superclass type.
Questions tagged [upcasting]
244 questions
160
votes
9 answers
What is the difference between up-casting and down-casting with respect to class variable
What is the difference between up-casting and down-casting with respect to class variable?
For example in the following program class Animal contains only one method but Dog class contains two methods, then how we cast the Dog variable…
Dhivakar
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114
votes
12 answers
Why do we assign a parent reference to the child object in Java?
I am asking a quite simple question, but I am bit confused in this.
Suppose I have a class Parent:
public class Parent {
int name;
}
And have another class Child:
public class Child extends Parent{
int salary;
}
And finally my Main.java…
Narendra Pal
- 6,474
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104
votes
6 answers
downcast and upcast
I am new to C# (and OOP). When I have some code like the following:
class Employee
{
// some code
}
class Manager : Employee
{
//some code
}
Question 1: If I have other code that does this:
Manager mgr = new Manager();
Employee emp…
user184805
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24
votes
9 answers
How do upcasting and vtables work together to ensure correct dynamic binding?
So, vtable is a table maintained by the compiler which contains function pointers that point to the virtual functions in that class.
and
Assigning a derived class's object to an ancestor class's object is called up-casting.
Up-casting is handling a…
Aquarius_Girl
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24
votes
3 answers
Can I cast a derived class to a private base class, using C-style cast?
Can I do this?
class A { ... };
class B : private A
{
const A &foo() const
{
return *((const A *)this);
}
};
Can I take a subclass that inherits privately from a base class and cast it to a public version of its base class? Can…
AdamIerymenko
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15
votes
2 answers
Does upcasting a null pointer lead to undefined behavior
I'm wondering whether the following code leads to undefined behavior:
#include
#include
struct IA {
virtual ~IA() {}
int a = 0;
};
struct IB {
virtual ~IB() {}
int b = 0;
};
struct C: IA, IB {};
int main() {
C* pc =…
Lingxi
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12
votes
1 answer
Why is upcasting necessary in this Scala code?
This compiles:
import scala.collection._
trait Foo[A, +This <: SortedSet[A] with SortedSetLike[A,This]]
extends SortedSetLike[A, This] { this: This =>
def bar: This = (this: SortedSetLike[A,This]).empty
}
But if the upcast is removed it fails…
Robin Green
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11
votes
2 answers
Implicit conversion vs. static_cast when upcasting
Let's say I have three classes: A (the mother, abstract), and B and C, the children of A.
So B and C inherit from A (public inheritance).
I have a list of pointers to A, which I populate with pointers of B or C.
The question is: which is the…
fern17
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11
votes
3 answers
Why Java object class remains same after casting?
I tried to upcast an objet. But at runtime object class is remained as a derived class.
Derived drv = new Derived();
Base base = (Base) drv;
System.out.println("Class : " + base.getClass());
//prints -> Class : class packagename.Derived
So…
Huseyin
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11
votes
5 answers
How Derived Class object is added to Base Class objects List
Given the following code, I have inherited a class Circle from Shape:
class Shape
{
void Draw();
}
class Circle : Shape
{
}
void Main(string[] args)
{
Shape s = new Shape();
Shape s2 = new Shape();
Circle c = new Circle();
…
Failed Scientist
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10
votes
2 answers
up-casting std::shared_ptr using std::dynamic_pointer_cast
I'm starting to work with smart pointers in C++0X/11 and I've run into a peculiar situation.
I want to up cast an instance of an object using shared_ptr.
Class Extend inherits from class Base, where Base class has a virtual destructor in order to…
Ælex
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10
votes
3 answers
Why does C style cast allow you to convert to a private base class?
Say we have this code
class A {
public:
A() : x(1) {}
virtual ~A() {}
int x;
};
class B {
public:
B() : y(2) {}
virtual ~B() {}
void g()
{
cout << "B::" << y << endl;
}
int y;
};
class C : private A,…
unkulunkulu
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9
votes
5 answers
How to implement a compile-time check that a downcast is valid in a CRTP?
I have a plain old CRPT (please don't get distracted by access restrictions - the question is not about them):
template
class Base {
void MethodToOverride()
{
// generic stuff here
}
void…
sharptooth
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9
votes
4 answers
Upcasting and its effect on the heap
For the following classes:
public class Parent {
//Parent members
}
public class ChildA : Parent {
//ChildA members
}
public class ChildB : Parent {
//ChildB members
}
If I upcast ChildA or ChildB instance to a Parent instance, then I can't…
Honey
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9
votes
1 answer
implicit upcasting and explicit downcasting in java
When java can implicitly do up casting , why does not it implicitly do down casting ?Please explain with some simple example? …
Number945
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