As stated above, is it redundant to inherit from Object in c#?
Do both sets of code below result in equivalent objects being defined?
class TestClassUno : Object
{
// Stuff
}
vs.
class TestClassDos
{
// Stuff
}
I snooped around on MSDN but wasn't able to find anything perfectly conclusive.
If left unspecified every class definition will implicitly inherit from System.Object hence the two definitions are equivalent.
The only time these two would be different is if someone actually defined another Object type in the same namespace. In this case the local definition of Object would take precedence and change the inheritance object
namespace Example {
class Object { }
class C : Object { }
}
Very much a corner case but wouldn't point it out if I hadn't seen it before
Note that the same is not true if you used object instead of Object. The C# keyword object is a type alias for System.Object and hence it wouldn't match Example.Object.
namespace Example2 {
class Object { }
class C : Object { } // Uses Example.Object
class D : object { } // Uses System.Object
}
Of course if you have a truly evil developer you could still cause confusion with object
namespace System {
class Object {
private Object() { }
}
}
namespace Example3 {
// This will properly fail to compile since it can't bind to the private
// Object constructor. This demonstrates that we are using our definition
// of Object instead of mscorlib's
class C : object { } // Uses our System.Object
}
Yes, everything ultimately inherits from an object if defined as class. Leave the explicit inheritance out of your code.
Yes it is redundant to inherit from object in class
MSDN : Object class : Supports all classes in the .NET Framework class hierarchy and provides low-level services to derived classes. This is the ultimate base class of all classes in the .NET Framework; it is the root of the type hierarchy.
Check this research : inherits from object? An investigation into how.
Object is the mother of all classes in .Net. There is nothing above it.
All classes inherit from it. So this code
class TestClassDos
{
// Stuff
}
automatically means it is inheriting from object.
Proof: You can typecast any entity to object which is possible if it is inheriting from it.
Summary of Object class says
// Supports all classes in the .NET Framework class hierarchy and provides low-level
// services to derived classes. This is the ultimate base class of all classes
// in the .NET Framework; it is the root of the type hierarchy.
Yes, they are both the same thing, I don't think I saw anyone mention structs, but all objects (that is regardless if you declare a class or a struct) they all ultimately inherit from Object, see this Object MSDN article and this other article on Structs
There is a time when inheriting from object makes sense — when you have a partial class definition, and you want to lock down inheritance and prevent other partial declarations from extending a different class. Attempting to inherit from another type in the partial class will then give you the CS0263 Compiler Error.
This only makes sense in the event that your partial class is not already inheriting from another type.
The partial keyword is not in your code example, but I thought it might be worth mentioning as I found my way here from Google after seeing a similar setup in an API. Aside from inheriting from objects that don't point to the official System.Object as others pointed out, there is no benefit in doing so as all classes inherit from object implicitly.
Related
I need to clarify a thing that how an object type variables accept class type instance an given in the below code snippet,
class MyClass
{
}
static void Main()
{
object obj = new MyClass();
}
Since the MyClass is not a type of object but still the instance of MyClass is accepted in the obj(object) variable.
Actually, your class is an object.
In C# all classes derives from object.
Referring to a class as it's base type is one way of Polymorphism.
It might be better understood using an analogy:
Your class is an object, like a Dog is an animal.
Also, If you try the following:
object obj = new MyClass();
bool isMyType = obj == typeof(MyClass); //<--this will be true.
Take a look at this SO thread for more information how Polymorphism can be useful.
The concept that you do not understand is polymorphism which basically say that you can define an is relation between your classes. For a simple logic every dog is an animal so you can have class Dog that inherits from Animal. This implies that you can assign to variable of type Animal an instance of a Dog but not the other way around - not every animal is a dog. Another thing is that every thing derives form object this is language concept that you simply can take for granted.
Evrything in c# is derived from Object...
even your class.
.Net follows OOPs (Object Oriented Programming Language) and here every class can act as a object. Every class inherits Object class and hence every class can act as an object. In your example, .Net creates a default constructor to create instance of the class. You can definitely write your own constructor there.
Hope it helps.
Everything in C# is derived from Object.
Even Value Types like struct(int,float,..) are all derived from Object type.
When you define your own class,it implicitly derives from the Object type.
It is mentioned in the docs
All classes, structures, enumerations, and delegates inherit from
Object class
MSDN:
Supports all classes in the .NET Framework class hierarchy and provides low-level
services to derived classes. This is the ultimate base class of all classes
in the .NET Framework; it is the root of the type hierarchy.
Inheritance Hierarchy:
All classes, structures, enumerations, and delegates.
This means when you use int.Parse() to cast some value to int, there is a class behind int type which makes it able to have methods and do such stuffs. Object has been rooted pretty much everywhere in .Net.
I have two sequences of objects 'A' and 'B'. Comparing the sequences should produce a third sequence 'C' of elements that indicate whether:
the objects were "deleted" from 'A' or
"inserted" from 'B'.
All remaining elements are considered as "matched".
What I would like to do:
Declare Inserted<T>, Deleted<T>, and Matched<T> generic classes that inherit all their properties from the T base class. The generic class must be able to instantiate itself from the object it inherits.
The code:
public interface IInstantiable<T>
{
void CopyFrom(T o);
}
[Serializable]
public class Inserted<T> : T
where T : IInstantiable<T>
{
public Inserted() { }
public Inserted(T t)
{
this.CopyFrom(t);
}
}
The error:
'MyNamespace.Inserted<T>' does not contain a definition for 'CopyFrom' and no
extension method 'CopyFrom' accepting a first argument of type 'MyNamespace.Inserted<T>'
could be found (are you missing a using directive or an assembly reference?)
Further discussion:
I define my own IInstantiable interface to enforce the existence of a CopyFrom method. I cannot use the standard ICloneable interface, because it only defines a method that copies the object to a new instance, whereas I need the object to copy its members in the constructor.
The error goes away if the generic defines its own implementation of the CopyFrom method; however, this does not achieve the desired goal of specializing the CopyFrom method to handle the specific needs of the base class. Only the base class could know what properties should be copied. (Or am I missing something?)
Note: The final object should have the same public members as its base class, as the object should be capable of serialization.
Is this possible in .NET?
The answer:
What I am attempting to do is impossible, simply because the generic class cannot be an extension of the template base class. Visual Studio complains "Cannot derive from 'T' because it is a type parameter." (I hadn't noticed this error yet because I had not implemented the CopyFrom method in the generic class yet.)
If I were to change the interface into a class and supply a stub implementation in that class, I could inherit from it as suggested below; however, this introduces a new base class into my inheritance hierarchy.
public class IInstantiable<T>
{
public virtual void CopyFrom(T o) { }
}
[Serializable]
public class Inserted<T> : IInstantiable<T>
where T : IInstantiable<T>
{
public Inserted() { }
public Inserted(T t)
{
base.CopyFrom(t);
}
}
Unfortunately, I cannot use this new base class in its templatized form because I must introduce it at the root of my inheritance hierarchy. It works only if I remove the template and make it as generic as possible.
public class IInstantiable
{
public virtual void CopyFrom(Object o) { }
}
However, this still does not make my Inserted<T> generic look like the object it is initialized from, and since I cannot inherit from the same type as the type parameter, it does not suit my initial purpose.
Moving away from "fancy generics" based on the type system to more (ahem) generic annotated structures might prove to be the best solution; however, the default behavior of my selected serialization approach (XmlSerialization) does not have the automatic support that would make this configuration a viable solution. Generics will not work; use hard-coded class definitions instead.
This is indirectly what you're trying to declare in your code above.
[Serializable]
public class Inserted<T> : IInstantiable<T>
where T : IInstantiable<T>
{
public Inserted() { }
public Inserted(T t)
{
this.CopyFrom(t);
}
}
Does this make sense?
.NET doesn't allow you to inherit from a generic parameter. How could it? Generics are evaluated at runtime but it needs to know what type your class is at compile time.
If I understand correctly, you want to annotate a sequence of objects with the notion of what their state is (inserted, deleted, or matched).
You don't really need fancy generics for this; what's wrong with:
enum ChangeState { Inserted, Deleted, Matched }
struct<T> Annotated {
public T Obj;
public ChangeState;
}
You can mark this for serialization however you want (the Annotated object can serialize just fine without the same properties/fields).
Though you can encode more information in the type system, it's unclear to me what the benefit would be here. Are you sure you want to do that?
I have a three classes A, B, and C shown below
public class A
{
public void add(int i, int k)
{
}
}
public class B:A
{
public void AddInt()
{
add(1, 2);
}
}
public class C
{
public void AddInt()
{
A objA = new A();
objA.add(1, 2);
}
}
We want access the "A" class method Add, there are two ways
1) Initiate the "A" class, then access the Add method
2) Inherit the "A" class, then access the Add method
If both those ways provide the same functionality, then why does C# provide two ways to achieve the same functionality.
What is the difference between initiating a class and inheriting a class?
First off, the word you're looking for is instantiate, not initiate.
What is the difference between instantiating a class and inheriting a class?
Inheritance expresses the "is a kind of" relationship between two classes:
The New York Times is a kind of newspaper.
A giraffe is a kind of animal.
An apple is a kind of fruit.
In each of these cases the first kind of thing is the "more derived" type -- it is more specific -- and the second thing is the "less derived" type, or "base" type. It is more general. More things are fruits than are apples.
In C# when you establish an inheritance relationship between two classes, you get two things:
Assignment compatibility: you can use an expression of the more derived type where an expression of the base type is needed.
Member inheritance: all methods, events, indexers, operators, fields, properties and nested types of the base class are automatically members of the derived class. (Constructors and destructors are not inheritable).
Instantiation is the process of making a new instance of a type.
Here, let me give you a copy of today's New York Times.
Here, let me give you a giraffe.
Here, let me give you an apple.
So in C#:
class Fruit {}
class Apple : Fruit { } // Apple inherits from Fruit
class Program {
static void Main() {
Apple apple = new Apple(); // Instantiating a new Apple
}
}
Make sense?
It's not about C# at all, it's about basic OOP concepts, that C#, in this case, simply manifests, being object oriented and strong typed language.
"Initialization" is a creation of an instance of a given type: A in your case.
Second example is a Polymorphism , where you derive from a given type A, and creating derived type B, is able to access public/protected members of the A class.
The access behaviour is the same in this case, but origin of that is completely different.
you are comparing Humans with food ... right no comparison
Initiating cost you some RAM of your system.
Inheriting lets you enable reuseability of common code
These two ways are available because your add method is public in class A. Change it to protected if you want to use it only in inherited classes. Simply saying inheritance makes all properties and methods except of private ones available in inherited classes. In your case class B is inherited from class A and instance of class B itself would be your instance to call method add on. In class C you simply created an instance of class A and called method add on it. All of this concepts would be much cleaner to you if you'll read about Access Modifiers and Inheritance.
Think of a class as a template, or plan, for how to build something. When you then use the template or plan to build one (think of architect plans for a house, and one of the many houses built from those plans), the words we use to describe this process are "Instantiation" and "Initialization".
You instantiate an instance of the object (build the house) using the class template (architects plan), and then initialize it (paint and decorate the house).
Inheritance, on the other hand, refers to something completely unrelated, in how classes are defined, using another existing class as a foundation or *base*line from which to start the definition of a new class that will extend the foundation or base class. When one class inherits from another, it means that "instances" of the derived class automatically get all the stuff that was defined in the parent base class without having to redefine it in the child.
A class is a type and acts as a template that allows you to create objects of this type. The creation of such objects is also called instantiation. This instantiation process involves allocating memory for this object (allocation) and then initializing this object, i.e. give its fields initial values. The latter is called initialization.
Inheritance is something completely different. Inheritance is about creating a new class (template) by inheriting existing code from a base class (also called superclass, or parent class).
This new derived class (also called subclass or child class) serves as template for the creation of a new type of objects.
The derived class can modify the behavior inherited from its base class and extend its possibilities. Inheritance creates a relation between the classes. Subclasses are assignment compatible with the superclasses above them in the inheritance hierarchy.
We know that the Array class in c# is abstract.
But the static CreateInstance method of this class returns an object of the Array class.
How is it possible?
Description
No, you cant create an instance of an abstract class.
MSDN: Abstract classes are closely related to interfaces. They are classes that cannot be instantiated, and are frequently either partially implemented, or not at all implemented. One key difference between abstract classes and interfaces is that a class may implement an unlimited number of interfaces, but may inherit from only one abstract (or any other kind of) class. A class that is derived from an abstract class may still implement interfaces. Abstract classes are useful when creating components because they allow you specify an invariant level of functionality in some methods, but leave the implementation of other methods until a specific implementation of that class is needed. They also version well, because if additional functionality is needed in derived classes, it can be added to the base class without breaking code.
More Information
MSDN - Abstract Classes
It's a static factory method that returns an instance of array. this example creates an array of length 10 for integer value types.
System.Array myIntArray = Array.CreateInstance(typeof(int),10);
This should give you some more detail http://msdn.microsoft.com/en-us/library/zb3cfh7k.aspx
The various overloads of the method Array.CreateInstance() are typed as returning Array, which indeed is an abstract class. But the type of the object they return is not directly Array, it's some type that inherits from Array (what type exactly depends on the overload used and the parameters you pass in).
For example:
Array a = Array.CreateInstance(typeof(int), 10); //create some array
Type type = a.GetType(); // type is int[], which is not abstract
Type baseType = type.BaseType; // baseType is Array
Basically, it's the same principle like the following factory method:
abstract class Animal
{
public static Animal CreateInstance(AnimalType animalType)
{
if (animalType == AnimalType.Cat)
return new Cat();
if (animalType == AnimalType.Dog)
return new Dog();
// etc.
}
}
Here, Animal is an abstract base type, Cat and Dog are concrete types that inherit from Animal and animalType tells us which type should the method return.
Now, arrays are treated specially in several ways in .Net (for example, there are IL instructions specifically for dealing with arrays). But they are not an exception in the type system (except, maybe for array covariance).
Array seems to be a special case of abstract class. From what I've read in Documentation I'd suggest that Array creation and functions are somehow handled internally in .NET Framework code - most probably extensively using native code for better performance results. I think that's why this class have been made abstract.
I'd be glad if someone more knowledgable of .NET Framework internals can improve my answer.
I think the best way to relate to this situation is by considering a method that returns you instance of an interface!!!
Well, you know that we can not create instance of an interface, but internally a method may know about a class implementing that interface and return instance of that class.
namespace ConsoleApplication1
{
public class Circle : Shape
{
public override void Draw()
{
Console.WriteLine("Draw a Circle");
}
}
public abstract class Shape
{
public abstract void Draw();
}
}
You can do like this
class Program
{
static void Main(string[] args)
{
Shape v;
v = new Circle();
v.Draw();
}
}
Not sure if it is not logical but want to learn. If we don't declare our base class when creating a new class, both visual studio and compiler knows it inherits "object". is there any way to tell the compiler and visual studio(for intellisense) that my base class is not "object", it is "myobject" for example? maybe any configuration on visual studio?
you can say "inherit all your classes from 'myobject'", i know it but just want to know is it possible.
No, absolutely not. This is part of the C# spec, and is in no way optional. From section 10.1.4.1:
If a class declaration has no class-base, or if the class-base lists only interface types, the direct base class is assumed to be object.
No implementation-specific wiggle-room - that's just the way it is. Personally I'm glad - I want to be able to tell the direct base class just from looking at the source code, without knowing any project configuration.
EDIT: Just to be clear, C# could have been designed such that a different type could be specified as the base type. For example, I could imagine (but dislike) a language where:
class Foo
{
}
compiled with:
csc /evil:DefaultBaseClass=System.IO.Stream Foo.cs
was equivalent to:
class Foo : Stream
{
}
That doesn't break .NET at all - it's a purely language decision. What is enforced by .NET is that most types end up with at least an indirect base class of System.Object. I don't think a language could be designed to allow you to set up a "parallel" type hierarchy.
That's not possible, the way C# is designed, (almost) everything derives from Object. If this were not the case you couldn't rely on the methods Object provides being there, which are pretty fundamental/useful.
Note that it is .Net that requires all objects to be derived from Object (directly or indirectly). C# specifies that objects declared with no base class inherit from Object, other languages are free to specify another type, however that type must inherit (directly or indirectly) from Object as per .net requirements.
Obviously you're free to have your own base class for all types you create, however that base class has to inherit from object (either directly or indirectly).
Do you want to add methods to all/existing types? In which case use extension methods.
You could modify the existing item templates (or create a new one) so that new classes automatically inherit from some base class:
using System;
using System.Collections.Generic;
$if$ ($targetframeworkversion$ >= 3.5)using System.Linq;
$endif$using System.Text;
namespace $rootnamespace$
{
class $safeitemrootname$ : SomeBaseClass
{
}
}
See Customizing Project and Item Templates
You can create your own custom abstract class and override the 4 methods defined by the Object class and further add new virtual and abstract methods to your custom base class. Then, you can use this class as the base class explicitly for all your other custom classes. But, that will still mean the super base class of all the classes will be Object only (you can't change that). e.g.
//your custom base class
public abstract class MyObject
{
public virtual void MyCustomMethod()
{
//Your custom method implementation
}
public abstract void MyCustomAbstractMethod();
public override string ToString( )
{
//your custom implementation for override
}
public override string Equals( )
{
//your custom implementation for override
}
public override string GetHashCode( )
{
//your custom implementation for override
}
public override string GetType( )
{
//your custom implementation for override
}
}
//your custom child class
public class CustomClass1 : MyObject //still derived from object
{
//implement and override the MyObject and object methods
}
//your custom child class
public class CustomClass2 : MyObject //still derived from object
{
//implement and override the MyObject and object methods
}
But all the built-in types provided by the .Net BCL will not be able to use your MyObject class, they still will be known to be derived from object.
Ok one thing: In C# and Java all classes declared are derived automatically from Object. There is no changing this. Object is the root of the class hierarchy. Now, you can have your classes inherit another class like:
public class A : B // A inherits B
but up the chain, you will still find Object at the top because anyway B inherited Object.
i think every thing in .NET inherites from object class. 4 example, becouse it, every object have ToString() method.
All the classes and struct inheret from Object, it is the parent of all, even you inherited from a class
public class A : B // A inherits B