对多个 inheritance 感到困惑

Question

I just read some where that C# class can't inherit from multiple class, at the same time I also read that each C# class is inherited from a base class "Object Class".

Now I am confused if I make another class make it to inherit some class, then it is inheriting from the class and the base class, ie two class.

Isn't it breaking the law?

Answer 1

Each class inherits from one other class. If you make your own class extend one of your other classes, then it will not directly inherit from Object but rather from your superclass. The superclass in its turn will inherit from Object .

Your subclass will have all the methods from Object available trough the superclass.

This will illustrate it:

void Main()
{
    Console.WriteLine (new Super().GetType().BaseType);
    Console.WriteLine (new Sub().GetType().BaseType);
}

class Super { }
class Sub : Super { }

Output:

Answer 2

This is possible in C#:

(One base class per derived class, aka "single inheritance ")

This is not possible in C#:

( Multiple inheritance , use interfaces instead in C#)

Answer 3

I just read some where that C# class can't inherit from multiple class, at the same time I also read that each C# class is inherited from a base class "Object. Now I am confused.

Every C# class except object inherits directly from exactly one other class. Object inherits from no class.

AC# class can inherit indirectly from any (non-negative!) number of classes.

class Animal : Object {}
class Giraffe : Animal {}

Are our rules met? Yes. Object inherits from no class. Animal inherits directly from Object and indirectly from no class. Giraffe inherits directly from Animal and indirectly from Object.

This eliminates the contradiction.

Answer 4

Every class, except Object itself, will implictly extend Object if it does not extend another class. Thus all classes implictly always eventually extend from Object.

The only common programming language supporting multiple inheritance is C++, it's explictly not allowed in most languages for good reason.

Answer 5

One class can inherit from one other class directly and implement multiple interfaces.
You can chain inheritance, eg class a inherits from class b while class c inherits from class a.

interface i {}
class a {}
class b : a {}   // OK
class c : i,b {} // OK
class d : a,b {} // Not OK

Answer 6

Multiple inheritance means that a class' inheritance tree can be branched as desired (ie it can inherit from more than one base classes at the same time). That's (thank god) not possible in C#.

But as long as the inheritance tree has always only one 'upper leg', it can be as deep as required (ie there is something like an inheritance 'chain', where one class inherits from the other).

Answer 7

It does not break the rule.

Every class in C# will inherit from exactly one class. That class either is any class the author of that class wants to extend, or, if none specified, it will extend the Object class.

public class MyClass {} // extends from default Object class

would be exactly the same as

public class MyClass : object {}

Or, when the author wants to extend a specified class:

public class MyClass : AnyBaseClass {}

Answer 8

3. What is Is-A relationship in Java?

Ans: Is-A relationship represents Inheritance. It is implemented using the “extends” keyword. It is used for code reusability.

4. What is super class and subclass?

Ans: A class from where a subclass inherits features is called superclass. It is also called base class or parent class.

A class that inherits all the members (fields, method, and nested classes) from other class is called subclass. It is also called a derived class, child class, or extended class.

5. How is Inheritance implemented/achieved in Java?

Ans: Inheritance can be implemented or achieved by using two keywords:

extends: extends is a keyword that is used for de