OOP

Sealed types cannot be inherited & are concrete.

Sealed modifiers can also be applied to instance methods, properties, events & indexes. It can't be applied to static members.

Sealed members are allowed in sealed and non-sealed classes.

Virtual Method has implementation & provide the derived class with the option to override it.

Polymorphism means one interface and many forms. Polymorphism is a characteristics of being able to assign a different meaning or usage to something in different contexts specifically to allow an entity such as a variable, a function or an object to have more than one form.

There are two types of Polymorphism.

Compile time: function or operator overloading

Runtime: Inheritence & virtual functions

Abstract method doesn't provide the implementation & forces the derived class to override the method.

Constructors are used for initializing the members of a class whenever an object is created with the default values for initialization.

If no constructor defined then the CLR will provide an implicit constructor which is called as Default Constructor.

A class can have any number of constructors provided they vary with the number of arguments that are passed, which is they should have different signatures.

Constructors do not return a value

Constructors can be overloaded

Public : Accessible to All

Private: Those classes in which only static members are there and you don't want there objects to be created in any class.

Static: Used for initializing only the static members of the class. These will be invoked for the very first time the class is being loaded on the memory. They cannot accept any arguments. Static Constructors cannot have any access modifiers.

Intern: implementations of the abstract class to the assembly defining the class. A class containing an internal constructor cannot be instantiated outside of the assembly (Namespace).

and External

The public keyword is an access modifier for types and type members ie. we can declare a class or its member (functions or methods) as Public. There are no restrictions on accessing public members.

When you define only function prototype in a base class without and do the complete implementation in derived class. This base class is called abstract class and client won’t able to instantiate an object using this base class.

A pure virtual function is a function that must be overridden in a derived class and need not be defined. A virtual function is declared to be "pure" using the curious "=0"

syntax:

class Base {

public:

void f1(); // not virtual

virtual void f2(); // virtual, not pure

virtual void f3() = 0; // pure virtual

};

Abstract Class:

Have constructors.

Not necessarily for the class inheriting it to Implement all the Methods.

Doesn't Support Multiple Inheritance.

Where everything is Opposite in the Interfaces.

The internal keyword is an access modifier for types and type members ie. we can declare a class as internal or its member as internal. Internal members are accessible only within files in the same assembly (.dll). In other words, access is limited exclusively to classes defined within the current project assembly.

The protected keyword is a member access modifier. It can only be used in a declaring a function or method not in the class ie. a class can't be declared as protected class.

A protected member is accessible from within the class in which it is declared, and from within any class derived from the class that declare this member. In other words access is limited to within the class definition and any class that inherits from the class

A protected member of a base class is accessible in a derived class only if the access takes place through the derived class type.

The private keyword is a member access modifier ie. we can't explicitly declare a class as Private, however if do not specify any access modifier to the class, its scope will be assumed as Private. Private access is the least permissive access level of all access modifiers.

Private members are accessible only within the body of the class or the struct in which they are declared. This is the default access modifier for the class declaration.

No, we can't specify the access modifier for the explicitly implemented interface method. By default its scope will be internal.

An enum has default modifier as public

A class has default modifiers as private . It can declare members (methods etc) with following access modifiers:

public

protected

internal

private

protected internal

An interface has default modifier as public

A struct has default modifier as private and it can declare its members (methods etc) with following access modifiers:

public

internal

private

Protected Internal is a access modifiers for the members (methods or functions) ie. you can't declare a class as protected internal explicitly. The members access is limited to the current assembly or types derived from the containing class.

Protected Internal means the method is accessible by anything that can access the protected method UNION with anything that can access the internal method.

Method overloading occurs when a class contains two methods with the same name, but different signatures.