Top Object-oriented programming (OOPs) Interview Preparation Guide

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Yep. But ..

► Its possible If its a static method.

► Its possible by inheriting from that class also.

► Its possible from derived classes using base keyword.

Use the new modifier to explicitly hide a member inherited from a base class. To hide an inherited member, declare it in the derived class using the same name, and modify it with the new modifier.

When you declare a Constructor with Private access modifier then it is called Private Constructor. We can use the private constructor in singleton pattern.

If you declare a Constructor as private then it doesn’t allow to create object for its derived class, i.e you loose inherent facility for that class.

Example:

Class A

{

// some code

Private Void A()

{

//Private Constructor

}

}



Class B:A

{

//code

}



B obj = new B();// will give Compilation Error



Because Class A constructor declared as private hence its accessibility limit is to that class only, Class B can't access. When we create an object for Class B that constructor will call constructor A but class B have no rights to access the Class A constructor hence we will get compilation error.

No. If you try to create a private class in a Namespace, Compiler will throw a compile time error “Namespace elements cannot be explicitly declared as private, protected, or protected internal”.

Reason: The message says it all. Classes can only be declared as private, protected or protected internal when declared as nested classes, other than that, it doesn't make sense to declare a class with a visibility that makes it unusable, even in the same module. Top level classes cannot be private, they are "internal" by default, and you can just make them public to make them visible from outside your DLL.

In OPP’S, polymorphism(Greek meaning “having multiple forms”) is the ablity of being able to assign a different meaning or usage to something in different contexts - specifically, to allow an entity such as a a function, or an object to have more than one forms.

In C# :
Parent classes may define and implement “virtual” methods(Which is done using the “virtual” keyword), and derived classes can override them(using the “override” keyword), which means they provide their own definition and implementation.At run-time, when user’s code calls the method, the CLR looks up the run-time type of the object, and invokes that override of the virtual method. Thus in your source code when a method of the base class is called it executes the overriden method.

An Attribute is a declarative tag which can be used to provide information to the compiler about the behaviour of the C# elements such as classes and assemblies.
C# provides convenient technique that will handle tasks such as performing compile time operations , changing the behaviour of a method at runtime or maybe even handle unmanaged code.
C# Provides many Built-in Attributes

Some Popular ones are

- Obsolete
- DllImport
- Conditional
- WebMethod

and Many more.
Members please keep on posting more responses providing more In-Built attributes.

Regards Hefin Dsouza

Well, Declare a class with public access specifier and mark all it's method to sealed . As anything which is declared with sealed keyword cannot be inherited.

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.

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

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

If you anticipate creating multiple versions of your component, create an abstract class. Abstract classes provide a simple and easy way to version your components. By updating the base class, all inheriting classes are automatically updated with the change. Interfaces, on the other hand, cannot be changed once created. If a new version of an interface is required, you must create a whole new interface.

If the functionality you are creating will be useful across a wide range of disparate objects, use an interface. Abstract classes should be used primarily for objects that are closely related, whereas interfaces are best suited for providing common functionality to unrelated classes.

If you are designing small, concise bits of functionality, use interfaces. If you are designing large functional units, use an abstract class.

If you want to provide common, implemented functionality among all implementations of your component, use an abstract class. Abstract classes allow you to partially implement your class, whereas interfaces contain no implementation for any 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
};

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.

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.

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.

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.

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

Method overriding is a feature that allows to invoke functions (that have the same signatures) and that belong to different classes in the same hierarchy of inheritance using the base class reference. In C# it is done using keywords virtual and overrides .

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

Use the override modifier to modify a method, a property, an indexer, or an event. An override method provides a new implementation of a member inherited from a base class. The method overridden by an override declaration is known as the overridden base method. The overridden base method must have the same signature as the override method.

You cannot override a non-virtual or static method. The overridden base method must be virtual, abstract, or override.

No, Struct can't be inherited as this is implicitly sealed.

Object is anything that is identifiable as a single material item.

A Class is the generic definition of what an object is a template.

The keyword class in C# indicates that we are going to define a new class (type of object)