Interview Questions and Answers on Dot Net Framework C Sharp Dot Net OOPS (Part-4)

Interview Questions and Answers on Dot Net Framework CSharp Dot Net OOPS

Question 71 – What are the different Access Modifiers available?

• Public – Access to same assembly or another assembly that references it.
• Private – Access to the same class or struct.
• Protected – Access to same class or struct, or in a class that is derived.
• Internal – Access to any code in the same assembly, but not from another assembly.
• Protected Internal – Access to any code in the assembly in which it is declared, or from within a derived class in another assembly.

Question 72 – What are the differences between Class and Struts?

Class Struct Class is a reference type Struct is a value type Class supports inheritance Struct will not support inheritance Class variables are stored on Heap Struct variables are stored on Stack Class can have destructor Struct will not have destructor Boxing a class object creates reference to same object Boxing a strut object will create a copy in diff type All the members of Class are private by default All the members of struct are public by default Class is well suited for Data hiding Struts are not suited for Data hiding

 Question 73 – What are the Similarities between Class and Struts?

Both are user defined types.

Both of them can have constructor without parameter and with parameter. Both can have delegates and events.Both can have methods, properties , fields, constants , enumerations, events.

 Question 74 – What is the term Virtual means?

When we need to override a method of the base class in the sub class, then we give the virtual keyword in the base class method. This makes the method in the base class to be overridable. Methods, properties, and indexers can be virtual, which means that their implementation can be overridden in derived classes. You cannot use the virtual modifier with the following modifiers:

• Static,
• Abstract
• Override

Question 75 – What is a Sealed Class?

• Sealed classes are used to restrict the inheritance feature of object oriented programming.
• Once class is defined as sealed class, this class cannot be inherited so we can’t derive class.
• Keywords: C# – Sealed , VB.NET – NotInheritable
• If you have ever noticed, struct are sealed. You cannot derive a class from a struct.
• A sealed class cannot be used as a base class. For this reason, it cannot also be an abstract class.
• The best usage of sealed classes is when you have a class with static members.
• Example – The Pens and Brushes classes of the System.Drawing namespace. The Pens class represent the pens for standard colors.
• This class has only static members. Pens.Blue represents a pen with blue color. Similarly, the Brushes class represents standard brushes.
• The Brushes.Blue represents a brush with blue color.

Question 76 – What is Polymorphism?

• Polymorphism is one of the primary characteristics (concept) of object-oriented programming.
• Poly means many and morph means form. Thus, polymorphism refers to being able to use many forms of a type without regard to the details.
• Polymorphism is the characteristic of being able to assign a different meaning specifically, to allow an entity such as a variable, a function, or an object to have more than one form.
• Polymorphism is the ability to process objects differently depending on their data types.
• Polymorphism is the ability to redefine methods for derived classes.

Question 77 – What are the Types of Polymorphism?

• Compile time Polymorphism (method overloading)
• Run time Polymorphism (method overriding)

Question 78 – What is Method Overloading? Or What is Early Binding?

Method overloading means having two or more methods with the same name but with different signatures

Question 79 – What is Method Overriding or What is Late Binding?

Method overriding means having two or more methods with the same name , same signature but with different implementation. (Base class and Child class implementation of a method with same name and signature)

Question 80 – What is an Inheritance?

It is the ability to use all of the functionality of an existing class, and extend those capabilities without re-writing the original class. It is the process by which one object acquires the properties of another object. A new class that is created by inheritance is sometimes called a child class or a subclass. The class you originally inherited from is called the base class, parent class, or the superclass.

Question 81 – What are the Types of Inheritance?

• Implementation inheritance refers to the ability to use a base class’s properties and methods with no additional coding.
• Interface inheritance refers to the ability to use just the names of the properties and methods, but the child class must provide the implementation.
• Visual inheritance refers to the ability for a child form (class) to use the base forms (class) visual representation as well as the implemented code.

Question 82 – What is Multiple Inheritance?

C# does not support multiple implementation inheritance. A class cannot be derived from more than one class, However, a class can be derived from multiple interfaces.

Question 83 – What are the examples of Multiple Inheritance?

Imagine a class named TransmitData, whose function is to transmit data, and another class named ReceiveData, whose function is to receive data. Now imagine that you want to create a class named SocketPort, whose function is to transmit and receive data. In order to accomplish this, you would want to derive SocketPort from both TransmitData and ReceiveData.

Question 84 – What are the Advantages of Inheritance?

• Once a behavior (method) or property is defined in a super class(base class),that behavior or property is automatically inherited by all subclasses (derived class).
• Code reusability increased through inheritance.
• Inheritance provide a clear model structure which is easy to understand without much complexity Using inheritance, classes become grouped together in a hierarchical tree structure Code are easy to manage and divided into parent and child classes.

Question 85 – What is an Encapsulation?

• Encapsulation is a process of hiding all the internal details of an object from the outside world.
• Encapsulation is the ability to hide its data and methods from outside the world and only expose data and methods that are required
• Encapsulation gives us maintainability, flexibility and extensibility to our code.
• Encapsulation makes implementation inaccessible to other parts of the program and protect from whatever actions might be taken outside the function or class.
• Encapsulation provides a way to protect data from accidental corruption
• Encapsulation hides information within an object
• Encapsulation is technique or process of making fields in a class private and providing access to the fields using public methods
• Encapsulation allows us to create a “black box” and protects an objects internal state from corruption by its clients.
• The idea of encapsulation comes from the need to cleanly distinguish between the specification and the implementation of an operation and the need for modularity.

Question 86 – What are the examples of Encapsulation?

• Let’s say you have an object named Bike and this object has a method named start(). When you create an instance of a Bike object and call its start() method you are not worried about what happens to accomplish this, you just want to make sure the state of the bike is changed to ‘running’ afterwards. This kind of behavior hiding is encapsulation and it makes programming much easier.
• Video Recorder, which has a record, play, pause buttons is another example of encapsulation, so VCR is encapsulated into a single object where the internals can change but stays the same for users interface point of view.
• Medical Capsules i.e. one drug is stored in bottom layer and another drug is stored in Upper layer these two layers are combined in single capsule.

Question 87 – What is an Abstraction?

• Abstraction means to show only the necessary details to the client of the object.
• Abstraction is about paying attention to the details that are relevant and ignoring the rest.
• It refers to act of representing essential features without including background details / explanations.

Question 88 – What are the examples of Abstraction?

• Do you know the inner details of the Monitor of your PC? What happen when you switch ON Monitor? No Right, Important thing for you is weather Monitor is ON or NOT.
• When you change the gear of your vehicle are you really concern about the inner details of your vehicle engine? No but what matter to you is that Gear must get changed that’s it!!
• Let’s say you have a method “CalculateSalary” in your Employee class, which takes EmployeeId as parameter and returns the salary of the employee for the current month as an integer value. Now if someone wants to use that method. He does not need to care about how Employee object calculates the salary? An only thing he needs to be concern is name of the method, its input parameters and format of resulting member. This is abstraction; show only the details which matter to the user.
• TV Remote Button in that number format and power buttons and other buttons there just we are seeing the buttons, we don’t see the button circuits .i.e buttons circuits and wirings all are hidden.

Question 89 – Difference between Encapsulation and Abstraction ?

Encapsulation Abstraction Hiding the internal details or mechanics of how an object does something. It focus on what the object does instead of how it does it. Binding data and member functions together inside a single unit. Hiding the complexities of your type from outside world. Eg: VCR Example Eg: Monitor Example

Question 90 – What is an Abstract Class?

• It is a class that cannot be instantiated, it exists extensively for inheritance and it must be inherited.
• Abstract classes cannot be used to instantiate objects; because abstract classes are incomplete
• Abstract classes may contain only definition of the properties or methods.
• Derived classes that inherit the abstract class needs to implements it’s properties or methods.
• An abstract class is essentially a blueprint for a class without any implementation.
• An abstract class is a class that must be inherited and have the methods overridden.
• An abstract class cannot be a sealed class.
• An abstract method cannot be private.
• An abstract member cannot be static.
• An abstract method cannot have the modifier virtual. Because an abstract method is implicitly virtual.
• The access modifier of the abstract method should be same in both the abstract class and its derived class. If you declare an abstract method as protected, it should be protected in its derived class. Otherwise, the compiler will raise an error.

Question 91 – What is an Interface?

• An interface looks like a class, but has no implementation.
• An interface is a named set of method signatures.
• An Interface is a reference type and it contains only abstract members.
• An interface is an array of related function that must be implemented in derived type.
• Members of an interface are implicitly public & abstract.
• It can contain definitions of events, indexers, methods parameter less and parameterful properties.
• The interface can’t contain constants, data fields, constructors, destructors and static members.
• All the member declarations inside interface are implicitly public. 
• Interfaces are great for putting together plug-n-play like architectures where components can be interchanged at will. Since all interchangeable components implement the same interface, they can be used without any extra programming.

Question 92 – What is a difference between Abstract Class and Interface?

Abstract Class  Interface Cannot be instantiated, means one cannot make a object of this class. We can only define method definition and no implementation. Access modifiers are allowed Access modifiers are not allowed Some methods can be concrete All methods are abstract A class can inherit only one abstract class A class can inherit many interface. Can have any access modifiers By default its public static final Can have constructor and destructor Cannot have constructor and destructor Only one abstract class can be derived Class can have multiple interfaces Requires more time to find actual method in class Faster Abstract class provides 0 to 100% generalization Interface provides 100% generalization It provides both generalization and specialization Interface provides only Generalization

 

Question 93 – What is a Constructor?

• Constructor is used to initialize an object (instance) of a class.
• Constructor is a like a method without any return type.
• Constructor has same name as class name.
• Constructor follows the access scope (Can be private, protected, public, Internal and external).
• Constructor can be overloaded, means we can have constructors with different set of parameters.
• We can always make the call to one constructor from within the other constructor. 
• Only this and base keywords allowed in initializing constructors, other method calls will raise error.

Question 94 – What is a Constructor chaining?

Overloading the constructor using the this and base keywords so that it overload is called constructor chaining

Question 95 – What are the Types of constructors?

• Static Constructor
• Default Constructor
• Private Constructor
• Copy Constructor 
• Parameterized Constructor

Question 96 – What is a Private Constructor?

• Used to prevent the user to instantiate the class directly.
• Used to prevent the creation of instances of a class when there are no instance fields or methods
• A private constructor is a special instance constructor.
• It is commonly used in classes that contain static members only.
• If a class has one or more private constructors and no public constructors, then other classes (except nested classes) are not allowed to create instances of this class.
• Note that if you don’t use an access modifier with the constructor it will still be private by default.
• Private constructors are used to restrict the instantiation of object using ‘new’ operator.
• This type of constructors is mainly used for creating singleton object.
• Can use nested class (Inner Class) or static method to initialize a class having private constructor. 
• Example of Private Constructor – Math class

Question 97 – What is a Static Constructors?

• Special constructor and gets called before the first object is created of the class.
• The time of execution cannot be determined, but it is definitely before the first object creation – could be at the time of loading the assembly.
• Static constructors might be convenient, but they are slow. The runtime is not smart enough to optimize them in the same way it can optimize inline assignments.
• The static constructor for a class executes before any of the static members for the class are referenced.
• The static constructor for a class executes after the static field initializers (if any) for the class.
• A static constructor cannot be called directly.
• The user has no control on when the static constructor is executed in the program. 
• Example – When the class is using a log file and the constructor is used to write entries to this file.

Question 98 – What are the features of Static Constructor?

• Only one Static constructor – Overloading needs the two methods to be different in terms to methods definition, so you can have at the most one static constructor 
• Without parameters – It is going to be called by CLR, who can pass the parameters to it, if required, No one, so we cannot have parameterized static constructor. 
• Access only static members – If allowed to work on non-static members, will reflect the changes in all the object instances, which is impractical. Non-static members in the class are specific to the object instance 
• No access modifier – The call to the static method is made by the CLR and not by the object, so we do not need to have the access modifier to it.

Question 99 – What is a Default Constructor?

• A default constructor is a constructor in both that has no parameters or where it has parameters they are all defaulted.
• If no constructor is supplied then the compiler will supply a default constructor. 
• This default constructor is a parameter less constructor with no body, which calls the parameter less constructor of the base class.

Question 100 – What is a COPY Constructor?

• C# does not provide a copy constructor.
• A copy constructor is a special constructor used to create a new object as a copy of an existing object.
• This constructor takes a single argument: a reference to the object to be copied.
• It is a great convenience to create copy constructor for C# classes using Reflection.
• If you create a new object and want to copy the values from an existing object, you have to write the appropriate method yourself.

Question 101 – What is a Parameterized constructor?

Constructor that accepts arguments is known as parameterized constructor. There may be situations, where it is necessary to initialize various data members of different objects with different values when they are created. Parameterized constructors help in doing that task.

Question 102 – What is a Singleton Class?

• A singleton class is such kind of class in which only one object is created throughout the life time of the class.
• A Singleton class is used when you wish to restrict instantiation of a class to only one object.

Question 103 – What is a Partial Class?

• It is possible to split the definition of a class or a struct, or an interface over two or more source files
• Each source file contains a section of class definition, and all parts are combined at compile time.
• All the partial definitions must proceed with the key word “Partial”.
• All the partial types must be defined within a same assembly and module.
• Method signatures (return type, name of the method, and parameters) must be unique
• The partial types must have the same accessibility.
• If any part is sealed, then the entire class is sealed.
• If any part is abstract, the entire class is abstract.
• Inheritance at any partial type applies to the entire class.

Question 104 – What is a Partial Method?

• A partial method is like a usual method in a class except that the user may or may not implement it.
• A partial method gets executed only when it has an implementation.
• Definition of a partial method is in one part of the partial class and implementation in another, but it is legal to have both in the same part of the partial class. Also, you can use a partial method in a partial structure but not in partial interface.
• Partial methods are indicated by the partial modifier.
• Partial methods must be private.
• Partial methods must return void.
• Partial methods must only be declared within partial classes.
• Partial methods do not always have an implementation. 
• Partial methods can be static and generic.
• Partial methods can have arguments including ref but not out. 
• You cannot make a delegate to a partial method.