OOPS Training

7/29/2019 OOPS Training

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OOP Fundamentals and Interview Questions

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Agenda

A word about www.dotnetfunda.com Introduction

What's the problem with functional programming ?

OOP's Fundamentals

Abstraction

Encapsulation Inheritance

Polymorphism

Acces*s modifiers

Aggregation and Composition

Implementing OOPS in tiered architecture Most asked Inter*view questions in OOPS
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Whats the problem with Functional

Programming ?

R eusability

E xtensibility

S implicity

M aintainability

Problem of Functional programming

RESM


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Different copies of same code in

both the UI Increase inredundant code


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New Functions created

rather than extending

Extensibility and simplicity Issues


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Reusability

Extensibility

Simplicity

Maintainability


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Can you define OOP and the 4 principles of OOP ?

Its a design philosophy where we visualize in terms of self sustained objects.

Classes and object

Reusability

Inheritance ,aggregation and composition

Extensibility

Abstraction , encapsulation and polymorphism

Simplicity

All the above 3 combined helps us to maintain the code better.

Maintainability


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Maintainability

Simplicity

Extensibility Reusability

Classes

&

Objects

InheritanceaggregationComposition

All the above

combine tomake the codemaintainable

Abstraction

EncapsulationPolymorphism

Abstraction

Encapsulation

Polymorphism

Inheritance


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Summarizing definition

Allows complex world to represented in a simplified manner byexposing only the necessary properties. For instance a color can beabstracted by RGB

Abstraction

Process of hiding inner details from the external world with thatmaking the object interface simple.Encapsulation

They are used to depict parent child relationship. So we can have aclass with just set and get , we can then inherit and create a newspecialized class which does database operations.Inheritance

We want a object to play different role depending on differentsituations. For instance we can class which does databaseoperations on SQL Server and Oracle. Depending on connectionstring it will MORPH its role to do SQL operations or Oracle

operations. Poly means many and morph means change

Polymorphism

Remember the word APIE


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What are classes and objects ?


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Addressesreusability

Classes and objects address reusability.

Think in termof objects

Rather than thinking in terms of functions think in terms of objects.

What is aclass ?

A class is simply a type of object. It is the blueprint/ plan/ template that describethe details of an object. A class is the blueprint from which the individual objectsare created. Class is composed of three things: a name, attributes, andoperations.

What isObject ?

Its an instance of a class. Class is brought live by creating objects. An object can

be considered a "thing" that can perform activities. The set of activities that theobject performs defines the object's behavior.


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Class

Object

Class used as object


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Same class reused in both UIs by creating objects


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What is Inheritance ?


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AddressesExtensibility

Inheritance addresses the problem ofextensibility.

Parent childrelationship

By using inheritance we can create afresh child class which has all the

qualities of parent plus some extra newqualities of himself also.

What is Inheritance ?


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New Functions created

rather than extending

Problems Extensibility and simplicity Issues


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Colon represent inheritance

clsProduct class is extended

and clsProductDicount class

is created using inheritance.


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What is Polymorphism , overloading , overriding and virtual ?


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Addresses Simplicity

By using polymorphism you can have more simplified interfaces and neatcode.

Meaning ofpolymorphism

'poly' means many, 'morphism' means forms. Its a ability of object ormethod to take different forms as per situation.

What is Polymorphism , overloading , overriding and virtual ?


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Both the method names aresame but they act differently

as per inputs

This will invoke thecalculation of total cost with

out discount.

This will invoke the

calculation of total cost withdiscount.


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Static Polymorphism

In Static Polymorphism the method to be called is decided at compile-timeonly. Method Overloading is an example of Static Polymorphism.

Dynamic Polymorphism

In dynamic polymorphism a call to a overridden function is resolved duringruntime. Dynamic polymorphism is acheived using inheritance and

overriding.

Two types of polymorphism


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Both the method names aresame but they act differently

as per inputs

This will invoke thecalculation of total cost with

out discount.

This will invoke the

calculation of total cost withdiscount.

Static polymorphism is achieved by using method overloading


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Parent Product class

Inherited Child Product class

Virtual keyword necessary to override the method

Override keyword necessary to define new implementation

Class inherited and getTotalCost overridden

with new functionality


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clsProduct objProduct;

objProduct = new clsProduct();

objProduct.getTotalCost(intQty, intPerProductCost,"INR")

objProduct = new clsProductWithDiscount();

objProduct.getTotalCost(intQty, intPerProductCost,"INR")

This invokes the parent class code

This invokes the child class code

Dynamic polymorphism is achieved by using overriding


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Can you explain encapsulation and abstraction ?


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clsProduct obj = new clsProduct();

Obj. IsQuantityGreater (intQty);

Obj. isProductCostZero (intPerProductCost);

obj.PerProductCost = intPerProductCost;

obj.Quantity = intQty;

int totalCost = obj.getTotalCost(10,100);

clsProduct obj = new clsProduct();

obj.PerProductCost = intPerProductCost;

obj.Quantity = intQty;

Encapsulation means hiding complexity Extraexpos

edfunctionalities

.

Complicationencapsulated


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Private: Only members of class have access.

Public: - All members have access in all classes andprojects

Protected:- All members in current class and in derivedclasses can access the variables.

Friend (internal in C#):- Only members in currentproject have access to the elements.

Protected friend (protected internal in C#) :- Allmembers in current project and all members inderived class can access the variables.


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Abstraction, difference between abstraction and encapsulation?

Abstraction means show only what is necessary.

Abstraction and Encapsulation both compliment each

other.

Abstraction is achieved through encapsulation

Abstraction is achieved throughencapsulation..Abstraction solves the problem in thedesign side while encapsulation is the implementation.


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What is an abstract class ?


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Whats a abstract class ?Abstract classes represent base classes, and we can not create objects of these

classes.

An abstract class means that, no object of this class can be instantiated, but can

make derivations of this.

An abstract class can contain either abstract methods or non abstract methods.

Abstract members do not have any implementation in the abstract class, but the

same has to be provided in its derived class.

An abstract class cannot be a sealed or a static class.

You can make use of abstract classes to implement such functionality in C# using

the modifier 'abstract'.


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An abstract class cannot be a sealed class.

An abstract method cannot be private.

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 asprotected, it should be protected in its derived class. Otherwise, thecompiler will raise an error.

An abstract method cannot have the modifier virtual. Because an abstractmethod is implicitly virtual.

An abstract member cannot be static.


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Define Interface and

Whats the difference between abstract and interface ?


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Whats a interface ?

What are interfaces ?

An interface looks like a class, but has no implementation. It only contains definitions ofevents, indexers, methods and/or properties. The reason interfaces only providedefinitions is because they are inherited by classes and structs, which must provide animplementation for each interface member defined.

So what good are empty

methods

They help decoupling

Enforce standardization of vocabulary


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Interface keyword is used to define interfaces.

Interface can not have field variables.

Interfaces can not have implemented functions and methods.

All methods in a interface needs to be implemented.

Interface can be used to implement run time polymorphism.

You can implement multiple interfaces.

All interface methods are public


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Whats a difference between interfaces and abstract classes ?

An abstract class can have abstract members as well non abstractmembers. But in an interface all the members are implicitly abstract andall the members of the interface must override to its derived class.

The members of the interface are public with no implementation.Abstract classes can have protected parts, static methods, etc.

Abstract classes can add more functionality without destroying the childclasses that were using the old version. In an interface, creation ofadditional functions will have an effect on its child classes, due to thenecessary implementation of interface methods to classes.

Defining an abstract class with abstract members has the same effect todefining an interface.


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