OOPs

 1. What is the concept of OOPs?

OOPs or Object Oriented Programming systems have a certain set of principles or concepts to write good programming logic. Basic OOPs concepts include:

• Abstraction
• Encapsulation
• Inheritance
• Polymorphism

2. What is class, object and method?

Object Oriented programming systems organize or manage the code by creating types in the form of classes. A Class contains the code that represents a specific entity and defines what an entity can do. For example, A BankAccount entity can be organized by a class 'BankAccount'.
An entity has certain behavior, The code implements this behavior in the form of operations or functions using Methods and Properties.
An Object is a block of memory that has been configured and allocated according to the entity - which exists in the form of class.

3. What is Abstraction?

 Abstraction means displaying only essential information and hiding the details. Data abstraction refers to providing only essential information about the data to the outside world, hiding the background details or implementation.

Consider a real life example of a man driving a car. The man only knows that pressing the accelerators will increase the speed of car or applying brakes will stop the car but he does not know about how on pressing accelerator the speed is actually increasing, he does not know about the inner mechanism of the car or the implementation of accelerator, brakes etc in the car. This is what abstraction is.

4. Explain Encapsulation.

Encapsulation is concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse.

Consider a real life example of encapsulation, in a company there are different sections like the accounts section, finance section, sales section etc. The finance section handles all the financial transactions and keep records of all the data related to finance. Similarly the sales section handles all the sales related activities and keep records of all the sales. Now there may arise a situation when for some reason an official from finance section needs all the data about sales in a particular month. In this case, he is not allowed to directly access the data of sales section. He will first have to contact some other officer in the sales section and then request him to give the particular data. This is what encapsulation is. Here the data of sales section and the employees that can manipulate them are wrapped under a single name “sales section”.

5. Explain Inheritance in detail.

The capability of a class to derive properties and characteristics from another class is called Inheritance. Inheritance is one of the most important features of Object-Oriented Programming.

Inheritance is a feature or a process in which, new classes are created from the existing classes. The new class created is called “derived class” or “child class” and the existing class is known as the “base class” or “parent class”. The derived class now is said to be inherited from the base class.

When we say derived class inherits the base class, it means, the derived class inherits all the properties of the base class, without changing the properties of base class and may add new features to its own. These new features in the derived class will not affect the base class. The derived class is the specialized class for the base class.

• Sub Class: The class that inherits properties from another class is called Subclass or Derived Class. 
• Super Class: The class whose properties are inherited by a subclass is called Base Class or Superclass.

6. Explain Polymorphism.

The word “polymorphism” means having many forms. In simple words, we can define polymorphism as the ability of a message to be displayed in more than one form. A real-life example of polymorphism is a person who at the same time can have different characteristics. Like a man at the same time is a father, a husband and an employee. So the same person exhibits different behavior in different situations. This is called polymorphism.

polymorphism is mainly divided into two types: 

• Compile-time Polymorphism 
• Runtime Polymorphism

Compile-time polymorphism: This type of polymorphism is achieved by function overloading or operator overloading.

Function Overloading: When there are multiple functions with the same name but different parameters, then the functions are said to be overloaded. Functions can be overloaded by changing the number of arguments or/and changing the type of arguments.

Operator Overloading: C++ also provides the option to overload operators. For example, we can make use of the addition operator (+) for string class to concatenate two strings. We know that the task of this operator is to add two operands. So a single operator ‘+’, when placed between integer operands, adds them and when placed between string operands, concatenates them.

Runtime polymorphism: This type of polymorphism is achieved by Function Overriding.

Function overriding occurs when a derived class has a definition for one of the member functions of the base class. That base function is said to be overridden.

7. What is Association?

Association is a relation between two separate classes which establishes through their Objects. Association can be one-to-one, one-to-many, many-to-one, many-to-many. In Object-Oriented programming, an Object communicates to another object to use functionality and services provided by that object. Composition and Aggregation are the two forms of association.

8. What is Aggregation?

It is a special form of Association where: It represents Has-A’s relationship. 

It is a unidirectional association i.e. a one-way relationship. 

For example, a department can have students but vice versa is not possible and thus unidirectional in nature. 

In Aggregation, both the entries can survive individually which means ending one entity will not affect the other entity. 

Aggregation is a weak Association.

9. What is composition?

Composition is a restricted form of Aggregation in which two entities are highly dependent on each other. 

It represents part-of relationship. 

In composition, both entities are dependent on each other. When there is a composition between two entities, the composed object cannot exist without the other entity. 

Composition is a strong Association

10. What is Cohesion?

Cohesion is the Object-Oriented principle most closely associated with making sure that a class is designed with a single, well-focused purpose. In object-oriented design, cohesion refers to how a single class is designed.

The advantage of high cohesion is that such classes are much easier to maintain (and less frequently changed) than classes with low cohesion. Another benefit of high cohesion is that classes with a well-focused purpose tend to be more reusable than other classes.

Example: Suppose we have a class that multiplies two numbers, but the same class creates a pop-up window displaying the result. This is an example of a low cohesive class because the window and the multiplication operation don’t have much in common. To make it high cohesive, we would have to create a class Display and a class Multiply. The Display will call Multiply’s method to get the result and display it. This way to develop a high cohesive solution.

Explanation: In the above image, we can see that in low cohesion only one class is responsible to execute lots of jobs that are not in common which reduces the chance of reusability and maintenance. But in high cohesion, there is a separate class for all the jobs to execute a specific job, which results in better usability and maintenance.

Difference between high cohesion and low cohesion: 

High cohesion is when you have a class that does a well-defined job. Low cohesion is when a class does a lot of jobs that don’t have much in common. 

High cohesion gives us better-maintaining facility and Low cohesion results in monolithic classes that are difficult to maintain, understand and reduce re-usability

11. What is Coupling?

Coupling is a degree of measure that indicates how closely connected two classes are. If the coupling is high then changes in one class affects the code in other classes and makes code difficult to maintain and change. Applications with low coupling ensure better code maintainability and any code changes can be easily implemented without affecting other classes or systems. A good application design must have High Cohesion and Low Coupling.