OOP Basic

Question 1

Inner Class

Answer 1

also nested class, group class together to be more readable and maintainable (can be private or protected)

Question 2

Sub Class

Answer 2

Class that inherits from another class

Question 3

Static methods

Answer 3

method directly accessible without instantiating an object

Question 4

Static variable

Answer 4

variable directly accessible without instantiating an object

Question 5

4 Principles of OOP

Answer 5

Encapsulation
Polymorphism
Abstraction
Inheritance

Question 6

Example/Definition of Encapsulation

Answer 6

Encapsulation is an attribute of an object, and it contains all data which is hidden. That hidden data can be restricted to the members of that class.

Levels are Public, Protected, Private, Internal, and Protected Internal.

Question 7

Overriding

Answer 7

allow subclass or child class to provide specific implementation (same signature)

Question 8

Overloading

Answer 8

same method name different signature

Question 9

Abstract Class

Answer 9

class declared abstract, may or may not include abstract methods. Cannot be instantiated but can be inherited

Question 10

Interface

Answer 10

completely abstract class used to group related methods with empty bodies. It is a concept of OOPs that allows you to declare methods without defining them.

Question 11

Interface vs Abstract Class

Answer 11

Abstract Class

• Can have both abstract and non abstract method
• Can be private, public,
• Can provide the implementation of an interface

Interface

• Only Abstract methods
• public by default
• cannot provide implementation of an abstract class

Question 12

Specifiers

Answer 12

Public - Visible to all classes
Protected - Visible to clases with in the package and subclasses of other package
Default - Visible to the classes within the package
Private - Visible within the class. Not accessible outside the class

Question 13

Example/Definition Polymorphism

Answer 13

Polymorphism is nothing but assigning behavior or value in a subclass to something that was already declared in the main class. Simply, polymorphism takes more than one form.

Question 14

Example/Definition Inheritance

Answer 14

Inheritance is a concept where one class shares the structure and behavior defined in another class. If Inheritance applied to one class is called Single Inheritance, and if it depends on multiple classes, then it is called multiple Inheritance.

Question 15

Example/Definition of Abstraction

Answer 15

Abstraction is a useful feature of OOPS, and it shows only the necessary details to the client of an object. Meaning, it shows only required details for an object, not the inner constructors, of an object. Example – When you want to switch on the television, it is not necessary to know the inner circuitry/mechanism needed to switch on the TV. Whatever is required to switch on TV will be shown by using an abstract class.

Question 16

Advantage of OOP

Answer 16

• OOPs allows clarity in programming thereby allowing simplicity in solving complex problems
• Code can be reused through inheritance thereby reducing redundancy
• Data and code are bound together by encapsulation
• OOPs allows data hiding, therefore, private data is kept confidential
• Problems can be divided into different parts making it simple to solve
• The concept of polymorphism gives flexibility to the program by allowing the entities to have multiple forms

Question 17

What is an Object

Answer 17

An object is a real-world entity which is the basic unit of OOPs for example chair, cat, dog, etc.

Question 18

What is a Class

Answer 18

An extensible program-code-template for creating objects, providing initial values for state (member variables) and implementations of behavior (member functions or methods)

Question 19

What are the limitations of inheritance?

Answer 19

• Increases the time and effort required to execute a program as it requires jumping back and forth between different classes
• The parent class and the child class get tightly coupled
• Any modifications to the program would require changes both in the parent as well as the child class
• Needs careful implementation else would lead to incorrect results

Question 20

Limitation of OOP

Answer 20

• Usually not suitable for small problems
• Requires intensive testing
• Takes more time to solve the problem
• Requires proper planning
• The programmer should think of solving a problem in terms of objects

Question 21

Association

Answer 21

is a relationship between two separate classes and the association can be of any type say one to one, one to may etc. It joins two entirely separate entities.

Question 22

Aggregation

Answer 22

specialized form of association. Child object can exist without parent (E.g. Wallet can have Money but doesnt need money)

Question 23

Composition

Answer 23

specialized form of aggregation. Child Object cannot exist without Parent (e.g. House and Room, you need a house to have a room)

Question 24

Covariant Return Type

Answer 24

Specifies that the return type may vary in the subclass

Question 25

Compile Time Polymorphism

Answer 25

Overloading a static method, where polymorphism is done during compile

Question 26

Runtime Polymorphism

Answer 26

A call to an overridden method is resolved at runtime. The program will determine the method to be called base on the object being referred to.

Question 27

Upcasting

Answer 27

The reference variable of Parent class refers to the object of Child class

Question 28

Downcasting

Answer 28

Casting a parent object to a child object, must be explicit.