Javascript Object Oriented Programming

Question 1

What 4 things happen when the NEW keyword gets called with a function call?

Answer 1

1. A brand new OBJECT gets created
2. An OBJECT gets linked
3. The context gets set to the THIS
4. returns THIS

Question 2

What are characteristics of Protypal Inheritance in JavaScript?

Answer 2

• Prototype Chain - behavior is delegated up the prototype chain if it is not available on the new object
• .prototype links the function to an object
• [[Prototype]] internally links one object to another (not public)
• __proto__ (dunder proto) “public property” a getter function which returns the prototypal linkage of THIS

Question 3

What is a CONSTRUCTOR?

Answer 3

A function called with the NEW keyword in front of it

Question 4

What is the execution context in JavaScript?

Answer 4

How Javascript code is executed depending on when and where functions and variables are called

Question 5

What is the Execution Context Stack?

Answer 5

• in Javascript it is single threaded
• Synchronous execution
• 1 global context
• Can have many function contexts
• each function call creates a new execution context

Question 6

How do you access a value in a JS Object that has a number as its property?

Answer 6

You have to use bracket notation

myObject[3]

Question 7

What is a Reference Data Type?

Answer 7

Stores the value of that data as a reference. You can change the value of that reference

ex: var person = "Kobe";  
​var anotherPerson = person;

Question 8

What are the 3 Attributes of Object Data Properties?

Answer 8

1. Configurable - tells if you can delete or change
2. Enumerable - can be returned in a for/in loop
3. Writable - property can be changed

Question 9

How do you SERIALIZE an object?

Answer 9

You convert it to a string. You can use JSON.stringify( )

Question 10

Explain how the concept of THIS works in JavaScript?

Answer 10

• used for dynamic scoping
  1. Explicit Binding - call and apply explicitly binds THIS to the first argument you pass in
  2. Default Binding - global scope

Question 11

What is Object Oriented Programming?

Answer 11

Object Oriented Programming is a paradigm in computer science or ‘style’ of programming where objects are instantiated via classes and can contain methods that are inherited by new class objects.

Question 12

What are the 4 basic concepts of OOP?

Answer 12

Abstraction.
Encapsulation.
Inheritance.
Polymorphism.

Question 13

What is a class?

Answer 13

A class is simply a representation of a type of object. It is the blueprint/ plan/ template that describe the details of an object.

Question 14

What is an object?

Answer 14

Object is termed as an instance of a class, and it has its own state, behavior and identity.

Question 15

What is Encapsulation?

Answer 15

Encapsulation limits prototype methods to the class object

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.

Question 16

What is Polymorphism?

Answer 16

assigning behavior or value in a subclass to something that was already declared in the main class.

Question 17

What is Inheritance?

Answer 17

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

Question 18

What are manipulators?

Answer 18

Manipulators are the functions which can be used in conjunction with the insertion (<>) operators on an object. Examples are endl and setw.

Question 19

What is a constructor?

Answer 19

Constructor is a method used to initialize the state of an object, and it gets invoked at the time of object creation.

Question 20

What is a destructor?

Answer 20

Destructor is a method which is automatically called when the object is destroyed.

Question 21

What is an Inline function?

Answer 21

Inline function is a technique used by the compilers and instructs to insert complete body of the function wherever that function is used in the program source code.

Question 22

What is a virtual function?

Answer 22

Virtual function is a member function ofclass and its functionality can be overridden in its derived class. This function can be implemented by using a keyword called virtual, and it can be given during function declaration.

Virtual function can be achieved in C++, and it can be achieved in C Languageby using function pointers or pointers to function.

Question 23

What is a friend function?

Answer 23

Friend function is a friend of a class that is allowed to access to Public, private or protected data in that same class. If the function is defined outside the class cannot access such information.

Friend can be declared anywhere in the class declaration, and it cannot be affected by access control keywords like private, public or protected.

Question 24

What is function overloading?

Answer 24

Function overloading is defined as a normal function, but it has the ability to perform different tasks. It allows creation of several methods with the same name which differ from each other by type of input and output of the function.

Example
void add(int& a, int& b);
void add(double& a, double& b);
void add(struct bob& a, struct bob& b);

Question 25

What is operator overloading?

Answer 25

Operator overloading is a function where different operators are applied and depends on the arguments. Operator,-,* can be used to pass through the function , and it has their own precedence to execute.

class complex {
double real,
imag; public: complex(double r, double i) : real(r),
imag(i) {} complex operator+(complex a, complex b);
complex operator*(complex a, complex b);
complex& operator=(complex a, complex b);
}

Question 26

What is an abstract class?

Answer 26

An abstract class is a class which cannot be instantiated. Creation of an object is not possible with abstract class , but it can be inherited. An abstract class can contain only Abstract methods. Java allows only abstract method in abstract class while for other language it allows non-abstract method as well.

Question 27

What is a ternary operator?

Answer 27

Ternary operator is said to be an operator which takes three arguments. Arguments and results are of different data types , and it is depends o
1
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AZ78-onditional operator.

Question 28

What is the use of finalize method?

Answer 28

Finalize method helps to perform cleanup operations on the resources which are not currently used. Finalize method is protected , and it is accessible only through this class or by a derived class.

Question 29

What are different types of arguments?

Answer 29

A parameter is a variable used during the declaration of the function or subroutine and arguments are passed to the function , and it should match with the parameter defined. There are two types of Arguments.

Call by Value – Value passed will get modified only inside the function , and it returns the same value whatever it is passed it into the function.
Call by Reference – Value passed will get modified in both inside and outside the functions and it returns the same or different value.

Question 30

What is super keyword?

Answer 30

Super keyword is used to invoke overridden method which overrides one of its superclass methods. This keyword allows to access overridden methods and also to access hidden members of the superclass.

It also forwards a call from a constructor to a constructor in the superclass.

Question 31

What is method overriding?

Answer 31

Method overriding is a feature that allows sub class to provide implementation of a method that is already defined in the main class. This will overrides the implementation in the superclass by providing the same method name, same parameter and same return type.

Question 32

What is an interface?

Answer 32

An interface is a collection of abstract method. If the class implements an inheritance, and then thereby inherits all the abstract methods of an interface.

Question 33

What is exception handling?

Answer 33

Exception is an event that occurs during the execution of a program. Exceptions can be of any type – Run time exception, Error exceptions. Those exceptions are handled properly through exception handling mechanism like try, catch and throw keywords.

Question 34

What are tokens?

Answer 34

Token is recognized by a compiler and it cannot be broken down into component elements. Keywords, identifiers, constants, string literals and operators are examples of tokens.

Even punctuation characters are also considered as tokens – Brackets, Commas, Braces and Parentheses.

Question 35

Difference between overloading and overriding?

Answer 35

Overloading is static binding whereas Overriding is dynamic binding. Overloading is nothing but the same method with different arguments , and it may or may not return the same value in the same class itself.

Overriding is the same method names with same arguments and return types associates with the class and its child class.

Question 36

Difference between class and an object?

Answer 36

An object is an instance of a class. Objects hold any information , but classes don’t have any information. Definition of properties and functions can be done at class and can be used by the object.

Class can have sub-classes, and an object doesn’t have sub-objects.

Question 37

What is an abstraction?

Answer 37

Abstraction is a good feature of OOPS , and it shows only the necessary details to the client of an object. Means, it shows only necessary details for an object, not the inner details of an object. Example – When you want to switch On television, it not necessary to show all the functions of TV. Whatever is required to switch on TV will be showed by using abstract class.

Question 38

What are access modifiers?

Answer 38

Access modifiers determine the scope of the method or variables that can be accessed from other various objects or classes. There are 5 types of access modifiers , and they are as follows:.

 Private.
Protected.
Public.
Friend.
Protected Friend.

Question 39

What is sealed modifiers?

Answer 39

Sealed modifiers are the access modifiers where it cannot be inherited by the methods. Sealed modifiers can also be applied to properties, events and methods. This modifier cannot be applied to static members.

Question 40

How can we call the base method without creating an instance?

Answer 40

Yes, it is possible to call the base method without creating an instance. And that method should be,.

Static method.

Doing inheritance from that class.-Use Base Keyword from derived class.

Question 41

What is the difference between new and override?

Answer 41

The new modifier instructs the compiler to use the new implementation instead of the base class function. Whereas, Override modifier helps to override the base class function.

Question 42

What are the various types of constructors?

Answer 42

There are three various types of constructors , and they are as follows:.

– Default Constructor – With no parameters.

– Parametric Constructor – With Parameters. Create a new instance of a class and also passing arguments simultaneously.

– Copy Constructor – Which creates a new object as a copy of an existing object.

Question 43

What is early and late binding?

Answer 43

Early binding refers to assignment of values to variables during design time whereas late binding refers to assignment of values to variables during run time.

Question 44

What is ‘this’ pointer?

Answer 44

THIS pointer refers to the current object of a class. THIS keyword is used as a pointer which differentiates between the current object with the global object. Basically, it refers to the current object.

Question 45

What is the difference betweenstructure and a class?

Answer 45

Structure default access type is public , but class access type is private. A structure is used for grouping data whereas class can be used for grouping data and methods. Structures are exclusively used for dataand it doesn’t require strict validation , but classes are used to encapsulates and inherit data which requires strict validation.

Question 46

What is the default access modifier in a class?

Answer 46

The default access modifier of a class is Private by default.

Question 47

What is pure virtual function?

Answer 47

A pure virtual function is a function which can be overridden in the derived classbut cannot be defined. A virtual function can be declared as Pure by using the operator =0.

C#

Virtual void function1() // Virtual, Not pure
Virtual void function2() = 0 //Pure virtual

Question 48

What are all the operators that cannot be overloaded?

Answer 48

Following are the operators that cannot be overloaded -.

Scope Resolution (:: )
Member Selection (.)
Member selection through a pointer to function (.*)

Question 49

What is dynamic or run time polymorphism?

Answer 49

Dynamic or Run time polymorphism is also known as method overriding in which call to an overridden function is resolved during run time, not at the compile time. It means having two or more methods with the same name,same signature but with different implementation.

Question 50

Do we require parameter for constructors?

Answer 50

No, we do not require parameter for constructors.

Question 51

What is a copy constructor?

Answer 51

This is a special constructor for creating a new object as a copy of an existing object. There will be always only on copy constructor that can be either defined by the user or the system.

Question 52

What does the keyword virtual represented in the method definition?

Answer 52

It means, we can override the method.

Question 53

Whether static method can use non static members?

Answer 53

False.

Question 54

What are base class, sub class and super class?

Answer 54

Base class is the most generalized class , and it is said to be a root class.

Sub class is a class that inherits from one or more base classes.

Super class is the parent class from which another class inherits.

Question 55

What is static and dynamic binding?

Answer 55

Binding is nothing but the association of a name with the class. Static binding is a binding in which name can be associated with the class during compilation time , and it is also called as early Binding.

Dynamic binding is a binding in which name can be associated with the class during execution time , and it is also called as Late Binding.

Question 56

How many instances can be created for an abstract class?

Answer 56

Zero instances will be created for an abstract class.

Question 57

Which keyword can be used for overloading?

Answer 57

Operator keyword is used for overloading.

Question 58

What is the default access specifier in a class definition?

Answer 58

Private access specifier is used in a class definition.

Question 59

Which OOPS concept is used as reuse mechanism?

Answer 59

Inheritance is the OOPS concept that can be used as reuse mechanism.

Question 60

Which OOPS concept exposes only necessary information to the calling functions?

Answer 60

Data Hiding / Abstraction

Question 61

What is one important difference / trade-off between OOP and Functional?

Answer 61

Object oriented programming makes code understandable by encapsulating moving parts. Functional programming makes code understandable by minimizing moving parts.