Object Orientated Programming

Question 1

What are the 4 pillars of OOP?

Answer 1

Abstraction, Encapsulation, Polymorphism, Inheritance.

Question 2

What is the default value of an object reference defined as an instance variable in an Object?

Answer 2

Null.

Question 3

Why do we need constructors?

Answer 3

Java is an OOP language, in which we create and use objects. A constructor is a piece of code, which is used to create and set the initial state of an object. Without a constructor there is no way to create an object. Java provides a default constructor for every object.

Question 4

Why are default constructors required?

Answer 4

As per the java specification, java provides a default no-arg constructor. Even if we provide an overridden constructor, java still provides the default.

Question 5

What is returned by the constructor?

Answer 5

A constructor returns the object it created.