19 interview questions on Object Oriented Programming for developers (2026)

Easy

14 votes1687 runs0 comment

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

IT Architect

OOP

javascript

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Eric Hostaleryat Dec 3, 2021

Easy

9 votes704 runs0 comment

You need to develop a class for which there should be only one instance throughout your application. Which design pattern should you use for this?

IT Architect

OOP

design pattern

singleton

Jean ALbin ELieat Mar 28, 2023

Medium

8 votes1566 runs0 comment

Can we extend an abstract class in Java?

IT Architect

OOP

abstract

class

Eric Hostaleryat Dec 3, 2021

Hard

7 votes1640 runs0 comment

Which design pattern allows to dynamically add responsibilities to an object?

IT Architect

OOP

design pattern

object

Eric Hostaleryat Sep 19, 2022

Easy

5 votes1578 runs0 comment

Implement the interface IEmailFormatter for the classes Person, Company, and ListOfPerson, which has a method GetEmailContent()

IT Architect

OOP

interfaces

classes

Eric Hostaleryat Mar 13, 2023

Easy

5 votes1553 runs0 comment

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

IT Architect

OOP

javascript

undefined

Eric Hostaleryat Dec 3, 2021

Easy

5 votes1553 runs

1 comment

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

IT Architect

OOP

undefined

Eric Hostaleryat Dec 3, 2021

Medium

5 votes1509 runs1 comment

Can an interface inherit from another interface?

IT Architect

OOP

interfaces

Vincent Cotroat Dec 3, 2021

Easy

4 votes1615 runs0 comment

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

IT Architect

OOP

javascript

undefined

Eric Hostaleryat Dec 3, 2021

Medium

4 votes1607 runs0 comment

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

IT Architect

OOP

javascript

undefined

Eric Hostaleryat Dec 3, 2021

Hard

3 votes1563 runs

1 comment

What are the public methods of the class `Person`?

IT Architect

OOP

methods

visibility

Eric Hostaleryat Dec 3, 2021

Hard

3 votes1549 runs1 comment

Implement the registration method on class A in a virtual way,Override the registration method on classes A1 and A2 when implementing these classes

IT Architect

OOP

classes

inheritance

Eric Hostaleryat Dec 3, 2021

Easy

3 votes395 runs0 comment

Inheritance, polymorphism and encapsulation

IT Architect

OOP

inheritance

polymorphism

encapsulation

Monemat Nov 3, 2023

Hard

2 votes1587 runs1 comment

What is the default value of a field in a class in Java?

IT Architect

OOP

constructor

object

Eric Hostaleryat Dec 3, 2021

Easy

2 votes1567 runs0 comment

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

IT Architect

OOP

undefined

Eric Hostaleryat Dec 3, 2021

Medium

2 votes575 runs

2 comments

Hiding complexity can be termed as Encapsulation

IT Architect

OOP

encapsulation

Lively George Dantzigat Dec 22, 2022

Hard

1 vote1544 runs2 comments

How to call a method from a parent class in a child class in PHP

IT Architect

OOP

classes

objects

Eric Hostaleryat Mar 20, 2023

Easy

1 vote1437 runs0 comment

Is an interface abstract?

IT Architect

OOP

interfaces

abstract

Clément Devos (W3D Team)at Dec 20, 2021

Hard

0 vote1562 runs

2 comments

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

IT Architect

OOP

javascript

undefined

Eric Hostaleryat Dec 3, 2021

19 interview questions on Object Oriented Programmingfor developers (2026)

Test your technical skills before an interview of Object Oriented Programming with 19 corrected questions. Beginner, Intermediate or Expert level.

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

You need to develop a class for which there should be only one instance throughout your application. Which design pattern should you use for this?

Can we extend an abstract class in Java?

Which design pattern allows to dynamically add responsibilities to an object?

Implement the interface IEmailFormatter for the classes Person, Company, and ListOfPerson, which has a method GetEmailContent()

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

Can an interface inherit from another interface?

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

What are the public methods of the class `Person`?

Implement the registration method on class A in a virtual way,Override the registration method on classes A1 and A2 when implementing these classes

Inheritance, polymorphism and encapsulation

What is the default value of a field in a class in Java?

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);

Hiding complexity can be termed as Encapsulation

How to call a method from a parent class in a child class in PHP

Is an interface abstract?

Is the following code valid? class Person { constructor(name, age) { this.name = name; this.age = age; } } const person = new Person('John', 20); console.log(person.name); console.log(person.age);