Great!

I’ll provide well-structured, interview-style answers to all your Object-Oriented

Programming (OOP) questions.

Since the list is long, I’ll start with the first section (Basic OOP Concepts). After that, I’ll
continue with the next sections one by one.

🧠 1. Basic OOP Concepts

1. What is the need for OOPs?

OOP addresses problems of procedural programming like code duplication, poor

modularity, and scalability. It helps organize complex code using real-world entities,
making software more maintainable and reusable.

2. What are some major Object Oriented Programming languages?

●​ Java​

●​ C++​

●​ Python​

●​ C#​

●​ Ruby​

●​ Kotlin​

●​ Swift​

3. What are some other programming paradigms other than OOPs?

 ●​ Procedural Programming (e.g., C)​

●​ Functional Programming (e.g., Haskell, Scala)​

●​ Logic Programming (e.g., Prolog)​

●​ Event-driven Programming (e.g., JavaScript in browsers)​

4. What is meant by Structured Programming?

It’s a subset of procedural programming where programs are written using structures like
sequence, selection (if-else), and loops, aiming for readable and maintainable code.

5. What are the main features of OOPs?

●​ Encapsulation​

●​ Abstraction​

●​ Inheritance​

●​ Polymorphism​

6. What are some advantages of using OOPs?

●​ Code reuse via inheritance​

●​ Better modularity​

●​ Easier troubleshooting​

●​ Real-world modeling​

●​ Extensibility​

7. Why is OOPs so popular?

OOP allows real-world modeling, modular code, better maintainability, and reuse of code,
making it ideal for large, complex applications.

8. What is meant by the term OOPs?

OOP is a programming paradigm where programs are organized around objects rather
than functions or logic.

9. What are the four main principles of OOP?

1.​ Encapsulation​

2.​ Abstraction​

3.​ Inheritance​

4.​ Polymorphism​

10. Explain the difference between a class and an object.

●​ A class is a blueprint or template (e.g., Car).​

●​ An object is an instance of the class (e.g., HondaCity).​

11. What is encapsulation? Provide an example.

Encapsulation means bundling data and methods in a single unit and restricting direct
access.​
Example (Java):

java
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class Student {
private int age;
public void setAge(int age) { this.age = age; }
public int getAge() { return age; }
}

12. What is abstraction? How is it different from encapsulation?

Abstraction hides complex logic and exposes only the necessary parts.​
Encapsulation hides internal data using access modifiers.

●​ Abstraction = Hiding implementation​

●​ Encapsulation = Hiding data​

13. What is polymorphism? Explain with an example.

Polymorphism means the ability of a single method or function to behave differently

based on context.​
Example:

java
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class Animal {
void sound() { System.out.println("Animal sound"); }
}
class Dog extends Animal {
void sound() { System.out.println("Bark"); }
}

14. What is inheritance? How does it promote code reusability?

Inheritance allows a class to derive properties/methods from another.​

It promotes code reuse by avoiding redefinition of common functionalities.

15. What are access specifiers in OOP?

They control visibility:

●​ public: Accessible everywhere​

●​ private: Accessible only within class​

●​ protected: Accessible within class and subclasses​

16. What do you understand by OOP?

OOP is a method of programming where code is grouped into objects that combine data
and behavior, enabling modular, reusable, and maintainable code.

17. Name any seven widely used OOP languages.

●​ Java​

●​ C++​

●​ Python​
 ●​ C#​

●​ Ruby​

●​ Kotlin​

●​ Swift​

18. What is the purpose of using OOPs concepts?

To build flexible, scalable, maintainable software by organizing code into reusable and
logical modules (objects).

19. What are the four main features of OOPs?

1.​ Encapsulation​

2.​ Abstraction​

3.​ Inheritance​

4.​ Polymorphism​

20. What are the advantages and disadvantages of OOP?

Advantages:

●​ Modular code​

●​ Code reuse​

●​ Scalability​

●​ Better debugging​

Disadvantages:

●​ Steeper learning curve​

●​ More memory usage​

●​ Not always ideal for small/simple tasks​

21. What are the limitations of OOPs?

●​ Can be overkill for small programs​

●​ Requires more design effort​

●​ Performance overhead due to abstraction​

22. What are the differences between object-oriented programming and structural
programming?
Feature Structural OOP
Programming

Structure Based on functions Based on objects

Code Reuse Limited High via inheritance

Data Handling Publicly accessible Secured via

encapsulation

Example C, Pascal Java, C++, Python

Languages

23. What do you understand by pure object-oriented language? Why is Java not a pure
object-oriented programming language?

A pure OOP language treats everything as an object.​

Java is not pure OOP because it supports primitive types (int, char, etc.), which are
not objects.

Let me know if you’d like me to continue with the next section: “Classes and Objects”.

You said:
yes continue
ChatGPT said:

Great! Let’s continue with the next section of OOP interview

questions:
🧱 2. Classes and Objects
1. What is a class?

A class is a blueprint or template for creating objects. It defines the attributes (data
members) and behaviors (methods) that the objects created from the class will have.

2. What is an object?

An object is an instance of a class. It contains real values instead of abstract definitions

and can use the class's methods and properties.

3. How do you define a class in Java?

java
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class Car {
String color;
void startEngine() {
System.out.println("Engine started");
}
}

4. How do you create an object from a class?

java
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Car myCar = new Car(); // myCar is an object of Car

5. What is the difference between a constructor and a method?

Feature Constructor Method

Purpose Initializes a new object Performs a specific

action

Name Same as class name Any valid name

Return No return type, not even void Must have a return type
Type

Call Called automatically on object Called manually

creation

6. What is a destructor? When is it called?

In languages like C++, a destructor is used to clean up resources and is called

automatically when an object goes out of scope.​
Java doesn't have destructors but uses a garbage collector and the finalize()
method (deprecated in recent versions).

7. Can a constructor be private? Why or why not?

Yes. A private constructor is used in the Singleton Design Pattern to restrict

instantiation of the class from outside.

java
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class Singleton {
private static Singleton instance = new Singleton();
private Singleton() {} // private constructor
public static Singleton getInstance() {
return instance;
}
}

8. How much memory does a class occupy?

A class itself doesn't occupy memory until an object is created. Memory is allocated only
when an object is instantiated.

9. Is it always necessary to create objects from a class?

No. You can use static methods and variables without creating objects. Also, in some
design patterns (e.g., utility/helper classes), objects are never created.

10. What do you understand by class and object? Also, give an example.

A class defines a structure, and an object is an actual entity created based on that class.

Example:

java
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class Student {
String name;
void study() {
System.out.println(name + " is studying");
}
}
Student s = new Student(); // object
s.name = "Abhi";
s.study(); // Output: Abhi is studying

11. What are the differences between class and object?

Aspect Class Object

Definitio Blueprint/template Instance of a class

n

Memory No memory Occupies memory when

allocation created

Access Cannot use directly Can use class members

12. What are the key differences between class and structure?
Feature Class Structure (in C/C++/C#)

Default Access Private Public

Inheritance Yes Limited or no support

Support

Type Reference type (in Value type (in C#/C++)

Java/C#)

Memory Heap Stack

Allocation

✅ Let me know if I should continue with the next section: Encapsulation.

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continue
ChatGPT said:

Perfect! Let’s move on to the next section:

🔒 3. Encapsulation
1. What is encapsulation?
Encapsulation is the bundling of data and methods that operate on that data into a
single unit (typically a class) and restricting direct access to some of the object’s
components to ensure data integrity.

✅ It’s achieved using access modifiers like private, public, and

protected.

2. How does encapsulation improve code maintainability?

●​ Reduces interdependence of code​

●​ Protects internal state of objects​

●​ Allows controlled access through getters/setters​

●​ Makes code more modular and easier to debug and maintain​

3. What are getters and setters?

Getters retrieve private field values, and setters modify them.

Example:

java
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class Student {
private int age;

public int getAge() {

return age;
}

public void setAge(int a) {

if (a > 0) age = a;
}
}

4. What is the difference between public, private, and protected access modifiers?
Modifier Accessible Within Within Subclass (other Outside
Class Package package) Package

public ✅ ✅ ✅ ✅
privat ✅ ❌ ❌ ❌
e

protec ✅ ✅ ✅ ❌
ted

(default) ✅ ✅ ❌ ❌
5. What is the concept of access specifiers, and when should we use these?

Access specifiers define the visibility of class members (fields and methods). Use them to:

●​ Protect sensitive data (use private)​

●​ Allow read-only or write-only access (using getter or setter)​

●​ Expose methods to external code (public)​

●​ Allow subclass access but not others (protected)​

Would you like to continue with the next section: 4. Abstraction?

You said:
continue
ChatGPT said:

Awesome! Let’s move forward with:

🎭 4. Abstraction
1. What is Abstraction?

Abstraction means hiding internal implementation details and exposing only the
essential features. It simplifies complexity and helps focus on what an object does
instead of how it does it.

2. How do abstract classes differ from interfaces?

Feature Abstract Class Interface
Methods Can have both abstract and Only abstract methods (until Java 7);
concrete methods default/static allowed from Java 8

Variables Can have instance variables Only constants (public static final)

Inheritance Supports single inheritance Supports multiple inheritance

Constructor Can have constructors Cannot have constructors

s

3. Can we create an instance of an abstract class?

No, an abstract class cannot be instantiated. You must extend it and implement its
abstract methods in a subclass.

4. What happens if a subclass does not implement all abstract methods of a parent class?

The subclass must also be declared abstract. Otherwise, the code will not compile.

5. How is abstraction implemented in different programming languages?

●​ Java/C++: Through abstract classes and interfaces​

●​ Python: Using abstract base classes (abc module)​

●​ C#: Via abstract classes and interfaces​

●​ JavaScript/TypeScript: Via interfaces and base classes​

6. How is data abstraction accomplished?

By:

●​ Using access modifiers (private, public, etc.)​

●​ Creating interfaces or abstract classes​

●​ Providing only necessary methods and hiding inner logic​

7. What is an abstract class?

An abstract class is a class that cannot be instantiated and may contain abstract
methods (methods without implementation) which must be implemented by subclasses.
java
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abstract class Animal {
abstract void makeSound();
}

8. How is an abstract class different from an interface?

To summarize:

●​ Abstract class can have concrete methods, interface could not (until Java 8).​

●​ You can extend only one abstract class, but implement multiple interfaces.​

●​ Interfaces represent a contract, while abstract classes provide partial

implementation.​

9. What are the characteristics of an abstract class?

●​ Cannot be instantiated​

●​ May have constructors​

●​ Can contain both abstract and non-abstract methods​

●​ Can include fields and access modifiers​

●​ Supports inheritance​

Ready to continue with 5. Inheritance?

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continue
ChatGPT said:

Great! Let's continue with the next major concept in OOP:

🧬 5. Inheritance
1. What is meant by Inheritance?

Inheritance is a mechanism where a child class (subclass) acquires properties and

behaviors (methods and fields) from a parent class (superclass). It promotes code
reusability and hierarchical relationships.

2. What is the difference between single and multiple inheritance?

Type Description

Single A subclass inherits from one superclass.

Inheritance

Multiple A subclass inherits from more than one class (C++, not supported
Inheritance in Java via classes but possible via interfaces).

3. What are the various types of inheritance?

●​ Single Inheritance​

●​ Multilevel Inheritance​

●​ Hierarchical Inheritance​

●​ Multiple Inheritance (via interfaces in Java)​

●​ Hybrid Inheritance​

4. What is a subclass?

A subclass (child class) is a class that inherits from another class (superclass). It can add
its own methods and properties or override parent methods.

5. Define a superclass?

A superclass (base class or parent class) is the class whose properties and behaviors are
inherited by another class.

6. What is an interface?

An interface is a reference type in Java (and other OOP languages) that contains only
abstract methods (until Java 7), and from Java 8 onwards, it can also include default and
static methods.

7. How does method overriding work in inheritance?

Method overriding allows a subclass to provide a specific implementation of a method
that is already defined in the superclass.

java
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class Animal {
void sound() { System.out.println("Animal sound"); }
}
class Dog extends Animal {
void sound() { System.out.println("Bark"); }
}

8. What is the role of the super keyword in inheritance?

●​ Access superclass methods and constructors​

●​ Call the immediate parent class constructor​

java
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super(); // call parent constructor
super.methodName(); // call parent method

9. Can constructors be inherited?

No, constructors are not inherited. However, a subclass can call the superclass’s
constructor using super().

10. How does the final keyword affect inheritance?

●​ A final class cannot be extended.​

●​ A final method cannot be overridden.​

java
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final class MyClass {} // cannot be inherited
final void method() {} // cannot be overridden

11. Are there any limitations of Inheritance?

 ●​ Tightly coupled classes​

●​ Increased complexity​

●​ May break encapsulation​

●​ Overuse can lead to fragile base class problem​

12. Explain Inheritance with an example:

java
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class Vehicle {
void start() { System.out.println("Vehicle started"); }
}
class Car extends Vehicle {
void horn() { System.out.println("Beep!"); }
}

13. Is it possible for a class to inherit the constructor of its base class?

No. Constructors are not inherited but can be invoked using super().

14. What are the limitations of inheritance?

●​ Promotes tight coupling​

●​ Can introduce unexpected behavior if not properly managed​

●​ Doesn’t support code hiding (every child knows parent details)​

15. What is the difference between Inheritance and Polymorphism?

Feature Inheritance Polymorphism

Purpos Enables code Enables method to behave

e reuse differently

Type "Is-a" relationship Many forms of a method

Exampl Dog extends Overridden sound() in Dog, Cat

e Animal
Shall we proceed to 6. Polymorphism?

You said:
continue
ChatGPT said:

Let’s dive into one of the most powerful features of OOP:

🌀 6. Polymorphism
1. What is Polymorphism?

Polymorphism means "many forms." It allows the same method or function to behave
differently based on the object that is calling it.

There are two main types:

●​ Compile-time polymorphism (Method Overloading)​

●​ Runtime polymorphism (Method Overriding)​

2. What is the difference between method overloading and method overriding?

Feature Method Overloading Method Overriding

Occurs In Same class Parent-child class

relationship

Based On Number/type of Implementation of method

parameters

Time of Compile-time Runtime

Resolution

Purpose Increase method Customize inherited

flexibility behavior

3. What is meant by static polymorphism?

Also known as compile-time polymorphism, this occurs when multiple methods have the
same name but different signatures.
java
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class MathUtils {
int add(int a, int b) { return a + b; }
double add(double a, double b) { return a + b; }
}

4. What is meant by dynamic polymorphism?

Also called runtime polymorphism, it happens when a method in a subclass overrides a

method in the superclass.

java
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class Animal {
void sound() { System.out.println("Animal sound"); }
}
class Cat extends Animal {
void sound() { System.out.println("Meow"); }
}

5. Can we override a static method? Why or why not?

No. Static methods belong to the class, not the instance. Hence, they cannot be
overridden. If you declare the same static method in a subclass, it's method hiding, not
overriding.

6. What is dynamic method dispatch?

Dynamic Method Dispatch is the process of calling an overridden method at runtime,

not compile time, using a reference of the parent class pointing to a child class object.

java
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Animal obj = new Dog();
obj.sound(); // Executes Dog's version
7. What is operator overloading?

Operator overloading allows you to define or alter the meaning of operators for
user-defined types.

●​ Supported in C++​

●​ Not supported in Java (except + for string concatenation)​

Example in C++:

cpp
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class Complex {
int real, imag;
Complex operator + (Complex const &obj) { ... }
};

8. How does C++ support Polymorphism?

C++ supports:

●​ Compile-time polymorphism: via function overloading and operator overloading​

●​ Runtime polymorphism: via virtual functions and method overriding​

9. What is Compile time Polymorphism and how is it different from Runtime Polymorphism?
Feature Compile-Time Runtime
Polymorphism Polymorphism

Other Name Static Polymorphism Dynamic Polymorphism

Mechanism Method Overloading Method Overriding

Resolution At Compile Time At Runtime

Time

Flexibility Less flexible More flexible

10. Explain overloading and overriding with examples.

Overloading:

java
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void print(int a) { }
void print(String b) { }

Overriding:

java
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class Parent {
void show() { System.out.println("Parent"); }
}
class Child extends Parent {
void show() { System.out.println("Child"); }
}

11. Give a real-world example of polymorphism.

Example:​
An interface Shape with a method draw(). Different classes (Circle, Rectangle,
Triangle) implement draw() in their own way.

java
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Shape s1 = new Circle();
Shape s2 = new Rectangle();
s1.draw(); // Draws circle
s2.draw(); // Draws rectangle

✅ Shall we move on to the next section: 7. Advanced OOP Concepts?

You said:
continue
ChatGPT said:
Awesome! Now let’s cover the advanced OOP concepts that often come up in technical
interviews:

⚙️ 7. Advanced OOP Concepts

1. What are access specifiers and what is their significance?

Access specifiers define the scope and visibility of class members.

●​ public: Accessible everywhere​

●​ private: Accessible only inside the class​

●​ protected: Accessible in the same package and subclasses​

●​ (default): Accessible within the same package​

✅ They help enforce encapsulation and restrict unauthorized access to sensitive data.
2. What is a static method? How is it different from an instance method?
Feature Static Method Instance Method

Binding Belongs to the class Belongs to an object

Call Style ClassName.method() object.method()

Access Can access only static Can access both static & instance
data data

Example Math.max(5, 10) emp.getName()

3. What is a singleton class? How do you implement it?

A singleton class allows only one instance to be created during the program lifecycle.

Java Implementation:

java
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class Singleton {
 private static Singleton instance = null;
private Singleton() {}
public static Singleton getInstance() {
if (instance == null) instance = new Singleton();
return instance;
}
}

4. What are design patterns in OOP?

Design patterns are proven solutions to common software design problems. They help
in writing maintainable, scalable code.

Examples:

●​ Singleton​

●​ Factory​

●​ Observer​

●​ Strategy​

●​ Decorator​

5. What is dependency injection?

It’s a design pattern where an object’s dependencies are provided from the outside,
rather than the object creating them itself.

Benefits:

●​ Reduces coupling​

●​ Improves testability​

6. What is the difference between composition and aggregation?

 Feature Composition Aggregation

Dependen Strong (child cannot exist Weak (child can exist

cy alone) independently)

Life Cycle Tied to parent Independent

Example House → Rooms Team → Players

7. How do mixins work in OOP?

A mixin is a class that provides methods to other classes without being a parent class.
It’s a way to share functionality horizontally (commonly used in Python, Ruby, etc.).

8. What is composition?

Composition is an OOP principle where a class has an object of another class, rather
than inheriting from it.

java
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class Engine { ... }
class Car {
Engine engine = new Engine(); // Car "has-a" Engine
}

9. What is the difference between Composition and Inheritance?

Feature Inheritance Compositio
n

Relationship "is-a" "has-a"

Type

Flexibility Less More

flexible flexible

Coupling Tighter Looser

10. What is constructor chaining?

Constructor chaining is when one constructor calls another constructor in the same
class using this() or the superclass constructor using super().

java
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class Car {
Car() { this(10); }
Car(int speed) { System.out.println(speed); }
}

11. What is Coupling in OOP, and why is it helpful?

Coupling refers to the degree of dependency between classes.

●​ Loose coupling is preferred: It makes code more maintainable, testable, and

modular.​

●​ Tight coupling makes the system rigid and hard to modify.​

12. Name the operators that cannot be overloaded.

In C++, the following cannot be overloaded:

●​ :: (scope resolution)​

●​ . (member access)​

●​ .* (member pointer access)​

●​ sizeof​

●​ typeid​

13. What is the difference between new and override?

In C#/C++:
 ●​ new hides the parent method (method hiding)​

●​ override replaces the parent method (method overriding)​

14. What is Cohesion in OOP?

Cohesion refers to how closely related the responsibilities of a class are.

●​ High cohesion = better organization and readability​

●​ Low cohesion = class is doing too many unrelated things​

15. What is the difference between a base class and a superclass?

Both terms refer to the parent class in inheritance. They are used interchangeably:

●​ Base class is more common in C++​

●​ Superclass is often used in Java​

✅ Let me know if you'd like to continue with 8. Exception Handling in OOP.

You said:
continue
ChatGPT said:

Let’s continue with:

⚠️ 8. Exception Handling in OOP

1. What is an exception?

An exception is an event that occurs during program execution that disrupts the normal
flow of instructions. It typically occurs due to invalid input, file issues, or resource errors.
2. What is meant by exception handling?

Exception handling is a mechanism to handle runtime errors so that the program’s flow
can be maintained smoothly without abrupt termination.

Languages like Java, Python, and C++ provide constructs like:

java
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try {
// code that may throw an exception
} catch (Exception e) {
// handling code
} finally {
// cleanup code
}

3. How do you handle exceptions in OOP?

●​ Java/C++/C#: Using try, catch, finally, and throw/throws keywords.​

●​ Python: Using try, except, finally, and raise.​

Example (Java):

java
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try {
int result = 10 / 0;
} catch (ArithmeticException e) {
System.out.println("Division by zero!");
} finally {
System.out.println("Cleanup done.");
}

4. What is the difference between checked and unchecked exceptions (Java)?

 Feature Checked Exception Unchecked Exception

Inheritance Inherits from Inherits from RuntimeException

Exception

Compiler Checked at Checked at runtime

Handling compile-time

Example IOException, NullPointerException,

SQLException ArithmeticException

5. Can a constructor throw an exception?

Yes. In Java, a constructor can throw both checked and unchecked exceptions.

java
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public class MyClass {
public MyClass() throws IOException {
// some file operation
}
}

6. What is the finally block used for?

The finally block executes regardless of whether an exception is thrown or caught.

It is typically used for cleanup, like closing files or releasing resources.

7. What are the differences between error and exception?

Feature Error Exception

Type Irrecoverable (e.g., Recoverable (e.g.,

OutOfMemoryError) FileNotFoundException)

Handlin Not meant to be caught Can be handled using try-catch

g

Origin Occurs due to environment Occurs due to code or logic

✅ Would you like to continue with 9. OOP in Practice?
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Let’s move ahead to:

🧩 9. OOP in Practice
1. How does OOP compare to procedural programming?
Feature Procedural Programming Object-Oriented Programming

Structure Based on functions Based on objects and classes

Code Reusability Limited High (via inheritance and

polymorphism)

Modularity Hard to manage in large Promotes modularity

projects

Example C Java, Python, C++

Language

2. What are the advantages of using OOP in software development?

●​ Reusability through inheritance​

●​ Modularity via classes and objects​

●​ Scalability using abstraction and polymorphism​

●​ Maintainability with encapsulated, well-structured code​

●​ Real-world modeling through object representation​

3. Can you give an example of an OOP-based real-world application?

Banking System:
 ●​ Account is a superclass.​

●​ SavingsAccount and CurrentAccount inherit from it.​

●​ Methods like deposit(), withdraw() are overridden as needed.​

●​ Each Customer is represented as an object with personal and account info.​

4. What are some common pitfalls when using OOP?

●​ Overuse of inheritance instead of composition​

●​ Tight coupling between classes​

●​ Poor encapsulation​

●​ Using objects where simple data structures are sufficient​

●​ Ignoring design principles like SOLID​

5. How does OOP support code scalability and maintainability?

●​ Through modularity, code can be divided into smaller, manageable units.​

●​ Polymorphism allows adding new behaviors without changing existing code.​

●​ Inheritance avoids duplication.​

●​ Encapsulation protects internal states and simplifies changes.​

6. Can we run a Java application without implementing the OOPs concept?

Technically, yes — simple Java applications (like HelloWorld) can run using just static
methods (main). But Java is designed for OOP, and real-world apps typically require
objects and classes.
7. Identify which OOPs concept should be used in the following scenario:

“A group of 5 friends, one boy never gives any contribution when the group
goes for the outing. Suddenly a beautiful girl joins the same group. The boy
who never contributes is now spending a lot of money for the group.”

✅ Answer: Polymorphism
Explanation: The boy (object) behaves differently in different contexts (before and after
the girl joins). This is runtime polymorphism — the same object shows different behavior
based on runtime situation.

✅ Ready to finish with the final section: 10. Miscellaneous OOP Questions?
You said:
yes
ChatGPT said:

Perfect! Let's wrap up with:

🧠 10. Miscellaneous OOP Questions

1. What is the difference between shallow copy and deep copy?
Copy Type Description

Shallow Copies reference to original objects (nested objects

shared)

Deep Creates copies of everything, including nested

objects

2. How does garbage collection work in OOP languages?

Garbage collection automatically reclaims memory occupied by objects that are no

longer reachable or referenced.

●​ In Java: Done by the JVM​

 ●​ In Python: Handled by the interpreter​

●​ C++: Manual memory management (via delete)​

3. What is meant by Garbage Collection in OOPs world?

Garbage Collection is a process where unreferenced objects are identified and removed
from memory, helping prevent memory leaks and improve performance.

4. What is method chaining?

Method chaining is a technique where multiple methods are called in a single

statement, using the return value of the previous method (usually this).

java
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builder.setName("Abhi").setAge(21).setEmail("a@gmail.com");

5. What is the difference between mutable and immutable objects?

Feature Mutable Object Immutable Object

Changeabl Can be changed after Cannot be changed after

e creation creation

Examples ArrayList, String, Integer (Java)

StringBuilder (Java)

6. What is reflection in OOP?

Reflection is the ability of a program to inspect and modify its own structure (classes,
methods, fields) at runtime.

In Java, done using the java.lang.reflect package:

java
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Class<?> clazz = Class.forName("MyClass");
Method m = clazz.getMethod("myMethod");

7. Are class and structure the same? If not, what's the difference between a class and a
structure?
Feature Class Structure

Default private (Java/C++) public (C++)

Access

Inheritance Supported Limited (not in C, partial in C++)

Memory Reference Type Value Type (C/C++)

(Java)

8. What are the various types of constructors in C++?

●​ Default constructor​

●​ Parameterized constructor​

●​ Copy constructor​

●​ Destructor (not a constructor but related)​

9. What is a copy constructor?

A copy constructor creates a new object by copying data from an existing object.

cpp
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class MyClass {
MyClass(const MyClass &obj) { ... }
};

10. What is a destructor?

A destructor is a special function that gets called automatically when an object goes
out of scope. It cleans up resources.
In C++:

cpp
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~MyClass() { }

11. What are the manipulators in OOP, and how do they work?

In C++, manipulators are used to format output, e.g. endl, setw, setprecision.

cpp
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cout << setw(10) << "Hello";

12. What are the rules for creating a constructor?

●​ Must have the same name as the class​

●​ Cannot have a return type​

●​ Can be overloaded​

●​ Can be private, protected, or public​

13. What are the differences between the constructor and the method in Java?
Feature Constructor Method

Purpose Initialize object Perform operations

Name Same as class name Any name

Return No return type Must have return

Type type

Call Time Called at object Called explicitly

creation

14. What are the types of variables in OOP?

 ●​ Instance variables – tied to object​

●​ Class (static) variables – shared among all objects​

●​ Local variables – defined within methods​

●​ Parameter variables – method arguments​

15. Is it possible to overload a constructor?

Yes. You can create multiple constructors with different parameters (constructor
overloading).

java
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class Student {
Student() {}
Student(String name) {}
}

16. Can we overload the main() method in Java? Also, give an example.

Yes, main() can be overloaded but only the standard one with public static void
main(String[] args) is used by JVM.

java
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public class Test {
public static void main(String[] args) {
System.out.println("Hello main");
main(10);
}

public static void main(int a) {

System.out.println("Overloaded main: " + a);
}
}
✅ That’s it! You now have a complete set of OOP interview questions and answers —
all explained clearly so you can speak them confidently in interviews.