Top 30+ OOPS Real Time Interview Questions
Top 30+ OOPS Real Time Interview Questions
OOP languages are embedded languages that support OOP principles such as encapsulation, inheritance, polymorphism, and abstraction. Now let’s take a look at the following example OOP languages:
Popular OOP Languages:
Top 30+ OOPS Real Time Interview Questions
Here’s a tabular comparison of popular OOP languages based on key features:
Language | Fully OOP? | Primary Use Case | Multi-Paradigm Support | Memory Management | Platform | Notable Features |
---|---|---|---|---|---|---|
C++ | No (Hybrid) | System Programming, Game Dev | Yes (OOP + Procedural) | Manual (with smart pointers) | Cross-platform | Fast performance, multiple inheritance |
Java | Yes | Enterprise, Web, Android | Yes (OOP + Functional) | Automatic (Garbage Collection) | Cross-platform (JVM) | Strong type safety, rich libraries |
Python | Yes | Web, AI, Scripting | Yes (OOP + Functional + Procedural) | Automatic (Garbage Collection) | Cross-platform | Dynamic typing, simplicity |
C# | Yes | .NET, Game Dev (Unity) | Yes (OOP + Functional) | Automatic (Garbage Collection) | Windows, Cross-platform (via .NET) | Strong integration with Microsoft ecosystem |
JavaScript | No (Prototype-based OOP) | Web Dev, Backend (Node.js) | Yes (Functional + OOP) | Automatic | Cross-platform (Browser, Node.js) | Prototype inheritance, event-driven |
Swift | Yes | iOS/macOS Apps | Yes (OOP + Functional) | Automatic (ARC) | Apple Ecosystem | Type safety, modern syntax |
Kotlin | Yes | Android, Backend | Yes (OOP + Functional) | Automatic (GC) | Cross-platform (JVM, Native) | Concise, null safety |
Ruby | Yes | Web Dev (Rails) | Yes (OOP + Metaprogramming) | Automatic (GC) | Cross-platform | Everything is an object |
PHP | No (Hybrid) | Web Dev (Backend) | Yes (Procedural + OOP) | Automatic (GC) | Web Servers | Easy to learn, wide adoption |
Objective-C | Yes | iOS/macOS (Legacy) | Yes (OOP + Procedural) | Automatic (ARC) | Apple Ecosystem | Message-passing, influenced by Smalltalk |

Top 30+ OOPS Real Time Interview Questions
- 4 Pillars of OOPS?
- What are Class and object?
- What is Abstraction?
- What is Encapsulation?
- What is Inheritance?
- Types of Inheritance?
- Diamond Problem?
- What is Polymorphism and its types?
- What is Compile-time polymorphism?
- What are Function Overloading and Operator Overloading?
- What is New Operator and Delete Operator?
- What is Run Time Polymorphism?
- What are VTable and VPtr?
- What is a Constructor?
- Types of Constructors?
- Write your own copy constructor and own assignment operator.
- What is Move Constructor?
- Write your own move constructor and own move assignment operator.
- What are Destructors?
- What is a Virtual Destructor?
- What are Const Variables and How do initialize in constructors?
- What are Static Variables and Static Methods?
- What is Friend Functions?
- What are Smart Pointers?
- What are weak Pointers, and shared Pointers?
- Types Of Casting?
- What are Dynamic Casting and Static Casting?
- What is Object Slicing?
- What is the use of an Explicit Keyword?
- What is a Function Pointer?
- 2D array Initiation?
- Write Your Own Vector?
- What are lambda functions?
Here’s a tabular format covering all your OOPs concepts in a structured manner:
Top 30+ OOPS Real Time Interview Questions
for JAVA ,C++,PYTHON etc
Concept | Explanation |
---|---|
4 Pillars of OOP | Encapsulation, Abstraction, Inheritance, Polymorphism |
Abstraction | Hiding implementation details and showing only the necessary features to the user (e.g., using abstract classes and interfaces). |
Encapsulation | Wrapping data and functions into a single unit (class) and restricting direct access using access modifiers (private , protected , public ). |
Inheritance | Mechanism where a class (child ) derives properties and behaviors from another class (parent ). Promotes code reusability. |
Types of Inheritance | – Single (one parent → one child) – Multiple (one child inherits multiple parents) – Multilevel (grandparent → parent → child) – Hierarchical (one parent → multiple children) – Hybrid (combination of multiple inheritance types) |
Diamond Problem | Occurs in multiple inheritance when a child class inherits from two classes that share a common base class, causing ambiguity. Solved using virtual inheritance in C++. |
Polymorphism | Ability of an entity (method or operator) to take multiple forms. Two types: Compile-time (early binding) and Run-time (late binding). |
Compile-time Polymorphism | Achieved using function overloading and operator overloading where function calls are resolved at compile-time. |
Function Overloading | Defining multiple functions with the same name but different parameters (different number or type of arguments). |
Operator Overloading | Redefining operators (+ , - , * , = , etc.) to work with user-defined types (classes). |
New and Delete Operators | new dynamically allocates memory for objects, delete deallocates it. Example: int* p = new int(5); delete p; |
Run-time Polymorphism | Achieved through method overriding and virtual functions, resolved at runtime using dynamic binding (vtable mechanism). |
VTable & VPtr | – VTable (Virtual Table): Table storing addresses of virtual functions. – VPtr (Virtual Pointer): Pointer to VTable, maintained per object to resolve function calls dynamically. |
Constructor | Special function executed when an object is created. Used for initialization. |
Types of Constructors | – Default (no arguments) – Parameterized (with arguments) – Copy (creates a new object as a copy of an existing object) – Move (optimizes resource transfer in temporary objects) |
Copy Constructor | ClassName(const ClassName &obj) { /* copy logic */ } |
Assignment Operator (Overloaded) | ClassName& operator=(const ClassName &obj) { /* assignment logic */ return *this; } |
Move Constructor | ClassName(ClassName&& obj) { /* move logic */ } |
Move Assignment Operator | ClassName& operator=(ClassName&& obj) { /* move assignment logic */ return *this; } |
Destructors | Special function (~ClassName() ) called when an object goes out of scope to free resources. |
Virtual Destructor | Ensures derived class destructor is called first in polymorphic scenarios. virtual ~ClassName() {} |
Const Variables in Constructor | Initialized using an initializer list: ClassName() : myConstVar(10) {} |
Static Variables & Methods | – Static Variables: Shared among all instances of a class. – Static Methods: Can be called without an object (ClassName::method() ). |
Friend Functions | Non-member function that can access private/protected members of a class (friend keyword). |
Smart Pointers | unique_ptr , shared_ptr , and weak_ptr manage memory automatically. |
Weak & Shared Pointers | – Shared Pointer (shared_ptr ): Reference-counted ownership. – Weak Pointer (weak_ptr ): Non-owning reference to prevent cyclic dependencies. |
Types of Casting | – static_cast (compile-time type conversion) – dynamic_cast (safe downcasting) – const_cast (removes const qualifier) – reinterpret_cast (converts pointer types) |
Dynamic vs Static Casting | – Static Casting (static_cast ): Compile-time conversion. – Dynamic Casting (dynamic_cast ): Used for polymorphism, checks type safety at runtime. |
Object Slicing | When a derived class object is assigned to a base class object, the extra properties of the derived class are sliced off. |
Explicit Keyword | Prevents implicit conversions when using single-parameter constructors. explicit ClassName(int x); |
Function Pointer | A pointer that stores the address of a function. Example: void (*ptr)() = &func; |
2D Array Initialization | int arr[3][3] = {{1,2,3}, {4,5,6}, {7,8,9}}; |
Write Your Own Vector | Implement dynamic array with push_back , pop_back , resize , etc. |
Lambda Functions | Anonymous functions used for short, inline operations. Syntax: [capture](parameters) { body } |
Top 30+ OOPS Real Time Interview Questions
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