Essential OOP/Database/Data Structures Interview Questions for Developers

Preparing for software developer interviews often means tackling questions from a variety of domains, including Object-Oriented Programming (OOP), Databases (DB), and Data Structures and Algorithms (DSA). These topics are fundamental to building scalable and efficient software systems, and mastering them can set you apart in the hiring process. Here’s a collection of commonly asked questions across these areas to help you sharpen your knowledge and practice effectively.

Object-Oriented Programming (OOP)

Basic Questions

1. What are the four main principles of Object-Oriented Programming?
2. Define a class and an object with an example.
3. What is inheritance? Give an example of single and multiple inheritance.
4. What is polymorphism? Explain compile-time and runtime polymorphism.
5. Explain the concept of abstraction. How is it implemented in programming?
6. What is encapsulation? How does it help in protecting data?
7. What is the difference between an interface and an abstract class?
8. Define method overloading and method overriding with examples.
9. What are access specifiers? Explain public, private, and protected.
10. What is a constructor? How is it different from a regular method?

Intermediate Questions

1. Explain the difference between inheritance and composition.
2. What is the difference between a shallow and deep copy?
3. What is the purpose of a static method and static variables?
4. Explain the difference between "is-a" and "has-a" relationships.
5. What are design patterns? Name a few common ones used in OOP.
6. How does multiple inheritance work?
7. What is the purpose of the super keyword in inheritance?
8. Explain the SOLID principles of OOP.
9. What is a virtual function? How is it used?
10. What is the concept of garbage collection in OOP?

Expert Questions

1. How would you implement a Singleton Design Pattern?
2. What are mixins? How do they differ from inheritance?
3. What is dependency injection? Why is it used in object-oriented design?
4. Explain the concept of method dispatch and its types (static vs dynamic).
5. How would you optimize a large OOP-based system for scalability?
6. Compare and contrast functional programming with OOP.
7. What are the limitations of OOP? How would you overcome them?
8. Explain metaprogramming and its significance in languages.
9. Discuss the pros and cons of inheritance vs composition.
10. How would you refactor a monolithic OOP codebase into a modular one?

Database

Basic Questions

1. What is a database? Explain the difference between SQL and NoSQL databases.
2. Define a primary key, foreign key, and unique key.
3. What are indexes? How do they improve query performance?
4. What is normalization? Explain the first, second, and third normal forms.
5. What are the differences between DELETE, TRUNCATE, and DROP?
6. What is a JOIN in SQL? Explain the types of joins.
7. Define ACID properties in database transactions.
8. What is a view in SQL? How is it different from a table?
9. What is a stored procedure? How is it different from a trigger?
10. What is a database schema?

Intermediate Questions

1. Explain the differences between relational and non-relational databases.
2. How do you optimize a SQL query? Name some techniques.
3. What is a foreign key constraint, and why is it important?
4. Explain the difference between a clustered and non-clustered index.
5. What is database sharding? When is it used?

Data Structures

Basic Questions

1. What is a data structure? Why is it important?
2. What is the difference between an array and a linked list?
3. What is a stack? How is it used?
4. What is a queue? How is it different from a stack?
5. What is a linked list? How is it different from an array?
6. What are the types of linked lists?
7. What is a binary tree?
8. What is a hash table?
9. What are the differences between linear and non-linear data structures?
10. What is a heap? How is it different from a binary tree?

Intermediate Questions

1. What is the time complexity of inserting an element into a binary search tree (BST)?
2. Explain the difference between depth-first search (DFS) and breadth-first search (BFS).
3. What is the purpose of a priority queue, and how is it implemented?
4. What is a graph? What are the different types of graphs?
5. What is a Trie (Prefix Tree)? How is it used?
6. What is dynamic programming? How does it relate to recursion?
7. What is a balanced binary search tree? Name a few types.
8. Explain the concept of hashing and hash collision. How can collisions be handled?
9. What is a circular queue? How does it work?
10. What is a set data structure? How is it different from a list?

Expert Questions

1. What are B- trees and B+ trees? How do they differ from binary search trees?
2. Explain the concept of a Bloom filter. What are its advantages and disadvantages?
3. What is the difference between a depth-first traversal and a breadth-first traversal in a graph?
4. What is the time complexity of various operations in a hash table (insert, delete, search)?
5. How would you detect a cycle in a directed graph?
6. What is the difference between a greedy algorithm and dynamic programming?
7. Explain how a red-black tree works. What are its properties?
8. What is the purpose of a disjoint-set (union-find) data structure?
9. What is a topological sort, and when is it used?
10. What is a skip list, and how does it improve performance over linked lists?