NBKRIST – Java Hub

Industry-Level OOP Design Interview Questions

Expert View

From my experience interacting with interviewers from top companies like Infosys and Google, I learned that they don’t just look for how well you code — they look for how well you design. Many times, you’re given a real-world problem and expected to apply Object-Oriented Analysis and Design (OOAD) using Java.

The best candidates translate vague requirements into clear class structures — identifying relationships, behaviors, and abstractions. That’s real engineering thinking. These questions mirror real industry challenges — where analysis, design, implementation, and testing work hand in hand. 🧠

1️⃣ Banking Domain – Account Management System

Design a system for NBKRIST Bank that handles multiple account types: Savings, Current, and Loan Accounts.

  • Abstract class Account with fields: accountNo, holderName, balance.
  • Subclasses override withdraw() with specific rules.
  • Polymorphism for interest calculation.
  • Include validation for insufficient balance.
💡 Hint: Identify “is-a” hierarchy and override interest computation. Implement toString() for reporting.

2️⃣ Medical Domain – Hospital Management

Develop a Hospital Management System that manages Patients, Doctors, and Appointments.

  • Abstract class Person → subclasses Doctor & Patient.
  • Class Appointment connects Doctor ↔ Patient.
  • Use aggregation and encapsulation effectively.
💡 Hint: Represent “Doctor has-many Patients” using composition. Implement appointment scheduling and cancellation methods.

3️⃣ Manufacturing Domain – Vehicle Assembly

Create a system for NBKRIST Motors to assemble vehicles (Car, Bus, Truck).

  • Use interface Assemble and abstract class Vehicle.
  • Each subclass implements assemble() differently.
  • Show polymorphism and composition (“Vehicle has Engine”).
💡 Hint: Think of UML “composition” — Vehicle owns Engine. Use dependency injection for flexible testing.

4️⃣ College Domain – Student Management

Develop a Student Management System for NBKRIST to manage Students, Courses, and Enrollments.

  • Classes: Student, Course, Enrollment.
  • Each student can enroll in multiple courses.
  • Store enrollments using Collections API.
💡 Hint: Use aggregation: Student “has-many” Courses. Model it as a one-to-many relationship using ArrayList.

5️⃣ Employee Domain – Payroll System

Design an Employee Payroll System with full-time and contract employees.

  • Abstract class Employee with id, name, baseSalary.
  • Override calculatePay() for each employee type.
  • Use interface Payable to ensure all employees get paid.
💡 Hint: Show method overriding and runtime polymorphism. Add validation for minimum wage check.

💎 Key Summary – OOP Analysis and Design using Java

Object-Oriented Programming (OOP) is not just about writing code — it’s about **designing reusable, maintainable, and scalable systems**. In real-world projects, analysis and design precede implementation. Engineers use UML (Unified Modeling Language) to visualize these designs before coding.

When designing any system using Object-Oriented Programming principles, the core pillars of OOP operate together in harmony to achieve effective modeling.

According to my expereince, As a Java developer, one should be well-equipped with these fundamental concepts to design robust and efficient systems

💡 Tip from Industry: Before coding in Java, design your model class diagram as a draft plan. It gives clarity, minimizes rework, and impresses interviewers who expect “design-first” thinking.

🚀 Final Thought

The power of OOP lies in how you model reality — classes, relationships, behaviors — before you code. Once you start visualizing your design modeling, you begin thinking like a software architect, not just a programmer. That’s the mindset Infosys, Google, and other innovators seek — and it starts here at NBKRIST Java Hub.