OOP Interview questions or Object-oriented Programming and design interview question are an integral part of any programming job interviews like Java, C++, or C#. Since Java is an Object-oriented programming language, it's expected from Java developers that he is good at Object-oriented analysis and design and familiar with essential OOP concepts like Abstraction, Encapsulation, and Polymorphism. Object-Oriented Programming Interview question in Java is mainly based around fundamental OOP concept and how those are implemented in Java like Abstraction OOP concept is implemented using an interface and abstract class, Encapsulation is using private keyword, etc.