This document discusses the key features of object-oriented programming in Java, including classes, objects, inheritance, encapsulation, abstraction, and polymorphism. It provides examples of each concept: classes define templates for objects, objects are instances of classes with state and behavior, inheritance allows subclasses to inherit properties and behaviors from parent classes, encapsulation binds data and code together restricting access, abstraction hides implementation details and exposes only necessary information, and polymorphism allows treating objects of different classes as common superclasses. The document is written by Swagato Biswas for a course on object-oriented programming.