A class in Java is a fundamental concept of object-oriented programming and serves as a blueprint or template for creating objects. It defines the structure and behavior that the objects created from it will have. In simple terms, a class specifies what data an object will store and what actions it can perform. Without classes, it would be difficult to organize and manage complex programs in Java.

A class consists of several important components. Data members, also known as variables or fields, are used to store the state or properties of an object, such as name, age, or ID. Methods define the behavior or functionality of the object, such as displaying details or performing calculations. Constructors are special methods used to initialize objects when they are created. Access specifiers like public, private, and protected control the visibility and accessibility of class members, helping to protect data from unauthorized access.

Classes play a vital role in supporting the core principles of object-oriented programming (OOP). Through encapsulation, data and methods are bundled together within a class. Abstraction allows a class to expose only essential features while hiding internal details. Inheritance enables one class to acquire properties and methods of another class, promoting code reuse. Polymorphism allows methods to behave differently based on the object that calls them.

Using classes helps in organizing code efficiently, improving readability, reusability, and maintainability. In real-world applications, classes represent real-life entities such as students, employees, or bank accounts. Therefore, understanding classes is essential for learning Java and building robust, scalable software applications.