In Java, a class is a user-defined blueprint or template used to create objects. It defines the data members (variables) and methods (functions) that describe the properties and behavior of objects. Every object created from a class has its own copy of instance variables but shares the same method definitions. Java follows the object-oriented programming paradigm, where classes and objects are the fundamental building blocks. A class promotes code reusability, modularity, encapsulation, and maintainability. A class declaration in Java begins with an optional access modifier followed by the keyword `class`, the class name, and the class body enclosed within curly braces. The class name should follow Java naming conventions by starting with an uppercase letter and using CamelCase. ```java public class Student { int rollNo; String name; void display() { System.out.println(rollNo + " " + name); } } ``` In the above example, `Student` is a class containing two instance variables and one method. Objects of this class can be created using the `new` keyword. ```java Student s1 = new Student(); s1.rollNo = 101; s1.name = "Amit"; s1.display(); ``` Java provides four types of access specifiers that determine the visibility and accessibility of classes, variables, methods, and constructors. These are `public`, `private`, `protected`, and default (no access modifier). Proper use of access specifiers supports data hiding and secure programming. The `public` access specifier provides the widest level of accessibility. A public class, method, or variable can be accessed