What is the purpose of the `final` keyword in Java?

• A. To declare a method as abstract
• B. To allow method overriding
• C. To restrict inheritance and declare constants
• D. To specify a method's default behavior

Answer: (C)

The purpose of the final keyword in Java is primarily to restrict inheritance and to declare constants. When applied to a class, it prevents the class from being subclassed, ensuring that the integrity and behavior of the class cannot be altered. For example, if you declare a class as final, no other class can extend it, which is useful for creating immutable classes or ensuring certain functionality remains intact.

When applied to a method, marking it as final indicates that the method cannot be overridden in any subclass. This is important when you want to maintain specific behavior in a method across the inheritance hierarchy, preventing subclasses from altering critical functionality.

Additionally, when final is used with a variable, it means that the variable's value cannot be changed once it has been assigned. This makes such variables constants, providing predictable behavior and enhancing the clarity of the code. Defining constants using the final keyword promotes better maintainability and readability.

Overall, the final keyword is a powerful feature in Java that enhances encapsulation and provides control over how classes, methods, and variables are used throughout the application.