Understanding the final Keyword in Java

final is a keyword in Java that indicates something cannot be changed. It has three usages: it can modify variables, methods, or classes.

final variables

When a variable is declared as final, its value cannot be changed after assignment. It is typically used for constants or variables that should remain unchanged.

final can modify member variables, static variables, local variables, and method parameters.

final methods

A method declared as final cannot be overridden by subclasses, ensuring the implementation remains unchanged. Template design patterns often use final methods to prevent core algorithmic logic from being overridden.

final classes

A class declared as final cannot be subclassed, guaranteeing that its implementation cannot be extended or altered. Java's immutable String class is an example of a final class.

Summary

When final is applied to a variable, method, or class, its meaning differs: for variables it makes the value immutable after assignment; for methods it prevents overriding; for classes it prevents inheritance.