In Java, the final keyword is used to restrict the modification of variables, methods, and classes to enhance code security and predictability. ① Variables declared as final cannot be changed once assigned, and are often used to define constants; ② Methods marked as final cannot be rewritten by subclasses to ensure that the logic is not changed; ③ Final class cannot be inherited to ensure that the implementation is not modified; ④ Uninitialized final variables (blank finals) can be assigned once in the constructor to improve flexibility and maintain invariance.
The final
keyword in Java is a versatile modifier used to restrict the user from changing the value, behavior, or structure of a variable, method, or class. It enforces immutability and can help improve code safety and performance. Here's how it works in different contexts.

final
Variables – Constants You Can't Change
When you declare a variable as final
, you're telling Java that this variable's value should not change once it's assigned. This is often used for constants, like mathematical values or configuration settings.
- A
final
variable can be assigned only once. - It can be initialized either at the time of declaration or inside a constructor (but not both).
- Example:
final double PI = 3.14159;
If you try to change a final
variable after it's assigned, the compiler will throw an error. This is useful when you want to ensure data integrity, like storing tax rates or conversion factors.

final
Methods – Preventing Method Overriding
If you mark a method as final
, it can't be overridden by subclasses. This is helpful when you want to protect critical logic from being altered in child classes.
- Helps maintain expected behavior across inheritance.
- Can also be a performance optimization hint (though modern JVMs usually optimize well regardless).
Example:

class Parent { final void display() { System.out.println("This method cannot be overridden"); } }
Trying to override this method in a subclass will cause a compile-time error.
final
Classes – Preventing Inheritance
A final
class cannot be subclassed. This is often used in utility classes (like java.lang.Math
) or when you want to ensure that no one can extend your class and change its behavior.
- Ensures the class's implementation remains unchanged.
- Enhances security and design integrity.
Example:
final class Utility { // methods here }
Trying to extend Utility
will result in a compilation error.
Bonus: Blank Final Variables – Delayed Assignment
A final
variable that isn't initialized at the time of declaration is called a blank final variable. It must be initialized in the constructor.
- Useful when you want to assign a value at runtime but not change it afterward.
- Ensures one-time initialization while keeping flexibility.
Example:
class Student { final String name; Student(String name) { this.name = name; } }
This allows the name to be set during object creation but prevents modification afterward.
That's how the final
keyword works in Java. It's not complicated, but it plays a big role in writing safer and more predictable code.
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