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Table of Contents
final Variables – Constants You Can't Change
final Methods – Preventing Method Overriding
final Classes – Preventing Inheritance
Bonus: Blank Final Variables – Delayed Assignment
Home Java javaTutorial what is the 'final' keyword in java

what is the 'final' keyword in java

Jul 19, 2025 am 03:58 AM

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.

what is the \'final\' keyword in java

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.

what is the 'final' keyword in java

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.

what is the 'final' keyword in java

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:

what is the 'final' keyword in java
 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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