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The `final` Keyword in Java - (BCA / B.Tech)

What is the `final` Keyword in Java?

The final keyword is a non-access modifier that can be applied to variables, methods, and classes. It is used to apply restrictions on these elements, essentially making them unchangeable in some way. Once declared as `final`, an entity cannot be modified, overridden, or inherited.

Applications of the `final` Keyword:

Final Variable (Constant): When a variable is declared as `final`, its value cannot be changed once it has been initialized. It effectively becomes a constant.

class Circle {
    final double PI = 3.14159; // This value can never be changed.

    double calculateArea(double radius) {
        // PI = 3.14; // This would cause a compile-time error.
        return PI * radius * radius;
    }
}

Final Method (Prevent Overriding): When a method is declared as `final`, it cannot be overridden by a subclass. This is used to enforce a specific implementation and prevent subclasses from altering it.

class Vehicle {
    final void displayInfo() {
        System.out.println("This is a vehicle.");
    }
}

class Car extends Vehicle {
    // void displayInfo() { ... } // Compile-time error: Cannot override the final method.
}

Final Class (Prevent Inheritance): When a class is declared as `final`, it cannot be extended or inherited by any other class. This is often done for security and immutability, as seen in core Java classes like `String` and `Integer`.
```
final class SecureData {
    // ... class members
}

// class ExtendedSecureData extends SecureData { ... } // Compile-time error: Cannot inherit from final class.
```

The `final` Keyword in Java

What is the `final` Keyword in Java?

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