Final keyword in Inheritance

In Java, the final keyword plays an important role in controlling inheritance and method overriding. Here's a detailed explanation.

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🔐 final Keyword in Inheritance

The final keyword can be applied to:

Usage	Purpose
final class	Prevents a class from being subclassed
final method	Prevents a method from being overridden
final variable	Prevents a variable from being reassigned

When applied in the context of inheritance, final helps to restrict changes to a class or method.

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📌 1. final Class

A final class cannot be extended. You use it when you want to stop inheritance completely.

✅ Example:

final class Vehicle {
    void start() {
        System.out.println("Vehicle starting");
    }
}

// ❌ This will give a compile-time error
class Car extends Vehicle {
    // Error: cannot inherit from final class
}

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📌 2. final Method

A final method cannot be overridden in any subclass. You use it when you want to prevent overriding, for example, for security or consistency.

✅ Example:

class Vehicle {
    final void start() {
        System.out.println("Vehicle starting");
    }
}

class Car extends Vehicle {
    // ❌ Compile-time error
    // void start() {
    //     System.out.println("Car starting");
    // }
}

🧠 Use Cases:

• Prevent overriding of sensitive logic

• Prevent subclass from changing inherited behavior

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🧠 Why Use final in Inheritance?

• Security: Prevent altering critical methods

• Optimization: Java compiler may optimize calls to final methods

• Design Integrity: Enforce that some classes/methods remain unchanged

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❌ What You Cannot Do with final in Inheritance

Action	Allowed?	Reason
Extend a final class	❌	Final class is sealed
Override a final method	❌	Final methods are locked
Modify a final variable	❌	Final variables are constants

✅ Summary

final Applied To	Effect in Inheritance
Class	Cannot be extended
Method	Cannot be overridden
Variable	Not related to inheritance, but value-fixed