Module 29: Final Keyword

🔒 What is the final Keyword?

The final keyword in Java is used to restrict the user. It can be applied to variables, methods, and classes.

🔹 Usage of final

• Final Variable: The value cannot be changed once initialized.
• Final Method: Cannot be overridden by subclasses.
• Final Class: Cannot be extended (inherited).

🧪 Examples

                    final class Vehicle {
                      void display() {
                        System.out.println("This is a vehicle");
                      }
                    }
                    
                    class Car /* extends Vehicle */ {  // ❌ Error: Cannot inherit from final class
                    }
                    
                    class Animal {
                      final void sound() {
                        System.out.println("Animal makes a sound");
                      }
                    }
                    
                    class Dog extends Animal {
                      // void sound() {}  // ❌ Error: Cannot override final method
                    }
                    
                    public class Main {
                      public static void main(String[] args) {
                        final int speed = 90;
                        // speed = 100;  // ❌ Error: Cannot assign a new value to final variable
                        System.out.println("Speed: " + speed);
                      }
                    }

🎯 Why Use final?

• To prevent value modification (constants)
• To secure method behavior from changes
• To prevent inheritance of sensitive classes