Using final

The final keyword in Java is used to apply restrictions on classes, methods, and variables. It can be used to prevent inheritance, method overriding, and modification of variables.

Key Points:

  1. final class: A class declared as final cannot be subclassed.
  2. final method: A method declared as final cannot be overridden by subclasses.
  3. final variable: A variable declared as final cannot be reassigned after initialization.

Example 1: Using final with a class

When a class is declared final, it cannot be extended (inherited).

final class Animal {
    void eat() {
        System.out.println("Eating...");
    }
}

// The following code will result in a compile-time error
// class Dog extends Animal { }

Example 2: Using final with a method

A final method cannot be overridden by a subclass.

class Animal {
    final void sound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    // The following code will result in a compile-time error
    // void sound() {
    //     System.out.println("Dog barks");
    // }
}

Example 3: Using final with a variable

A final variable can only be initialized once. Once initialized, its value cannot be changed.

class Dog {
    final String name = "Buddy";

    void changeName() {
        // The following line will cause a compile-time error
        // name = "Max";
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        System.out.println(dog.name);  // Output: Buddy
    }
}

Example 4: Using final with method parameters

A method parameter can also be declared final to prevent modification within the method.

class Animal {
    void setName(final String name) {
        // The following line will cause a compile-time error
        // name = "Buddy";
    }
}

🔗 Related Notes