final class and method

Learn non-extendability with final.

final class

If you mark a class as final, no class can inherit from it. This ensures the class's behavior cannot be changed. Many Java classes like String and Integer are final.

Example: final class Seal { }. You cannot write class Sub extends Seal { }; you get a compile error. final classes are used for security and consistency; they prevent the class design from being broken. They are common in value classes and immutable structures.

final method

If you mark a method as final, subclasses cannot override it. This ensures the method's behavior does not change. Even if the class itself is not final, some of its methods can be final.

Example: class Animal { final void breathe() { } }. A subclass inheriting Animal cannot override breathe with @Override. This prevents critical behavior from being broken. final methods can also be a performance advantage; the compiler can turn them into direct calls.

Exercise Add a final method to Animal

Define a class Animal. Add a String name field. Add a final void describe() method; its body writes System.out.println(name + " is an animal");. In main create an Animal instance, assign name and call the describe method.

Show example solution

class Animal {
    String name;
    final void describe() {
        System.out.println(name + " is an animal");
    }
    public static void main(String[] args) {
        Animal a = new Animal();
        a.name = "Tiger";
        a.describe();
    }
}

Test yourself

final class Seal is defined. Which does not compile?
- Seal s;
- Seal s = new Seal();
- class Dog { }
- class Sub extends Seal { }
Show answer

class Sub extends Seal { } — A final class cannot be inherited; extends is not allowed.
Match the final uses

final class

Cannot inherit
final method

Cannot override
String

Final class example
breathe

Final method example

Complete the final method definition

class Animal {
    ____ void breathe() {
        System.out.println("Nefes");
    }
}

Show answer

class Animal {
    final void breathe() {
        System.out.println("Nefes");
    }
}

Next lesson: Summary - Inheritance

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies