final class and method
- Java course
- Intermediate
- Lesson 17/116
- 5 min
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.
Practice 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.
Starter code
// Define the Animal class
// Add a final describe method
// Instantiate and call in mainSample 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();
}
}Expected output
Tiger is an animal
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 final class Seal is defined. Which does not compile?
- Seal s;
- Seal s = new Seal();
- class Dog { }
- class Sub extends Seal { } Correct answer
Explanation: A final class cannot be inherited; extends is not allowed.
2 Match the final uses
| Term | Meaning |
|---|---|
final class |
Cannot inherit |
final method |
Cannot override |
String |
Final class example |
breathe |
Final method example |
3 Complete the final method definition
class Animal {
____ void breathe() {
System.out.println("Nefes");
}
}class Animal {
final void breathe() {
System.out.println("Nefes");
}
}Explanation: A final method cannot be overridden.