Overriding methods in Java

Hello,

I am currently learning Java.
I have just learnt that we can modify methods in the child class, and in order to protect them from being edited, we can use the keyword final?
In the previous exercise, they were able to modify a method in the child class without using override. In the next exercise, they use override.
My question is whether override must be present or not to modify a child class method?

Thank you for your help,

Seanna

https://www.codecademy.com/courses/learn-java/lessons/java-inheritance-and-polymorphism/exercises/parent-class-aspect-modifiers
https://www.codecademy.com/courses/learn-java/lessons/java-inheritance-and-polymorphism/exercises/method-overriding

I don’t think its required, but I guess it might help the compiler compile the code faster.