why use contractor in method overriding

Answer 1

Do you mean constructor? You can override any method, not just those.

Answer 2

It's a good idea to have a no argument constructor.

You don't always want to supply an argument to a constructor.

In fact, there is a design principle for classes called Java Beans where it is a requirement to have a no argument constructor.

You can also create more constructors and supply them with parameters. The compiler will know which one to refer to based on the supplied parameters.