Will x going to: Qual é o correto?

Eu encontrei isso aqui na minha lição de inglês e não entendi se isso não seria a função do going to.

You can talk about something that will happen in the far future.
It will not happen today or tomorrow.
It will happen next month or next year.
You can talk about something that will happen a lot later.
You say:
I will go to college next year.
He will buy a house after he starts his new job.
They will have children after they have been married for several years.