Ｉ thought "in future" meant "from now on" and a little different from "in the future."
Therefore, I was using, "You must be careful in future." and "He will come to Japan in the future."
I wonder if "in future" is acceptable in the US, because Longman Dictionary of Contemporary English says "in future" is British English.
I can't say about AmE, but you're certainly using them correctly from a BrE perspective- I didn't know that this was BrE.