Future Perfect Progressive

(c) I will ho to bed at ten P.M. Ed will get home at midnight. At midnight I will be sleeping. I will have been sleeping for two hours by the time Ed gets home.
The future perfect progressive emphasize the duration for an activity that will be in progress before another time or event it the future.

(d) When Professor Jones retires next month, he will have taught for 45 years.
(e) When Professor Jones reties next month, he will have been teaching for 45 years.
Sometimes the future perfect and the future perfect progressive have the same meaning, as in (d) and (e). Also, notice that the activity express by either of these two tenses may begin it the past