The future perfect continuous verb tense is used to:
emphasize how long an event will be in progress at a future time
stress the the length of time of an event or action in the future
is used to state the results of an action or event in the future.
represent a continuous action that stated at some point, and continues into some point in the future
state that results of a future action, after an other future action. (2 actions that will take place in the future, one action takes place before, the 2nd action)
Rules for using the future perfect continues verb tense:
The future period of time if usually states :
next year
next week
next month etc.
the exact came can be stated
the approximate can can be stated
The period of time until the present point of time.
The future perfect continuous verb tense is usually not used with static verbs.
The future perfect continuous verb tense is also called the future perfect progressive tense.
The future perfect continuous verb tense can't be used with "time clauses" such as when, while, "by the time", soon, before, after, if, unless, until etc.
Examples:
In the fall I will have been studying here for 2 years.
My son will have been in teaching for 10 years next month.
The teacher will have been teaching
my children for 5 years next month.
The dogs will have been playing for 3 hours in 10 minutes.
Tammy will be very tired when she comes home, because she will have been flying over 24 hours.