The future simple perfect verb tense often used with "by" and "not", "for" and "until" to state that the action or event will be completed at time in the future.
The future simple perfect verb tense is used to state an action that occurs into the future until a later time in the future.
To state an event or action that will finish before an other action event in the future.
Rules for using the future simple perfect verb tense:
The future simple perfect verb tense is used for actions that are non continuous.
A specific time is usually stated or is understood.
It is common to use the future simple perfect verb tense to clarify the order of 2 future events.
The future simple perfct verb tense can't be used with "time claueses" such as when, while, "by the time", soon, before, after, if, unless, until etc.
The future simple pefect verb tense is also known as the "future perfect 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
Examples:
We will have worked at the school 25 years next week.
My brother will be tired when he gets here, because he will have fl owen 12 hours.
The students will have finished all their exams tomorrow. I sure they will be happy.