FUTURE PERFECT

(Subject + will have\shall have + 3rd form of verb + object)

FOR NEGATIVE SENTENCE

 will + not + have + verb (ending in -ed or irregular form) 

FOR QUESTION SENTENCE

will + subject + have + verb (ending in -ed or irregular form).

It is used for: 

1. talking about actions that will be completed in a certain future time.
2. It’s possible to use shall instead of will, especially for I and we.
3. In most cases, it is used with expressions of time that begin with: by that time, by midnight, by the end of the year, by then. 
4. In time clauses, this tense can not be used  with expressions: while, before, as soon as , if , unless, when , after etc.

Examples 

1. I shall have written my exercise by then.
2. He will have left before you go to see him.
3. I will have sent the assignment by Friday.