A sentence in future perfect tense tells that an action of future (denoted by verb) has been completed.
1) 3rd form of verb is used.
2) Helping verb à Shall have/ will have is used as
a) Shall have à I, we.
b) Will haveà all other Subjects.
Affirmativeà Subject+ Shall have / will have + verb + Object.
Negative à Subject + shall / will + not have + verb + object.
Interrogativeà shall / will + Subject + have +verb + Object?
Negative + Interrogative à shall / will + Subject+ not have + verb + Object?
1) He will have completed his homework.
2) She will not have eaten the food.
3) Will they have reached the school?
4) Shall we have reached the Nanital tomorrow by this time?
5) Will river not have crossed the danger mark?
For practice see