what is future perfect tenses
Future perfect tense has been called the past of the future. It is used:
a) to talk about an action or event that will happen before another action or event, both of which are in future. The action or event that will happen first is often put into the future perfect tense while the other action is put in simple present tense.
For Example: Imagine that it is 5pm today and you have completed your homework. But, unless you go to school, you haven’t submitted it yet. So, you can say that
By 9am tomorrow, I will have submitted my school assignment.
b) when we use the expressions by the time or by (next month; next year)
By next year, I will have a degree.
By the time you go to mall, I will have done my shopping.