This Tense is used to express an action which is imagined to have been completed at some point of time in future. It may be noted that this tense is basically theoretical and rarely used.
The formula for future perfect is Subject+Aux+Aux+V3
I will have eaten an apple by this time tomorrow.
We will have eaten apples by this time tomorrow.
We will have eaten apples by this time tomorrow.
You will have eaten an apple by this time tomorrow.
He will have eaten an apple by this time tomorrow.
She will have eaten an apple by this time tomorrow.
It will have eaten an apple by this time tomorrow.