In Chapter 18.5 we had a look at the future I in German as a compound tense that describes actions in the future. In German there is (as also in English) a perfect future, which is also called future II. This future describes something that will be finished in the future. The perfect future (or future II) is

He will say that he will have done it already.
He will not be able to buy a car, because until then he will have spent all his money.

The formation of the future II is as a general rule future + perfect (therefore also the name future perfect):
conjugated form of werden + partciple perfect + infinitive form of haben.

Future II   conj. form of werden + perfect participle + haben conj. form of to will (future) perfect ich werde gegessen haben I will have eaten   du wirst you will   er / sie / es wird he / she / it   wir werden we will   ihr werdet you will   sie werden they will

for comparison here once more the same verb as future I

Future I   conj. form of werden + infinitive   conj. form of to will (future) perfect ich werde essen   I will / am going to eat   du wirst you will / are going to   er / sie / es wird he / she / it will / is going to   wir werden we will / are going to   ihr werdet you will / are going to   sie werden they will / are going to

The use of future II is in German as well as in English to describe something that will happen in the future and the action is going to be finished. You might ask why the future II is not translated into the future II of the will-be-going-to-future. Let's have a look:
He is going to have gone to England when you are going to arrive at his home.
Doesn't sound like something one would usually say in a conversation!?!

Let's rather concentrate on the use of the future forms:

Examples       future I       Ich werde gehen.   I will go. / I am going to go.   Du wirst es lesen.   You will read. / You are going to read.   Wir werden es machen.   We will do it. / We are going to do it.   future II       Ich werde gegessen haben.   I will have eaten.   Du wirst es gelesen haben.   You will have read.   Wir werden es gemacht haben.   We will have done it.