概念：表示某种情况下一直持续到说话人所提及的时间。将来完成时用来表示在将来某一时间以前已经完成或一直持续的动作。经常与before+将来时间或by+将来时间连用，也可与before或by the time引导的现在时的从句连用。
结构：shall/will + have +过去分词。 例如：

Before long he will have forgotten all about the matter.

不久他就会全然忘记这件事的。

I shall have been working here in this factory for twenty years by the end of the year.

到今年年底，我将在这个工厂工作20年了

If we don't hurry up the store will have been closing before we get there.

咱们如不快一点儿，等我们到了那儿，店门就会关了。

The play is coming off in August. By then the play will have been running for three months.

这个剧将于8月停演。到那时为止，这个剧将连演三个月了。

1.表示在将来某一时间之前已完成的动作，并往往对将来某一时间产生影响。
We shall have learned 12 units by the end of this term.

到这个学期末，我们将学完12个单元。

By the time you get home I will have cleaned the house from top to bottom.

你到家之前我将把房子彻底打扫一遍。

2.表示推测，相当于"must have done"结构。
You will have heard of this, I guess.

我想你已经听说过这件事了。

I am sure he will have got the information.

我相信他一定得到了这个信息。