1.概念：表示动作从某一时间开始一直延续到将来某一时间。是否继续下去，要视上下文而定。

2.基本结构：shall/will have been doing

3.例：

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。