1．构成：shall / will have + 过去分词
2．功能：表示将来某时之前已经完成的动作。
They will have been here for 5 years next Friday.
By the end of next term, the students will have finished the book.
过去将来完成时：
1．构成：would / should have + 过去分词
2．功能：表示从过去某个时间看将来某时之前已经完成的动作。
He said that they would have arrived by seven o'clock.
将来完成进行时：
1．构成：shall / will have been + 现在分词
2．功能：表示某一动作将继续到将来某时，且该动作此时尚未发生。
We shall have been staying here for four weeks when Tom arrives.
It will have been raining for a week if it does not stop tomorrow.
注：此句型过于复杂，人们很少运用，了解而已。
