Future Perfect Continuous

Future Perfect Continuous Tense:
It has been done for a time and it will be continued
EXAMPLE: "will have been walking":
At 6 p.m. tomorrow, he will have been walking home for 15 minutes, and will reach home at about 6.15p.m.

It's a bit same with perfect tense because we us past participle.And it is continuous so it add "ing"

Future Perfect Continuous

The format: will have been + verb-ing

It’s Tom’s party in June. He will have been working here for thirty years. We hope that he will stay on as long as possible. He is such a nice guy.

We use this form when we imagine ourselves looking back from a time in the future, e.g. June. We look back at an action that will continue up to that time. e.g. The action is: Tom working. We emphasize the duration of activity (beginning in the past, present, or future) before a specific future time or another future event.

One more example:
If I manage to finish this book by Friday, I’ll have been reading it for eight weeks.

What is the difference between Future Perfect and Future Perfect Continuous?

Future Perfect focuses on the result of the action. (~ emphasizes the completion of an activity before a specific time or another future event.) Future Perfect Continuous focuses on the action going on.

I’ll have written the report by six, so it’ll be on your desk tomorrow morning. (The activity will have been finished at a certain time in the future. We are more concerned with the result of action.)

This report is taking ages. I’ll have been writing it for two weeks by the time I finish.
(Here we are more concerned with the duration of the activity.)

No offence to anyone.
回答者 003: statements 1, 2 and 4 are not quite right in some circumstances.
4. The act should have a definite end time in the future.
1. The act (verb) must have started already
2. The act is still continuing now.

It’s Tom’s party in June. He will have been working here for thirty years....

Tom doesn’t have a definite end time for the action in the future. He may work for five more years. We simply don’t know. By the time in June, imagine we look back, Tom 工作三十年了. ~ focus on duration of activity

The activity can begin in the future. For example:

By 2040, they will have been living there for twenty years.
~ quoted from "Competency-Based Grammar" by Elaine Kirn
It implies the activity will begin in 2020.

The examples given by 001 and 002 both are not correct representation of future perfect tense. 002's explanation and example is better but still does not truely show the relative time of combining "future" and "pefect continuous".

The are some criteria in using FPC tense.
1. The act (verb) must have started already (sometime ago)
2. The act is still continuing now.
3. The act is expected to continue into near future.
4. The act should have a definite end time in the future.

Using 001's example of walking home:
the mistake was that the act has not happen, the only false is item 1, Combining 002's example, instead of walking all night. consider the situation is stating this morning (instead of tomorrow at 6pm)

He will have been walking all morning through the (XXX) mountain for 6 hours before reaching home for lunch.
{The context of this statment is said during his journey for the act of walk starts in the morning (before now) and it is expecting after 6 hours he will reach home for lunch (the end).}
1. walk from morning (if lunch approx. 1200-1300, started at about 0600or0700)
2. he's still on the mountain, the time now is between this morning and lunch time.
3. from now until lunch time / reach home.
4. lunch time or reach home.

假如英文唔明用少少中文解

1. 動作(動詞)是已經開始了的
2. 動作仍在進行中
3. 動作將會繼續一段時間的
4. 動作將會有一個結束的時間標示
e.g.
I will have been working on this project for 2 weeks by end of this week.

1. work on the project started one weeks ago (one week+this week = 2weeks)
2. work has not been finished
3. work will still be continued this week.
4. no indication if the project is finish by end of this week, just a count of working period since the begining until the end of this week.

Re:-The perfect continuous form consists of "having been" and the present participle. It is rarely used.
eg.Having been walking on the mountain for a week,--------

The future perfect=will/shall have----------while the perfect using past participle.

Hence the combinations sentence:-will have been walking;
eg:-They will have been walking all evening on the Mt.