What's the difference?

[richard001]

Hi teachers,
I am confused by the phrase below,can you tell me the differences between them?

1.has happened
2.has been happening
3.used to happen

4.will happen
5.will be happening
6.will have been happening

Thanks a lot!

[Casiopea]

1. has happened (It happened at some unspecified time in the past)
2. has been happening (It is still going on)
3. used to happen (It happened in the past but no longer happens today)

4.will happen (It will happen in the future)
5.will be happening (It will be going on in the future)
6.will have been happening (It will be going on in the future, but only after some other event in the future takes place)

[richard001]

what's the difference between
1.used to happen & had happened
2.happen & going on

The room will has been getting cool after the air-condition turns on. does this sentence correct?

[Casiopea]

1. had happened (It happend first, then something else happened)
2. going on (In an ongoing state; continuous; still going on)

The room will have cooled down once the air-condition kicks in.

[richard001]

He will have been sleeping till we get there. Is this correct?If not,could you show me a example with "will have been doing" phrase?I find it is really hard to understand.