Hi. Just wondering about which one is correct and more preferred.

1. They will have an important exam tomorrow.
2. They will be having an important exam tomorrow.
* If possible, could you please give some other examples as well? So I can really know when to use either one? Thank you.
Either one is OK.

You can use the -ing form of have when t does not mean own or possess. Examples are behave, conduct, celebrate, or some other dynamic activity.

He will be having a new house next week. (Wrong)
I have been having my car for 6 years. (Wrong)
I probably will be having the flu in the next few days. (wrong) All my friends and family are having it now. (wrong)

My two-year-old has been having tantrums all day today. I am exhausted. (OK)
We will be having high tea tomorrow. Can you come? (OK - have here means celebrating, )

When you have the choice, the simple form is usually the right way to go..
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I see. That helps a lot. Oh, one more thing. Since i come across the sentence "My two-year-old has been having tantrums all day today." , may I know if..
My two-year-old is having tantrums all day today is correct?

I always get confused when it comes to using is -ing /has been.
My two-year-old is having tantrums all day today is correct? No, because the tantrums began in the past (eg when he woke up this morning. ) Use the present perfect when the action began in the past, and continues as you speak.)

We have been having a lot of car trouble lately. The car has been in and out of the garage and the mechanics can't seem to find the problem.

Use the present for near-term future plans:

We are having a party tonight. Please come.
We will be having liberty to mortgage house
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