How to prevent whatsapp from adding all the contacts?

[acsurfer]

From my understanding, if I install whatsapp, all my phone contacts will see me inside their whatsapp (if my contacts are using whatsapp),

There are some contacts that I do not wish to see them inside whatsapp. (e.g. some friends that I am not so close, some contacts I will only contact them if I need their service.)

How to prevent whatsapp from adding all the contacts?