Static intestitial variable or non static

Hello guys

I have a question about how you display interstitial in the code. Lets take admob example. Do you actually create an interstitial object when the activity starts and then request an ad and display the interstitial hoping an ad has been received before the activity is closed? Then on the next activity do the same thing?

Or do you create a static variable that will fetch ad so you dont care about activity finishing and new one is opening, because your intersisitial variable is not destroyed and you can display?

I am not sure of the right way of implementing
Thank you

static variables result in more crashes-- from my experience with various ad network sdk’s including startapp and admob

So this mean that every activity will need to create a new interstitial and do an request. Then we are making assumption that user should stay on the same activity for 3 seconds or more
Makes sense?