Can i use quotation mark for one's thought?

Question

i know if one say something we need quotation mark

such as he says,"xxxxxxxxx."

but can i use(or do i have to use) quotation mark on thought

like

he thought,"xxxxxx."

or

"xxxx." he thought.

Answer 1

yes

Answer 2

I've seen it in quotes or italics.  

Answer 3

Yes, you can and should--unless you say, he thought that....