The Bang Bang hitmaker helped to pen Cyrus' 2009 smash and admits she spent years living off the royalty payments she received for her work.
Jessie J tells Britain's Glamour magazine, "You've got to write songs; that's where the money is, being an artist. Party In The U.S.A. paid my rent for, like, three years. Actually it was way longer than that. That's where I get most of my money. I write songs."