Black Cats boss Paolo Di Canio has made seven signings already this summer and Johnson is looking forward to the new-look squad coming together under the Italian.
"When they all first came in I thought it might take a while but everyone has fitted in so quick, it's been amazing," Johnson told reporters.
"Over the last couple of days, everyone has bonded well by sharing rooms with each other. We're getting on well.
"It's tough at times, being away for long periods with morning and afternoon sessions, but you've got to keep focused and do the work because at the end of it we're going to be the ones who benefit."
So far this offseason, Sunderland has signed American striker Jozy Altidore, Cape Verde midfielder Cabral, young Swedish attacker David Moberg Karlsson, Italian goalkeeper Vito Mannone, promising midfielder El-Hadji Ba and French defenders Modibo Diakite and Valentin Roberge.