Johnson says the influx of new players to Sunderland has come as a major boost, as this is "the toughest" pre-season training programme he's ever faced.
England international Johnson, 25, said: "When they all first came in I thought it might take a while, but everyone has fitted in so quick it's been amazing.
"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."