"Competition is healthy," the England international said at his unveiling.
"I did not want to come to this club and have an easy training session. I wanted to come here and fight for my place in the team."
Johnson has been impressed with the set-up at Fulham and is relishing the chance to play under manager Roy Hodgson.
The 27 year old said: "Fulham are a top team and they have a great gaffer here, a great training ground and it was my first choice.
"I was always confident the deal would happen and I'm happy to be a Fulham player. I wish Everton all the best, but I'm looking forward now.
"I had a good few years there and enjoyed it, although I had a few injuries in my second year.
"I have a few family back this way which is one of the reasons I wanted to come back down south."