Celtic's Forster replaced underfire Manchester City keeper Hart in the starting line-up for the Wembley friendly - which England lost 2-0 - as boss Roy Hodgson gave him the opportunity to gain some valuable international experience.
"Joe was fantastic," Forster said. "He talked to me a lot before the game and at half-time. He's obviously very experienced at this level and a top-quality keeper.
"He's a fantastic guy and I can't speak highly enough of him."
Hodgson is now set to recall Hart for the visit of Germany to Wembley on Tuesday and Forster expects him to respond well after his recent problems.
He said: "Joe's proven what a top-class keeper he is and made save after save. He'll come back stronger. He's a great lad. He's someone I speak to all the time.
"He's one of the best people I've come across in football.
"It's just a case of me doing as well as I can at club level and when I'm with the squad just trying to make as good an impression as I can.
"It's just a case of waiting your turn and trying to impress in training.
"It's fantastic to make my debut. I've worked very hard ever since coming to Newcastle to get to this point.
"I've had a taste of international football being in and around the squad and had an opportunity to work with (England goalkeeping coach) Dave Watson and the gaffer (Hodgson).
"This is what you want to be a part of. This is what you dream of as a kid. It's brilliant. It's a real inspiration to make me go and work harder."