Taken as the club's first pick (12), the tall 17-year-old met his teammates for the first time on Monday.
And the spearhead was in a light-hearted mood after some confusion over the seating arrangements.
"I sat in Barry Hall's seat in the meeting," Johnston said with a smile.
"He just sat on me. I was a bit nervous and didn't know what to say, so I moved away."
The South Australian teenager said he aimed to one day play in Hall's position.
"My goal is to be a key position forward for the Swans, that's my dream," Johnston said.
Swans' coach Paul Roos said he was loathe to put too many expectations on his young draftees but said Johnston was one who could potentially step up.
"Potentially he could play full forward, centre half forward, back, wing, he's quite an athletic guy and a tall," Roos said.
"But we know we need to replace Barry (Hall) and Mick (O'Loughlin) at some point."
Johnston is the only one of the new draftees who will move to Sydney and is set to play for the reserves in the Canberra league.
Dan Hannebery, who was taken at No. 30, will remain in Melbourne to finish high school as will pick No.61 pick, Campbell Heath.
Roos is hoping the acquisition will cement generational change over the next few seasons, particularly after the success of Kieren Jack (21), Craig Bird (19) and Jarred Moore (22) last season.
"I wouldn't expect any of them to play in the seniors next year," Roos said.
"Hopefully they'll develop over the next couple of years."
"It happened so quickly," Johnston said of his whirlwind draft. "I was at my house and all my friends were yelling and screaming," he said.
