Roger Federer says he hopes to play for at least another three or four years

Roger Federer. AFP[/caption]The 35-year-old Federer said Friday he's not sure of the form he'll produce upon his return, but that retirement isn't part of his thought process."Only when I get asked do I think of things like this," said Federer, who has 17 Grand Slam singles titles, the most of any male player."I don't see it like this, that this could be my last Australian trip, even though it might very well be," he added."I'm really positive. I took these six months off so I would be playing for hopefully another two to three years, not just another six months or so. So my mindset is for the long-term."Federer hasn't won a Grand Slam singles title since Wimbledon in 2012, and with his injury, has slipped to No. 16 in the world rankings."Winning titles is a beautiful feeling, rankings at the moments ... completely secondary," Federer said Friday. "As long as I'm healthy and injury free I think I can really do some damage."Federer and Bencic begin play against Britain, represented by Heather Wilson and Dan Evans, on Monday night at Perth Arena.Defending champions Australia, represented by Daria Gavrilova and Nick Kyrgios, begin play Sunday night against Spain.Americans Coco Vandeweghe and Jack Sock take on Czech Republic's Lucie Hradecka and Adam Pavlasek earlier Sunday in the men's singles, women's singles and mixed doubles format.