As others have said I really think it depends on what you want to see and who you're traveling with. I have done both parks in one day, but I was with a friend and we pretty much just hit the thrill rides and skipped everything else.
You can definitely do both parks in one day, but not all of both parks. I think it will be the hardest to do both parks if your party wants to see a lot of shows. Since those have specific times it might be really hard to juggle the timing between both parks.
If you're just going to hit the highlights, it can definitely be done.