Interview: Justin Bartha

"It was something I really identified with because when I was a younger man, I had this idea of what I was looking for in a woman and what I was looking for with love," explains Bartha, who is dating actress Mary-Kate Olsen, "and what it took to take care of a woman, and how I wanted my life to turn out."

If you're going to die, you might as well die on stage

To him, it did not read like a traditional romantic comedy, but he says: "I think as it went along it became a little more like what we've seen before. But I still think that it has an intelligence and a humour to it that's a lot smarter than most romantic comedies."

He once quipped that with a name like Aram Finklestein, there were only so many directions he could go with the character. Indeed, it arguably conjures up the kind of awkward, nebbishy types that Woody Allen made his stock-in-trade. Joking with Bartha that such names need to be reclaimed, perhaps by giving them to superheroes, Bartha suprisingly says Aram is a super hero. Really?

"He makes a complete transformation in his life. He starts off as this heartbroken boy that doesn't know how to get what he wants and he becomes a man that knows how to get what he wants. So I think he is a superhero, in my mind. That's how I played him."

Bartha has been through his own transformations. He was born in Florida and moved to the suburbs of Detroit with his family when he was nine. Although his mother has said that religion was "very important" in their home, her son tells a different story.

"We weren't religious, really. We were kind of the usual secular Jews that didn't really celebrate Judaism, just the tradition of Judaism." Bartha went to Hebrew school, but after his barmitzvah "stopped doing anything organised". He nonetheless remains proud of his Jewish roots.

As is often the case, he became an actor by accident. Needing something to get him out of the house after breaking a wrist playing tennis in high school, he noticed that there were a lot of girls in the drama department, and thought he'd join in. He landed a role in A Midsummer Night's Dream, after auditioning on a whim. But he says: "Right when I got on stage I kind of fell in love with it and I never looked back."

Bartha moved away from home when he was 17 to study acting at New York University. Thanks to films such as Mean Streets and Midnight Cowboy, he had fantasised about moving to New York for years, and settled in immediately. He still lives there, but times have changed. In May, for instance, a stage performance of Lend Me a Tenor took a frightening turn when a bomb was discovered in Times Square, a block down from the theatre. "We still performed, even though half of our audience didn't show and the half that were in there were just thinking about getting blown up," he laughs. "But if you're going to die, you might as well die on stage. And we died on stage that day."

If The Rebound captures New York's positive vibe, Holy Rollers, a low-budget drama inspired by actual events, gives it a grittier spin. The film casts Bartha as a drug-addicted Chasid with ties to an Israeli drugs cartel, who lures his brother's friend into becoming a drug courier.

Darker than anything else on Bartha's CV, the film, a hit at this year's Sundance Film Festival, gave him the opportunity to draw on memories of living above a fractious Chasidic family in Los Angeles.

"I could hear this family fighting . . . the son was kind of wayward and uncontrollable and would constantly be screaming and running out of the house," he said.

"I would always fantasise about what it was like inside that house, this seemingly insular Chasidic family that obviously has a lot of problems."

The son helped to inspire his performance as Yosef, though we will have to wait to see the results - Holy Rollers does not yet have a UK release date.

Meanwhile, Bartha is gearing up for a sequel to The Hangover. He says he always knew the first one would be funny, but never expected it to become a "phenomenon".

While it benefited by effectively coming in under the radar, public expectations for the follow-up will be enormous. Bartha is not worried, though. "Everyone making the movie is dedicated to making something really funny, and that hasn't changed at all."

This is not surprising as you get the feeling talking to Bartha that he would never do anything half-heartedly.

He compared doing a physically-demanding farce such as Lend Me a Tenor to playing a sport, but says competitiveness is what drives him to keep his performance fresh, even after more than 100 shows.

"Once you get on stage that obsessiveness kicks in," he says, "and you just want to make it perfect."

The Rebound opens today