The LA Times put together a handy Venn diagram that shows what Americans (specifically, Los Angeles residents, or 'Angelenos') think to be Japanese food, and it's been compared to what native Japanese include in their own cuisine.
Sushi restaurant mainstays – like California rolls and mochi ice cream – were popular votes among Americans, as was teriyaki chicken, which is often served alongside the sushi at the same place.
Look at what the Japanese include in their own cuisine, though, and you'll find a few surprises. "Hamburg" is basically a hamburger patty served on its own and topped with a sauce. "Curry" is the same in substance to the Indian variety, but the flavor is closer to a beef stew than Chicken Tikka Masala.