Seriously people. Taking one year of Japanese in high school is not a terribly good indicator of how easy it is to master an entire language. Like ANYTHING, it gets much harder as you progress. You begin learning math with basic addition. Basic addition is pretty easy. It doesn't necesarily follow that calculus is a snap... or that your ability to read "The Very Hungry Catterpillar" qualifies you to be writing a college-level thesis.
Your first year of Japanese will likely entail learning 50 kanji.
You need to learn 2,000 to be considered functional in daily life.
At that rate, you will either need to devote 40 years to studying at the same rate as your first year... or you'll need to start memorizing things a heck of a lot quicker.