[MMM]

Getting a BA isn't necessarily required, but it is going to make things a lot easier.

To get a working visa you need a sponsor. In other words, a company that is willing to hire you. That company then needs to go to the government and say "We want to give Yamiko a job, please give him a visa."

Then the government will say "Why should we let him in?"

And your sponsor will say "He is qualified at Java language"

"Are there not enough Japanese to do that job?"

"No."

"Does he have a 4-year degree?"

"No."

At this point you are at the government's mercy. They may decide that your skills are valuable enough that the usual standard of a 4-year degree is waved. Or they may not.

The important point is that 1) you bring something to make your sponsor and Japan a better place and 2) you have unique skills that Japanese don't have.

99% of the time those skills are English, but there are a lot of foreign computer programmers in Japan as well.