Why is java impprtant?

Answer 1

It's good for Android development and for visual applications .
And not only Java every language is important because of some specific features so it is you who have to determine what to learn.

Answer 2

Java is used by big companies working with huge amount of precise data, bank apps, as backend for some of your favorite websites - Google Facebook YouTube all have some java running in the background.

You can also make games (although it's not the best tool due to memory leak etc), Minecraft and Equilinox and more are made in this engine.

The market is still huge for java devs and its imo one of the core languages that you should learn.