i am 16 years old, my purpose is to became Software Enginer, who will develop mobile apps, also web pages, desktop apps, etc. So as main language i chosed Java, i learnt java core, soon i am starting learning Spring, Hibernate, etc. But Spring is for web-development, so how can i develop mobile apps, or i will need to learn kotlin definetly? Give me some suggestions, i will be glad, Thank you in advance.

Now i am using ecplise, Intelij Id is better, but i cant switch to it, because it paid application, how can i use it for free?