Why do you learn java for android?

Answer 1

Java runs on what's called the JVM (Java Virtual Machine) and is compiled via bytecode. This is what allows Java to be as cross-platform friendly and is one of the main selling points of its popularity. Unlike most other languages, you can easily run Java code on most platforms easily, including mobiles devices. As such, it makes it an ideal language for most things, and why it's also a better choice for mobile since you don't have to install additional libraries/dependencies/etc..., which may not even be available for mobile.

It's worth noting that Kotlin is officially supported now and is on the rise. It's worth learning that also.