Java is far more popular and you can use other JVM-based languages such as Kotlin (I would recommend Kotlin over Java). Also, for Java, there are many more libraries, tools, etc. Also, if you learn Java, you can do almost anything - mobile (Android), web, and desktop apps - without "hacks". There is native support for all of these.
As with any programming language, it's not hard to learn the syntax but it's hard to understand the ecosystem, know libraries, best practices, etc. From that point of view, I would also prefer java - more tools, more libraries, more resources, guides, how-tos, etc.