I also like to recommend to you [if you don't like books, paperback books], the use of java tutorials in android apps. It is good and very handy, kind of a quick reference when you're programming and your stuck in the void because of something else, also the AIDE android app is good for java programming basically when you want to figure out some logic if it will work or not, although it won't support GUI if you're an avid GUI programmer in java, but if you're using console then it's good, it also has a tutorial but is limited in free mode, you'll buy the app for its tutorials if you liked it, but what I find interesting in the AIDE application is that I can program java from my phone, [even in a cheap smart phone], so I could always
test logics. Otherwise, you can always check stuff in java online tutorials and online courses, also thenewboston videos about java programming is good, but remember that all of that stuff is no substitute for an endless practice in coding in java, reading lots of books in java, and also visiting the oracle website for the latest discussions and trends in java, also you would consider making more programs so that you can practice what have you read on the books, or read on the net, or in the tutorials, just try it out and enjoy. Thanks.