Ask HN: How much Java do you need to know to write Android apps?

You don't need to know much Java is you are starting out. If you are familiar with OOP, that's really all you need.

For an overview of Java, the book resource you cited (Deitel Java - How to Program), is an excellent source. I would suggest that you use it to familiarize yourself with the very basics of Java.

You don't have to go through the entire book cover to cover, but enough of it that you are at least familiar with basic java concepts and syntax. With that, proceed immediately to Android specific programming.

I had suggested some resources for starting out with Android development which you may want to look at: https://news.ycombinator.com/item?id=7016067

I would try to program first something in Java like a small project (without gui) that uses some libraries and has an OOP design. Just experiment with classes, structures and maybe access a database. Then when you know what interfaces, subclasses etc are , migrate and take a course on android development from a MOOC such as udacity or coursera.

Then build an awesome app :)

The answer: as much as you can learn. But actually, to start, a basic skillset is enough. I would say that you should start with Java first then you can learn the Android stuff. Thinking in Java is the book I always recommend (by Bruce Eckel); Android has a good tutorial on Google's Android site, I think that is good for beginners. I have not read any books on Android but I am sure there are some good books on advanced topics if you are familiar with the basics. Start with some easy, small thing then you will learn the pieces with time.

In summary I would recommend you don't worry about being right from the start. Spend a little time (like you are with this HN post) to find out enough to pick at least two very different quick routes for developing at least two very different simple apps. Then come back to HN to discuss your experience and at that point you have a decent chance of picking a right path.

Some further food for thought:

> I know you need to know Java to do Android

There are several languages and tools that codegen to the JVM, and more specifically, Dalvik, the special version of the JVM used for Android, so you don't have to learn Java per se.

For example, there's Clojure, a flavor of lisp that targets the JVM and supports Android/Dalvik.

> My goal is to develop mobile apps, starting with Android.

There's already at least one non-Java language/tool I know of that not only codegens to Android but also iOS and other platforms. So you can write code once and just push a button to have it run on Android, push another and it runs on iOS. I'm not going to mention the language/tool because it's controversial (eg it's not open source), but I'd be surprised if there aren't open source equivalents either already in existence or set to arrive soonish.

> My background is only perl/bash/SQL - just scripting.

The "Are We There Yet?" Perl 6 codegens to multiple platforms including the JVM. Unfortunately a key piece of their current codegen strategy doesn't work with Dalvik so I'd say Android's probably out for Perl 6 for at least a year or ten.

I'd suggest learning Android straight up. Java Android is a crippled version of Java IMO. If you want to learn Java specifically learn up to generics. That's all you really need. You can make things quickly using base Android without knowing much about Java.