Java is Java, Android or not. Go to your library, and get a book on programming.
Download Java, and try out this book. Write a simple program, like - finding what day of the week will be January 1st, 2099.
Download an ANdroid development platform (these days, it seems Android Studio is the norm). Move your simple program to Android.
Only after that - start thinking what your game will look like, and how to implement in what you already know.