For the most part, Android programs are written in the Java language, and they use the Java 6 Standard Edition (SE) library APIs. I say “for the most part” because there are a few differences. This appendix highlights the differences between regular Java and what you’ll find in Android. ART (the runtime system used for Android 5.0 and above) and Dalvik (the system used prior to Android 5.0) have the same restrictions.
If you’re already proficient in Java development on other platforms, you should take a close look to see what things you need to “unlearn.”