Do I need Java JDK for using Android Studio?
Android Studio version 2.2 and higher comes with the latest OpenJDK embedded in order to have a low barrier to entry for beginners.
It is, however, recommended to have the JDK installed on your own as you are then able to update it independent of Android Studio.
If you are working with an Android API < 24, then you'll need to compile the project with Java 7 or do some extra steps to enable Java 8 features. (Note: Java 8 support is relatively new).
Android Studio 3.0 and later supports all Java 7 language features and a subset of Java 8 language features
This is what Google says on https://developer.android.com/studio/intro/studio-config.html:
A copy of the latest OpenJDK comes bundled with Android Studio 2.2 and higher, and this is the JDK version we recommend you use for your Android projects.
So if you are using the newest version, you won't need any additional JDK. Furthermore, the official installation instructions don't include anymore any hints towards the JDK, compared to June 2016.