Hi,
Firstly, we don't have to write extern for Java target anymore - just use
-java-lib path/to/library.jar. In the case of Android, you can download a particular platform target version, then find the android.jar in the Android SDK platforms folder.
However, the setup of using haxe Java for Android development is slightly non-trivial. You will have to understand both haxe and Android pretty well to do so. You still need to use the Android SDK tools to compile and deploy to a device/emulator. That means, you better have a usable emulator and/or fix the Android Studio device connection problem. Or you have to do everything in the command line.
Here is how to use the command line tools:
Use "-java ." to output to the top-level of the Android project. Notice the Java sources will be placed inside "src" folder. Use -D no-compilation to prevent haxe to compile the java output using the JDK, which is likely to produce jar that wouldn't work on Android. Instead, use the Android SDK build tools to build the Java output (ant debug) and deploy to a device (ant installd).
Of course, instead of using the haxe Java target with the Android SDK, you may use OpenFL, or Titanium, or even Processing. All of them can be used in haxe in someway.
Hope it helps.
Best,
Andy