Question

Do Android devices have a unique ID, and if so, what is a simple way to access it using Java?

Answer 1

Settings.Secure#ANDROID_ID returns the Android ID as an unique for each user 64-bit hex string.

import android.provider.Settings.Secure;

private String android_id = Secure.getString(getContext().getContentResolver(),
                                                        Secure.ANDROID_ID);

Also read Best practices for unique identifiers: https://developer.android.com/training/articles/user-data-ids