If I read the JSONArray constructors correctly, you can build them from any Collection (arrayList is a subclass of Collection) like so:
ArrayList<String> list = new ArrayList<String>();
list.add("foo");
list.add("baar");
JSONArray jsArray = new JSONArray(list);
References:
- jsonarray constructor:
http://developer.android.com/reference/org/json/JSONArray.html#JSONArray%28java.util.Collection%29 - collection:
http://developer.android.com/reference/java/util/Collection.html