To convert an array to an ArrayList, use Arrays.asList():
String[] arr = {"a", "b", "c"};
ArrayList<String> list = new ArrayList<>(Arrays.asList(arr));
Wrap the result in new ArrayList<>() because Arrays.asList() returns a fixed-size list. Without the wrapper, calling .add() or .remove() throws an UnsupportedOperationException.
To go the other direction, use .toArray():
String[] back = list.toArray(new String[0]);
You pass an empty array of the target type. Java creates a properly sized array and fills it. The new String[0] looks odd, but it tells Java the return type. If you call .toArray() with no argument, you get an Object[] instead, which loses the type information.