Modify Common Object References In Lists - MyArrList And UrArrList

"What happens if you modify the common object references in these lists, myArrList and urArrList ? We have 2 cases here: In the first one, you reassign the object reference using either of the lists. In this case, the value in the second list will remain unchanged.In the second case, you modify the internals of any of the common list elements - in this case, the change will be reflected in both lists."

I have written the following code, which tests the first case mentioned above, and i get the output as expected: myarrList remains unchanged. How can i test the second case ? My thoughts are ....'second case is untestable the following code, because String is immutable. I need to use StringBuilder or something else to write code for test of second case mentioned'.

ArrayList<String> myarrList = new ArrayList<>();
myarrList.add("one");
myarrList.add("two");
ArrayList<String> urarrList = new ArrayList<>();
urarrList.add("three");
urarrList.add("four");
System.out.println("ArrayLists setup");

[code]....