Refering to book "Sierra K., Bates B. - OCA OCP Java SE 7 Programmer I & II Study Guide - 2015" Chapter 05 page 295, says that
"When encapsulating a mutable object like a StringBuilder, or an array, or an ArrayList, if you want to let outside classes have a copy of the object, you must actually copy the object and
return a reference variable to the object that is a copy. If all you do is return a copy of the original object's reference variable, you DO NOT have encapsulation."