Question: Do you want to copy the references to the Person or do you want to make a copy (clone) of the Person. It is a huge difference.
If I have this:
there is now 3 objects created. Two Person-objects and one ArrayList that holds references to the Persons.
If I now do this:
all I have done is creating a new TreeSet-object and copied the references from the pList into it.
However, if I want to be able to manipulate on a new object that is a copy of the original persons, then I need to do this:
We now have six object and even if I manipulate on the p1 or p2, it won't effect the copies of the Persons in the Set.
See
http://en.wikipedia.org/wiki/Clone_%28Java_method%29