Dear Steven,
It's a trick question.
To answer this question, imagine the following case :
Imagine that you have four friends and everybody are alone in an Island.
Your friend #1 holds the hand of your friend #2.
Your friend #2 holds the hand of your friend #3
And finnally your friend# holds the hand of your friend #1.
At this point you can conclude that both are in a circle.
What about you ?
Well, you don't want to stay in this Island together with all the others, so you go out and abandon your friends going to another island.
This is the point :
Althrough all your friends can reach each other you are unable to reach them because you are not on the same Island.
This situation in
Java is called as "Island of isolation" and in face of this all of your friends are eligible for garbage collector.