Questions about the definition of the Java language for loop inside and outside variables

Today, when reading a book, see a code, a variable that is not used outside the loop, and then have my problem, in the back:

My question:

Variables are defined within the loop, for example:
while (true) {
String splitstr = null;
}
This "some" of the splitstr is placed in the stack, but their name is the same, then they are the same scope, if so, how do they distinguish? Id? Of course this doesn't seem to make sense, so I have a question that they are useless in the loop, when did the GC clean them up?

This site is a problem I have found, some similar. Feel better.

http://www.iteye.com/problems/74037

Questions about the definition of the Java language for loop inside and outside variables