[Java] Null

[nemoprincess]

Allora tutto il codice, trovato sul libro è questo:
import java.io.*;
import java.util.*;
class reverseLines {
public static void main(String[] arg) throws Exception {
BufferedReader f = new BufferedReader(new InputStreamReader(System.in));
Vector v = new Vector();
String s;
s = f.readLine();
while (s != null) {
v.add(s);
s = f.readLine();
}
int k;
k = v.size()-1;
while (k != -1) {
System.out.println(v.elementAt(k));
--k;
}
}
}