Problem using List of Lists in loop

Question

I'm working on a test program that will pull in two text files and return a list of the words that are common among in each. I'm running into a logistical problem when trying to add elements of a list to a list of lists, and then clear the primary list for the next iteration of the loop. Here's my code:
import java.util.*;
import java.io.*;
public class IOList {
   private static List<File>();
   public static void main(String[] args) {
      files = new ArrayList<File>();
      Scanner s;
      List<String> words = new ArrayList<String>();
      List<List<String>> allWords = new ArrayList<List<String>>();
      File a = new File(args[0]);
      File b = new File(args[1]);
      files.add(a);
      files.add(b);
      for (File file : files) {
         try {
            s = new Scanner(new BufferedReader(new FileReader(file)));
            while (s.hasNext()) {
               words.add(s.next());
            int n = words.size();
            allWords.add(words.subList(0, n));
            words.clear();
         } catch(FileNotFoundException e) {
            System.err.println("Could not find file " + file);
            System.exit(1);
      List<String> fileA = allWords.get(0);
      List<String> fileB = allWords.get(1);
      fileA.retainAll(fileB);
      fileB.retainAll(fileA);
      fileA.addAll(fileB);
      int size = fileA.size();
      for (int i = 0; i < size; i++) {
         String str = fileA.get(i - 1);
         System.out.println(str);
}When I step through this code, netbeans gives me a message:
words.subList = >"subList" is not a known variable in current context<
If I use allWords.add(words); instead, the String elements populate to the first List of Strings contained in allWords, and are then removed when I call
words.clear();in the next step to prep it for the next iteration.
Can anyone suggest another way to do this while still working with the loop?
Thanks in advance

Answer 1

Just to make clear: subList() does not (necessarily)
create a new list but a view on the original list. If
that original list is modified, the sublist might
change and vice versa.subList() never creates a new list, the subList is always backed by the original list. If the original list is modified, the sublist is too, always. If the original list is structurally modified, the result is undefined, so don't do that.
http://java.sun.com/j2se/1.5.0/docs/api/java/util/List.html#subList(int, int)