Learning To Iterate A List And Search Through Another

I am learning iterating through lists. What I have so far is two Hash Sets and two Tree sets. Hash Set 1 and Tree set 1 include the words from Roughing it by Mark Twain. Hash set 2 and tree set 2 include the words from Adventures of Huckleberry Finn by Mark Twain. (Everything is read from a file I made).

I am stuck trying to find out how to "Iterate through the words in HashSet1 and search for these words in both TreeSet2 and in HashSet2".Here is my code:

public class UsingSets {
public static void main(String[] args) throws FileNotFoundException {
String riHashIterator = null;
HashSet<String> riHash = new HashSet<>();
Scanner input = new Scanner(new File("roughingit.txt"));
while(input.hasNext()){
String riHashWords = input.next();
riHashWords = riHashWords.toLowerCase();
riHash.add(riHashWords);

[code]....