Which of the following option will sort the keys in HashMap ?

Problem statement:

Given java code as follows, can you find out the correct option to sort the keys in HashMap?

1. import java.util.HashMap;
2. import java.util.Set;
3. import java.util.TreeSet;
4. public class Test {
5. public static void main(String[] args) {
6. HashMap<String, String> m = new HashMap<String, String>();
7. m.put("key45", "aa");
8. m.put("key12", "bb");
9. m.put("key39", "cc");
10. Set<String> s = m.keySet();
11.   // code goes here
12. s = new TreeSet(s);
13.  }
14. }

• Arrays.sort(s);
• s = new TreeSet(s);
• Collections.sort(s);
• s = new SortedSet(s);

Correct option: 

s = new TreeSet(s);
Explanation:
Arrays.sort(s) // sorts for static array 
Collection.sort(s) // sort the List type of object not Set type
s =new SortedSet(s); // SortedSet is an interface