Given below the sample code :
4. HashMap hm = new HashMap();
5. hm.put("key45", "some value");
6. hm.put("key12", "some other value");
7. hm.put("key39", "yet another value");
8. Set a = hm.keySet();
9. // insert code here
What code should be at line 9 to sort the keys in HashMap "hm"?
1. a = new SortedSet(a) ;
2. Collections.sort(a);
3. a = new TreeSet(a);
4. a = Collections.sort(a);
(3)