group anagrams

public List<List<String>> groupAnagrams(String[] strs) {
    List<List<String>> ans = new ArrayList<List<String>>();
    if (strs == null || strs.length == 0)
        return ans;
    HashMap<String, List<String>> map = new HashMap<String, List<String>>();
    for (String str : strs) {
        String key = sort(str);
        if (map.containsKey(key)) {
            map.get(key).add(str);
        } else {
            List<String> list = new ArrayList<String>();
            list.add(str);
            map.put(key, list);
        }
    }
    Iterator it = map.entrySet().iterator();
    while (it.hasNext()) {
        Map.Entry pair = (Map.Entry)it.next();
        Collections.sort((List)pair.getValue());
        ans.add((List)pair.getValue());
    }
    return ans;
}

public String (String str) {
    char[] array = str.toCharArray();
    Arrays.sort(array);
    String ans = new String(array);
    return ans;
}