Common String in Lists

Given a List of List of String, find the common String in all Lists, output them in sorted order. (could contain duplicates)

Naive Way:Need to consider case [[a,a,a],[a,a],[a,a,b]] outputs [a,a]. Use a HashMap as pattern, go through the lists, for each list, match it with the pattern, update the pattern, what left in the pattern is common string.

 public List<String> commonString(List<List<String>> lists){  
           List<String> rslt = new ArrayList<String>();  
           // edge case  
           if(lists.size()==0) return rslt;  
           // initialize pattern   
           Map<String, Integer> pattern = new HashMap<String, Integer>();  
           List<String> temp = lists.get(0);  
           setMap(pattern, temp);  
           // match pattern with other lists  
           for(int i = 1;i < lists.size();i++){  
                Map<String, Integer> map = new HashMap<String, Integer>();  
                setMap(map, lists.get(i));  
                Iterator it = pattern.entrySet().iterator();  
                List<String> toBeRemove = new ArrayList<String>();  
                while(it.hasNext()){  
                     Map.Entry pair = (Map.Entry)it.next();  
                     if(map.containsKey(pair.getKey()))  
                          pattern.put((String)pair.getKey(), Math.min(map.get(pair.getKey()),(int)pair.getValue()));  
                     else  
                          toBeRemove.add((String)pair.getKey());  
                }  
                for(int j = 0;j < toBeRemove.size();j++)  
                     pattern.remove(toBeRemove.get(j));  
           }  
           // collect results  
           Iterator it = pattern.entrySet().iterator();  
           while(it.hasNext()){  
                Map.Entry pair = (Map.Entry)it.next();  
                for(int i = 0;i < (int)pair.getValue();i++)  
                     rslt.add((String)pair.getKey());  
           }  
           // sort the result  
           Collections.sort(rslt);  
           return rslt;  
      }  
      private void setMap(Map<String, Integer> map, List<String> list){  
           for(int i = 0;i < list.size();i++){  
                if(!map.containsKey(list.get(i)))  
                     map.put(list.get(i), 1);  
                else  
                     map.put(list.get(i), map.get(list.get(i))+1);  
           }  
      }