private void show(int max_doc_num) throws Exception
		{
				if(doc_weight_map.size() != 0)
				{
						System.out.println(doc_weight_map.size() + " acticles contain the word(s)!");
						ValueComparator value_compr = new ValueComparator(doc_weight_map);
						TreeMap<String, Double> sorted_map = new TreeMap<String, Double>(value_compr);
						sorted_map.putAll(doc_weight_map);
						int doc_num = 0;
						for(String file_name: sorted_map.keySet())
						{
								if(doc_num < max_doc_num)
								{
										Double tf_idf = doc_weight_map.get(file_name);
										System.out.println(file_name + ": score=" + tf_idf);
										searchDoc(file_name);
								}
								doc_num++;
						}
				}
				else
				{
						System.out.println("the word(s) cannot be found!");
				}
		}