code: package org.rosettacode;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.FileReader;
  import java.io.IOException;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  public class InvertedIndex {
  
  	List<String> stopwords = Arrays.asList("a", "able", "about",
  			"across", "after", "all", "almost", "also", "am", "among", "an",
  			"and", "any", "are", "as", "at", "be", "because", "been", "but",
  			"by", "can", "cannot", "could", "dear", "did", "do", "does",
  			"either", "else", "ever", "every", "for", "from", "get", "got",
  			"had", "has", "have", "he", "her", "hers", "him", "his", "how",
  			"however", "i", "if", "in", "into", "is", "it", "its", "just",
  			"least", "let", "like", "likely", "may", "me", "might", "most",
  			"must", "my", "neither", "no", "nor", "not", "of", "off", "often",
  			"on", "only", "or", "other", "our", "own", "rather", "said", "say",
  			"says", "she", "should", "since", "so", "some", "than", "that",
  			"the", "their", "them", "then", "there", "these", "they", "this",
  			"tis", "to", "too", "twas", "us", "wants", "was", "we", "were",
  			"what", "when", "where", "which", "while", "who", "whom", "why",
  			"will", "with", "would", "yet", "you", "your");
  
  	Map<String, List<Tuple>> index = new HashMap<String, List<Tuple>>();
  	List<String> files = new ArrayList<String>();
  
  	public void indexFile(File file) throws IOException {
  		int fileno = files.indexOf(file.getPath());
  		if (fileno == -1) {
  			files.add(file.getPath());
  			fileno = files.size() - 1;
  		}
  
  		int pos = 0;
  		BufferedReader reader = new BufferedReader(new FileReader(file));
  		for (String line = reader.readLine(); line != null; line = reader
  				.readLine()) {
  			for (String _word : line.split("\\W+")) {
  				String word = _word.toLowerCase();
  				pos++;
  				if (stopwords.contains(word))
  					continue;
  				List<Tuple> idx = index.get(word);
  				if (idx == null) {
  					idx = new LinkedList<Tuple>();
  					index.put(word, idx);
  				}
  				idx.add(new Tuple(fileno, pos));
  			}
  		}
  		System.out.println("indexed " + file.getPath() + " " + pos + " words");
  	}
  
  	public void search(List<String> words) {
  		for (String _word : words) {
  			Set<String> answer = new HashSet<String>();
  			String word = _word.toLowerCase();
  			List<Tuple> idx = index.get(word);
  			if (idx != null) {
  				for (Tuple t : idx) {
  					answer.add(files.get(t.fileno));
  				}
  			}
  			System.out.print(word);
  			for (String f : answer) {
  				System.out.print(" " + f);
  			}
  			System.out.println("");
  		}
  	}
  
  	public static void main(String[] args) {
  		try {
  			InvertedIndex idx = new InvertedIndex();
  			for (int i = 1; i < args.length; i++) {
  				idx.indexFile(new File(args[i]));
  			}
  			idx.search(Arrays.asList(args[0].split(",")));
  		} catch (Exception e) {
  			e.printStackTrace();
  		}
  	}
  
  	private class Tuple {
  		private int fileno;
  		private int position;
  
  		public Tuple(int fileno, int position) {
  			this.fileno = fileno;
  			this.position = position;
  		}
  	}
  }
  