wordsort.java

learning java的源代码。书中每个实例都有相关的代码example。

//file: WordSort.java
import java.io.*;
import java.util.*;

public class WordSort {
  public static void main(String[] args) throws IOException {
    // get the command-line arguments
    if (args.length < 2) {
      System.out.println("Usage: WordSort inputfile outputfile");
      return;
    }
    String inputfile = args[0];
    String outputfile = args[1];


/* Create the word map. Each key is a word and each value is an
 * Integer that represents the number of times the word occurs
 * in the input file.
 */

    Map map = new TreeMap(  );

    // read every line of the input file
    BufferedReader in =
        new BufferedReader(new FileReader(inputfile));
    String line;

    while ((line = in.readLine(  )) != null) {
      // examine each word on the line
      StringTokenizer st = new StringTokenizer(line);
      while (st.hasMoreTokens(  )) {
        String word = st.nextToken(  );
        Object o = map.get(word);
        // if there's no entry for this word, add one
        if (o == null) map.put(word, new Integer(1));
        // otherwise, increment the count for this word
        else {
          Integer count = (Integer)o;
          map.put(word, new Integer(count.intValue(  ) + 1));
        }
      }
    }
    in.close(  );

    // get the map's keys and sort them
    List keys = new ArrayList(map.keySet(  ));
    Collections.sort(keys);

    // write the results to the output file
    PrintWriter out = new PrintWriter(new FileWriter(outputfile));
    Iterator iterator = keys.iterator(  );
    while (iterator.hasNext(  )) {
      Object key = iterator.next(  );
      out.println(key + " : " + map.get(key));
    }
    out.close(  );
  }
}