How do I count the frequency of some word/object?

Created Nov 14, 1999

John Zukowski

The Map interface can be used to count the number of times a word/object appears. The following program demonstrates counting word frequency from the command line:

import java.util.*;

public class MapExample {
  public static void main(String args[]) {
    Map map = new HashMap();
    Integer ONE = new Integer(1);
    for (int i=0, n=args.length; i<n; i++) {
      String key = args[i];
      Integer frequency = (Integer)map.get(key);
      if (frequency == null) {
        frequency = ONE;
      } else {
        int value = frequency.intValue();
        frequency = new Integer(value + 1);
      }
      map.put(key, frequency);
    }
    System.out.println(map);
    Map sortedMap = new TreeMap(map);
    System.out.println(sortedMap);
  }
}