This example shows how to compute days between 2 dates.

 import java.util.*;

public class TestDate {
  public static void main(String args[]){
    /*
     ex . 
       java TestDate 1999 0 1 1999 8 1
           to get days between 1999-01-01 and 1999-09-01
          (remember months are zero-based...)
   */
  
    TestDate a = new TestDate(args);
    }

  TestDate(String args[]) {
    Calendar c1 = new GregorianCalendar();;
    Calendar c2 = new GregorianCalendar();;

    //  need more error checking here...
    c1.set(Integer.parseInt(args[0]),
           Integer.parseInt(args[1]) , 
           Integer.parseInt(args[2]), 0, 0, 0); 
    c2.set(Integer.parseInt(args[3]),
          Integer.parseInt(args[4]) , 
          Integer.parseInt(args[5]), 0, 0, 0); 

    System.out.println
       (daysBetween(c1.getTime(),c2.getTime()) +
        " day(s) between " + args[0] + "-" + args[1] + "-" + args[2] +
        " and " + args[3] + "-" + args[4] + "-" + args[5]);
    }

  static final long ONE_HOUR = 60 * 60 * 1000L;
  public long daysBetween(Date d1, Date d2){
    return ( (d2.getTime() - d1.getTime() + ONE_HOUR) / 
                  (ONE_HOUR * 24));
     }   
  }