Semanas de diferencia entre dos fechas usando Calendar

diferencia-semanas.java

import java.util.Calendar;
import java.util.GregorianCalendar;

public class DateDiff{

    public static void main(String[] args) {
        Calendar cal1 = new GregorianCalendar();
        Calendar cal2 = new GregorianCalendar();
        cal1.set(2013, 8, 10);
        cal2.set(2013, 12, 31);
        int diff = (int)( (cal2.getTime().getTime() - cal1.getTime().getTime()) / (1000 * 60 * 60 * 24)) / 7;
        System.out.println(diff);
    }

}