java 计算两个日期之间天数

import java.text.ParseException;
import java.text.SimpleDateFormat;


/**
 * @author JavaAlpha
 * @date 2011-8-23
 * @version V 1.0
 */

public class TT {

  /**
   * @param args
   */
  public static void main(String[] args) {
    SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd");
      long to = 0;
    try {
      to = df.parse("2011-4-15").getTime();
    } catch (ParseException e) {
      e.printStackTrace();
    }
      long from = 0;
    try {
      from = df.parse("2011-8-20").getTime();
    } catch (ParseException e) {
      e.printStackTrace();
    }
      System.out.println((from - to) / (1000 * 60 * 60 * 24));
  }

}