Here you can find the source of addDays(Date date1, long days)
public static Date addDays(Date date1, long days)
//package com.java2s; import java.util.*; public class Main { public static long ONE_DAY_SECONDS = 86400; public static Date addDays(Date date1, long days) { return addSeconds(date1, days * ONE_DAY_SECONDS); }//from ww w.j ava 2s . c o m /** * @param date1 * @param secs * * @return */ public static Date addSeconds(Date date1, long secs) { return new Date(date1.getTime() + (secs * 1000)); } }