Here you can find the source of getStartDate(Date date)
public static Date getStartDate(Date date)
//package com.java2s; import java.util.Calendar; import java.util.Date; public class Main { public static Date getStartDate(Date date) { return getFirstOfMonthCalendar(date).getTime(); }//from ww w.j a v a 2s . c o m public static Calendar getFirstOfMonthCalendar(Date date) { Calendar calendar = Calendar.getInstance(); calendar.setTime(date); calendar.set(Calendar.DAY_OF_MONTH, 1); calendar.set(Calendar.HOUR_OF_DAY, 0); calendar.set(Calendar.MINUTE, 0); calendar.set(Calendar.SECOND, 0); calendar.set(Calendar.MILLISECOND, 0); return calendar; } }