java实现某个月的第一天/中间结束/中间开始/下个月的第一天的算法

package com.test;

import java.text.SimpleDateFormat;
import java.util.Date;

public class Test {

/**
* @param args
*/
public static void main(String[] args) {

Date todayDate = new Date();// 取时间

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
String dateStr = sdf.format(todayDate);

String[] formatDate=dateStr.split("-");
int year=Integer.parseInt(formatDate[0]);
int month=Integer.parseInt(formatDate[1]);
int day=Integer.parseInt(formatDate[2]);

String halfMonthFlag = "1";//默认上半月
String fistDayStart = "";
String middleDayEnd = "";
String middleDayStart = "";
String lastDayEnd = "";

if(day>15){
halfMonthFlag = "2";//下半月
}

fistDayStart = year+"-"+(month<10?("0"+month):(month))+"-"+"01 00:00:00";
middleDayEnd = year+"-"+(month<10?("0"+month):(month))+"-"+"15 23:59:59";
middleDayStart = year+"-"+(month<10?("0"+month):(month))+"-"+"16 00:00:00";
month++;
if(month>12)  {   year++;   month=1;  }
lastDayEnd = year+"-"+(month<10?("0"+month):(month))+"-"+"01 00:00:00";

System.out.println("当前日期是（上半月or下半月）:"+halfMonthFlag);
System.out.println("当前第一天开始时间:"+fistDayStart);
System.out.println("当月中间结束时间:"+middleDayEnd);
System.out.println("当月中间开始时间:"+middleDayStart);
System.out.println("当月结束时间（即下个月第一天的开始时间）:"+lastDayEnd);

}

}