java获取当前月第一天和最后一天，上个月第一天和最后一天

 package com.test.packager;

 import java.text.ParseException;
 import java.text.SimpleDateFormat;
 import java.util.Calendar;

 public class Test {
   private static String firstDay;
   private static String lastDay;
     public static void main(String[] args) {
         SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd"); 

         //获取前月的第一天
         Calendar   cal_1=Calendar.getInstance();//获取当前日期
         cal_1.add(Calendar.MONTH, -1);
         cal_1.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
         firstDay = format.format(cal_1.getTime());
         System.out.println("-----1------firstDay:"+firstDay);
         //获取前月的最后一天
         Calendar cale = Calendar.getInstance();
         cale.set(Calendar.DAY_OF_MONTH,0);//设置为1号,当前日期既为本月第一天
         lastDay = format.format(cale.getTime());
         System.out.println("-----2------lastDay:"+lastDay);

         //获取当前月第一天：
         Calendar c = Calendar.getInstance();
         c.add(Calendar.MONTH, 0);
         c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天
         String first = format.format(c.getTime());
         System.out.println("===============first:"+first);

         //获取当前月最后一天
         Calendar ca = Calendar.getInstance();
         ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));
         String last = format.format(ca.getTime());
         System.out.println("===============last:"+last);

     }
     /**
    * 字符串的日期格式的计算
    */
   public static int daysBetween(String smdate,String bdate) throws ParseException{
           SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
           Calendar cal = Calendar.getInstance();
           cal.setTime(sdf.parse(smdate));
           long time1 = cal.getTimeInMillis();
           cal.setTime(sdf.parse(bdate));
           long time2 = cal.getTimeInMillis();
           long between_days=(time2-time1)/(1000*3600*24);
           return Integer.parseInt(String.valueOf(between_days));
   }
 }