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

 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));

}

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