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)); 

     }