java 获取当月第一天和最后一天 获取前一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);