java獲取當前月第一天和最後一天，上個月第一天和最後一天

        SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd"); 
         
        //獲取前月的第一天
        Calendar   cal_1=Calendar.getInstance();//獲取當前日期 
        cal_1.add(Calendar.MONTH, -1);
        cal_1.set(Calendar.DAY_OF_MONTH,1);//設置爲1號,當前日期既爲本月第一天 
        firstDay = format.format(cal_1.getTime());
        System.out.println("-----1------firstDay:"+firstDay);
        //獲取前月的最後一天
        Calendar cale = Calendar.getInstance();   
        cale.set(Calendar.DAY_OF_MONTH,0);//設置爲1號,當前日期既爲本月第一天 
        lastDay = format.format(cale.getTime());
        System.out.println("-----2------lastDay:"+lastDay);
         
         
        //獲取當前月第一天：
        Calendar c = Calendar.getInstance();    
        c.add(Calendar.MONTH, 0);
        c.set(Calendar.DAY_OF_MONTH,1);//設置爲1號,當前日期既爲本月第一天 
        String first = format.format(c.getTime());
        System.out.println("===============first:"+first);
         
        //獲取當前月最後一天
        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計算 
	 */ 
	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)); 
	}