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;
10     public static void main(String[] args) {
11         SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd"); 
12         
13         //获取前月的第一天
14         Calendar   cal_1=Calendar.getInstance();//获取当前日期 
15         cal_1.add(Calendar.MONTH, -1);
16         cal_1.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天 
17         firstDay = format.format(cal_1.getTime());
18         System.out.println("-----1------firstDay:"+firstDay);
19         //获取前月的最后一天
20         Calendar cale = Calendar.getInstance();   
21         cale.set(Calendar.DAY_OF_MONTH,0);//设置为1号,当前日期既为本月第一天 
22         lastDay = format.format(cale.getTime());
23         System.out.println("-----2------lastDay:"+lastDay);
24           
25           
26         //获取当前月第一天：
27         Calendar c = Calendar.getInstance();    
28         c.add(Calendar.MONTH, 0);
29         c.set(Calendar.DAY_OF_MONTH,1);//设置为1号,当前日期既为本月第一天 
30         String first = format.format(c.getTime());
31         System.out.println("===============first:"+first);
32           
33         //获取当前月最后一天
34         Calendar ca = Calendar.getInstance();    
35         ca.set(Calendar.DAY_OF_MONTH, ca.getActualMaximum(Calendar.DAY_OF_MONTH));  
36         String last = format.format(ca.getTime());
37         System.out.println("===============last:"+last);
38          
39     }
40     /** 
41    * 字符串的日期格式的计算 
42    */ 
43   public static int daysBetween(String smdate,String bdate) throws ParseException{ 
44           SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd"); 
45           Calendar cal = Calendar.getInstance(); 
46           cal.setTime(sdf.parse(smdate)); 
47           long time1 = cal.getTimeInMillis(); 
48           cal.setTime(sdf.parse(bdate)); 
49           long time2 = cal.getTimeInMillis(); 
50           long between_days=(time2-time1)/(1000*3600*24); 
51           return Integer.parseInt(String.valueOf(between_days)); 
52   }
53 }