计算两个日期之间相差几天（Date类型与String类型互相转换）

 1 /**
 2  * 
 3  */
 4 package com.hlcui.date;
 5 
 6 import java.text.ParseException;
 7 import java.text.SimpleDateFormat;
 8 import java.util.Calendar;
 9 import java.util.Date;
10 
11 import org.junit.Test;
12 
13 /**
14  * @author Administrator
15  * 
16  */
17 public class DateTest {
18 
19     @Test
20     public void testBetweenDays() throws ParseException {
21         int days = betweenDays("20160102", "20160303");
22         System.out.println(days);
23     }
24 
25     /**
26      * 计算两个日期相差的天数
27      * 
28      * @throws ParseException
29      */
30     public int betweenDays(String oldDate, String newDate)
31             throws ParseException {
32         Calendar cal = Calendar.getInstance();
33         cal.setTime(stringToDate(oldDate));
34         long oldTime = cal.getTimeInMillis();
35         cal.setTime(stringToDate(newDate));
36         long newTime = cal.getTimeInMillis();
37         return (int) ((newTime - oldTime) / (1000 * 24 * 3600));
38     }
39 
40     /**
41      * String转换为Date
42      * 
43      * @throws ParseException
44      */
45     public Date stringToDate(String date) throws ParseException {
46         SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
47         return sdf.parse(date);
48     }
49 
50     /**
51      * Date转换为String
52      */
53     public String dateToString(Date date) {
54         SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd");
55         return sdf.format(date);
56     }
57 }