Date類與Calendar類之間的轉換

 1 package date;
 2 
 3 import java.util.Calendar;
 4 import java.util.Date;
 5 
 6 public class DateDemo {
 7 
 8     public static void main(String[] args) {
 9         /**
10          * 可以直接輸出Date,不可以直接輸出Calendar
11          * 已知當前Date類的日期now，Calendar類的日期calendar，
12          * 1.將Date--->Calendar，用calendar.setTime(now);
 
13          * 2.將Calendar--->Date，那麽now=calendar.getTime();
14          */
15         Date now=new Date();
16         Calendar calendar=Calendar.getInstance();
17         long now1=System.currentTimeMillis();
18         long now2=now.getTime();
19         long now3=calendar.getTimeInMillis();
20         System.out.println("now :"+now);
 
21         System.out.println("calendar.Year :"+calendar.get(Calendar.YEAR));
22         System.out.println("now1 :"+now1);
23         System.out.println("now2 :"+now2);
24         System.out.println("now3 :"+now3);
25         
26         calendar.add(Calendar.YEAR,-19);
27         System.out.printf("%d-%d-%d\n",calendar.get(Calendar.YEAR),
 
28                 calendar.get(Calendar.MONTH),calendar.get(Calendar.DAY_OF_MONTH));
29         //Date-->Calendar
30         Calendar c1=Calendar.getInstance();//調用Calendar類中的靜態方法getInstance()來得到一個Calendar對象
31         c1.setTime(now);
32         
33         //Calendar-->Date
34         Date birth=calendar.getTime();
35         System.out.println("birth :"+birth);
36         
37         System.out.println(birth.toLocaleString());
38         
39     }
40 
41 }

輸出如下內容：

now :Sun Dec 30 11:32:57 CST 2018
calendar.Year :2018
now1 :1546140777528
now2 :1546140777390
now3 :1546140777468
1999-11-30
birth :Thu Dec 30 11:32:57 CST 1999
1999-12-30 11:32:57

DateFormat類：

 1 package date;
 2 
 3 import java.text.ParseException;
 4 import java.text.SimpleDateFormat;
 5 import java.util.Calendar;
 6 import java.util.Date;
 7 import java.util.Locale;
 8 
 9 public class DateFormatDemo {
10 
11     public static void main(String[] args) {
12         Date now = new Date();
13         
14         // Date ==> Calendar
15         Calendar calendar = Calendar.getInstance();
16         calendar.setTime(now);
17         
18         // 加8周
19         calendar.add(Calendar.WEEK_OF_YEAR, 8);
20         
21         // Calendar ==> Date
22         now = calendar.getTime();
23         System.out.println(now);
24         
25         // 格式化
26         SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS", 
27 
28 Locale.CHINA);
29         // Date ==> String
30         String result = format.format(now);//format為DateFormat類中的一個方法，用於Formats a Date into a date/time string.
31         System.out.println(result);
32         
33         // String ==> Date
34         String d = "2018-01-12 09:21:21.000";
35         try {
36             Date date = format.parse(d);//parse解析，也是DateFormat類中的一個方法，解析給定字符串中的文本內容，以產生一個日期
37             System.out.println(date);
38         } catch (ParseException e) {
39             e.printStackTrace();
40         }
41         
42     }
43 }

Date、Calendar、DateFormat類