日期时间相关类

 1 package classwork8;
 2 
 3 import java.util.Date;
 4 
 5 public class DateTest {
 6 
 7     public static void main(String[] args) {
 8         Date currentDate = new Date();
 9         System.out.println("当前日期时间=" + currentDate);
10         String out = "自1970年1月1日起经历的毫秒数:";
11         System.out.println(out + currentDate.getTime());
12         Date newDate = new Date(100000000);
13         System.out.println("经过100000000毫秒后的新日期=" + newDate);
14         System.out.println("两日期的先后比较" + currentDate.before(newDate));
15         System.out.println("两日期的先后比较" + currentDate.after(newDate));
16     }
17 
18 }

 1 package classwork8;
 2 
 3 import java.util.Calendar;
 4 
 5 public class CalendarTest {
 6 
 7     public static void main(String[] args) {
 8         //获取当前日期对象
 9         Calendar calendar=Calendar.getInstance();
10         //利用calendar对象输出当前日期
11         System.out.println("当前时间:"+calendar.getTime());
12         System.out.println("当前年份:"+calendar.get(Calendar.YEAR));
13         System.out.println("当前月份:"+calendar.get(Calendar.MONTH));//返回值加1为当前月份
14         System.out.println("当前日期:"+calendar.get(Calendar.DATE));
15         System.out.println("当前小时(12小时制):"+calendar.get(Calendar.HOUR));
16         System.out.println("当前小时(24小时制):"+calendar.get(Calendar.HOUR_OF_DAY));
17         System.out.println("当前星期"+calendar.get(Calendar.DAY_OF_WEEK));//返回值1~7代表周日到周六,返回值为4,代表周四
18         
19     }
20 
21 }

 1 //日期时间格式化
 2 package classwork8;
 3 
 4 import java.text.ParseException;
 5 import java.text.SimpleDateFormat;
 6 import java.util.Date;
 7 //Date date = new Date()； //获取当前系统时间，格式为: Thu Nov 01 18:27:06 CST 2018
 8 //format: 按指定的目标格式把Date对象转换为String
 9 //parse: 按指定的源格式把String转换为Date对象
10 public class SimpleDateFormateTest {
11 
12     public static void main(String[] args) {
13         SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy年MM月dd日HH时mm分ss秒");
14         SimpleDateFormat sdf2 = new SimpleDateFormat("yy/MM/dd HH:mm");
15         SimpleDateFormat sdf3 = new SimpleDateFormat("yyyy-MM-dd HH:mm");
16         Date now = new Date();
17         System.out.println("输出格式1:" + sdf1.format(now));
18         System.out.println("输出格式2:" + sdf2.format(now));
19         System.out.println("输出格式3:" + sdf3.format(now));
20         String s = "2020-09-15 23:36";
21         Date date;
22         try {
23             date = sdf3.parse(s);
24             System.out.println("输出格式4:" + date);
25         } catch (ParseException e) {
26             e.printStackTrace();
27         }
28     }
29 
30 }