package date;

 import java.util.Calendar;

 import java.util.Date;

 public class DateDemo {

     public static void main(String[] args) {

         /**

          * 可以直接输出Date,不可以直接输出Calendar

          * 已知当前Date类的日期now，Calendar类的日期calendar，

          * 1.将Date--->Calendar，用calendar.setTime(now);

          * 2.将Calendar--->Date，那么now=calendar.getTime();

          */

         Date now=new Date();

         Calendar calendar=Calendar.getInstance();

         long now1=System.currentTimeMillis();

         long now2=now.getTime();

         long now3=calendar.getTimeInMillis();

         System.out.println("now :"+now);

         System.out.println("calendar.Year :"+calendar.get(Calendar.YEAR));

         System.out.println("now1 :"+now1);

         System.out.println("now2 :"+now2);

         System.out.println("now3 :"+now3);

         calendar.add(Calendar.YEAR,-19);

         System.out.printf("%d-%d-%d\n",calendar.get(Calendar.YEAR),

                 calendar.get(Calendar.MONTH),calendar.get(Calendar.DAY_OF_MONTH));

         //Date-->Calendar

         Calendar c1=Calendar.getInstance();//调用Calendar类中的静态方法getInstance()来得到一个Calendar对象

         c1.setTime(now);

         //Calendar-->Date

         Date birth=calendar.getTime();

         System.out.println("birth :"+birth);

         System.out.println(birth.toLocaleString());

     }

 }

 package date;

 import java.text.ParseException;

 import java.text.SimpleDateFormat;

 import java.util.Calendar;

 import java.util.Date;

 import java.util.Locale;

 public class DateFormatDemo {

     public static void main(String[] args) {

         Date now = new Date();

         // Date ==> Calendar

         Calendar calendar = Calendar.getInstance();

         calendar.setTime(now);

         // 加8周

         calendar.add(Calendar.WEEK_OF_YEAR, 8);

         // Calendar ==> Date

         now = calendar.getTime();

         System.out.println(now);

         // 格式化

         SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS",Locale.CHINA);

         // Date ==> String

         String result = format.format(now);//format为DateFormat类中的一个方法，用于Formats a Date into a date/time string.

         System.out.println(result);

         // String ==> Date

         String d = "2018-01-12 09:21:21.000";

         try {

             Date date = format.parse(d);//parse解析，也是DateFormat类中的一个方法，解析给定字符串中的文本内容，以产生一个日期

             System.out.println(date);

         } catch (ParseException e) {

             e.printStackTrace();

         }

     }

 }