java的时间

　　先看例子：

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class DateTest
{
    public static void main(String[] args)
    {
        Date date = new Date();
        System.out.println("Today**********");
        printDate(date);
        
        GregorianCalendar d = new GregorianCalendar();
        d.add(Calendar.DAY_OF_MONTH, -1);
        Date yesterDate = d.getTime();
        System.out.println("Yesterday**********");
        printDate(yesterDate);
    }
    
    private static void printDate(Date date)
    {
        System.out.printf("epoch毫秒数： %s%n", date.getTime());
        System.out.printf("LONG Date: %s%n", DateFormat.getDateInstance(DateFormat.LONG));
        System.out.printf("SHORT Date: %s%n", DateFormat.getDateInstance(DateFormat.SHORT));
        
        System.out.printf("LONG Time: %s%n", DateFormat.getTimeInstance(DateFormat.LONG));
        System.out.printf("SHORT Time: %s%n", DateFormat.getTimeInstance(DateFormat.SHORT));
        
        System.out.printf("LONG DateTime: %s%n", DateFormat.getDateTimeInstance(DateFormat.LONG, DateFormat.LONG));
        System.out.printf("SHORT DateTime: %s%n", DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT));
        
        DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        System.out.printf("指定格式: %s%n", df.format(date));
    }
}

　　输出：

Today**********
epoch毫秒数： 1534952854644
LONG Date: java.text.SimpleDateFormat@a87fc158
SHORT Date: java.text.SimpleDateFormat@d5391ab7
LONG Time: java.text.SimpleDateFormat@787e63cb
SHORT Time: java.text.SimpleDateFormat@58715d3
LONG DateTime: java.text.SimpleDateFormat@a0ba3d93
SHORT DateTime: java.text.SimpleDateFormat@b5341f2a
指定格式: 2018-08-22 23:47:34
Yesterday**********
epoch毫秒数： 1534866454874
LONG Date: java.text.SimpleDateFormat@a87fc158
SHORT Date: java.text.SimpleDateFormat@d5391ab7
LONG Time: java.text.SimpleDateFormat@787e63cb
SHORT Time: java.text.SimpleDateFormat@58715d3
LONG DateTime: java.text.SimpleDateFormat@a0ba3d93
SHORT DateTime: java.text.SimpleDateFormat@b5341f2a
指定格式: 2018-08-21 23:47:34