Date，Calendar，SimpleDateFormat的使用

package datetest;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class Test {

    public static void main(String[] args) {
        Date date = new Date();
        System.out.println(date);
        System.out.println(date.getTime());
        //表示 1970 年 1 月 1 日 00:00:00 GMT 以后 time 毫秒的时间点
        Calendar rightNow = Calendar.getInstance();
        System.out.print(rightNow.get(Calendar.YEAR)+"年");
        System.out.print((rightNow.get(Calendar.MONTH)+1)+"月");
        System.out.println(rightNow.get(Calendar.DAY_OF_MONTH)+"日");

        rightNow.set(Calendar.DAY_OF_YEAR,rightNow.get(Calendar.DAY_OF_YEAR)+20);
        System.out.print(rightNow.get(Calendar.YEAR)+"年");
        System.out.print((rightNow.get(Calendar.MONTH)+1)+"月");
        System.out.println(rightNow.get(Calendar.DAY_OF_MONTH)+"日");
        Date data2 = rightNow.getTime();//Calendar转化为Date

        SimpleDateFormat format = new SimpleDateFormat("yyyy年MM月dd日    HH:mm:ss");
        //时间转化为字符串
        String time = format.format(rightNow.getTime());
        System.out.println(time);

        //字符串转化为时间
        try {
            Date date3 = format.parse(time);
            System.out.println(date3.getTime());
        } catch (ParseException e) {
            e.printStackTrace();
        }

    }
}