GregorianCalendar 类为Calendar的子类

具体的用法如下：

package com.baidu.lianxi;

import java.util.Calendar;

import java.util.GregorianCalendar;

public class Demo2 {

/*

    *@param args

    */

    public static void main(String[] args) {

//获得一个日历对象

        Calendar ca = Calendar.getInstance();

//      ca.setFirstDayOfWeek(Calendar.SATURDAY);

        disPlay(ca);

//创建日历对象时间为2012.12.12.12,12,12

        Calendar c2 = new GregorianCalendar(2012, 11, 12, 12, 12, 12);

        disPlay(c2);

//根据在年中的天数,求相隔天数。

        int days = c2.get(Calendar.DAY_OF_YEAR)-ca.get(Calendar.DAY_OF_YEAR);

        System.out.println("相差"+days+"天");

//重新设定c2对象的时间

        System.out.println("+++++++++++++++++重新设定后时间++++++++++++：");

        c2.set(2012,11,23);//月份和日期都是0开头。月份中0表示一月。月中的日期，0表示一日。

        c2.set(Calendar.HOUR_OF_DAY, 19);

        c2.set(Calendar.MINUTE,12);

        c2.set(Calendar.SECOND, 11);

        disPlay(c2);

/*

* +++++++++++++++++修改后时间++++++++++++：

2020年一月4日星期六时间：14:50:57

2020年一月4日星期六时间：18:50:57*/

        System.out.println("+++++++++++++++++修改后时间++++++++++++：");

//向后延长29天

        ca.add(Calendar.DAY_OF_MONTH,29);

        disPlay(ca);

//再延长10小时

        ca.add(Calendar.HOUR, 4);

        disPlay(ca);

    }

  public static void disPlay(Calendar ca) {

        String []mon = {"一月","二月","三月","四月","五月","六月","七月","八月","九月","十月","十一月","十二月"};

        String []week = {"","星期日","星期一","星期二","星期三","星期四","星期五","星期六"};

        System.out.print(ca.get(Calendar.YEAR)+"年");

        System.out.print(mon[ca.get(Calendar.MONTH)]);

        System.out.print(ca.get(Calendar.DAY_OF_MONTH)+"日");

        System.out.println(week[ca.get(Calendar.DAY_OF_WEEK)]);

        System.out.print("时间：");

        System.out.print(ca.get(Calendar.HOUR_OF_DAY)+":");

        System.out.print(ca.get(Calendar.MINUTE)+":");

        System.out.println(ca.get(Calendar.SECOND));

    }

}