date类 和 Calendar日历类

package cn.hp.test;



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

public class demo {
    public static void main(String[] args) {
        Date date1 = new Date();
        System.out.println(date1);

        //获取日期字段的方法
        System.out.print(date1.getYear()+1900+"年");
        System.out.print(date1.getMonth()+1+"月");
        System.out.print(date1.getDate()+"日");
        System.out.print(date1.getHours()+":");
        System.out.print(date1.getMinutes()+":");
        System.out.println(date1.getSeconds());

        //获取从1970到现在的毫秒数
        System.out.println(date1.getTime());

        //格式化日期,返回对应格式的字符串,一般用于显示
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss E");
       //返回对应格式的字符串,一般用于显示
        String s = sdf.format(date1);
        System.out.println(s);

        //解析字符串返回对象

    }
}

例题:

package cn.hp.test;

import java.util.Date;


public class demo02 {
    public static void main(String[] args) throws Exception {
        //倒计时多少秒后关机
        int m = 60;

        //60秒后的时间
        Date date = new Date();
        date.setMinutes(date.getMinutes()+1);
        long a = date.getTime();

        while(true){
            Date now = new Date();
            long b = now.getTime();
            //时间差
            long c = a - b;
            //是否时间到了
            if(c<=0){
                System.out.println("时间到了,开始关机");
                //Runtime是计算机环境 getRuntime()获取环境对象
                Runtime runtime = Runtime.getRuntime();
                runtime.exec("shutdown -s -t 60 -f");
                break;
            }
            System.out.println("剩余"+c/1000+"秒关机");

            //休眠
            Thread.sleep(1000);
        }

    }
}

Calendar日历类

package cn.hp.test;

import java.time.LocalTime;
import java.util.Calendar;
import java.util.Date;


public class demo03 {
    public static void main(String[] args) {
        //创建日历对象
        Calendar cal = Calendar.getInstance();
        System.out.println(cal+"=cal");


        //设置日期
        cal.set(Calendar.MONTH, 10);
        System.out.println("cal="+cal);
        //获取日期
        System.out.print(cal.get(Calendar.YEAR)+"年");
        System.out.print(cal.get(Calendar.MONTH)+1+"月");
        System.out.print(cal.get(Calendar.DATE)+"日");
        System.out.print(cal.get(Calendar.HOUR_OF_DAY)+":");
        System.out.print(cal.get(Calendar.MINUTE)+":");
        System.out.println(cal.get(Calendar.SECOND));

        //如何转为Date
        Date date = cal.getTime();
        System.out.println("date="+date);

        //获取1970至今的毫秒
        System.out.println(cal.get(Calendar.MILLISECOND));

        //演示Fu调用方法,简介创建子类型对象
        Fu fu = Fu.getInstance();
        System.out.println(fu);

        //jdk1.8新增的内容
        LocalTime now = LocalTime.now();
        System.out.println("now="+now);
    }
}

//理解通过一个类方法获取子类对象
abstract class Fu{
    public static Fu getInstance(){
        return new Zi();
    }
}
class Zi extends Fu{

}