Java日期函数使用

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

public class Data {

    public static void main(String[] args) throws ParseException {
        java.text.SimpleDateFormat format = new java.text.SimpleDateFormat(
                "yyyy-MM-dd");
        Calendar cal = Calendar.getInstance();// 使用默认时区和语言环境获得一个日历。
        // cal.add(Calendar.DAY_OF_MONTH, +1);//取当前日期的后一天.
        System.out.println("Today is:"
                + format.format(Calendar.getInstance().getTime()));

        //当前日期的第二种写法
        java.util.Date today=new java.util.Date();    
        System.out.println("Today is "+format.format(today));   

        cal.add(Calendar.DAY_OF_MONTH, -1);// 取当前日期的前一天.
        System.out.println("yesterday is:" + format.format(cal.getTime()));
        Date d = new Date();
        System.out.println("今天的日期：" + format.format(d));
        System.out.println("两天前的日期："
                + format.format(new Date(d.getTime() - (long) 2 * 24 * 60 * 60
                        * 1000)));
        System.out.println("三天后的日期："
                + format.format(new Date(d.getTime() + (long) 3 * 24 * 60 * 60
                        * 1000)));
        //Date date = sdf.parse("2015-09-18");
        // 比如100天后是星期几 这里打出来的是0-6的数字
        int dayweek = (d.getDay() + 100 )%7;// 周天是0
        System.out.println("星期"+(dayweek==0?7:dayweek));


        //取日期的部分:
        int year =cal.get(Calendar.YEAR);    
        int month=cal.get(Calendar.MONTH)+1;//java的月份是0-11，设置的时候记得-1 输出记得+1
        int day =cal.get(Calendar.DAY_OF_MONTH);    
        int hour =cal.get(Calendar.HOUR_OF_DAY);    
        int minute =cal.get(Calendar.MINUTE);    
        int seconds =cal.get(Calendar.SECOND);   
        System.out.printf("年:%d 月:%d 日:%d %d时%d分%d秒\n",year,month,day,hour,minute,seconds);

        //当前月份的最大天数
        int maxDayOfthisMonth=cal.getActualMaximum(Calendar.DAY_OF_MONTH);    

        //取当月的第一天
        java.text.SimpleDateFormat format2 = new java.text.SimpleDateFormat("yyyy-MM-01");    
        java.util.Date firstDay=new java.util.Date();    
        System.out.println(format2.format(firstDay));   

        //取当月最后一天
        int maxDay=cal.getActualMaximum(Calendar.DAY_OF_MONTH);    
        java.text.Format formatter3=new java.text.SimpleDateFormat("yyyy-MM-"+maxDay);    
        System.out.println(formatter3.format(cal.getTime()));   

        //求相隔天数
        Date date1=format.parse("2017-8-4");
        Date date2=format.parse("2017-8-3");
        long duringDay=(date1.getTime()-date2.getTime())/(24*60*60*1000);   
        System.out.println(Math.abs(duringDay)+1);//相邻的两天间隔视为2天  

        //求10小时后的时间
        java.util.Calendar cal2=java.util.Calendar.getInstance();    
        cal2.setTime(new Date());    
        cal2.add(java.util.Calendar.HOUR_OF_DAY,10);    
        System.out.println("date:"+format.format(cal2.getTime()));//想获得具体时间看39-44行 

    }

}

算法中的使用 https://blog.csdn.net/wdays83892469/article/details/79774716?utm_source=copy