时间点的类Date和日历表示的类GregorianCalendar

1、表示时间点的类Date在java.util.Date中

获得当前时间点：System.out.println("当前时间" + new Date());

将时间点转化为字符串：String s = new Date().toString();

2、日历表示使用的类GregorianCalendar在java.util.GregorianCalendar中

GregorianCalendar now = new GregorianCalendar();

获得月份：int month = now.get(Calendar.MONTH);

获得当日是一周中的第几天：int weekday = now.get(Calendar.DAY_OF_WEEK);

修改日历的时间 now.set(field, amount); now.add(field, amount);

日历转时间点：Date time = now.getTime();

时间点转日历：now.setTime(time);

示例小程序：输出当前一个月的日历

package test;

import java.text.DateFormatSymbols;
import java.util.Calendar;
import java.util.Date;
import java.util.GregorianCalendar;

public class Main {
	public static void main(String args[]) {
		//GreforianCalendar示例程序
		GregorianCalendar d = new GregorianCalendar();//获取当前时间的信息

		int today = d.get(Calendar.DAY_OF_MONTH);//获取当日的日期
		int month = d.get(Calendar.MONDAY);//获取月份

		d.set(Calendar.DAY_OF_MONTH,1);//将时间设置为每月的1号
		int weekday = d.get(Calendar.DAY_OF_WEEK);//查询本月1号是一周中的第几天
		int firstDayOfWeek = d.getFirstDayOfWeek();//查询当前地区一周的第一天
		int indent= 0;
		while(weekday != firstDayOfWeek) {//通过逐渐将日期-1，来找出本月开始应该空几个日期
			indent++;
			d.add(Calendar.DAY_OF_MONTH, -1);
			weekday = d.get(Calendar.DAY_OF_WEEK);
		}
		//DateFormatSymbols在java.text.DateFormatSymbols中
		//getShortWeekdays获得当前地区的一周的简称
		String[] weekdayNames = new DateFormatSymbols().getShortWeekdays();
		do{
			System.out.printf("%4s", weekdayNames[weekday]);
			d.add(Calendar.DAY_OF_MONTH,1);
			weekday = d.get(Calendar.DAY_OF_WEEK);
		}while(weekday != firstDayOfWeek);
		System.out.println();
		//输出日期，当天的日期后要打印*
		for(int i = 0; i < indent; i++)
			System.out.printf("    ");
		d.set(Calendar.DAY_OF_MONTH,1);
		do{
			int day = d.get(Calendar.DAY_OF_MONTH);
			System.out.printf("%3d", day);
			if(day == today) System.out.print("*");
			else System.out.print(" ");
			d.add(Calendar.DAY_OF_MONTH, 1);
			weekday = d.get(Calendar.DAY_OF_WEEK);
			if(weekday == firstDayOfWeek) System.out.println();
		} while(d.get(Calendar.MONDAY) == month);
		if(weekday != firstDayOfWeek) System.out.println();
	}
	
}