Java 中的日期与时间

package org.lovian.date;

import java.util.Date;

/**
 * java.util.Date Demo
 * @author PENG Zhengshuai
 * @lovian.org
 *
 */
public class DateDemo {
	public static void main(String[] args) {
		// 无参构造器，默认为当前时间
		Date date = new Date();
		System.out.println("date: " + date);

		// 带参构造器, 给定当前时间的毫秒值
		long time = System.currentTimeMillis();
		Date date2 = new Date(time);
		System.out.println("date2: " + date2);

		// 给定时间一小时，结果应该是 1970-01-01 01：00
		long time2 = 1000 * 60 * 60;
		Date date3 = new Date(time2);
		System.out.println("date3: " + date3);
	}
}

package org.lovian.date;

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

/**
 * Date format demo: Date -- Sting (格式化） String -- Date （解析）
 *
 * @author PENG Zhengshuai
 * @lovian.org
 *
 */
public class DateFormatDemo {
	public static void main(String[] args) {
		// Date -- String, 格式化
		// 创建日期对象
		Date date = new Date();
		// 默认格式创建格式化对象
		DateFormat df = new SimpleDateFormat();
		// 格式化日期
		String s = df.format(date);
		System.out.println(s);

		// 给定模式创建格式化对象
		DateFormat df2 = new SimpleDateFormat("yyyy年MM月dd日HH：mm：ss");
		String s2 = df2.format(date);
		System.out.println(s2);

		// String -- Date 解析
		String str = "2008-08-08 12:12:12";
		DateFormat df3 = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); //这里格式必须要匹配
		Date date2 = null;
		try {
			date2 = df3.parse(str);
		} catch (ParseException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			System.err.println("parse error");
		}
		System.out.println(date2);
	}
}

package org.lovian.calendar;

import java.util.Calendar;

/**
 * Calendar Class Demo
 *
 * @author PENG Zhengshuai
 * @lovian.org
 *
 */
public class CalendarDemo {
	public static void main(String[] args) {
		// get instance of calendar
		Calendar c = Calendar.getInstance();

		// get year
		int year = c.get(Calendar.YEAR);

		// get month, Remember month count from 0!!!
		int month = c.get(Calendar.MONTH);

		// get date
		int date = c.get(Calendar.DATE);
		System.out.println("now: " + year + "-" + (month + 1) + "-" + date);
		System.out.println("===================");

		// today of three years ago
		c.add(Calendar.YEAR, -3);
		System.out.println("3 years ago: " + c.get(Calendar.YEAR) + "-" + (c.get(Calendar.MONTH) + 1) + "-"
				+ c.get(Calendar.DATE));

		// set date as 2011-11-11
		c.set(2011, 10, 11);
		System.out.println("single day: " + c.get(Calendar.YEAR) + "-" + (c.get(Calendar.MONTH) + 1) + "-"
				+ c.get(Calendar.DATE));
	}
}

package org.lovian.date;

import java.util.Calendar;

/**
 * Get the day numbers of each Feb
 *
 * @author PENG Zhengshuai
 * @lovian.org
 *
 */
public class EachFebrary {
	public static void main(String[] args) {
		System.out.println("2014-02 has " + getDaysOfFeb(2014) + "days");
		System.out.println("2016-02 has " + getDaysOfFeb(2016) + "days");
	}

	public static int getDaysOfFeb(int year) {
		Calendar c = Calendar.getInstance();
		// set year-01-31
		c.set(year, 2, 1);
		c.add(Calendar.DATE, -1); // last day of Feb
		int date = c.get(Calendar.DATE);
		return date;

		/*
		Calendar c = Calendar.getInstance();
		// set year-02-1
		c.set(year, 1, 1);
		long lastDayofJan = c.getTimeInMillis();
		c.getTime();

		// set year-03-01
		c.set(year, 2, 1);
		long firstDayOfMar = c.getTimeInMillis();

		//3月1号 - 1月31 = 二月天数 + 1, 所以这里需要用3月1号-2月1号
		int date = (int) ((firstDayOfMar - lastDayofJan) / 1000 / 60 / 60 / 24);
		return date;
		 */
	}
}