题目1 --日期

借助随机数，创建一个从1995.1.1 00:00:00 到 1995.12.31 23:59:59 之间的随机日期

package date;import java.util.Date;public class TestDate {public static void main(String[] args) {long second = 1000;long minute = 60*second;long hour = minute * 60;long day = hour*24;long year = day * 365;long year1995Start  = (1995-1970) * year;long leapDay = (1995-1970)/4*day; //每隔4年有一个润日year1995Start+=leapDay;long eightHour = hour*8; //8个小时的毫秒数，因为从0毫秒对应的是1970.1.1 08:00:00year1995Start-=eightHour;Date dStart = new Date(year1995Start);System.out.println("1995年第一天："+dStart);long year1995End = year1995Start + year - 1;Date dEnd = new Date(year1995End);System.out.println("1995年最后一天："+dEnd);long randomTime = (long) (Math.random()*(year-1) + year1995Start);Date dRandom = new Date(randomTime);System.out.println("1995年这一年中的一个随机时间:" + dRandom);}
}

笔记

SimpleDateFormat sdf =new SimpleDateFormat("yyyy/MM/dd HH:mm:ss" );
String str = "2016/1/5 12:12:12";
Date d = sdf.parse(str);
字符串对象有一个parse(str) 可以转成Date 对象

Date对象转字符串:
SimpleDateFormat sdf =new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS" );
Date d= new Date();
String str = sdf.format(d);

题目2--日期格式化

准备一个长度是9的日期数组
使用1970年-2000年之间的随机日期初始化该数组
按照这些日期的时间进行升序排序
比如 1988-1-21 12:33:22 就会排在 1978-4-21 19:07:23 前面，因为它的时间更小，虽然日期更大

package date;import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;public class TestDate {public static void main(String[] args) {int yearStart = 1970;int yearEnd = 2000;Date[] ds = new Date[9];for (int i = 0; i < ds.length; i++) {ds[i] = getRandomDate(yearStart, yearEnd);}System.out.println("得到的随机日期数组:");for (int i = 0; i < ds.length; i++) {System.out.print(toString(ds[i])+"\t");if(2==i%3)System.out.println();}//选择法排序for (int j = 0; j < ds.length-1; j++) {for (int i = j+1; i < ds.length; i++) {String strTimeI = toString(ds[i],"HHmmss");String strTimeJ = toString(ds[j],"HHmmss");int lTimeI = Integer.parseInt(strTimeI);int lTimeJ = Integer.parseInt(strTimeJ);if( lTimeI<lTimeJ  ){  Date temp = ds[j];ds[j] = ds[i];ds[i] = temp;}}}      System.out.println("排序后的随机日期数组:");for (int i = 0; i < ds.length; i++) {System.out.print(toString(ds[i])+"\t");if(2==i%3)System.out.println();}}public static String toString(Date d) {return toString(d, "yyyy-MM-dd HH:mm:ss");}public static String toString(Date d, String format) {SimpleDateFormat sdf = new SimpleDateFormat(format);return sdf.format(d);}private static Date getRandomDate(int yearStart, int yearEnd) {SimpleDateFormat sdf = new SimpleDateFormat("yyyy");try {Date dStart = sdf.parse(String.valueOf(yearStart)); // 1970Date dEnd = sdf.parse(String.valueOf(yearEnd + 1)); // 2001 不是 2000，要在2001的基础上减少以毫秒，才表示2000最后一刻long timeStart = dStart.getTime();long timeEnd = dEnd.getTime() - 1;long timeRandom = (long) (timeStart + Math.random() * (timeEnd - timeStart));return new Date(timeRandom);} catch (ParseException e) {// TODO Auto-generated catch blocke.printStackTrace();}return null;}
}

笔记：可以通过日历对象得到日期对象

//采用单例模式获取日历对象Calendar.getInstance();
Calendar c = Calendar.getInstance();

    //通过日历对象得到日期对象Date d = c.getTime();

日期对象
add方法，在原日期上增加年/月/日
set方法，直接设置年/月/日

题目3--Calendar

找出下个月的倒数第3天是哪天

package date;import java.text.SimpleDateFormat;
//
import java.util.Calendar;
import java.util.Date;public class TestDate {private static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");public static void main(String[] args) {Calendar c = Calendar.getInstance();System.out.println("今天是:" + format( c.getTime()));//先翻到下下个月c.add(Calendar.MONTH,2);//设置到月初c.set(Calendar.DATE,1);//再往回翻3天c.add(Calendar.DATE,-3);Exception e;System.out.println("下个月倒数第三天是:" + format(c.getTime()));}private static String format(Date time) {return sdf.format(time);}
}