java日期比较例子等...

数据库中employ表，入职日期，今天日期：

测试代码：

 package javademo;

 import java.sql.Connection;

 import java.sql.DriverManager;

 import java.sql.ResultSet;

 import java.sql.Statement;

 import java.text.SimpleDateFormat;

 import java.util.Calendar;

 import java.util.Date;

 public class TimeCompare {

     public static void main(String args[]) throws Exception{

         Class.forName("com.mysql.jdbc.Driver");

         Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test_demo?user=root&password=root");

         Statement stmt = conn.createStatement();

         ResultSet rs = stmt.executeQuery("select * from employ");

         while(rs.next()){

             String hireDatestr = rs.getString("hiredate");

             Date hireDate = new SimpleDateFormat("yyyy-MM-dd").parse(hireDatestr);

             System.out.println("(方法一)入职天数： " + compartDay(new Date(), hireDate));

             System.out.println("(方法二)入职天数： " + intervalDays(new Date(), hireDate));

             System.out.println("入职日期距今月数： " + getMonthSpace(hireDate, new Date()));

             System.out.println("入职日期是否超过了2个月：" + afterFewMonth(hireDate, 2));

             System.out.println("入职是否已经有半年：" + afterFewMonth(hireDate, 6));

             System.out.println("入职是否已经有两周：" + afterFewWeek(hireDate, 2));

             System.out.println();

         }

         rs.close();

         stmt.close();

         conn.close();

     }

     //比较入职日期距今是否过了n个月

     public static boolean afterFewMonth(Date hireDate, int n){

         boolean result = false;

         Calendar c = Calendar.getInstance();

         c.add(Calendar.MONTH, n);

         if(hireDate.after(c.getTime())){

             result = true;

         }

         return result;

     }

     //比较入职是否有了n周

     /**

      * Calendar.DATE  : 代表天数

      * Calendar.WEDNESDAY: 代表周数

      * Calendar.MONTH : 代表月数

      * Calendar.YEAR :代表年数

      */

     public static boolean afterFewWeek(Date hireDate, int n){

         boolean result = false;

         Calendar c = Calendar.getInstance();

         c.add(Calendar.WEDNESDAY, n);

         System.out.println("计算"+n+"周后日期：" + c.getTime());

         if(hireDate.after(c.getTime())){

             result = true;

         }

         return result;

     }

     /**

      * 比较两个日期之间相差的月数

      * 只能比较月数，计算的不精确，只是单纯的月数之间的比较

      */

     public static int getMonthSpace(Date start, Date end){

         if(start.after(end)){

             Date temp = start;

             start = end;

             end = temp;

         }

         Calendar c = Calendar.getInstance();

         c.setTime(start);

         int year1 = c.get(Calendar.YEAR);

         int month1 = c.get(Calendar.MONTH);

         c.setTime(end);

         int year2 = c.get(Calendar.YEAR);

         int month2 = c.get(Calendar.MONTH);

         int result;

         if(year1==year2){

             result = month2 - month1;

         }else{

             result = 12*(year2-year1) + month2 - month1;

         }

         return result;

     }

     /**

      * 比较和今天相差的天数 方法一

      * 用毫秒计算差值

      */

     public static int compartDay(Date date1, Date date2){

         if(date1.after(date2)){

             Date temp = date1;

             date1 = date2;

             date2 = temp;

         }

         long intervalMilli = date2.getTime() - date1.getTime();

         return (int)(intervalMilli/(24*60*60*1000));

     }

     /**

      * 比较和今天相差的天数方法二   ----不对，纠正结果见下面!!!!!!

      * 用日历的日来计算差值

      */

     public static int intervalDays(Date date1, Date date2){

         if(date1.after(date2)){

             Date temp = date1;

             date1 = date2;

             date2 = temp;

         }

         Calendar calendar = Calendar.getInstance();

         calendar.setTime(date1);

         int day1 = calendar.get(Calendar.DAY_OF_YEAR);

         calendar.setTime(date2);

         int day2 = calendar.get(Calendar.DAY_OF_YEAR);

         return day2 - day1;

     }

 }

控制台打印：

纠正：比较和今天相差的天数方法二这个计算方法不对。更新如下：

上面的方法中，如果不是同一个年份的，计算的结果就不对，参考博客：https://blog.csdn.net/ZeroBz/article/details/80757391

代码如下：

package com.cy.test.date;

import java.text.ParseException;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

public class TestDate2 {

    public static void main(String[] args) throws ParseException {

        String str = "2010-08-19 14:20:00";

        SimpleDateFormat s = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        Date date1 = s.parse(str);

        Date date2 = new Date();

        System.out.println(intervalDays1(date1, date2));

        System.out.println(intervalDays2(date1, date2));

    }

    /**

     * 方法一

     * 计算两个日期的天数之差 这里默认date1<date2，date精确到时分秒

     * 使用日历的日来计算差值

     * @param date1

     * @param date2

     * @return

     */

    public static int intervalDays1(Date date1, Date date2){

        Calendar calendar = Calendar.getInstance();

        calendar.setTime(date1);

        int day1 = calendar.get(Calendar.DAY_OF_YEAR);

        int year1 = calendar.get(Calendar.YEAR);

        calendar.setTime(date2);

        int day2 = calendar.get(Calendar.DAY_OF_YEAR);

        int year2 = calendar.get(Calendar.YEAR);

        if (year1 != year2) {   //不同年

            int timeDistance = 0;

            for (int i = year1; i < year2; i++) {

                if (i % 4 == 0 && i % 100 != 0 || i % 400 == 0) {  //闰年

                    timeDistance += 366;

                }else{  //平年

                    timeDistance += 365;

                }

            }

            return timeDistance + (day2 - day1);

        }else{

            return day2 - day1;

        }

    }

    /**

     * 方法二

     * 计算两个日期的天数之差 这里默认date1<date2，date精确到时分秒

     * 使用SimpleDateFormat将时分秒的日期转化为只有年月日，再利用毫秒计算差值

     * @param date1

     * @param date2

     * @return

     */

    public static int intervalDays2(Date date1, Date date2){

        SimpleDateFormat s = new SimpleDateFormat("yyyy-MM-dd");

        try {

            Date day1 = s.parse(s.format(date1));

            Date day2 = s.parse(s.format(date2));

            int intervalDay = (int) ((day2.getTime() - day1.getTime()) / (1000 * 60 * 60 * 24));

            return intervalDay;

        } catch (Exception e) {

            e.printStackTrace();

            System.out.println("calculateTkDay，parseException");

        }

        return 0;

    }

}

console打印结果计算结果相同：

3289

3289

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java日期比较例子等...

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