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feat: add java date demo
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‎README.md‎

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- [Java 接口](https://www.wdbyte.com/java/interface/)
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- [Java 抽象类](https://www.wdbyte.com/java/abstract/)
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- [Java 多态](https://www.wdbyte.com/java/polymorphism/)
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- [Java Scanner](https://www.wdbyte.com/java/scanner/)
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- [Java 日期时间 Date](https://www.wdbyte.com/java/date/)
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## 🌿 SpringBoot 2.x 教程
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‎core-java-modules/core-java-base/src/main/java/com/wdbyte/date/JavaDateCalc.java‎

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package com.wdbyte.date;
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import java.text.SimpleDateFormat;
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import java.util.Calendar;
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import java.util.Date;
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/**
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* @author niulang
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* @date 2023/04/26
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*/
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public class JavaDateCalc {
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public static void main(String[] args) {
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SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
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Date date = new Date();
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System.out.println(String.format("当前时间：%s", sdf.format(date)));
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date = new JavaDateCalc().addDay(date, 3);
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System.out.println(String.format("增加三天：%s", sdf.format(date)));
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date = new JavaDateCalc().minDay(date, 1);
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System.out.println(String.format("减去一天：%s", sdf.format(date)));
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date = new JavaDateCalc().addMonth(date, 2);
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System.out.println(String.format("增加两个月：%s", sdf.format(date)));
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}
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/**
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* 增加天数
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*
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* @param date
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* @param addDay
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* @return
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*/
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public Date addDay(Date date, int addDay) {
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Calendar cal = Calendar.getInstance();
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cal.setTime(date);
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cal.add(Calendar.DATE, addDay);
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Date newDate = cal.getTime();
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return newDate;
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}
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/**
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* 减少天数
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*
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* @param date
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* @param minDay
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* @return
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*/
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public Date minDay(Date date, int minDay) {
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Calendar cal = Calendar.getInstance();
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cal.setTime(date);
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cal.add(Calendar.DATE, -minDay);
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Date newDate = cal.getTime();
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return newDate;
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}
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/**
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* 增加月份
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*
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* @param date
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* @param addMonth
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* @return
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*/
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public Date addMonth(Date date, int addMonth) {
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Calendar cal = Calendar.getInstance();
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cal.setTime(date);
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cal.add(Calendar.MONTH, addMonth);
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Date newDate = cal.getTime();
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return newDate;
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}
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}

‎core-java-modules/core-java-base/src/main/java/com/wdbyte/date/JavaDateCalc2.java‎

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package com.wdbyte.date;
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import java.text.SimpleDateFormat;
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import java.util.Calendar;
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import java.util.Date;
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/**
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* @author niulang
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* @date 2023/04/26
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*/
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public class JavaDateCalc2 {
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public static void main(String[] args) {
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SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
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Date date = new Date();
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System.out.println(String.format("当前时间：%s", sdf.format(date)));
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// 三天的毫秒数：3 * 24 * 3600 * 1000
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date = new Date(date.getTime() + 3 * 24 * 3600 * 1000);
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System.out.println(String.format("增加三天：%s", sdf.format(date)));
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date = new Date(date.getTime() - 1 * 60 * 1000);
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System.out.println(String.format("减去一分钟：%s", sdf.format(date)));
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}
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}

‎core-java-modules/core-java-base/src/main/java/com/wdbyte/date/JavaDateCreate.java‎

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package com.wdbyte.date;
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import java.util.Date;
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/**
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* @author niulang
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* @date 2023/04/25
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*/
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public class JavaDateCreate {
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public static void main(String[] args) {
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Date date = new Date();
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// 输出时间
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System.out.println(date); // Tue Apr 25 20:28:23 CST 2023
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// 输出毫秒数
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System.out.println(date.getTime()); // 1682425703429
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// 当前毫秒数创建对象
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//Date date2 = new Date(System.currentTimeMillis());
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Date date2 = new Date(1682425703429L);
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System.out.println(date2); // Tue Apr 25 20:28:23 CST 2023
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}
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}

‎core-java-modules/core-java-base/src/main/java/com/wdbyte/date/JavaDateDiff.java‎

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package com.wdbyte.date;
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import java.text.SimpleDateFormat;
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import java.util.Date;
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/**
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* @author niulang
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* @date 2023/04/25
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*/
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public class JavaDateDiff {
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public static void main(String[] args) throws InterruptedException {
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// 获取当前时间
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Date date1 = new Date();
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// 休眠 3 秒
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Thread.sleep(3000);
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// 再获取一次当前时间
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Date date2 = new Date();
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// 很明显 date1 在 date2 之前，,所以 true
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boolean before = date1.before(date2);
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System.out.println(before); // true
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// 很明显 date2 在 date1 之后,所以 true
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boolean after = date2.after(date1);
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System.out.println(after); // true
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// date2 不在 date1 之前,所以 false
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System.out.println(date2.before(date1)); // false
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SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
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System.out.println("date1："+sdf.format(date1));
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System.out.println("date2："+sdf.format(date2));
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Long diff = date1.getTime() - date2.getTime();
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if (diff > 0) {
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System.out.println("date1 > date2");
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}
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if (diff < 0) {
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System.out.println("date1 < date2");
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}
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if (diff == 0) {
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System.out.println("date1 = date2");
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}
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exec();
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}
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public static void exec() throws InterruptedException {
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long start = System.currentTimeMillis();
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// 做点什么
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Thread.sleep(3000);
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long end = System.currentTimeMillis();
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System.out.println("耗时:" + (end - start) + "ms");
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}
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}

‎core-java-modules/core-java-base/src/main/java/com/wdbyte/date/JavaDateFormat.java‎

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package com.wdbyte.date;
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import java.text.ParseException;
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import java.text.SimpleDateFormat;
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import java.util.Date;
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/**
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* @author niulang
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* @date 2023/04/25
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*/
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public class JavaDateFormat {
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public static void main(String[] args) throws ParseException {
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Date date = new Date();
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// 时间格式化，yyyy 年份，MM 月份， dd 当月第多少天, hh:mm:ss 分别为时分秒
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SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
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String formatDate = simpleDateFormat.format(date);
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System.out.println(formatDate);
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SimpleDateFormat sdf1 = new SimpleDateFormat("当前日期是: yyyy-MM-dd");
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SimpleDateFormat sdf2 = new SimpleDateFormat("当前时间是: hh:mm:ss");
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System.out.println(sdf1.format(date));
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System.out.println(sdf2.format(date));
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String strDate = "2023-01-19 10:30:00";
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SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
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Date myDate = sdf.parse(strDate);
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System.out.println(sdf.format(myDate));
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}
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}

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