1. Introduction

The Date class in the java.util package represents a specific time, accurate to milliseconds. If we want to use our Date class, then we must introduce our Date class.

Writing the year directly into the Date class will not get the correct result. Because Date in Java is calculated from 1900, so as long as you fill in the first parameter with the number of years since 1900, you will get the year you want. The month needs to be subtracted by 1, and the day can be inserted directly. This method is rarely used, and the second method is commonly used.

This method is to convert a string that conforms to a specific format, such as yyyy-MM-dd, into Date type data. First, define a Date type object Date date = null; Then define a String type string that conforms to the format String dateStr = "2010-9-10"; Split this string dateDivide = dateStr.split("- "); Take out the year, month and day respectively and assign them to Calendar. Use Calendar's getTime(); to obtain the date and assign it to date.

2. Introduction to knowledge points

• 1. Declaration of Date class

• 2. Common methods of Date class

• 3. SimpleDateFormat formatted date

3. Explanation of knowledge points

1. Declaration of Date class

If we want to get the date and time, we can instantiate the Date class

(1) Get the current date and time

Date d=new Date();

(2) Obtain the specified date and time

Date d=new Date(long date);

Note: To get the long date of the current time, we can use the getTime(); method

Code demonstration:

package Test2;
import java.util.Date;
public class Tested {
private final static String name = "磊哥的java歷險(xiǎn)記-@51博客";

public static void main(String args[]){
//產(chǎn)生日期對(duì)象
Date d=new Date();
System.out.println(d);
//獲取時(shí)間為長(zhǎng)整型，時(shí)間戳
long l=d.getTime();
System.out.println(l);
Date d1=new Date(l);
System.out.println(d1);
System.out.println("============="+name+"=============");

}
}

2. Common methods of the Date class

• (1) getYear()//Year, the value after subtracting 1900 from the year in the Date object, so the corresponding year needs to be displayed Then you need to add 1900

• to the return value (2) getMonth()//Month, the Date class stipulates that January is 0, February is 1, and March is 2 , and so on for subsequent steps.

• (3)getDate()//Date

• (4)getHours()//Hour

• (5)getMinutes()//Minutes

• (6)getSeconds()//Seconds

• (7)getDay ()//Week of the week, the Date class stipulates that Sunday is 0, Monday is 1, Tuesday is 2, and so on.

Code demonstration:

package Test2;
//導(dǎo)入時(shí)間包
import java.util.Date;
public class Tested {
private final static String name = "磊哥的java歷險(xiǎn)記-@51博客";
public static void main(String args[]){
//創(chuàng)建時(shí)間對(duì)象
Date d2 = new Date();
//年份,Java中的Date表示的是自1900年以來(lái)所經(jīng)過(guò)的時(shí)間
int year = d2.getYear() + 1900;
//月份,最后一個(gè)月取決于一年中的月份數(shù)。 因?yàn)檫@個(gè)值的初始值是0，因此我們要用它來(lái)表示正確的月份時(shí)就需要加1。
int month = d2.getMonth() + 1;
//日期
int date = d2.getDate();
//小時(shí)
int hour = d2.getHours();
//分鐘
int minute = d2.getMinutes();
//秒
int second = d2.getSeconds();
//星期幾
int day = d2.getDay();
System.out.println("年份：" + year);
System.out.println("月份：" + month);
System.out.println("日期：" + date);
System.out.println("小時(shí)：" + hour);
System.out.println("分鐘：" + minute);
System.out.println("秒：" + second);
System.out.println("星期：" + day);
System.out.println("============="+name+"=============");
}
}

3. SimpleDateFormat format date

SimpleDateFormat Is a class for formatting and parsing dates in a locale-sensitive manner. SimpleDateFormat allows you to choose any user-defined date-time format to run on.

(1) SimpleDateFormate initialization:

SimpleDateFormate sdf=new SimpleDateFormate (date format);

Note: Date format

(2) SimpleDateFormat common methods:

• ## format(Date d):Convert date format to string Data

• parse(String s):Convert string format to date data

Code demonstration ：

package Test2;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
class Person extends Object{
public static void main(String args[]){
Date d=new Date();
//傳入指定時(shí)間格式
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd");
//日期格式化輸出
System.out.println(sdf.format(d));
}
}

Define a tool class:

package Test2;
//導(dǎo)入時(shí)間包import java.text.SimpleDateFormat;
import java.util.Date;
public class MyDate {
private final static String name = "磊哥的java歷險(xiǎn)記-@51博客";
// 定義的MyDateDemo類(lèi)
private SimpleDateFormat sd = null;
// 聲明SimpleDateFormat對(duì)象sd
public String getDate01() {
// 定義getDate01方法
this.sd = new SimpleDateFormat("yyyy-MM-dd HH:mm;ss.sss"); // 得到一個(gè)"yyyy-MM-dd
// HH:mm;ss.sss"格式日期
return this.sd.format(new Date());
// 將當(dāng)前日期進(jìn)行格式化操作
}
public String getDate02() { // 定義getDate02方法
this.sd = new SimpleDateFormat("yyyy年MM月dd日 HH時(shí)mm分ss秒sss毫秒");
// 得到一個(gè)"yyyy年MM月dd日
//HH時(shí)mm分ss秒sss毫秒"格式日期
return this.sd.format(new Date()); // 將當(dāng)前日期進(jìn)行格式化操作 }
public String getDate03() {// 定義getDate03方法
this.sd = new SimpleDateFormat("yyyyMMddHHmmsssss");
// 得到一個(gè)"yyyyMMddHHmmsssss"格式日期(也就是時(shí)間戳)
return this.sd.format(new Date());// 將當(dāng)前日期進(jìn)行格式化操作
}
}

Main method call:

package com.Test;
import Test2.MyDate;
import java.util.Date;
public class Main {

private final static String name = "磊哥的java歷險(xiǎn)記-@51博客";

public static void main(String[] args) { // 主方法
MyDate dd = new MyDate(); // 聲明dd對(duì)象，并實(shí)例化
System.out.println("默認(rèn)日期格式: " + new Date());
// 分別調(diào)用方法輸入不同格式的日期
System.out.println("英文日期格式: " + dd.getDate01());
System.out.println("中文日期格式: " + dd.getDate02());
System.out.println("時(shí)間戳: " + dd.getDate03());
System.out.println("============="+name+"=============");

}
}

• (1) Get the current date and print out yyyy -MM-dd hh:mm:ss format

• (2) Get the year and month of the current date and output it

• (1) Use the date object to get the current date

• (2) Use simpleDateFormat to format the date

• (3) Use the common method of date to obtain the year and month

package com.Test;
import Test2.MyDate;
import java.text.SimpleDateFormat;
import java.util.Date;
public class Main {
private final static String name = "磊哥的java歷險(xiǎn)記-@51博客";
public static void main(String[] args) { // 主方法
//獲取當(dāng)前日期
Date d2=new Date();
//轉(zhuǎn)換為yyyy-MM-dd hh:mm:ss
SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
//日期格式化
System.out.println("日期格式化:"+sdf.format(d2));
int year = d2.getYear() + 1900;//年份
int month = d2.getMonth() + 1;//月份
System.out.println("年份：" + year);
System.out.println("月份：" + month);
System.out.println("============="+name+"=============");
}
}

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