Java对时间的计算，时间转换，字符串格式化

package temp;

import java.text.DateFormat;

import java.text.SimpleDateFormat;

import java.util.Calendar;

import java.util.Date;

public class Cal_days {

public static final String[] month_list= {"Jan","Feb","Mar","Apr","May","Jun","Jul","Aug","Sep","Oct","Nov","Dec"};

public static final String fail_refs_fileName= "/Result_fail_Refs.xlsx";

public static void main(String[] args) {

get();

Calendar cld = Calendar.getInstance();

System.out.println(cld.YEAR);

System.out.println(get_month_number("Dec"));

//SimpleDateFormat formatter= new SimpleDateFormat("yyyy-MM-dd 'at' HH:mm:ss z");

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

Date date = new Date(System.currentTimeMillis());

System.out.println(formatter.format(date));

String s = formatter.format(date);

s= s.substring(0,s.length()-2);

s = s+"01";

System.out.println(s);

int a =(int)(Math.random()*1000);

System.out.println("a::::::::::: "+a);

}

public static String get_month_number(String M) {

for(int i=0;i<month_list.length;i++) {

if(month_list[i].equals(M)) {

int index = i+1;

if(index>=10) {

return index+"";

}else {

return "0"+index;

}

}

}

return "NONE";

}

public static void get() {

DateFormat dft = new SimpleDateFormat("yyyy-MM-dd");

try {

Date star = dft.parse("2021-02-03");//开始时间

Date endDay=dft.parse("2021-07-02");//结束时间

Date nextDay=star;

int i=0;

while(nextDay.before(endDay)){//当明天不在结束时间之前是终止循环

Calendar cld = Calendar.getInstance();

cld.setTime(star);

cld.add(Calendar.DATE, 1);

star = cld.getTime();

//获得下一天日期字符串

nextDay = star;

i++;

}

System.out.println("相差天数为："+i);

} catch (Exception e) {

e.printStackTrace();

}

}

}

计算工作日

package temp;

import java.io.InputStreamReader;

import java.text.SimpleDateFormat;

import java.time.DayOfWeek;

import java.time.LocalDate;

import java.time.temporal.ChronoField;

import java.time.temporal.ChronoUnit;

import java.time.temporal.TemporalAdjuster;

import java.time.temporal.TemporalAdjusters;

import java.util.Calendar;

import java.util.Scanner;

public class Cal_workday {

private String startDate;

private String endDate;

public static void main(String[] args){

get();

//Cal_workday daysCounter=new Cal_workday();

//daysCounter.calculateDate();

}

public static void get() {

TemporalAdjuster nextWorkingDay = TemporalAdjusters.ofDateAdjuster(temporal -> {

DayOfWeek dow =DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK));

int dayToAdd = 2;

if (dow ==DayOfWeek.THURSDAY){dayToAdd = 4;}

if (dow ==DayOfWeek.FRIDAY){dayToAdd = 4;}

if (dow ==DayOfWeek.SATURDAY){dayToAdd = 3;}

System.out.println(temporal.plus(dayToAdd, ChronoUnit.DAYS));

return temporal.plus(dayToAdd, ChronoUnit.DAYS);

});

LocalDate localDate = LocalDate.now().with(nextWorkingDay);//测试

}

public void calculateDate(){

@SuppressWarnings("resource")

Scanner in=new Scanner(new InputStreamReader(System.in));

System.out.println("Enter the starting date (DD/MM/YY) :");

startDate=in.next();

System.out.println("Enter the End date (DD/MM/YY) :");

endDate=in.next();

SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy");

try{

Calendar start = Calendar.getInstance();

start.setTime(sdf.parse(startDate));

Calendar end = Calendar.getInstance();

end.setTime(sdf.parse(endDate));

int workingDays = 0;

while(!start.after(end)){

int day = start.get(Calendar.DAY_OF_WEEK);

if ((day != Calendar.SATURDAY) && (day != Calendar.SUNDAY))

workingDays++;

start.add(Calendar.DATE, 1);

}

System.out.println(workingDays);

}catch(Exception e){

e.printStackTrace();

}

}

}