关于java的Calendar类的bug
这篇文章废话比较多，想看bug和本人的逆天操作的话，可以直接去看“解决办法”和“结论”部分
起源
一切的一切都起源于软测这一道看似无比简单的题
简单来说就是输出20221019这样的格式，然后输出是星期几
错误的代码
这是我最开始写的错误的代码
import java.util.*;
public class day {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
while (in.hasNext()) {
System.out.println("输入任意1900从年到2400年之间的8位数的一个日期（日期格式例子：20221014）");
String next = in.next();
char[] chars = next.toCharArray();
String tempYear = "";
String tempMonth = "";
String tempDay = "";
for (int i = 0; i < 4; i++) {
tempYear = tempYear + chars[i];
}
for (int i = 4; i < 6; i++) {
tempMonth = tempMonth + chars[i];
}
for (int i = 6; i < 8; i++) {
tempDay = tempDay + chars[i];
}
int year = Integer.parseInt(tempYear);
int month = Integer.parseInt(tempMonth);
int day = Integer.parseInt(tempDay);
// System.out.println(year+" "+month+" "+day+" ");
if (year < 1900 || year > 2400) {
System.out.println("日期格式错误！");
continue;
}
if (month < 1 || month > 12) {
System.out.println("日期格式错误！");
continue;
}
if (day < 1 || day > 31) {
System.out.println("日期格式错误！");
continue;
}
int leapYear = 0;
int commonYear = 0;
for (int i = 1900; i < year; i++) {
if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) {
leapYear++;
} else
commonYear++;
}
int counts = 0;
counts = counts + leapYear * 366;
counts = counts + commonYear * 365;
switch (month){
case 12:
counts+=30;
case 11:
counts+=31;
case 10:
counts+=30;
case 9:
counts += 31;
case 8:
counts += 31;
case 7:
counts += 30;
case 6:
counts += 31;
case 5:
counts += 30;
case 4:
counts += 31;
case 3:
//sumDays += 28;
//判断year是否是闰年
if((year%4==0&&year%100!=0)||year%400==0){
counts+=29;
}else{
counts+=28;
}
case 2:
counts+=31;
case 1:
counts+=day;
}
System.out.println("counts = " + counts);
int temp = counts % 7;
if (temp == 0) {
System.out.println("星期日");
}
if (temp == 1) {
System.out.println("星期一");
}
if (temp == 2) {
System.out.println("星期二");
}
if (temp == 3) {
System.out.println("星期三");
}
if (temp == 4) {
System.out.println("星期四");
}
if (temp == 5) {
System.out.println("星期五");
}
if (temp == 6) {
System.out.println("星期六");
}
}
}
}因为要考虑的错误输入，所以代码看起来非常的冗余
不知道为什么会错，求发现问题的大佬联系qq1473220685，请喝奶茶
口头描述下遇到的bug吧，19000101往后几年，基本上没什么问题的，但是时间跨度一大，就出问题了。
解决办法
于是就干脆去网上找到现成的工具类了
下面是更改后的代码，这边写的简介明了点
代码
public class Test02 {
public static void main(String[] args) {
LocalDate date = LocalDate.of(2022,10,19);
ZoneId zone = ZoneId.systemDefault();
Instant instant = date.atStartOfDay().atZone(zone).toInstant();
java.util.Date da = Date.from(instant);
String weekDayString = getWeek(da);
System.out.println(weekDayString);
}
public static String getWeek(Date date){
String[] weeks = {"星期日","星期一","星期二","星期三","星期四","星期五","星期六"};
Calendar cal = Calendar.getInstance();
cal.setTime(date);
int i = cal.get(Calendar.DAY_OF_WEEK);
System.out.println(i);
int week_index = i - 1;
System.out.println(week_index);
if(week_index<0){
week_index = 0;
}
return weeks[week_index];
}
}
输出
bug描述
看起来没什么毛病对不对？
但是换个测试用例，那就出问题了
代码
public class Test02 {
public static void main(String[] args) {
LocalDate date = LocalDate.of(1900,1,1);
ZoneId zone = ZoneId.systemDefault();
Instant instant = date.atStartOfDay().atZone(zone).toInstant();
java.util.Date da = Date.from(instant);
String weekDayString = getWeek(da);
System.out.println(weekDayString);
}
public static String getWeek(Date date){
String[] weeks = {"星期日","星期一","星期二","星期三","星期四","星期五","星期六"};
Calendar cal = Calendar.getInstance();
cal.setTime(date);
int i = cal.get(Calendar.DAY_OF_WEEK);
System.out.println(i);
int week_index = i - 1;
System.out.println(week_index);
if(week_index<0){
week_index = 0;
}
return weeks[week_index];
}
}
输出
1900的1月1日，怎么可能是周日呢？明明是周一啊
再测试
我们再试试1900年1月2日的输出时什么
代码
public class Test02 {
public static void main(String[] args) {
LocalDate date = LocalDate.of(1900,1,2);
ZoneId zone = ZoneId.systemDefault();
Instant instant = date.atStartOfDay().atZone(zone).toInstant();
java.util.Date da = Date.from(instant);
String weekDayString = getWeek(da);
System.out.println(weekDayString);
}
public static String getWeek(Date date){
String[] weeks = {"星期日","星期一","星期二","星期三","星期四","星期五","星期六"};
Calendar cal = Calendar.getInstance();
cal.setTime(date);
int i = cal.get(Calendar.DAY_OF_WEEK);
System.out.println(i);
int week_index = i - 1;
System.out.println(week_index);
if(week_index<0){
week_index = 0;
}
return weeks[week_index];
}
}
输出
结论
综上，我认为这是Calendar类本身的bug。当然这个bug问题也不大，毕竟也没什么正常的需求需要去看19000101是星期几吧？
但本着“你就说有没有解决吧”的精神，我还是给这坨代码用if给救了回来…..
最终代码
import java.time.Instant;
import java.time.LocalDate;
import java.time.ZoneId;
import java.util.*;
public class day {
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
System.out.println("输入任意1900从年到2400年之间的8位数的一个日期（日期格式例子：20221014）");
while (in.hasNext()) {
String next = in.next();
int i1 = 0;
try {
i1 = Integer.parseInt(next);
} catch (NumberFormatException e) {
System.out.println("日期格式错误！请重新输入");
continue;
}
if (19000000 > i1 || i1 > 24000000) {
System.out.println("日期格式错误！请重新输入");
continue;
}
char[] chars = next.toCharArray();
String tempYear = "";
String tempMonth = "";
String tempDay = "";
for (int i = 0; i < 4; i++) {
tempYear = tempYear + chars[i];
}
for (int i = 4; i < 6; i++) {
tempMonth = tempMonth + chars[i];
}
for (int i = 6; i < 8; i++) {
tempDay = tempDay + chars[i];
}
int year = Integer.parseInt(tempYear);
int month = Integer.parseInt(tempMonth);
int day = Integer.parseInt(tempDay);
if (year < 1900 || year > 2400) {
System.out.println("日期格式错误！请重新输入");
continue;
}
if (month < 1 || month > 12) {
System.out.println("日期格式错误！请重新输入");
continue;
}
if (day < 1 || day > 31) {
System.out.println("日期格式错误！请重新输入");
continue;
}
LocalDate date = null;
try {
System.out.println("year = " + year);
System.out.println("month = " + month);
System.out.println("day = " + day);
if (year==1900&&month==1&&day==1){
System.out.println("星期一");
continue;
}
date = LocalDate.of(year, month, day);
} catch (Exception e) {
System.out.println("日期格式错误！请重新输入");
continue;
}
ZoneId zone = ZoneId.systemDefault();
Instant instant = date.atStartOfDay().atZone(zone).toInstant();
java.util.Date da = Date.from(instant);
String week = getWeek(da);
System.out.println(week);
}
}
public static String getWeek(Date date) {
String[] weeks = {"星期日", "星期一", "星期二", "星期三", "星期四", "星期五", "星期六"};
Calendar cal = Calendar.getInstance();
cal.setTime(date);
int week_index = cal.get(Calendar.DAY_OF_WEEK) - 1;
System.out.println(week_index);
if (week_index < 0) {
week_index = 0;
}
return weeks[week_index];
}
}
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