我的代码可以编译并完美运行，但是当我输入任何星期六的日期时，输出为“ null”而不是“ SATURDAY”。下面将提供示例以进一步解释此问题。
我试图更改我的“ getDayOfWeek”方法上的if语句，但似乎没有解决方案，我也曾尝试从经验丰富的编码人员那里获得帮助，但由于Java不是它们的主要语言，它们似乎很挣扎...
代码：
class MyDate {
// properties of date object
private int day, month, year;
// constructor with arguments
public MyDate(int day, int month, int year) {
this.day = day;
this.month = month;
this.year = year;
}
public boolean isDateValid() {
if (month > 12 || month < 1 || day < 1) { // if values exceed 12 or are negative: return false
return false;
} else if (year <= 1582 && month <= 10 && day <= 15) { // starting date
// checking
return false;
} // for 31 day months: January, March, May, July, August, October, December
else if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
if (day > 31) {
return false;
}
} // for 30 day months: April, June, September, November
else if (month == 4 || month == 6 || month == 9 || month == 11) {
if (day > 30) {
return false;
}
} // February check
else if (month == 2) {
// leap year check for February
// 29 days in a leap year
// 28 days in a common year
if (isLeapYear()) {
if (day > 29) {
return false;
}
} else {
if (day > 28) {
return false;
}
}
}
return true;
}
// checks if input year is leap year
private boolean isLeapYear() {
if (year % 4 != 0) {
return false;
} else if (year % 400 == 0) {
return true;
} else if (year % 100 == 0) {
return false;
} else {
return true;
}
}
// method returns the day of MyDate object
public int getDay() {
return day;
}
// parameter for day to set
public void setDay(int day) {
this.day = day;
}
// method returns the month of MyDate object
public int getMonth() {
return month;
}
// parameter for month
public void setMonth(int month) {
this.month = month;
}
// method returns the year of MyDate object
public int getYear() {
return year;
}
// parameter for year
public void setYear(int year) {
this.year = year;
}
// method returns all variables: day/month/year of MyDate object
public String toString() {
return day + "/" + month + "/" + year;
}
}
public class MyCalendar {
//enums for days of week
public static enum Day {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY;
};
//enums for month of year
public static enum Month {
JANUARY, FEBRUARY, MARCH, APRIL, MAY, JUNE, JULY, AUGUST, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER;
};
//enums for week number of month
public static enum Week {
FIRST, SECOND, THIRD, FOURTH, FIFTH;
};
//to store Date object
private MyDate date;
//constructor taking mydate object
public MyCalendar(MyDate enteredDate) {
this.date = enteredDate;
}
//main method
public static void main(String[] args) {
boolean dateValid = false; //valid date false
Scanner input = new Scanner(System.in); //scanner for input
MyDate enteredDate = null;
//till valid date found
while (!dateValid) {
System.out.print("Enter the date as day month year : ");
//taking input and creating date output
enteredDate = new MyDate(input.nextInt(), input.nextInt(), input.nextInt());
//validating date input
if (enteredDate.isDateValid()) { //if valid
MyCalendar myCalendar = new MyCalendar(enteredDate);
//creating calendar table
myCalendar.printDateInfo(); //printing date info
myCalendar.printCalendar(); //printing calendar
dateValid = true; //setting validate to true
} else {
System.out.println(enteredDate + " is not a valid date, please re-input a valid date: ");
}
}
input.close();
}
// returns number of days in current month
private int getNumberOfDays() {
int days = 31;
int month = date.getMonth();
if (month == 4 || month == 6 || month == 9 || month == 11)
days = 30;
return days;
}
//print calendar of input month
public void printCalendar() {
System.out.println("\n\nThe Calendar of "+Month.values()[date.getMonth()-1]+" "+date.getYear()+" is :");
int numberOfMonthDays = getNumberOfDays();
Day firstWeekdayOfMonth = getDayOfWeek(1, date.getMonth(), date.getYear());
int weekdayIndex = 0;
System.out.println("Su Mo Tu We Th Fr Sa");
// The order of days depends on the input of date
// to display output of calendar
for (int day = 0; Day.values()[day] != firstWeekdayOfMonth; day++) {
System.out.print(" "); // this loop to print the first day in the
// correct place
weekdayIndex++;
}
for (int day = 1; day <= numberOfMonthDays; day++) {
if (day < 10)
System.out.print(day + " ");
else
System.out.print(day);
weekdayIndex++;
if (weekdayIndex == 7) {
weekdayIndex = 0;
System.out.println();
} else {
System.out.print(" ");
}
}
System.out.println();
}
//method to print about date information in literal form
public void printDateInfo() {
System.out.println(date + " is a " + getDayOfWeek(date.getDay(), date.getMonth(), date.getYear())
+ " located in the " + Week.values()[getWeekOfMonth() - 1] + " week of "
+ Month.values()[date.getMonth() - 1] + " " + date.getYear());
}
/*
* gets day of the week, returns enum type Day
*
* Zellar's congruence to calculate the day of week
* for any given date after October 15 1582
* (h) = (q+(13*(m+1)/5)+K+(K/4)+(J/4)+5J)%7 ,q- day of month,
* m- month, k = year of century (year%100), J = (year/100)
*/
public Day getDayOfWeek(int day, int month, int year) {
int q = day;
int m = month;
if (m < 3) {
m = 12 + date.getMonth();
year = year - 1;
}
int K = year % 100;
int J = year / 100;
//calculating h value
int h = (q + (13 * (m + 1) / 5) + K + (K / 4) + (J / 4) + 5 * J) % 7;
Day output = null;
if (h < Day.values().length && h > 0) {
output = Day.values()[h - 1]; //getting respective enum value
}
return output; //returning enum value
}
// get week number of current date
public int getWeekOfMonth() {
int days = date.getDay();
int weeks = days / 7;
days = days % 7;
if (days > 0)
weeks++;
return weeks;
}
}
预期结果：
java MyCalendar 29/02/2019
29/02/2019 in not a valid date, please re-input a valid date: 25/05/2019
25/05/2019 is a Saturday and located in the fourth week of May 2019
The calendar of May 2019 is:
SUN MON TUE WED THU FRI SAT
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
实际结果：
25/05/2019 is a null located in the FOURTH week of MAY 2019
The calendar of May 2019 is:
SUN MON TUE WED THU FRI SAT
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
另一个日期（不是星期六）的结果：
24/05/2019 is a FRIDAY located in the FOURTH week of MAY 2019
The calendar of May 2019 is:
SUN MON TUE WED THU FRI SAT
1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31
指定问题： 在星期六的所有日期，输出显示为空，而不是星期六的其他日期将实现所需的正确输出。
答案 0 :(得分：1)
if (h < Day.values().length && h > 0) {
应更改为
if (h < (Day.values().length + 1) && h > 0) {
答案 1 :(得分：0)
MyDate类，而应依赖内置的LocalDate类。您用于计算星期几的公式是：
//calculating h value
int h = (q + (13 * (m + 1) / 5) + K + (K / 4) + (J / 4) + 5 * J) % 7;
（顺便说一句，请找到更好的变量名并遵守Java命名约定：变量名不能为大写字母。）我不理解该公式，但假设它是正确的，它将计算日期一周中的0 =星期六，1 =星期日至6 =星期五。要将这个数字用作对您的Day枚举的查找，请使用
output = Day.values()[(h + 6) % 7]; //getting respective enum value
由于h始终为非负数且小于7，因此不需要括起来的if语句。只需无条件分配给output。通过这些更改，我得到了
Enter the date as day month year : 25 5 2019 25/5/2019 is a SATURDAY located in the FOURTH week of MAY 2019 The Calendar of MAY 2019 is : Su Mo Tu We Th Fr Sa 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31