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fadilthrejk

[java] Checking for a valid date

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I am workin on a program to check if a date inputted by the user is valid, and output whether it''s valid or not and whether it''s a leap year. I got it all working, except for the leap year thing. I''m not sure if I have the rules right. I think this is what it is: it''s a leap year if a) it''s divisible by 400, or b) it''s divisible by 4 and it''s not divisible by 100. i dunno. I am also not sure if i''ve translated the rules into java correctly or not. here''s my code for that section: double rem = month%400; double rem2 = month%100; double rem3 = month%4; if (year < 3000 && year > 1999) { yearValid = true; if ((rem == 0) || ((rem2 > 0) && (rem3 == 0))) //Determine whether it''s a leap year { leapYear = true; } //no need to tell it to make it false otherwise, because it''s initialized } //as false Ok, i think that''s right. here''s the full code for the program. I know it''s sloppy, but I just threw most of it together in like 30 minutes or so. import cs1.Keyboard; /** * Write a description of class Dates here. * * @author David Grimsley * @version 10-22-03 */ public class Dates { /** * Main...everything is done here (in this case)...only works like that in the console tho...applets don''t even have a main method * */ public static void main(String[] args) { int month, days, year; //date read in from user int daysInMonth; //number of days in month read in boolean monthValid = true; boolean yearValid = true; boolean dayValid = true; //true if input from user is valid boolean leapYear = false; //true if user''s year is a leap year //Get integer month, day, and year from user System.out.println("Enter the month number"); month = Keyboard.readInt(); System.out.println("Enter the day of the month"); days = Keyboard.readInt(); System.out.println("Enter the year"); year = Keyboard.readInt(); //Check to see if month is valid if (month <= 12 && month >= 1) monthValid = true; else monthValid = false; int rem = month%400; int rem2 = month%100; int rem3 = month%4; if (year < 3000 && year > 1999) { yearValid = true; if ((rem == 0) || ((rem2 > 0) && (rem3 == 0))) //Determine whether it''s a leap year { leapYear = true; } //no need to tell it to make it false otherwise, because it''s initialized } //as false else yearValid = false; //Determine number of days in month int monthDays; //User number of days in month to check to see if day is valid //Probably a bit more complex than necessary, I may fix eventually if(month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) { monthDays = 31; if (days > 31) dayValid = false; } else{ if(leapYear && month == 2) monthDays = 29; if (days > 29) dayValid = false; else if(month == 4 || month == 6 || month == 9 || month == 11) { monthDays = 30; if (days > 30) dayValid = false; } else { monthDays = 28; if (days > 28) { dayValid = false; } } } //Determine whether date is valid and print appropriate message if (monthValid == true && yearValid == true && dayValid == true) { System.out.println("Date is valid"); if (leapYear) System.out.println("Leap year"); } else System.out.println("Date is not valid"); } //end main() } //end class Dates if anyone can help me, thanks. if not, i''ll figure it out on my own eventually.

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i''m not. this is where it''s checked:


double rem = month%400;
double rem2 = month%100;
double rem3 = month%4;
if ((rem == 0) || ((rem2 > 0) && (rem3 == 0))) //Determine whether it''s a leap year
{
leapYear = true;

but it tells me when i put in a leap year the year isn''t valid at all. I was wondering if i screwed up in the algorithm or something. i still don''t know why it''s doing it.

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yeah, and you''re using month. month is between 1 and 12, it''s not the year. the year is what determines a leap year.

Just pick a value for month, say 5 for May. Run 5 through that little snippet of code manually, and see what you get. It shouldn''t make any sense.

Then try running 1996 though that snippet manually.

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Are you doing this just as like a practice challenge? Or are you doing it because it actually needs to be done? Because, if it''s not just as a challenge, turn to the Java API, there is a class GregorianCalender that stores dates (the class Date has been deprecated) and it has a method isLeapYear(int year) that returns a boolean value.

Java provides a lot of useful classes for you, always check the API if you''re having trouble.

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I think I fixed it. I''ve tested a wide range of months, days, and years. They all work. I could have used the GregorianCalendar class, had I known about it, but I figure since I''ve already done it and it works fine for what I need it for, I''ll just leave it as is. Thanks for pointing out about the leap year validation. I don''t know what I was thinking putting month to test instead of date. Like I said, I threw it together in like 35 minutes. Here''s the code, finished (hopefully):

import cs1.Keyboard;
/**
* Write a description of class Dates here.
*
* @author David Grimsley
* @version 10-22-03
*/
public class Dates
{
/**
* Main...everything is done here (in this case)...only works like that in the console tho...applets don''t even have a main method
*
*/
public static void main(String[] args)
{
int month, days, year; //date read in from user
int daysInMonth; //number of days in month read in
boolean monthValid = true;
boolean yearValid = false;
boolean dayValid = false; //true if input from user is valid
boolean leapYear = false; //true if user''s year is a leap year

//Get integer month, day, and year from user
System.out.println("Enter the month number");
month = Keyboard.readInt();

System.out.println("Enter the day of the month");
days = Keyboard.readInt();

System.out.println("Enter the year");
year = Keyboard.readInt();

//Check to see if month is valid
if (month <= 12 && month >= 1)
monthValid = true;

else monthValid = false;

int rem = year%400;
int rem2 = year%100;
int rem3 = year%4;

if (year < 3000 && year > 1999)
{
yearValid = true;

if (yearValid && ((rem == 0) || ((rem2 > 0) && (rem3 == 0)))) //Determine whether it''s a leap year
{
leapYear = true;
}

}
else yearValid = false;

//User number of days in month to check to see if day is valid
//Probably a bit more complex than necessary, I may fix eventually
if(month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12)
{
if (days <= 31)
dayValid = true;
}
else{
if (month == 2)
{
if (leapYear && days <= 29)
dayValid = true;
else
if (days <= 28)
dayValid = true;
}
else
if(month == 4 || month == 6 || month == 9 || month == 11)
{
if (days <= 30)
dayValid = true;
}
}



//Determine whether date is valid and print appropriate message
if (monthValid == true && yearValid == true && dayValid == true)
{
System.out.println("Date is valid");
if (leapYear)
System.out.println("Leap year");
}
else System.out.println("Date is not valid");

} //end main()

} //end class Dates


thanks for all the help, especially tortoise for pointing out my stupid error with the leapYear checker.

IrateGoldfish: Where can I view the source of the class? I thought the Java sdk just came with the class files.

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You can see all the source files by extracting an archive called source.zip that is located in the directory where you installed the java sdk....

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