Thread: Testing if dates are real or not.

I'm having some trouble with this code that asks for input and then displays if it is a real date or not. We were given the first code and we had to write the second code based on a provided UML diagram. I finished writing the second one and got it to compile but it displays the wrong results such as Invalid Date: No such month every single time. I've reviewed the code several times and the logic makes sense to me, what am I missing?

/*
	Test program for Date class
*/
 
import java.util.Scanner;
 
public class Assignment5
{
	/* Test driver for Date class
 
		Prompt for the number of Date objects to test, then create Date objects and determine
		if they are valid dates.
 
	*/
 
	public static void main (String [] args)
	{
		Scanner keyboard = new Scanner(System.in);
 
		int monthVal;
		int dayVal;
		int yearVal;
 
		int maxLoop;
 
		System.out.println ("Enter number of dates to test");
		maxLoop = keyboard.nextInt();
 
		for (int time = 0; time < maxLoop; time++)
		{
			System.out.println ("Enter the month, day and year separated by a space");
			monthVal = keyboard.nextInt();
			dayVal = keyboard.nextInt();
			yearVal = keyboard.nextInt();
 
			Date aDate = new Date (monthVal, dayVal, yearVal);
 
			if (aDate.isValid())
				System.out.println ("Valid Date: " + aDate);
			else
				System.out.println ("Invalid Date: " + aDate);
			System.out.println();
		}
	}
}

and then here is the second code:

public class Date
{
	private int month;
	private int day;
	private int year;
 
	public Date (int month, int day, int year)
	{
		int newMonth = month;
		int newDay = day;
		int newYear = year;
 
	}
 
	public boolean isValid()
	{
		if (year >= 1582)
 
			if(month >= 1 && month <=12)
 
				if (month == 4 || month == 6 || month == 9 || month== 11)
 
					if (day >=1 && day <= 30)
						return true;
					else
						return false;
				else
					if (month == 2)
						if (isLeapYear())
							if (day >=1 && day <= 29)
								return true;
							else
								return false;
						else
							if (day >= 1 && day <=28)
								return true;
							else
								return false;
 
 
 
					else
						if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12)
							if (day >=1 && day <= 31)
								return true;
							else
								return false;
						else
							return false;
 
			else
				return false;
		else
			return false;
 
	}
 
	public String toString()
	{
		switch (month)
		{
			case 1:
				return "January" + "," + day + "," + year;
			case 2:
				return "February" + "," + day + "," + year;
			case 3:
				return "March" + "," + day + "," + year;
			case 4:
				return "April" + "," + day + "," + year;
			case 5:
				return "May" + "," + day + "," + year;
			case 6:
				return "June" + "," + day + "," + year;
			case 7:
				return "July" + "," + day + "," + year;
			case 8:
				return "August" + "," + day + "," + year;
			case 9:
				return "September" + "," + day + "," + year;
			case 10:
				return "October" + "," + day + "," + year;
			case 11:
				return "November" + "," + day + "," + year;
			case 12:
				return "December" + "," + day + "," + year;
			default:
				return "No such month";
		}
	}
 
	private boolean isLeapYear()
	{
		if (year % 4 == 0)
 
			if (year % 100 == 0 && year % 400 !=0)
				return true;
 
			else
				return false;
 
		else
			return false;
	}
}

Take a close look at your Date constructor. By the way giving your class the same name as a class in the Java API can only lead to confusion.

Thank you I see the problem now within my constructor, and that part is functioning. Everything works except the leap year part. It still see February 29, 2008, for example, as an invalid date.

Obviously your algorithm in the isLeapYear method is wrong. Google for the correct algorithm.

Thanks once again! Much appreciated!