Thread: Newbie Java Question

Please help me out.
I understand most everything in this program,
but there is one bit that's driving me crazy.

Let's say my inputs are year=1800, month=1
On line 80 ---> return (totalNumberOfDays + startDay1800) % 7;
which means (31 + 3) % 7 = 6

On line 57 ---> for (i = 0; i < startDay; i++)
so doesn't this mean for (i=0; i<6; i++)

How can the remainder be 6. I must be reading it wrong but how.

import javax.swing.JOptionPane;
 
public class PrintCalendar
{
	public static void main (String[]args)
	{
 
		String strMonth = JOptionPane.showInputDialog(null,"Please enter the month","MONTH",JOptionPane.QUESTION_MESSAGE);
		int month = Integer.parseInt(strMonth);
 
		String strYear = JOptionPane.showInputDialog(null,"Please enter a year","YEAR",JOptionPane.QUESTION_MESSAGE);
		int year = Integer.parseInt(strYear);
 
		printMonth(year,month);
	}
	//Run - print Title and Body
	static void printMonth(int year, int month)
	{
		printMonthTitle(year, month);
 
		printMonthBody (year, month);
	}
	//Run - Title Print
	static void printMonthTitle(int year, int month)
	{
	System.out.println("      " + getMonthName(month) + year);
	System.out.println("----------------------------");
	System.out.println(" Sun Mon Tue Wed Thu Fri Sat");	
	}
	//Validate - Month String
	static String getMonthName(int month)
	{
		String monthName = null;
		switch (month){
			case 1: monthName = "January"; break;
			case 2: monthName = "February"; break;
			case 3: monthName = "March"; break;
			case 4: monthName = "April"; break;
			case 5: monthName = "May"; break;
			case 6: monthName = "June"; break;
			case 7: monthName = "July"; break;
			case 8: monthName = "Ausgust"; break;
			case 9: monthName = "September"; break;
			case 10: monthName = "October"; break;
			case 11: monthName = "November"; break;
			case 12: monthName = "December"; break;
		}
		return monthName;
	}
	//Run - Body Print 
	static void printMonthBody(int year,int month)
	{
		int startDay = getStartDay(year, month);
		int numberOfDaysInMonth = getNumberOfDaysInMonth(year, month);
 
 
		for(int i=0; i<startDay; i++)
		{
			System.out.print("    ");
		}
		for(int i=1; i<=getNumberOfDaysInMonth(year, month); i++)
		{
			if (i<10)
				System.out.print("   " + i);
			else 
				System.out.print("  " + i);
 
			if ((i + startDay)%7 == 0)
				System.out.println();
		}
	}
	//Validate - which day the date starts on.
	static int getStartDay(int year, int month)
	{
		//On the 1/1/1800 starts on a Wednesday 3 days away from Sunday
		int startDay1800 = 3;
		int totalNumberOfDays = getTotalNumberOfDays(year, month);
 
		//if the total "number of days + startDay1800 in this case is 3 days" is divisible by seven
		return (totalNumberOfDays + startDay1800)%7;
	}
	//Validate - the total number of days in the year and month
	static int getTotalNumberOfDays(int year, int month)
	{
		int totalDays = 0;
		//Add 366 or 365 days if it is more then 1800 year
		for(int i=1800; i<year; i++)
			if (isLeapYear(i))
				totalDays = totalDays + 366;
			else
				totalDays = totalDays + 365;
 
		//add the days in as each month rows by
		for(int i=1; i<month; i++)
			totalDays = totalDays + getNumberOfDaysInMonth(year, i);
 
		return totalDays;
	}
	//Validate - the days for each of the month
	static int getNumberOfDaysInMonth(int year, int month)
	{
		if(month==1 || month==3 || month==5 || month==7 || month==8 || month==10 || month==12)
			return 31;
		if(month==4 || month==6 || month==9 || month==11)
			return 30;
		if(month==2)
			return isLeapYear(year)? 29:28;
		else 
			return 0;
	}
	//Testing - Leap Year ? True or False
	static boolean isLeapYear(int year)
	{
		return year % 400 == 0 || (year % 4 == 0 && year % 100 !=0);
	}
}

Can you add some println statements to output data that shows the problem?
Add some comments to the output and post it here.

i am a noob to Java, though a programmer for 25 years, but...

(i = 0; i < startDay; i++)
so doesn't this mean for (i=0; i<6; i++)

if the for next loop is going to stop when i is not less than 6 (I<6) and i = 6 it does not satisfy the condition to go through the loop. you can change this to i <= 6.
Buddy