Multiple conditions in a while loop

Question

import java.util.Calendar;
import java.util.GregorianCalendar;

public class CountingSundays {

    public static void main(String args[]) {

        Calendar cal = new GregorianCalendar(1901, 00, 01); // month set to 0for jan , 1= feb etc

        while((cal.get(Calendar.YEAR) != 2001) && (cal.get(Calendar.MONTH) != 0) && cal.get(Calendar.DAY_OF_MONTH) != 1) { // while not 1/1/2001

                System.out.print(cal.get(Calendar.MONTH));
            // cal.add(Calendar.DAY_OF_MONTH, 1);
        }
    }
}

Im trying to iterate through the while loop by adding on a day at a time but it wont even access the while loop the first time. Are the conditions in the while loop right? When i tested it it worked with just one condition but stopped when i added the second condition.

Axel · Accepted Answer · 2013-07-26 16:08:04Z

5

It should be

while( !(cal.get(Calendar.YEAR) == 2001 && cal.get(Calendar.MONTH) == 0 && cal.get(Calendar.DAY_OF_MONTH) == 1) ) { // while not 1/1/2001

answered Jul 26, 2013 at 16:08

Axel

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Comments

Vyassa Baratham · Accepted Answer · 2013-07-26 16:10:14Z

3

This is just a simple logic error. If even one of those is false (say, if the month IS 0), then you have true && false && true, which is false.

You need the "not" outside of the entire expression, or you need to use "||" to combine them:

while( !(year == 2001 && month == 0 && day == 1) )

or

while( (year != 2011) || (month != 0) || (day != 1) )

answered Jul 26, 2013 at 16:10

Vyassa Baratham

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2 Comments

But I'm Not A Wrapper Class Over a year ago

+1 because you actually explain the logical error in the opening post.

Todd Davies Over a year ago

For those that are interested, the relationship between the two statements here is an application of De Morgan's law: en.wikipedia.org/wiki/De_Morgan's_laws

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