Multiple conditions in a while loop

问题

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.

回答1:

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

回答2:

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) )

来源：https://stackoverflow.com/questions/17886077/multiple-conditions-in-a-while-loop