java while循环内部或外部循环

Question

I have the below code to show when the next leap year is. In the while loop, I didn't have the line inside the while loop leapYear = (((y % 4 == 0) && (y % 100 != 0)) || (y % 400 == 0)) at the first attempt. My reason for not including that line was if leapYear false, y will plus 1. And then while (!leapYear) condition is tested again using the new y value by plugging into the line above the while loop boolean leapYear = (((y % 4 == 0) && (y % 100 != 0)) || (y % 400 == 0)) .

I don't understand why I need to put that leapYear line in the while loop again. I already had it above the loop which will be used to test the condition after y++ since the while condition requires to test whether leapYear.

import java.util.Scanner;

public class NextLeapYear {
    public static void main(String[] args) {
        Scanner year = new Scanner (System.in);
        System.out.print("Enter a year: ");
        int y = year.nextInt();
        boolean leapYear = (((y % 4 == 0) && (y % 100 != 0)) || (y % 400 == 0));        
        while (!leapYear) {
            y++; 
            leapYear = (((y % 4 == 0) && (y % 100 != 0)) || (y % 400 == 0));
        }
        System.out.println("The next leap year is " + y + "."); 
    }
}

Answer 1

Because your y is changing inside the loop. leapYear depends on y so you need to re-calculate once y changes.

Answer 2

Since your Y Value Changes inside the loop so, for examples if 1994 is the value of Y. then it is a leapyear , Then inside the loop it checks for not leapyear and value of y is pre incremented ++y . So, now if it is 1995, then it is tested for the condition, ie !leapyear and a while loop executes until it satisfies the condition, so until the next leapyear which is 1998. so then it terminates and prints the leapyear. Hope this helps.!