Checking Whether a Year Is a Leap Year

This lesson covers checking whether a year is a leap year in Java, so you understand how to write judgment logic that combines several conditions. It's for anyone searching "Java leap year check implementation."

A year is a leap year if it's divisible by 4, and not divisible by 100, or if it's divisible by 400. It's a basic piece of logic used a lot in calendar and date-calculation programs.

The example expresses this entire complex rule in a single expression: (year % 4 == 0 && year % 100 != 0) || year % 400 == 0. The year 2024 is divisible by 4 and not by 100, so it's a leap year; 1900 is divisible by 100 but not by 400, so it's not.

A common early mistake is judging leap years using only "a multiple of 4." The classic example: 2000 is a leap year because it's divisible by 400, while 1900 is a normal year because it's divisible by 100 but not 400.

In real projects, this leap-year check is essential for accurate day-count calculations when implementing calendar or date-calculation functionality.

📖 Reference code

public class Main {
    static boolean isLeapYear(int year) {
        return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
    }

    public static void main(String[] args) {
        System.out.println(isLeapYear(2024));
        System.out.println(isLeapYear(2023));
        System.out.println(isLeapYear(1900));
    }
}

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