Help is needed writing a simple JAVA class to check to see if a year is a leap year

Question

A student wrote to me asking for help writing a JAVA program to calculate leap year. The assignment specified that the year must be evenly divisible by 4, but not 100. However, years divisible by 400 were also considered leap years. The assignment said the calculation must call a method that has only one if statement.

Answer 1

There are a few different ways to approach this. A simple, console/terminal-based approach that meets the assignment requirements might look like the following (explanatory comments are in the code):

/*

LEAP YEAR CHECKER

Years divisible by 4 are leap years, except those divisible by 100.

Years divisible by 400 are also leap years. The assignment requires

the use of only ONE if statement in a single isLeapYear method.

There are more "elegant" ways to do this, but this approach was chosen

so as to be clear to beginning programmers.

SHM+

*/

import java.util.Scanner; // Required to read input from the keyboard.

class Main {

public static void main(String[] args) {

int theYear; // Need to place this here since the do/while loop checks for it.

do {

// Get the keyboard input

Scanner kb = new Scanner(System.in);

System.out.print("\nEnter the year to check (enter 0 to exit): ");

// Coerce input to INT to avoid user-breakage.

String y = kb.next();

try {

theYear = Integer.parseInt(y); // Could also use valueOf(y) here.

} catch (NumberFormatException e) {

// If there is a parsing problem, just set theYear to 0.

theYear = 0;

}

if (theYear > 0) {

System.out.print(theYear + " is ");

if (!isLeapYear(theYear)) {

System.out.print("NOT ");

}

System.out.println("a leap year.");

}

}

// Repeat the loop until the user enters 0

while (theYear != 0);

}

// A static method can be called without any instance/object.

// This method returns a boolean value.

private static boolean isLeapYear(int x) {

boolean returnValue = false;

// x is a leap year if it is divisible by 4 AND

// (not(divisible by 100) OR divisible by 400)

if (x % 4 == 0 && (!(x % 100 == 0) || x % 400 == 0)) {

returnValue = true;

}

return returnValue;

}

}