How to check if a number is even

Short answer

A number is even if the remainder of dividing it by 2 is zero:

void main() {
    int number = 14;
    IO.println(number % 2 == 0);
}

Output:

true

A method

Move the check into a method and apply it to several numbers:

boolean isEven(int n) {
    return n % 2 == 0;
}
 
void main() {
    for (int n : new int[] {3, 8, 0, -4}) {
        IO.println(n + " " + (isEven(n) ? "even" : "odd"));
    }
}

Output:

3 odd
8 even
0 even
-4 even

Filtering even numbers

In a stream the check becomes a filter() condition:

void main() {
    var evens = IntStream.rangeClosed(1, 10).filter(n -> n % 2 == 0).boxed().toList();
    IO.println(evens);
}

Output:

[2, 4, 6, 8, 10]

Common mistake

Checking for odd numbers with n % 2 == 1. For negative numbers the remainder is negative, and the check fails:

void main() {
    int n = -3;
 
    IO.println(n % 2);
    IO.println(n % 2 == 1);
    IO.println(n % 2 != 0);
}

Output:

-1
false
true

Write n % 2 != 0 or Math.floorMod(n, 2) == 1.

Thanks for reading!

Short answer

A method

Filtering even numbers

Common mistake

Functions used in this recipe

Thanks for reading!