How to Check Even or Odd Number in Java

The Challenge

Determine if a number is even or odd - a fundamental programming task!

Solution

Using Modulus Operator (%)

java

public class Main {
    public static void main(String[] args) {
        int number = 7;
        
        if (number % 2 == 0) {
            System.out.println(number + " is even");
        } else {
            System.out.println(number + " is odd");
        }
    }
}
// Output: 7 is odd

Using Ternary Operator

java

int number = 10;
String result = (number % 2 == 0) ? "even" : "odd";
System.out.println(number + " is " + result);
// Output: 10 is even

Using Bitwise AND

java

int number = 15;
if ((number & 1) == 0) {
    System.out.println(number + " is even");
} else {
    System.out.println(number + " is odd");
}
// Output: 15 is odd

How It Works

The modulus operator % returns the remainder of division. Even numbers are divisible by 2 with no remainder (remainder = 0), while odd numbers have a remainder of 1.

10 % 2 = 0 Even
7 % 2 = 1 Odd

Did You Know?

The bitwise AND method (number & 1) is faster than modulus because it directly checks the least significant bit. If it's 0, the number is even; if it's 1, the number is odd!

Pro Tip

For readability, stick with the modulus operator %. For performance-critical code, use bitwise AND &.

Real-World Use Cases

Pagination: Alternate row colors in tables
Scheduling: Determine alternating shifts
Games: Determine player turns
Data validation: Check if input meets criteria

›Short versionOpen if you only have a minute.

An int is even when n % 2 == 0. Zero is even.
In Java the remainder takes the sign of the dividend, so a negative odd value yields -1, not 1.
Test odd with n % 2 != 0. The check n % 2 == 1 misses every negative odd int.
Parity is a property of integers. Do not ask it of a double.

Even or odd

Determine whether an integer is divisible by 2.

Working approach

Use n % 2 == 0 for the even test.
Return a boolean from a method such as isEven so callers do not reimplement the sign rule.
Parse input outside the test. The test itself is one expression.

Walk the sample

Input 7
7 % 2 leaves 1
The remainder is not 0, so 7 is odd

The trap

n % 2 == 1 is the check that fails for negatives. -3 % 2 is -1 in Java, so the number is odd and the condition is still false.

java

static boolean isEven(int n) {
    return n % 2 == 0;
}

static boolean isOdd(int n) {
    return n % 2 != 0;   // not == 1; negatives leave a remainder of -1
}

Is -4 even, and what does -3 % 2 produce?

-4 % 2 is 0, so -4 is even. Zero is even for the same reason.

-3 % 2 is -1. A test written as == 1 classifies every negative odd integer as even.

Time O(1), space O(1).

Easy to get wrong

Writing n % 2 == 1 and then feeding it a negative odd value.
Using a floating-point value in a parity test.