Simple Java program to calculate double factorial (n!!) of given non-negative integer.

import java.util.Scanner;

// 2018 TheFlyingKeyboard and released under MIT License
public class Main {
    public static void main(String[] args) {
        Scanner reader = new Scanner(;
        int n;

        System.out.println("Enter a number: ");
        n = reader.nextInt(); //Reads integer from keyboard

        System.out.println("Double Factorial of: " + n + " is equal to: " + doubleFactorial(n));

    private static int doubleFactorial(int n){
        int doubleFact = 1;

        for(int i = n; i > 1; i -= 2){
            doubleFact *= i;

        return doubleFact;


Java DoubleFactorial n!!
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