Factorial using Recursion in Java

Question

I am learning Java using the book Java: The Complete Reference. Currently I am working on the topic Recursion.

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Answer 1

public class Factorial {

    public static void main(String[] args) {
        System.out.println(factorial(4));
    }

    private static long factorial(int i) {

        if(i<0)  throw new IllegalArgumentException("x must be >= 0"); 
        return i==0||i==1? 1:i*factorial(i-1);
    }
}