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 Factorial2 {
    public static long factorial(long x) {
        if (x < 0) 
            throw new IllegalArgumentException("x must be >= 0");
        if (x <= 1) 
            return 1;  // Stop recursing here
        else 
           return x * factorial(x-1);  // Recurse by calling ourselves
    }
}