Question

import java.math.BigInteger;
import java.util.HashMap;

/**
 *
 * @author cypronmaya
 */
public class test {
    static HashMap<Integer, BigInteger> cache = new HashMap<Integer, BigInteger>();
    public static void main(String[] args) {
     System.out.println(factorial(20000));
  }

    public static BigInteger factorial(int n) {
        BigInteger ret;
        if (n == 0) {
            return BigInteger.ONE;
        }
        if (null != (ret = cache.get(n))) {
            return ret;
        }
        ret = BigInteger.valueOf(n).multiply(factorial(n - 1));
        cache.put(n, ret);
        return ret;
    }
}

Exception in thread “main” java.lang.StackOverflowError at
java.util.HashMap.get(Unknown Source)

Hi,
Why am i getting stackoverflow exception to this program?

i know that stackoverflow usually means you have an infinite loop,
but this works fine when i’m using 10000 or some other numbers lesser, wht becomes suddenly infinite with big numbers?

Answer 1

A StackOverflowError occurs when the call stack overflows. This happens when you have too many nested calls (because each call requires space to be reserved on the stack, and it’s a finite size). I guess in your case, 20000 is too many.

You can modify the stack size of the JVM with the -Xss flag. But I’d suggest that you find a different way to compute a factorial.