CODEWITHSUNDEEP
javarecursionstack-overflowbiginteger
Nazmul Khan
Nazmul Khan

Reputation: 650

StackOverFlowError with BigInteger in java

Why does this java code throw a StackOverflowError exception?

public class factorial2 {

     public BigInteger fact( BigInteger n)
     {
         BigInteger one = new BigInteger("1");
         if(n.equals("0"))
              return one;
         else
             return n.multiply(fact(n.subtract(one)));      
     }

     public static void main(String[] args) {       
        @SuppressWarnings("resource")
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        factorial2 f = new factorial2();
        for(int i=0;i<n;i++)
        {
           BigInteger b = sc.nextBigInteger();
           System.out.println(f.fact(b));
        }
        sc.close();
    }
}

I have attempted to generate a factorial using BigInteger. But, why does my code give the reference exception on input?

Upvotes: 4

Views: 1276

Answers (2)

Elliott Frisch
Elliott Frisch

Reputation: 201497

The issue is with your base case; n (which is a BigInteger) will not equal "0" (which is a String). So you continue to the else block, which re-curses. Also, BigInteger includes constants for ONE and ZERO so you could write something like

public static BigInteger fact(BigInteger n) {
    if (n.equals(BigInteger.ZERO) || n.equals(BigInteger.ONE))
        return BigInteger.ONE;
    else
        return n.multiply(fact(n.subtract(BigInteger.ONE)));
}

or using a ternary operation (conditional operator ? :) like

public static BigInteger fact(BigInteger n) {
    return (n.equals(BigInteger.ZERO) || n.equals(BigInteger.ONE)) ? BigInteger.ONE 
            : n.multiply(fact(n.subtract(BigInteger.ONE)));
}

Upvotes: 5

AdamSkywalker
AdamSkywalker

Reputation: 11619

BigInteger#equals method

public boolean equals(Object x) {
    // This test is just an optimization, which may or may not help
    if (x == this)
        return true;
    if (!(x instanceof BigInteger))
        return false;

This condition is always false

if (n.equals("0"))

Instead, use

if (BigInteger.ZERO.equals(n))

Upvotes: 2

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