CODEWITHSUNDEEP
javaexceptionstack-overflow
user6232985
user6232985

Reputation:

My thrown exception running into StackOverflowError

I have the following simple recursive Fibonacci code:

public class FibPrac5202016
{
public static void main(String [] args)  {
    Scanner input = new Scanner(System.in);
    System.out.println("Enter index number: ");
    int integer = input.nextInt();
  FibPrac5202016 object = new FibPrac5202016();

System.out.println(object.operation(integer));
}

public static long operation(long n) {
 if(n==0)
     return 0;
 if(n==1)
     return 1;
 try {
     if( n < 0)
     throw new Exception("Positive Number Required");

 }
 catch(Exception exc)
 {
     System.out.println("Error: " + exc.getMessage());

 }

 return operation((n-1))+operation((n-2));
}

}

As I recently learned about exceptions, I'm trying to use that here when the user inputs negative integer.However, my program runs into StackOverflowError.

Upvotes: 1

Views: 46

Answers (2)

Juan_H
Juan_H

Reputation: 387

the problem is that these throws a execcion within a try block and this creates a cycle in which is testing the code and as always will be a smaller number than 0 always threw the exception infinitely until the exception is given

Exception in thread "main" java.lang.StackOverflowError

I think the solution is to make the program a stop when you find a number less than 0

as follows

public class FibPrac5202016 {
public static void main(String [] args)  {
    Scanner input = new Scanner(System.in);
    System.out.println("Enter index number: ");
    int integer = input.nextInt();
    FibPrac5202016 object = new FibPrac5202016();

        System.out.println(object.operation(integer));
 }

 public static long operation(long n) {
  if(n==0)
    return 0;
  if(n==1)
    return 1;
  try 
{
    if( n < 0)            
        throw new Exception("Positive Number Required");   
}
catch(Exception exc)
{
    System.out.println("Error: " + exc.getMessage());
    //return -1;
}

return operation((n-1))+operation((n-2));
}

}

Upvotes: 0

Elliott Frisch
Elliott Frisch

Reputation: 201439

Well yes, because you recurse after you catch an Exception. You could trivially fix it by returning -1 in the catch. 

catch(Exception exc)
{
    System.out.println("Error: " + exc.getMessage());
    return -1;
}

or not throwing an Exception in the first place like

public static long operation(long n) {
   if (n < 0) { 
       return -1;
   } else if (n == 0) {
       return 0;
   } else if (n == 1 || n == 2) {
       return 1;
   }
   return operation((n-1))+operation((n-2));
}

or you could implement the Negafibonaccis. And, you could extend it to support BigInteger (and optimize with memoization) like

private static Map<Long, BigInteger> memo = new HashMap<>();
static {
    memo.put(0L, BigInteger.ZERO);
    memo.put(1L, BigInteger.ONE);
    memo.put(2L, BigInteger.ONE);
}

public static BigInteger operation(long n) {
    if (memo.containsKey(n)) {
        return memo.get(n);
    }
    final long m = Math.abs(n);
    BigInteger ret = n < 0 //
            ? BigInteger.valueOf(m % 2 == 0 ? -1 : 1).multiply(operation(m))
            : operation((n - 2)).add(operation((n - 1)));
    memo.put(n, ret);
    return ret;
}

Upvotes: 1

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