Why do I get an ArrayIndexOutOfBoundsException in this prime number check?

Question

I was finding out highest prime factor which divides num, as shown in program, there\'s a issue with array and

arr[j] = i;
j++;

Excepti         


        

Answer 1

This line

int arr[] = {j};

Creates an array that only contains the value of j when it is executed. You probably want

int arr[] = new int[j];

UPDATE: Based on the answer you left below, trial division is taking too long. The Sieve of Eratosthenes is a classic algorithm that is pretty efficient, but the Sieve of Atkin is one of the most advanced algorithms for finding primes.