Largest prime factor program takes aaaages - Java

Question

So this is problem 3 from project Euler. For those who don\'t know, I have to find out the largest prime factor of 600851475143. I have the below code:

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Answer 1

The number of prime factors a number can have is always less than sqrt of that number so that there is no need to iterate through the number n to find its largest prime factor.

See this code.

    public class LargestPrimeFactor {
        public static void main(String[] args) {

            Scanner sc=new Scanner(System.in);
            long num=sc.nextLong();

            if(num>0 && num<=2)
            {
                System.out.println("largest prime is:-" + num);
                System.exit(0);
            }

            int i=((Double)Math.sqrt(num)).intValue();
            int j=3;
            int x=0;

            //used for looping through the j value which can also be a prime. for e.g in case of 100 we might get 9 as a divisor. we need to make sure divisor is also a prime number.
            int z=0;
//same function as j but for divisor
            int y=3;
            int max=2;
//divisor is divisible
            boolean flag=false;
//we found prime factors
            boolean found=false;

            while(x<=i)
            {
                y=3;
                flag=false;

                if(num % j ==0)
                {
                    if(j>max)
                    {
                        for(z=0;z