Scope for declaration in java

Question

public class PerfectNumber {
        public static boolean isPerfectNumber(int num)
        {
            int sum;//sum initialization
            for(int i=1;i<num;i++)
            {
                if(num%i==0)
                    sum+=i;//Here it is showing the error that sum might not have been initialized
            }
        }
}

Answer 1

int sum;//sum initialization

wrong, this is just a declaration

try

int sum = 0;//sum initialization