Problem 27 java solution

Problem specification: ProjectEuler.net Problem 27

Considering quadratics of the form:

    n^2 + an + b, where |a| < 1000 and |b| < 1000

    where |n| is the modulus/absolute value of n
    e.g. |11| = 11 and |-4| = 4

Find the product of the coefficients, a and b, for the quadratic expression that produces the maximum number of primes for consecutive values of n, starting with n = 0.

Execution time: 390ms (laptop)

CODE
package projecteuler;

import java.util.ArrayList;

/**
* Project euler problem 27 java solution
* @author Mike
*/
public class Problem_27 {

   private int aa;
   private int bb;
   private int[] primes;
   private int num;
  
   public static void main(String[] args){
     new Problem_27();
   }
  
   public Problem_27(){
     long start = System.currentTimeMillis();
     aa = 0;
     bb = 0;
     num = 0;
     primes = new int[100000];
     for(int i = 2; i < 99999; i++){
        primes[i] = i;
     }
     for(int i = 2; i < 50000; i++){
        if(primes[i] != 0){
           for(int j = 2 * i; j < 50000; j+=i){
             primes[j] = 0;
           }
        }
     }      
    
     // now we have our thingy...
    
     boolean cont = true;
        for(int a = -1000; a <= 1000; a++){
           for(int b = -1000; b <= 1000 && cont; b++){
             for(int n = 0; n < 600 && cont; n++){
                double res = Math.pow(n, 2) + (a * n) + b;
                int result = (int) res;
                if(result > 0){
                   if(primes[result] == 0){
                     cont = false;
                   } else {
                     if(n > num){
                        num = n;
                        aa= a;
                        bb = b;
                     }
                   }
                } else {
                   cont = false;
                }
             }
             cont = true;
           }
             cont = true;
        }
     System.out.println("b = " + bb + " a = " + aa + " with total " + num);
     long end = System.currentTimeMillis();
     System.out.println(end - start + " ms");
        
   }
  
}

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