java number factorization

import java.util.ArrayList;
import java.util.Scanner;

public class MainClass {

    static ArrayList<Integer> primes = new ArrayList<Integer>();

    public static void main(String[] args) {
        generatePrimes(50000);

        @SuppressWarnings("resource")
        Scanner input = new Scanner(System.in);

        int num = input.nextInt();

        ArrayList<Integer> factors = factorize(num);

        System.out.print(factors.toString());
    }

    public static ArrayList<Integer> factorize(int num) {

        ArrayList<Integer> factors = new ArrayList<Integer>();

        if (isPrime(num))
            factors.add(num);
        else {
            while (num != 1) {
                for (int prime : primes) {
                    while ((num % prime) == 0) {
                        factors.add(prime);
                        num /= prime;
                        if (num == 1)
                            return factors;
                    }
                }
                generatePrimes(200000);
            }
        }

        return factors;
    }

    private static void generatePrimes(int limit) {
        primes.clear();
        for (int i = 2; primes.size() < limit; i++)
            if (isPrime(i))
                primes.add(i);
    }

    private static boolean isPrime(int n) {
        if (n == 1)
            return false;
        if (n == 2)
            return true;
        if (n % 2 == 0)
            return false;
        for (long i = 3; i * i <= n; i += 2) {
            if (n % i == 0)
                return false;
        }
        return true;
    }

}