Project Euler #3 takes forever in Java

Question

Problem #3 on Project Euler is:

The prime factors of 13195 are 5, 7, 13 and 29.

What is the largest prime factor of the number 60085147514

Answer 1

You could just prime factorize the number and then the largest prime factor would be the answer:

import java.util.ArrayList;
import java.util.Collections;

public class PrimeFactorization {

    /* returns true if parameter n is a prime number, 
         false if composite or neither */
    public static boolean isPrime(long n) {
        if (n < 2) return false;
        else if (n == 2) return true;
        for (int i = 2; i < Math.pow(n, 0.5) + 1; i++)
            if (n % i == 0)
                return false;
        return true;
    }

    /* returns smallest factor of parameter n */
    public static long findSmallestFactor(long n) {
        int factor = 2; // start at lowest possible factor
        while (n % factor != 0) { // go until factor is a factor
            factor++; // test the next factor
        }
        return factor;
    }

    /* reduces the parameter n into a product of only prime numbers
       and returns a list of those prime number factors */
    public static ArrayList primeFactorization(long n) {

        ArrayList primes = new ArrayList();
          // list of prime factors in the prime factorization
        long largestFactor = n / findSmallestFactor(n);    

        long i = 2;
        while (i <= largestFactor) { 
          // for all possible prime factors 
          // (2 - largest factor of the number being reduced)

            if (isPrime(i) && n % i == 0) { 
                // if this value is prime and the number is divisible by it

                primes.add(i); // add that prime factor to the list
                n /= i; // divide out that prime factor from the number 
                        // to start reducing the new number
                largestFactor /= i; // divide out that prime factor 
                       // from the largest factor to get the largest 
                       // factor of the new number
                i = 2; // reset the prime factor test
            } else {
                i++; // increment the factor test
            }
        }

        primes.add(n); // add the last prime number that could not be factored
        Collections.sort(primes);
        return primes;
    }
}

And then call it like this:

ArrayList primes = PrimeFactorization.primeFactorization(600851475143L);
System.out.println(primes.get(primes.size() - 1));

The entire thing takes only a few milliseconds.