Finding prime numbers with the Sieve of Eratosthenes (Originally: Is there a better way to prepare this array?)

Question

Note: Version 2, below, uses the Sieve of Eratosthenes. There are several answers that helped with what I originally asked. I have chosen the Sieve of Era

Answer 1

As Paul Tomblin points out, there are better algorithms.

But keeping with what you have, and assuming an object per result is too big:

You are only ever appending to the array. So, use a relatively small int[] array. When it's full use append it to a List and create a replacement. At the end copy it into a correctly sized array.

Alternatively, guess the size of the int[] array. If it is too small, replace by an int[] with a size a fraction larger than the current array size. The performance overhead of this will remain proportional to the size. (This was discussed briefly in a recent stackoverflow podcast.)