[tim]

Hello gapper

Here's a spoiler:

Code:

public class Prime{
	protected Vector<Integer> getFactors(int integer){
		Vector<Integer> result = new Vector<Integer>();
		for (int i = 1; i <= integer; i++)
			if (integer % i == 0) result.add(new Integer(i));
		return result;
	}
	public Prime(int bound){
		System.out.println("Prime numbers up to " + bound + ":");
		for (int i = 2; i <= bound; i++){
			if (getFactors(i).size() == 2) System.out.println(i);
		}
	}
}

Use the constructor to run it

Code:

new Prime(20);

gives Output

Code:

Prime numbers up to 20:
2
3
5
7
11
13
17
19

This is a classical assignment. I could not resist.