import java.util.regex.Pattern;
import java.util.HashMap;

class test {

    private static Pattern p = Pattern.compile(" ");
    private static HashMap<String, Integer> results = new HashMap<String, Integer>();    

    private static int test(String str) {
        int res = 0;
        
        if(results.keySet().contains(str)) {
            res = results.get(str);
        } else {
            res = p.split(str, 0).length;
            results.put(str, res);
        }
        
        return res;
    }

    public static void main(String[] args) {
        long start = System.currentTimeMillis();

        int res = 0;
        for(int i = 0;i < 1000000;i++) {
            res += test("123 345 asdf 23453 asdfas");
        }
        System.out.println(res);

        long end = System.currentTimeMillis();
        System.out.println(end - start);
    }
}

Celeron 2.5, 1Gb, WinXP Pro

java -server test

5000000
125