equals is not [java task - solution]

public class PlayTime {

    public static void main(String[] args) {

        String string = "isnotis xxnotx isnononot";
        System.out.println(equalsIsNot(string));
    }

    static boolean equalsIsNot(String string) {

        int nIs = countOccurences(string, "is");
        int nNot = countOccurences(string, "not");

        return nIs == nNot;
    }

    //helper method...
    static int countOccurences(String str, String sub) {

        int count = 0, len = sub.length();

        for (int i = 0; i <= (str.length() - len); i++) {
            String it = str.substring(i, i + len);
            if (it.equals(sub)) {
                count++;
            }
        }
        return count;
    }
}