Determine whether a string is composed by its substring

.java

public static boolean composedBySubString(String s) {
    if (s == null || s.length() < 2) {
      return false;
    }
    int step = 1;
    while (step <= (s.length() / 2)) {
      if (s.length() % step == 0) {
        String subString = s.substring(0, step);
        int start = step;
        boolean found = true;
        while (start + step < s.length()) {
          if (!s.substring(start, step).equals(subString)) {
            found = false;
            break;
          }
          start += step;
        }
        if (found) {
          return true;
        }
      }
      step += 1;
    }
    return false;
  }