Okay, but that doesn't answer the question. You could still have the following:

public class NullabilityCheck {
  public static Set<NonTerminal> getReachableNullableNT(NonTerminal starrtNt) {
    NullabilityCheck check = new NullabilityCheck();
    return check.checkNullability(startNt);
  }

  private NullabilityCheck() {
  }
}