@Override
    public void visitClass(@NotNull PsiClass aClass) {
      // no call to super, so that it doesn't drill down to inner classes
      PsiElement parent = aClass.getParent();
      if (!(parent instanceof PsiJavaFile file)) {
        return;
      }
      int numClasses = 0;
      final PsiElement[] children = file.getChildren();
      for (final PsiElement child : children) {
        if (child instanceof PsiClass) {
          numClasses++;
        }
      }
      if (numClasses <= 1) {
        return;
      }
      registerClassError(aClass);
    }
@Override
    public void visitClass(@NotNull PsiClass aClass)