ExposedPrivateType
Private member classes should not be referenced in signatures of non-private members.

The problem

Classes referenced in signatures of non-private APIs should usually also be non-private.

For example, consider:

class Foo {
  private record Person(String name) {}

  public static void printMessage(Person person) {
    System.out.printf("hello %s\n", person.name());
  }
}

Because Person is private, clients outside the current compilation unit will be unable to create an instance of it to pass to printMessage.

Prefer to make classes referenced in APIs at least as visible as the API, or else if the API is only intended to be used in the current compilation unit it should also be private.

That is, prefer:

class Foo {
  public record Person(String name) {}

  public static void printMessage(Person person) {
    System.out.printf("hello %s\n", person.name());
  }
}

or:

class Foo {
  private record Person(String name) {}

  private static void printMessage(Person person) {
    System.out.printf("hello %s\n", person.name());
  }
}

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("ExposedPrivateType") to the enclosing element.