> ## Documentation Index
> Fetch the complete documentation index at: https://mehen.ophi.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# NPA — Number of Public Attributes

> Number of public attributes declared on classes and interfaces.

**NPA** (Number of Public Attributes) counts public fields/properties exposed by classes and interfaces
in a file. A high NPA usually signals weak encapsulation — internal state leaking outside the type.

## What mehen emits

| Key                        | Type  | Description                                            |
| -------------------------- | ----- | ------------------------------------------------------ |
| `npa`                      | int   | Total public attributes across classes and interfaces. |
| `npa.classes`              | int   | NPA contributed by classes.                            |
| `npa.interfaces`           | int   | NPA contributed by interfaces.                         |
| `npa.class_attributes`     | int   | Same as `npa.classes` (alias).                         |
| `npa.interface_attributes` | int   | Same as `npa.interfaces` (alias).                      |
| `npa.classes_average`      | float | Mean attributes per class.                             |
| `npa.interfaces_average`   | float | Mean attributes per interface.                         |
| `npa.total_attributes`     | int   | Total NPA in the file (alias of `npa`).                |
| `npa.average`              | float | Mean attributes per declaration (class or interface).  |

## What counts as "public"

The exact rule is language-specific:

| Language        | Public attribute is…                                                                       |
| --------------- | ------------------------------------------------------------------------------------------ |
| Java / Kotlin   | A field declared `public` (or with no modifier in Kotlin classes).                         |
| TypeScript / JS | A class field without `private` / `protected` / `#` prefix.                                |
| Python          | A class attribute that does not start with `_`.                                            |
| Ruby            | An `attr_accessor` / `attr_reader` / `attr_writer` declaration (Ruby fields are private by |
| default).       |                                                                                            |
| C#              | A field with `public` access modifier (mehen support is partial — see analyzer notes).     |

## How to read it

A "few" public attributes is usually fine. Many can mean:

* Data classes / records: `NPA = number of fields` is expected and benign.
* Property bags or "god objects": NPA grows past 10 — refactor candidate.

Read NPA alongside [NPM](/metrics/code/npm). A class with NPA much greater than NPM is a struct in
disguise; a class with NPM much greater than NPA is encapsulating state behind methods.

## References

* Lorenz, M. & Kidd, J. (1994). *Object-Oriented Software Metrics: A Practical Guide.* Prentice Hall.
* Chidamber, S. R. & Kemerer, C. F. (1994). *A Metrics Suite for Object Oriented Design.* IEEE TSE
  20(6): 476–493. [DOI](https://doi.org/10.1109/32.295895).
* Briand, L. C., Daly, J. W. & Wüst, J. K. (1998). *A Unified Framework for Coupling Measurement in
  Object-Oriented Systems.* IEEE TSE 25(1): 91–121.
  [DOI](https://doi.org/10.1109/32.748920).

## See also

* [NPM](/metrics/code/npm) — number of public methods.
* [NOM](/metrics/code/nom) — number of methods (public + private).