GoogleNonConstantFieldName

Since Checkstyle 13.3.0

Description

Checks that non-constant field names conform to the Google Java Style Guide for non-constant field naming.

This check enforces Google's specific non-constant field naming requirements:

Non-constant field names must start with a lowercase letter and use uppercase letters for word boundaries.
Underscores may be used to separate adjacent numbers (e.g., version numbers like guava33_4_5), but NOT between letters and digits.

Static fields are skipped because Checkstyle cannot determine type immutability to distinguish constants from non-constants. Fields in interfaces and annotations are also skipped because they are implicitly public static final (constants)

Examples

Example with violations:


<module name="Checker">
  <module name="TreeWalker">
    <module name="GoogleNonConstantFieldName"/>
  </module>
</module>

Code Example:


class Example1 {

  static final int STATIC_FINAL = 0;
  private static final int Invalid_Name = 1;

  static int staticField;
  private static int Static_Bad;

  interface ExampleInterface {
    int CONSTANT = 1;
    String Invalid_Name = "test";
  }

  @interface ExampleAnnotation {
    int DEFAULT = 0;
    String Bad_Name = "test";
  }

  final int Bad = 0;
  // violation above, 'Non-constant field name 'Bad' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  public final int mValue = 0;
  // violation above, 'Non-constant field name 'mValue' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  private final int f = 0;
  // violation above, 'Non-constant field name 'f' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  protected final int foo_bar = 0;
  // violation above, 'Non-constant field name 'foo_bar' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  int fA;
  // violation above, 'Non-constant field name 'fA' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  public int mField;
  // violation above, 'Non-constant field name 'mField' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  private int foo$bar;
  // violation above, 'Non-constant field name 'foo\$bar' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  protected int a;
  // violation above, 'Non-constant field name 'a' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  int gradle_9_5_1;
  // violation above, 'Non-constant field name 'gradle_9_5_1' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'

  int _foo;
  // violation above, 'Non-constant field name '_foo' must start lowercase, be at least 2 chars, avoid single lowercase letter followed by uppercase, contain only letters, digits or underscores, with underscores allowed only between adjacent digits.'
}

Example with valid names:


<module name="Checker">
  <module name="TreeWalker">
    <module name="GoogleNonConstantFieldName"/>
  </module>
</module>

Code Example:


class Example2 {

  static final int STATIC_FINAL = 0;
  private static final int PRIVATE_STATIC_FINAL = 1;

  static int staticField;
  private static int privateStatic;

  interface ExampleInterface {
    int CONSTANT = 1;
    String VALID_NAME = "test";
  }

  @interface ExampleAnnotation {
    int DEFAULT = 0;
    String GOOD_NAME = "test";
  }

  final int foo = 0;
  public final int httpClient = 0;
  private final int version123 = 0;
  protected final int guava33_4_5 = 0;

  int bar;
  public int xmlParser;
  private int count99;
  protected int release22_1_0;

  int id;
  int version1_2;
}

Example of Usage

Violation Messages

google.non.constant.field.name.format

All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.

Package

com.puppycrawl.tools.checkstyle.checks.naming

Parent Module

TreeWalker