Description

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.

Examples

To configure the check:

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

Code Example:

class Example1 {

  int fooBar;
  int guava33_4_5;
  int httpClient;
  int version1_2;

  int Foo;
  // violation above, ''Foo' must start with a lowercase letter'

  int f;
  // violation above, ''f' must start with a lowercase letter, min 2 chars'

  int gradle_9_5_1;
  // violation above, ''gradle_9_5_1' has invalid underscore usage'

  int foo_bar;
  // violation above, ''foo_bar' has invalid underscore usage'
}

Example of Usage

Violation Messages

• google.non.constant.field.name.format
• google.non.constant.field.name.underscore

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