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 PRIVATE_STATIC_FINAL = 1;
static int staticField;
private static int privateStatic;
interface ExampleInterface {
int CONSTANT = 1;
String Invalid_Name = "test";
}
@interface ExampleAnnotation {
int DEFAULT = 0;
String Bad_Name = "test";
}
final int bad = 0;
final int Bad = 0;
// violation above, 'Non-constant field name 'Bad' must start lowercase'
public final int httpClient = 0;
public final int mValue = 0;
// violation above, 'avoid single lowercase letter followed by uppercase'
private final int foo = 0;
private final int f = 0; // violation, 'be at least 2 chars'
protected final int fooBar1_1 = 0;
protected final int foo_bar = 0;
// violation above, 'underscores allowed only between adjacent digits'
int loginFails;
int fA; // violation, 'avoid single lowercase letter followed by uppercase'
int fooBar2;
int foo$bar; // violation, 'contain only letters, digits or underscores'
int version1_2_3;
int gradle_9_5_1; // violation, 'underscores allowed only between adjacent digits'
int count99;
int _foo; // violation, 'underscores allowed only between adjacent digits'
}
Example of Usage
Violation Messages
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