GoogleNonConstantFieldName
Since Checkstyle 13.3.0
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. 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;
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 myValue = 0;
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 foo = 0;
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 fooBar = 0;
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 fieldA;
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."""
int xmlParser;
int xml$parser;
// violation above """Non-constant field name 'xml\$parser' 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 gradle9_5_1;
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 foo2;
int _foo2;
// violation above """Non-constant field name '_foo2' 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 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.
Fully Qualified Name
com.puppycrawl.tools.checkstyle.checks.naming.GoogleNonConstantFieldNameCheck
Use this fully qualified class name in configuration when an exact class reference is required.