IllegalIdentifierName

Since Checkstyle 8.36

Description

Checks identifiers against a regular expression pattern to detect illegal names. Since this check uses a pattern to define valid identifiers, users will need to use negative lookaheads to explicitly ban certain names (e.g., "var") or patterns (e.g., any identifier containing $) while still allowing all other valid identifiers.

Properties

name	description	type	default value	since
format	Sets the pattern to match valid identifiers.	Pattern	`^(?!var$\|\S*\$)\S+$`	8.36
tokens	tokens to check	subset of tokens CLASS_DEF , INTERFACE_DEF , ENUM_DEF , ANNOTATION_DEF , ANNOTATION_FIELD_DEF , PARAMETER_DEF , VARIABLE_DEF , METHOD_DEF , ENUM_CONSTANT_DEF , PATTERN_VARIABLE_DEF , RECORD_DEF , RECORD_COMPONENT_DEF , LAMBDA .	CLASS_DEF , INTERFACE_DEF , ENUM_DEF , ANNOTATION_DEF , ANNOTATION_FIELD_DEF , PARAMETER_DEF , VARIABLE_DEF , METHOD_DEF , ENUM_CONSTANT_DEF , PATTERN_VARIABLE_DEF , RECORD_DEF , RECORD_COMPONENT_DEF , LAMBDA .	8.36

Examples

To configure the check:

Configuration:


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

Example:


public class Example1 {
  Integer var = 4; // violation, 'Name 'var' must match pattern'
  int record = 15;
  String yield = "yield";

  String test$stuff = "test"; // violation, 'must match pattern'
  String when = "today";
  record Record(Record r){}

  record R(Record record){}

  String yieldString = "yieldString";

  record MyRecord(){}

  Integer variable = 2;

  int open = 4;
  Object transitive = "transitive";

  int openInt = 4;

  Object transitiveObject = "transitiveObject";

}

To configure the check to include some of JLS Keywords in the set of illegal identifiers (See Java Language Specification for the full list of JLS keywords):

Configuration:


<module name="Checker">
  <module name="TreeWalker">
    <module name="IllegalIdentifierName">
      <property name="format"
        value="(?i)^(?!(when|record|yield|var|permits|sealed|open|transitive|_)$|(.*\$)).+$"/>
    </module>
  </module>
</module>

Example:


public class Example2 {
  Integer var = 4; // violation, 'Name 'var' must match pattern'
  int record = 15; // violation, 'Name 'record' must match pattern'
  String yield = "yield";
  // violation above, 'Name 'yield' must match pattern'
  String test$stuff = "test"; // violation, 'must match pattern'
  String when = "today"; // violation, 'Name 'when' must match pattern'
  record Record(Record r){} // violation, 'Name 'Record' must match pattern'

  record R(Record record){} // violation, 'Name 'record' must match pattern'

  String yieldString = "yieldString";
  // ok above, word 'yield' is not used as an identifier by itself
  record MyRecord(){}
  // ok above, word 'Record' is not used as an identifier by itself
  Integer variable = 2;
  // ok above, word 'var' is not used as an identifier by itself
  int open = 4; // violation, 'Name 'open' must match pattern'
  Object transitive = "transitive";
  // violation above, 'Name 'transitive' must match pattern'
  int openInt = 4;
  // ok above, word 'open' is not used as an identifier by itself
  Object transitiveObject = "transitiveObject";
  // ok above, word 'transitive' is not used as an identifier by itself
}

Example of Usage

Checkstyle Style

Violation Messages

name.invalidPattern

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