[Java] (JDK24 in my case) use of underscore variable triggers checkstyle LambdaParameterName

[patpatpat123]

Hello team,

I am using JDK 24, and since a couple of last Java versions, we can use the underscore sign to substitute a variable that will not be used, what Java called an unnamed variable.

https://medium.com/@benweidig/looking-at-java-22-unnamed-variables-patterns-f9de0b1e2750

For instance:

final boolean someboolean = Optional.ofNullable(getMap()).map(_ -> getHeaders()) [...]

While this is perfectly fine and compiles, checkstyle will flag:

LambdaParameterName

<plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-checkstyle-plugin</artifactId>
                <version>3.6.0</version>
                <configuration>
                    <outputDirectory>target/reports/checkstyle</outputDirectory>
                    <configLocation>google_checks.xml</configLocation>
                    <outputFileFormat>xml</outputFileFormat>
                </configuration>
            </plugin>

Could you please help take into account the new java underscore unnamed variable?

Thank you very much and good day.

[ryleighmikami]

Hey Google, same issue there. Could you help?

[romani]

Issue should be reported without any reference to checkstyle. @patpatpat123 , @ryleighmikami , please report it properly

[cushon]

We are planning to update the style guide to allow this, the intent is not to discourage unnamed variables or patterns.

[eamonnmcmanus]

We can certainly update the style guide to make this clearer, but I don't think anything in it right now precludes the use of unnamed variables or patterns. Technically, _ is not an identifier so it is not covered by the rules about identifier naming. We don't currently have anything at all to say about patterns, unnamed or otherwise.