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There is a javaLauncher property on a task: https://docs.gradle.org/current/dsl/org.gradle.api.plugins.quality.Checkstyle.html#org.gradle.api.plugins.quality.Checkstyle:javaLauncher Something like this should do the trick:

// Groovy
tasks.withType(Checkstyle).configureEach {
    javaLauncher = javaToolchains.launcherFor {
        languageVersion = JavaLanguageVersion.of(11)
    }
}

// Kotlin
tasks.withType<Checkstyle>().configureEach {
    javaLauncher.set(javaToolchains.launcherFor {
        languageVersion.set(JavaLanguageVersion.of(11))
    })
}

Edit: Changed javaCompiler with javaLauncher

Ah thanks! I only checked the javadoc of the checkstyle extension 🤦‍♂️