When compiling Kotlin code for the Java Virtual Machine (JVM), a specific target Java version must be specified. This target dictates which Java platform APIs and features are available during compilation and ensures compatibility with the intended runtime environment. An error message indicating an “unknown target” typically arises when the Kotlin compiler encounters a Java version identifier it does not recognize. For instance, a configuration specifying Java 21 might produce this error if the compiler is older than the Java 21 release, or if the required Java Development Kit (JDK) for Java 21 is not installed or correctly configured.
Correctly configuring the Java target version is essential for several reasons. It prevents the accidental use of APIs unavailable on the target JVM, avoiding runtime crashes. It allows developers to leverage the latest features and performance improvements in newer Java versions while maintaining compatibility with older environments if needed. Historically, as Java has evolved, new versions have introduced enhancements and deprecated older features, necessitating this target specification for seamless interoperability between Kotlin and the JVM.
