Exit in Groovy

Here’s an idiomatic Groovy example demonstrating the concept of exiting a program:

// Exit.groovy

// Import necessary classes
import groovy.transform.CompileStatic

@CompileStatic
class Exit {
    static void main(String[] args) {
        // This closure will not be executed due to System.exit()
        def goodbye = { println "Goodbye!" }
        Runtime.runtime.addShutdownHook(new Thread(goodbye))

        println "Starting the program"

        // Exit with status code 3
        System.exit(3)

        // This line will never be reached
        println "This won't be printed"
    }
}

This Groovy script demonstrates how to exit a program with a specific status code. Let’s break it down:

1. We use the @CompileStatic annotation to enable static compilation, which can improve performance.

2. We define a main method, which is the entry point of our Groovy script.

3. We create a closure goodbye that prints “Goodbye!” and add it as a shutdown hook. Shutdown hooks are normally executed when the JVM is shutting down, but they won’t be executed when using System.exit().

4. We print a message to indicate the start of the program.

5. We use System.exit(3) to immediately terminate the program with a status code of 3. This is equivalent to the os.Exit(3) in the original Go example.

6. The last println statement will never be executed because the program exits before reaching it.

To run this Groovy script:

1. Save the code in a file named Exit.groovy.
2. Open a terminal and navigate to the directory containing the file.
3. Run the script using the groovy command:

$ groovy Exit.groovy
Starting the program

To compile the Groovy script into a Java class and run it:

$ groovyc Exit.groovy
$ java -cp .:$GROOVY_HOME/lib/groovy-3.0.9.jar Exit
Starting the program

To check the exit status in Unix-like systems:

$ groovy Exit.groovy
Starting the program
$ echo $?
3

Note that the “Goodbye!” message is never printed because System.exit() bypasses the normal shutdown process, including shutdown hooks.

In Groovy, like in Java, the main method doesn’t return an integer to indicate the exit status. Instead, you need to use System.exit() to set a non-zero exit status explicitly. This is similar to the behavior in the original Go example.

This example demonstrates how to exit a Groovy program with a specific status code and shows that code after the exit call is not executed, mirroring the behavior of the original Go example.