Java shutdown hook

Question

I have added the following code to my program:

Runtime.getRuntime().addShutdownHook(new Thread(new Runnable() {
    @Override
    public void run() {
        System.out.println("exit");
    }
}){});

I however do not see the message. Additional information: I am running the program from inside the Netbeans IDE on Java 7.

EDIT: I forgot to add that there is a global Thread that keeps the program alive. I close it by pressing the [x] in Netbeans lower right corner.

Answer 1

The JVM can shutdown in either an orderly or abrupt manner. A shutdown hook runs for an orderly shutdown: when the last normal thread terminates, someone calls System.exit or by other platform specific means (such as typing Ctrl-C).

Shutdown hooks will not run for an abrupt shutdown of the JVM. As you are pressing the [x] in Netbeans lower right corner, this will cause an abrupt shutdown of the JVM and this is why the shutdown hook was not started.

For example :

public class ShutdownHook {
public void attachShutDownHook() {
    Runtime.getRuntime().addShutdownHook(new Thread() {
        @Override
        public void run() {
            System.out.println("exit");
        }
    });

}

public static void main(String[] args) {
    ShutdownHook sample = new ShutdownHook();
    sample.attachShutDownHook();
    try {
        Thread.sleep(3000);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

}

If you run the above code, and let the program complete normally, you will see exit printed on the console. But if you press [x] (within 3 secs) to close it abruptly, the shutdown hook will not run and there will not be any exit printed on the console.

Answer 2

I forgot to add that there is a global Thread that keeps the program alive. I close it by pressing the [x] in Netbeans lower right corner.

Well this is it, closing program by "x" in netbeans lower right corner is not regular shut down, it just breaks everything and shut it down.

ShutdownHook works only when the program regulary exits...