[b]package john2; [/b]  /**  * test shutdown hook  * All rights released and correctness not guaranteed.  */ public class ShutdownHook implements Runnable {     public ShutdownHook() {         // register a shutdown hook for this class.         // a shutdown hook is an initialzed but not started thread, which will get up and run         // when the JVM is about to exit. this is used for short clean up tasks.         Runtime.getRuntime().addShutdownHook(new Thread(this));         System.out.println(">>> shutdown hook registered");     }     // this method will be executed of course, since it's a Runnable.     // tasks should not be light and short, accessing database is alright though.     public void run() {         System.out.println("/n>>> About to execute: " + ShutdownHook.class.getName() + ".run() to clean up before JVM exits.");         this.cleanUp();         System.out.println(">>> Finished execution: " + ShutdownHook.class.getName() + ".run()");     }         // (-: a very simple task to execute     private void cleanUp() {         for(int i=0; i < 7; i++) {             System.out.println(i);         }     }     /**      * there're couple of cases that JVM will exit, according to the Java api doc.      * typically:      * 1. method called: System.exit(int)      * 2. ctrl-C pressed on the console.      * 3. the last non-daemon thread exits.      * 4. user logoff or system shutdown.      * @param args      */     public static void main(String[] args) {         new ShutdownHook();         System.out.println(">>> Sleeping for 5 seconds, try ctrl-C now if you like.");         try {             Thread.sleep(5000);     // (-: give u the time to try ctrl-C         } catch (InterruptedException ie) {             ie.printStackTrace();         }         System.out.println(">>> Slept for 10 seconds and the main thread exited.");     } }