发布于 2016-07-14 04:47:49 | 223 次阅读 | 评论: 0 | 来源: 网友投递
Java程序设计语言
java 是一种可以撰写跨平台应用软件的面向对象的程序设计语言,是由Sun Microsystems公司于1995年5月推出的Java程序设计语言和Java平台(即JavaEE(j2ee), JavaME(j2me), JavaSE(j2se))的总称。
package john2;
/**
* 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.");
}
}