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ShutDownHook - the last breath of an application

ShutDownHook allows you to perform operations (e.g. close opened resources, remove temporary files and so on) just before virtual machine shuts down. A documentation says that JVM may shut down in two cases:
  • program finishes execution normally when all threads finishes their work (except deamon-threads like garbage collector)
  • virtual machine receives a termination signal (for example after sending kill signal under unix or ctrl + C key combination under windows)
Below is an example which will start endless loop which do nothing. But an important thing in this code is a part where shutDownHook is added. When an termination signal will be send to JVM a code from a run() method will be executed just before JVM shuts down.
public class ShutDownHook {
 public static void main(String[] args) {

  Runtime.getRuntime().addShutdownHook(new Thread() {
   public void run() {
    System.out.println("Close opened resources");
   }
  });

  while (true) {
   // do nothing
  }
 }

}
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