public boolean removeShutdownHook(Thread hook){
  if (hook == null) {
    throw new NullPointerException("hook == null");
  }
  if (shuttingDown) {
    throw new IllegalStateException("VM already shutting down");
  }
synchronized (shutdownHooks) {
    return shutdownHooks.remove(hook);
  }
}

public boolean removeShutdownHook ( Thread hook ) { if ( hook == null ) { throw new NullPointerException ( "hook == null" ) ; } if ( shuttingDown ) { throw new IllegalStateException ( "VM already shutting down" ) ; } synchronized ( shutdownHooks ) { return shutdownHooks . remove ( hook ) ; } }
unregisters a previously registered vm shutdown hook .
