IdentityHashMap Implementation

/**

 * IdentifyHashMap  - 

 *   - Implements Map Interface with a hash table using reference-equality instead of object-equality when comparing keys.

 *    Eg:  if ( k1 == k2 ) unlike HashMap equality if( K1 == null ? k2 ==null : k1.equals(k2)).

 *   - It's not a general purpose implementation and designed to use only in rare cases where reference-equality semantics are required

 *   - Use cases like topology-preserving object graph, deep-copying, adding application shutdown hook.

 *   - This Map is not synchronized.  To synchronize use Collections SynchronizedMap

 *       Map identifyHashMap = Collections.synchronizedMap( new IdentifyHashMap(..)) ; 

 *

 */

import java.util.Collection;

import java.util.IdentityHashMap;

public class ApplicationDaemons

{

    private static IdentityHashMap<Thread, Thread> applicationdaemons = new IdentityHashMap<>();

    public synchronized void runDaemonsInSeperateThread() {

        new Runnable()

        {

            public void run()

            {

                runDaemons() ;

            }

        } ;    

    }

    private ApplicationDaemons() {}

    static synchronized void add(Thread hook) {

        if(applicationdaemons != null)

            applicationdaemons.put(hook, hook);

    }

    static synchronized boolean remove(Thread hook) {

        return applicationdaemons.remove(hook) != null;

    }

    static void runDaemons() {

        Collection<Thread> threads;

        synchronized(ApplicationDaemons.class) {

            threads = applicationdaemons.keySet();

            applicationdaemons = null;

        }

        for (Thread hook : threads) {

            hook.start();

        }

        for (Thread hook : threads) {

            try {

                hook.join();

            } catch (InterruptedException x) { }

        }

    }

}