Question

I have enough knowledge on creating Synchronized static objects.
However for a Map (Collection) in Java,

I found default implementations in Java individually (one for Synchronized list and one for for Singleton map).

http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Collections.html#synchronizedMap(java.util.Map)
http://docs.oracle.com/javase/1.5.0/docs/api/java/util/Collections.html#singletonMap(K, V)

I am thinking of getting the desired result by following implementation

Map<K,V> initMap = new HashMap<K,V>(); 
Map<K,V> syncSingMap = Collections.synchronizedMap(Collection.singletonMap(initMap));

Am i making right sense? Because documentation at oracle shows some warning on this

It is imperative that the user manually synchronize on the returned map when iterating over any of its collection views:

 Map m = Collections.synchronizedMap(new HashMap());
  ...
 Set s = m.keySet();  // Needn't be in synchronized block
  ...
 synchronized(m) {  // Synchronizing on m, not s!
  Iterator i = s.iterator(); // Must be in synchronized block
  while (i.hasNext())
      foo(i.next());
 }

 Failure to follow this advice may result in non-deterministic behavior

How about using ConcurrentMap over this.

Requriement: static synchronized singleton map which will be used by tons of threads for some processing operations

UPDATE

After going through few articles, found that ConcurrentMap is much preferable than HashMap in multi-thread environment
http://java.dzone.com/articles/java-7-hashmap-vs

Answer 1

Use ConcurrentMap if you are using Java 6+:

public class MapHolder {
    public static final ConcurrentMap<String, Object> A_MAP = new ConcurrentHashMap<String, Object>();
}