Fast Hashmap doubt .

[suhas]

I was going through put ( ) and putAll ( ) methods in Fast HashMap code in the struts . But did not get why we need to clone the HashMap and add a entry to that cloned map then move that cloned map to original HashMap . In multi- threaded enviornment anyway we synchronized the code that accesses the HashMap in the put method .. ?       public Object put(Object key, Object value) {           if (fast) {             synchronized (this) {                                            // IF U synchronize the code like this then easily only one thread can manipulate the HashMap                 HashMap temp = (HashMap) map.clone();        // What this do then ?                 Object result = temp.put(key, value);                //                 map = temp;                                                   //                 return (result);             }         } else {             synchronized (map) {                 return (map.put(key, value));             }         }       }