public <K, V> Map<K, V> unmodifiable(Map<K, V> input)
    {
        if (input == null) {
            return null;
        }
        return Collections.unmodifiableMap(input);
    }
public < K , V > Map < K , V > unmodifiable ( Map < K , V > input ) { if ( input == null ) { return null ; } return Collections . unmodifiableMap ( input ) ; }
Returns an unmodifiable view of the specified map.

@param <K> the type of keys maintained by this map
@param <V> the type of mapped values
@param input the map to wrap in an unmodifiable bridge
@return an unmodifiable view of the map