##########################################	The MapReduce module includes the MapReduce interface.#	When submiting a mapreduce job, the user should implement this interface and upload it to DFS.#	map() collect a pair of (key , value) into collector.#	reduce() collect pairs of (key , value) which have the same key into collector.#	filt() filt the input FileBlock and change it into list of (key , value).#	if the mapreduce job is combinable (It means that the value meets the commutative law and associative law),#	combine() will combine pairs of (key , value) which have the same key into (key , value).#	keySpaceSize() return the hash size of hashKey();#	hashKey() return the hash number of the key. The result of mapper tasks will be divided into blocks according to the hash key,#	they are sent to different reducer tasks.#	#	@author Yang Fan(fyabc)#########################################  MapReduce : module{	init : fn(); 	map : fn(key : string , value : string , collector : ref IOUtil->OutputCollector); 	reduce : fn(key : string , values : list of string , collector : ref IOUtil->OutputCollector); 	filt : fn(line : string) : list of (string , string); 	combine : fn(key : string, values : list of string) : (string, string); 	keySpaceSize : fn() : int; 	hashKey : fn(key : string) : int;};