LetterCountBolt.java

a storm bolt that takes a letter as an input and outputs a letter with a count of the number of times a letter has been seen previously. 
the class LetterCountBolt is extending an abstract class BaseBasicBolt whose execute method is overridden. the method execute(); is using an argument of Interface Tuple . The interface Tuple is  the main data structure.it has helper methods i.e. getStringByField(String field)
another method declareOutputFields(); is also overridden.