Update BookTopology.java

BookTopology  has TopologyBuilder, which has setBolt functions with different number of arguments to create new bolts in the topology. To create a new Bolt, we can use a function from the TopologyBuilder class and pass another class instance as an argument to the setBolt function i.e. setBolt(String id, IBasicBolt bolt, Number parallelism_hint) 
          Define a new bolt in this topology.
two new bolts to split words into letters and count the number of times the letter is seen are as follows;
builder.setBolt("letterSplitter", new LetterSplitBolt(), 2).shuffleGrouping("word");
builder.setBolt("letterCount", new LetterCountBolt(), 2).shuffleGrouping("letterSplitter");

To add more bolts, i have created more classes extending  abstract class BaseBasicBolt i.e.
public class LetterSplitBolt extends BaseBasicBolt
public class LetterCountBolt extends BaseBasicBolt 

both of these classes are extending an abstract class called BaseBasicBolt, which has two different functions inherited from IBasicBolt and IComponent respectively i.e. execture() and declareOutputField(); both of these are going to be overridden in Class LetterSplitBolt and Class LetterCountBolt.