Question

In this bit of code, i am attempting to split a string into Characters and place each character into a map. If the same Character appears more than once I put a counter on it and place it back into the map, incrementing the integer(frequency).

public class FrequencyMap {
   public static Map<Character, Integer> generateMap(String s){
       HashMap<Character, Integer> myMap = new HashMap<Character, Integer>();
       //generate a map of frequencies of the characters in s
       //need to break the string down into individual characters, sort them
       //in there frequencies then place them in map
       for(int i = 0; i < s.length(); i++){
           //break string into characters
           //need to determine how many characters make up the string, can do this by 
           //putting a counter on each letter that appears when the string is being 
           //broken down, if a letter reoccurs increment the counter by one.
           s.substring(i);
           char ch = s.charAt(i);
           myMap.put(ch, i);
           //calculating the occurence of a character in a string.
           if(myMap.containsKey(ch)){                   
               myMap.put(ch, myMap.get(i) + 1);                   
                  }//end of if statement
           }//end of for loop          
           return myMap;
       }//end of public generateMap()
   }//end of FrequencyMap

Here is the main

   public static void main(String args[]){

       String str = "missisippi";

       Map frequencyMap = FrequencyMap.generateMap(str);
       HuffmanTree tree = new HuffmanTree(frequencyMap);
       Map<Character, String> encodingMap = tree.getEncodingMap();

       String encoded = tree.encode(str, encodingMap);
       System.out.println(encoded);     
   }//end of main  

Answer 1

Okay a few things…

Strings are immutable!!

s.substring(i);

should really be

s = s.substring(i);

Although I’m still not quite sure what the point of this is altogether.

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Secondly..

These lines don’t make sense

myMap.put(ch, i);

if(myMap.containsKey(ch)){                   
    myMap.put(ch, myMap.get(i) + 1);                   
}

You just added the key ch and then you immediately ask if the map contains ch – that will always be true.

I think you might have meant to put the if-statement first and to put myMap.put(ch, 1) in an else-clause. Oh, and myMap.get(i) probably should have been myMap.get(ch).