Question

I am getting the below error:

Exception in thread “main” java.lang.NullPointerException at
HashMap.CountLetters.tallyPrint(CountLetters.java:12) at
HashMap.CountLetters.main(CountLetters.java:21)

The goal is to get store the occurrences of each letter in a HashMap. The key is the letter and the value is the # of occurrences.

package HashMap;

import java.util.HashMap;

public class CountLetters {
    public HashMap tallyPrint(String phrase) {
        int count = 0;
        HashMap<String, Integer> fav = new HashMap<String, Integer>();
        for (int i = 0; i<phrase.length(); i++)
        {
            if (fav.containsKey(phrase.substring(i,i+1)))
                fav.put("" + phrase.substring(i,i+1), fav.get(phrase)+1);
            else
                fav.put("" + phrase.substring(i,i+1),1);
        }
        return fav;
    }

    public static void main(String[] args) {
        CountLetters x = new CountLetters();
        System.out.println(x.tallyPrint("my feet smell and my nose runs"));
    }
}

Answer 1

Replace
fav.put("" + phrase.substring(i,i+1), fav.get(phrase)+1);

with:

fav.put("" + phrase.substring(i,i+1), fav.get(phrase.substring(i,i+1))+1);

Side note1: You should extract that substring and store it in a temp variable to be more efficient so you don’t keep calling substring over and over for the same substring.

Side note2: Thanks for posting the whole (with the main method) in your question. It’s make it simpler if all the askers did it like this.