Array of ArrayLists in java

Question

I'm trying to make an array of ArrayLists of Strings in java because I need a list of words for every letter of alphabet. I'm doing in in this way:

ArrayList<String>[] letters = new ArrayList[32];

But I'm getting a NullPointerException when I try to add something to my list.

while ((line = bufferedReader.readLine()) != null) {
 letter = (int)line.charAt(0) - 1040;
 if (letters[letter] == null) {
 letters[letter] = new ArrayList<>();
 }
 letters[letter].add(line);
}

I also tried to create it like that

ArrayList<String>[] leters = (ArrayList<String>[])new ArrayList[32];

But it didn't changed the situation. Please help me to solve my problem.

• Andreas: Which line throws the exception? My guess would be the if statement because leters is null, and not the array. Please read this: How to create a Minimal, Complete, and Verifiable example.
• Andreas: Also, why 25? There are 26 letters in the base alphabet. Many languages have more than that.
• Andreas: Unable to reproduce: IDEONE. As you may also notice, letter Z is missing since you only have 25 letters.
• Andreas: That's impossible with the code you showed.
• Andreas: So you're using the cyrillic alphabet, but only the first 25? АБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШ

Answer 1

I would use a hash map:

HashMap<Character, ArrayList<String>> letters = new HashMap<Character, ArrayList<String>>();

Then you can add words by doing:

ArrayList<String> words = new ArrayList<String>();
words.add(word);
letters.put("A", words);