Huffman code algorithm implementation

Main.java

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        // create a new file
        File file = new File("testFile.txt");
        // handel the checked exception "FileNotFoundException"
        try {
            // A scanner to get file content Text I/O
            Scanner in = new Scanner(file);
            // string builder is preferable than 
            // appending a string whereas a string creates
            // a new instance each time we append
            StringBuilder builder = new StringBuilder();
            // while we haven't reached the end of the stream
            while (in.hasNext()) {
                // append the line read from file
                builder.append(in.nextLine());
            }
            // obtain file content as an array of characters
            char[] charContent = builder.toString().toCharArray();
            ArrayList<Character> charactersList = new ArrayList<>();
            ArrayList<Integer> weightsList = new ArrayList<>();
            // to lists to store both distinct character and their weights
            int index;
            for (int i = 0; i < charContent.length; i++) {
                if ((index = charactersList.indexOf(charContent[i])) >= 0) {
                    // the character exists in the list
                    // increment its weight
                    weightsList.set(index, weightsList.get(index) + 1);
                } else {
                    // character doesn't exist in the list
                    // add it
                    // and assign weight 1 
                    charactersList.add(charContent[i]);
                    weightsList.add(1);
                }
            }
            char[] characters = new char[charactersList.size()];
            int[] weights = new int[weightsList.size()];

            for (int i = 0; i < charactersList.size(); i++) {
                characters[i] = charactersList.get(i);
                weights[i] = weightsList.get(i);
                // obtain a fixed size array from the two array lists
            }
            // start the huffman generatir
            HuffmanCodeGenerator generator = new HuffmanCodeGenerator(characters, weights);
            generator.printResult(charContent);
        } catch (FileNotFoundException ex) {
            System.out.println("File not found");
        }

    }
}