打印文件中字母的水平直方图。如何扩展？Java

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

public class HorizontalHistogram {
    public static void main(String[] args) {
        String filePath = "path/to/your/file.txt";
        Map<Character, Integer> letterFrequency = new HashMap<>();

        try (BufferedReader reader = new BufferedReader(new FileReader(filePath))) {
            int c;
            while ((c = reader.read()) != -1) {
                char character = (char) c;
                if (Character.isLetter(character)) {
                    character = Character.toLowerCase(character);
                    letterFrequency.put(character, letterFrequency.getOrDefault(character, 0) + 1);
                }
            }
        } catch (IOException e) {
            e.printStackTrace();
        }

        int maxFrequency = 0;
        for (int frequency : letterFrequency.values()) {
            if (frequency > maxFrequency) {
                maxFrequency = frequency;
            }
        }

        for (char letter = 'a'; letter <= 'z'; letter++) {
            int frequency = letterFrequency.getOrDefault(letter, 0);
            int histogramHeight = (int) Math.ceil((double) frequency / maxFrequency * 10); // 10 is the desired height of the histogram

            System.out.print(letter + ": ");
            for (int i = 0; i < histogramHeight; i++) {
                System.out.print("*");
            }
            System.out.println();
        }
    }
}