(Occurrences of each letter) Write a program that prompts the user to enter a file name and displays the occurrences of each letter in the file. Letters are case-insensitive

/*********************************************************************************
* (Occurrences of each letter) Write a program that prompts the user to enter a  *
* file name and displays the occurrences of each letter in the file. Letters are *
* case-insensitive.                                                              *
*********************************************************************************/
import java.util.*;
import java.io.*;

public class Exercise_12_30 {
	/** Main method */
	public static void main(String[] args) throws FileNotFoundException {
		// Create a File object from user input
		File file = new File(getFileName());
		
		// Check if file exists
		if (!file.exists()) {
			System.out.println("File " + file.getName() + " does not exist");
			System.exit(0);
		}


		int[] count = new int[26]; // Counts each letter
		try (
			// Create input file
			Scanner input = new Scanner(file);
		) {
			// Read file
			while (input.hasNext()) {
				String line = (input.nextLine()).toUpperCase();
				countLetters(count, line);
			}
		}

		// Display results
		for (int i = 0; i < count.length; i++) {
			System.out.println("Number of " + (char)('A' + i) + "\'s: " + count[i]);
		}
	}

	/** Counts the occurrences of each letter in a string */
	public static void countLetters(int[] count, String str) {
		for (int i = 0; i < str.length(); i++) {
			if (Character.isLetter(str.charAt(i)))
				count[(int)(str.charAt(i) - 'A')]++;
		}
	}

	/** Prompts the user to enter a filename 
	  * and returns it as a string */
	public static String getFileName() {
		Scanner input = new Scanner(System.in);

		System.out.print("Enter a filename: ");
		return input.next();
	}
}