Java文本文件字母统计程序异常：读取文件名而非内容后崩溃

Let's break down what's going wrong with your code and fix it step by step:

Key Problems in Your Current Code #

• Processing the filename instead of file content: Your inner loop iterates over the filename string instead of the actual text lines you read from the file. That's why you're seeing characters from the filename in your output.
• Closing the file scanner too early: You call fileScan.close() inside the while loop. This closes the scanner after the first line is read, causing a crash when the loop tries to check fileScan.hasNext() again.
• Incorrect counting logic: Your approach to tracking letter counts is flawed—you're overwriting the array with filename characters and using the character itself as the count value, which makes no sense.
• Misplaced output: The header "Letters - Frequencies in file:" is printed inside the loop, so it will repeat for every line in the file instead of appearing once at the start.

Corrected Code #

Here's the fixed version that properly counts letter frequencies from the file content:

/*
* Program that reads in a text file and counts the frequency of each letter
* Displays the frequencies in descending order
*/
import java.util.*; // Needed for Scanner
import java.io.*; // Needed for File related classes

public class LetterCounter {
    public static void main(String args[]) throws IOException{
        Scanner keyboard = new Scanner(System.in); 
        System.out.println("Enter the name of the text file to read:");
        String filename = keyboard.next();
        keyboard.close(); // Close the input scanner after getting the filename

        String alphabet = "abcdefghijklmnopqrstuvwxyz";
        // Initialize an array to track counts: index 0 = 'a', 1 = 'b', ..., 25 = 'z'
        int[] letterCounts = new int[26];

        Scanner fileScan = new Scanner(new File(filename));

        // Loop through each line in the file
        while (fileScan.hasNextLine()) {
            String line = fileScan.nextLine().toLowerCase(); // Convert line to lowercase
            // Iterate over each character in the current line
            for (char c : line.toCharArray()) {
                int index = alphabet.indexOf(c);
                // Only count if the character is a letter (index != -1)
                if (index != -1) {
                    letterCounts[index]++;
                }
            }
        }

        fileScan.close(); // Close the file scanner after processing all lines

        // Print the final results
        System.out.println("Letters - Frequencies in file:");
        for (int i = 0; i < letterCounts.length; i++) {
            char letter = alphabet.charAt(i);
            System.out.printf("Number of Occurrence of %c is: %d%n", letter, letterCounts[i]);
        }
    }
}

What Changed? #

1. Proper count tracking: We use an int[] letterCounts array where each index corresponds to a letter (0 for 'a', 1 for 'b', etc.). Every time we find a letter in the file, we increment the corresponding array position.
2. Processing file content: The inner loop now iterates over each character in the line read from the file, not the filename.
3. Correct scanner closure: fileScan.close() is moved outside the while loop, so we only close the scanner after reading all lines of the file.
4. Single output header: The results header and final count printout are done after processing the entire file, so they only appear once.
5. Letter validation: We check if alphabet.indexOf(c) returns a valid index (not -1) to ensure we only count actual letters, ignoring punctuation, spaces, etc.

Testing this with your sample input Hi, I like to play sports. will give you the expected output, showing counts like i: 3, h:1, a:1, etc.

内容的提问来源于stack exchange，提问作者ThatBoy123