Java文件字符统计代码输出不符，请求排查错误

评分器十分严苛，我花了30分钟排查代码错误却毫无头绪。

我的代码 #

import java.util.Scanner;
import java.io.*;
public class FileLetterCounter
{
    public static void main(String[] args) throws IOException
    {
        Scanner scan = new Scanner(System.in);
    
        System.out.print("Enter file name: ");
        String filename = scan.nextLine();
        File afile = new File(filename);
        Scanner input = new Scanner(afile);
    
        System.out.print("Enter character to count: ");
        char character = input.next().charAt(0);
    
       String line;
       int count = 0;
    
       while (input.hasNext())
        {
            line = input.nextLine();
            for (int a=0;a<line.length();a++)
            {
               if (line.charAt(a)==character) 
               {
                   count++;
               }
            }
        }
         input.close();
         System.out.printf("The character '%c' appears in the file %s %d times.", character, filename, count);
     }

 }

预期输出 #

Enter file name: mydata.txt
Enter character to count: a
The character 'a' appears in the file mydata.txt 17 times.

错误提示 #

Checking output
Your standard output is not what was expected.

问题排查与修复 #

核心错误点 #

• 字符读取源逻辑错误：你用读取文件的input Scanner获取要统计的字符，这会直接从文件开头读取第一个字符，而非读取用户在控制台输入的字符，完全偏离需求逻辑。
• 换行符遗留导致统计遗漏：即便读取逻辑正确，input.next()执行后会遗留换行符，后续input.nextLine()会先读取这个空行，导致文件第一行被跳过，统计结果少了第一行的字符数量。

修正后的代码 #

import java.util.Scanner;
import java.io.*;
public class FileLetterCounter
{
    public static void main(String[] args) throws IOException
    {
        Scanner scan = new Scanner(System.in);
    
        System.out.print("Enter file name: ");
        String filename = scan.nextLine();
        File afile = new File(filename);
        Scanner input = new Scanner(afile);
    
        System.out.print("Enter character to count: ");
        // 改用读取控制台的scan获取目标字符
        char character = scan.next().charAt(0);
    
        String line;
        int count = 0;
    
        // 用hasNextLine更贴合按行读取的逻辑
        while (input.hasNextLine())
        {
            line = input.nextLine();
            for (int a=0;a<line.length();a++)
            {
               if (line.charAt(a)==character) 
               {
                   count++;
               }
            }
        }
        input.close();
        scan.close();
        System.out.printf("The character '%c' appears in the file %s %d times.", character, filename, count);
    }
}

修正说明 #

1. 修正字符读取来源：用scan.next().charAt(0)从控制台获取用户输入的目标字符，确保逻辑符合需求。
2. 优化文件读取判断：用input.hasNextLine()替代input.hasNext()，更适配按行读取文件的场景。
3. 补充资源关闭：添加scan.close()关闭控制台输入的Scanner，避免资源泄漏。

内容的提问来源于stack exchange，提问作者Mot J