java - 检查是否存在 .txt 文件。 FileWriter.exists 方法不起作用

Question

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我正在编写一个需要输入用户名和密码的程序。如果用户在创建用户名和密码时输入的用户名已经存在，我将尝试检查用户是否存在文件。

.exists 方法不起作用，我无法弄清楚。错误找不到符号回来了。我已经改变了一些东西，移动了一些东西并将其归结为一个错误。尝试使用循环和 if 语句，但使用 if 只会导致一个错误。任何帮助都会很棒。

import java.util.Scanner;
import java.io.*;

class UserData 
{
  public static void main ( String[] args ) throws IOException
  {
  Scanner kb = new Scanner(System.in);

  System.out.println("Do you have an account? Yes or No: ");
  String answer = kb.next().trim();

  if ((answer.startsWith("N")) || (answer.startsWith("n")))
  {

System.out.println("Create user name: ");
String user = kb.next().trim();

String fileName = user + ".txt";
FileWriter userData = new FileWriter(fileName);

 if (userData.exists())
 {
   System.out.println("User already exists");
   System.out.println("Create user name: ");
   user = kb.next().trim();

   fileName = user + ".txt";
   userData = new FileWriter(fileName);
 }

System.out.println("Create Password: ");
String ps = kb.next().trim();

userData.write(user + " ");
userData.write(ps);
userData.close();


  }

  else if ((answer.startsWith("Y")) || (answer.startsWith("y")))
  {
System.out.println("Enter user name: ");
String user = kb.next().trim();

System.out.println("Enter Password: ");
String ps = kb.next().trim();

String fileName = user + ".txt";
Scanner inFile = new Scanner(new File(fileName));

String userName = inFile.next();
String password = inFile.next();

//     If ((userName != user) || (password != ps))
//     {
//       System.out.println("User Not Found");
//       System.out.println("Enter user name: ");
//       String user = kb.next().trim();
// 
//       System.out.println("Enter Password: ");
//       String ps = kb.next().trim();
//  
//       String fileName = user + ".txt";
//       Scanner inFile = new Scanner(new File(fileName));
//  
//       String userName = inFile.next();
//       String password = inFile.next();
//     }
//     else
//     {
   System.out.println("User Found");
//     }
}





}}

Answer 1

你这里有编译错误:

FileWriter userData = new FileWriter(fileName);
if (userData.exists())

将其更改为:

File userDataFile = new File(fileName);
if (userDataFile.exists())

当然还有:

FileWriter userData = new FileWriter(userDataFile);
userData.write(user + " ");
userData.write(ps);
userData.close();

如果文件根本不存在，您可能正在查找错误的目录。尝试添加这个:

System.out.println(new File(fileName).getAbsolutePath());

并自行检查文件在打印路径上是否可用。