使用while（）循环检查元素的.txt文件

Question

I'm writing a program that asks a user to log in and checks if their ID is inside a file "Employees.txt" and if it is then it will print out VALID __ ID if they're a Manager or an Assistant. But when I enter an invalid ID, say "x" in and then try again, it loops forever, not checking if the ID is valid. How can I fix this issue? I have Employees.txt in the same directory as Account.java and

E12,Manager
E13,Assistant

is what's inside the file. Any help would be appreciated as I've tried everything I could. Thanks.

import java.io.*;
import java.util.*;
public class Account
{
    public static String  accountInput;
    public static boolean inSystem      = true;
    public static boolean displayLogIn  = true;
    public static boolean managerLogIn  = false;
    public static Scanner userInput     = new Scanner(System.in);
    public static File stockFile        = new File("Stock.txt");
    public static File employeesFile    = new File("Employees.txt");
    public static File transactionsFile = new File("Transactions.txt");
    public static void main(String[] args) throws IOException
    {
        String[] contents;
        System.out.println("\tWorking Files");
        System.out.println("-------------------------------------------");
        System.out.println("Stock File:\t\tStock.txt\nEmployee File:\t\tEmployees.txt\nTransactions File:\tTransactions.txt\n\n");
        Scanner readEmployeesFile = new Scanner(employeesFile);
        while(inSystem)
        {
            while(displayLogIn)
            {
                System.out.print("Enter Employee ID(i.e E1)\tEnter Q to Quit Program.\nEnter here: ");
                accountInput = userInput.nextLine();

                while(readEmployeesFile.hasNextLine())
                {
                    contents = readEmployeesFile.nextLine().split(",");
                    if(contents[0].equals(accountInput) & contents[1].equals("Manager"))
                    {
                        displayLogIn = false;
                        System.out.print("Valid MGR ID");
                        inSystem     = false;
                    }
                    else if(contents[0].equals(accountInput) & contents[1].equals("Assistant"))
                    {
                        displayLogIn = false;
                        System.out.print("Valid AST ID");
                        inSystem     = false;
                    }
                    else if(accountInput.equals("Q"))
                    {
                        displayLogIn = false;
                        inSystem     = false;
                    }
                }
            }
        }
    }
}

Answer 1

When you enter an ID, you start looping on your file to see if that ID matches.

You reach the end of the file. readEmployeesFile.hasNextLine() is false. So you iterate again, read the next ID.

But the readEmployeesFile is still at the end of the file. There is nothing that takes it back to the beginning. So when it gets to the while again, readEmployeesFile.hasNextLine() is still false.

Possible solutions:

• Open the scanner, readEmployeesFile , not at the beginning of the method, but right before you use it. Then close it right after you reach the end of the file. So you will be opening and closing it every time the user enters an ID.
• Read all the IDs from the file into a Map before you start prompting the user, and then look for the ID in that map instead of directly in the file. This would be more efficient.

Answer 2

The problem is that you open the Scanner inside the loop, forcing it to read all the contents of the file on the first iteration. This means that the condition in while(readEmployeesFile.hasNextLine()) will always evaluate to false after the first iteration and the loop will never be entered again. For this reason only the first trial may be valid, afterwards your loop cannot terminate.

Here is adjusted code that worked for me:

import java.io.*;
import java.util.*;
public class Account
{
    public static String  accountInput;
    public static boolean inSystem      = true;
    public static boolean displayLogIn  = true;
    public static Scanner userInput     = new Scanner(System.in);
    public static File employeesFile    = new File("Employees.txt");
    public static void main(String[] args) throws IOException
    {
        List<String[]> contents = new ArrayList<>();
        System.out.println("\tWorking Files");
        System.out.println("-------------------------------------------");
        System.out.println("Stock File:\t\tStock.txt\nEmployee File:\t\tEmployees.txt\nTransactions File:\tTransactions.txt\n\n");
        Scanner readEmployeesFile = new Scanner(employeesFile);
        while(readEmployeesFile.hasNextLine()) {
            String[] current = readEmployeesFile.nextLine().split(",");
            contents.add(current);
        }
        while(inSystem)
        {
            while(displayLogIn)
            {
                System.out.print("Enter Employee ID(i.e E1)\tEnter Q to Quit Program.\nEnter here: ");
                accountInput = userInput.nextLine();

                for(String[] content: contents) {
                    if (content[0].equals(accountInput) & content[1].equals("Manager")) {
                        displayLogIn = false;
                        System.out.print("Valid MGR ID");
                        inSystem = false;
                    } else if (content[0].equals(accountInput) & content[1].equals("Assistant")) {
                        displayLogIn = false;
                        System.out.print("Valid AST ID");
                        inSystem = false;
                    } else if (accountInput.equals("Q")) {
                        displayLogIn = false;
                        inSystem = false;
                    }
                }
            }
        }
        readEmployeesFile.close();
    }
}

As you can see, the input file is read a single time before entering the loop and stores all the lines in contents which is now of type List<String[]> . In the for loop you simply need to check the contents of the file that have already been read.

On a side note, you should always close the resources that you are using. In this case I refer to the Scanner object and this is why I included the line readEmployeesFile.close(); after your loop.

Answer 3

Change

contents[0].equals(accountInput) & contents[1].equals("Manager")
contents[0].equals(accountInput) & contents[1].equals("Assistant")

to

contents[0].equals(accountInput) && contents[1].equals("Manager")
contents[0].equals(accountInput) && contents[1].equals("Assistant")

The AND operator is represented with a double ampersand (&&), not one.