Question

我正在为类分配创建一个登录页面，并且在方法接收用户名和密码然后在多行文本文件中搜索匹配后，在退出while循环时出现问题。它可以找到匹配但返回主方法中的输入区域并再次询问用户名。希望这是有道理的。

任何帮助都将非常感激。正如你所知道的那样，我是Java的新手，因为这个代码到处都是，而且可能有很多错误。我一整夜都想弄明白，但没有运气。谢谢！

package course.registration;
import java.io.FileNotFoundException;
import java.util.Scanner;


public class Welcome {

public static void main(String[] args) throws FileNotFoundException {
    Scanner input = new Scanner(System.in);
    System.out.println("Welcome to the Course Registration System" + "\n");
    System.out.print("Please type Login or Register: ");
    String choice = input.nextLine();

    while (choice.equalsIgnoreCase("Login")){
        System.out.print("Please enter email address to log in: ");
        String email = input.nextLine();
        System.out.print("Please enter password: ");
        String password = input.nextLine();

        //goes to method to search and match inputs
        VerifyLogin verify = new VerifyLogin();
        verify.VerifyInfo(email, password);
        }

    if (choice.equalsIgnoreCase("Register")) {
        System.out.println("Going to registration Page...");
        }
    input.close();
    }
}

以下是搜索文本文件并尝试查找输入匹配项的方法。我觉得问题是当方法退出并返回main方法中的while循环时。我无法找到退出while循环的方法。以下是字符串在“students_logins.txt”文件中的显示方式：

jthomas@gmail.com,1234
kwatson@time.com,3333
legal@prog.com,d567
lavern@shirley.com,34
kwatson@gmail.com,12200

package course.registration;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class VerifyLogin {
    private String tempUsername;
    private String tempPassword;

    public void VerifyInfo(String email, String password) throws FileNotFoundException {
        boolean login = false;
        File file = new File("student_logins.txt");
        Scanner info = new Scanner(file);
        info.useDelimiter("[,\n]");

        while (info.hasNextLine()) {
            tempUsername = info.next();
            tempPassword = info.next();

            if (tempUsername.trim().equals(email.trim()) && (tempPassword.trim().equals(password.trim()))) {
                System.out.println("Email Address or Password Works!!");
                break;
            }
        }

        if (!login) {
            System.out.println("Email Address or Password is Invalid.");
        }
        info.close();
    }

}

Answer 1

在main方法中，你总是停留在while循环中，因为你再也没有获得输入了。

在while循环之前你有：

String choice = input.nextLine();

因此，当您提供登录作为输入，而条件始终为 true 时，您将继续使用此循环。

如果您想要用户提供正确的输入登录/注册，直到他/她提供，您可以尝试使用我的欢迎类的版本：

public class Welcome {

public static void main(String[] args) throws FileNotFoundException {
    Scanner input = new Scanner(System.in);
    System.out.println("Welcome to the Course Registration System" + "\n");
    System.out.print("Please type Login or Register: ");
    String choice = input.nextLine();

    while (!choice.equalsIgnoreCase("Login") && !choice.equalsIgnoreCase("Register")) {
        choice = input.nextLine();
    }

    if(choice.equalsIgnoreCase("Login")){
        System.out.print("Please enter email address to log in: ");
        String email = input.nextLine();
        System.out.print("Please enter password: ");
        String password = input.nextLine();

        //goes to method to search and match inputs
        VerifyLogin verify = new VerifyLogin();
        verify.VerifyInfo(email, password);
    }

    if (choice.equalsIgnoreCase("Register")) {
        System.out.println("Going to registration Page...");
    }
    input.close();
}

}

Answer 2

只需移动条件insede while循环，如果选择的条件是最终的，例如用户输入了有效的登录名和密码，然后使用break退出循环。否则，循环将继续：

public class Welcome {

    public static void main(String... args) throws IOException {
        final LoginValidator loginValidator = new LoginValidator(Welcome.class.getResourceAsStream("student_logins.txt"));

        try (Scanner scan = new Scanner(System.in)) {
            System.out.println("Welcome to the Course Registration System");

            int choice = 0;

            while (choice >= 0) {
                System.out.println();
                System.out.println("1: LoginPlease");
                System.out.println("2: Register");
                System.out.print("Your choice: ");

                choice = scan.nextInt();
                scan.nextLine();

                if (choice == 1) {
                    System.out.print("Please enter email address to log in: ");
                    String email = scan.nextLine();
                    System.out.print("Please enter password: ");
                    String password = scan.nextLine();

                    if (loginValidator.isValid(email, password)) {
                        System.out.println("Email Address or Password Works!!");
                        break;
                    } else
                        System.out.println("Email Address or Password is Invalid.");
                } else if (choice == 2) {
                    System.out.println("Going to registration Page...");
                    break;
                }
            }
        }
    }
}

对于验证，最好在应用程序启动时从文件加载所有登录，然后使用它只需检查Map：

final class LoginValidator {

    private final Map<String, String> map = new HashMap<>();

    public LoginValidator(InputStream in) {
        try (Scanner scan = new Scanner(in)) {
            scan.useDelimiter("[,\n]");

            while (scan.hasNextLine()) {
                map.put(scan.next(), scan.next());
                scan.nextLine();
            }
        }
    }

    public boolean isValid(String email, String password) {
        return map.containsKey(email) && map.get(email).equals(password);
    }
}

在方法迭代字符串文件并找到匹配的输入答案后退出while循环

2 个答案: