Question

我为身份验证类型的系统拼凑了一些循环，因此有些挣扎。我正在尝试获取代码以重新提示用户如果不输入'q'则退出，它将显示消息，表明他们仍在登录，但又返回到主循环并要求再次输入用户名。我在玩continue和break，但到目前为止，它不会重复内部的If语句。任何指导将不胜感激。

    package zooauthfinal;


import java.util.Scanner;
import java.io.File;
import java.security.MessageDigest;


public class ZooAuthFinal {

    public static void main (String[] args) throws Exception {

        //Creates new scanner for user input
        Scanner scan = new Scanner(System.in);

        //variable to attempts to track login attempts
        int attempts = 0;

        //While loop to start collecting user credentials for login
        while(true) {
            System.out.print("Enter username: ");
            String user = scan.nextLine(); //reads user input and assigns to variable "user"

            System.out.print("Enter password: ");
            String original = scan.nextLine(); //reads user input and assigns to variable "original" for original password

            //MD5 conversion script
            MessageDigest md = MessageDigest.getInstance("MD5");
            md.update(original.getBytes());

            byte[] digest = md.digest();

            StringBuffer sb = new StringBuffer();

            for (byte b : digest) {

                sb.append(String.format("%02x", b & 0xff));
            }

                //System.out.println("original:" + original); //Used to check and compare password conversion - shows original user input
        //System.out.println("digested:" + sb.toString()); //Used to check and compare password conversion - shows MD5 conversion of original user input

            //assigns boolean value to variable "done"
            boolean done=false;

            //new scanner to read "credentials.txt" file to authenticate user
            Scanner file = new Scanner (new File("credentials.txt"));

            //While loop to split text file into columns
            while(file.hasNextLine ()) {

                String record = file.nextLine();
                String columns[] = record.split("\t");

                //If statement to match value to username
                if(columns[0].trim().equals(user)) {

    if(columns[1].trim().equals(sb.toString())) {

                             done=true;

                             Scanner sc = new Scanner (new File(columns[3].trim() +".txt"));

                             while(sc.hasNextLine()) {

        System.out.println(sc.nextLine());
                          }

                          break;

                    }
                }
            }

            //If statment to start logout procedure, starts when user has been authenticated and user role message has been delivered based on user role
            if(done) {
                //Instructs user to logout with value 'q'

                System.out.println("Type 'q' to logout: ");

                String ch = scan.nextLine();

                if(ch.toLowerCase().charAt(0) != 'q') {

                    System.out.println("You are still logged in as " + user +".");


                }


                //Assigns user input to lowercase value and checks if matches required 'q'
                else {


                    System.out.println("Successfully logged out. Have a nice day!");


                }

            }



            }
            //If/else to track number of login attempts (limit 3) and adds 1 to each unsuccessful attempt until 3 attempts, then displays exit protocol   
            else {

                attempts ++;

                if(attempts==3) {

                    System.out.println("Could not verify credentials. Goodbye.\n");

                    break;

                }
                //displays login error message on each unsucessful attempt until the third unsuccessful attempt    
                else {

                    System.out.println("Invalid username or password, please try again.");
                }


                }
            }
        }

Answer 1

在if（done）块的最后一行添加break语句。

Answer 2

if(!ch.toLowerCase().equals("q"))

继续特定的循环（内部还是外部）？

2 个答案: