java - 如何根据 HashMap 的键和值检查两个输入？

Question

这个问题已经有答案了:

Scanner is skipping nextLine() after using next() or nextFoo()? (25 个回答)

已关闭 6 年前。

我刚刚学习 HashMap，并且刚刚使用它们编写了我的第一个程序。由于某种原因，我检查输入的输入是否与键匹配及其相应的值总是返回 false。谁能告诉我这是为什么？

import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashMap;
import java.util.Scanner;

public class Exercise {
    public static void main(String[] args) throws FileNotFoundException {
        HashMap<String, String> userPass = new HashMap<String,String>();
        HashMap<String, String> userFull = new HashMap<String, String>();
        Scanner keyboard = new Scanner(System.in);
        System.out.print("Enter the filename to read from: ");
        String filename = keyboard.nextLine();

        File file = new File(filename);
        Scanner inputFile = new Scanner(file);

        while (inputFile.hasNext()){
            String fullname=inputFile.next()+" "+inputFile.next();
            String username=inputFile.next();
            String pass=inputFile.nextLine();
            userPass.put(username, pass);
            userFull.put(username, fullname);
        }

        inputFile.close();

        //initialize variable for use after loop
        String inputUsr = null;
        //checks if key/value is found
        boolean b=false;
        int tries=1;
        while(b==false){
            System.out.print("Login: ");
            inputUsr=keyboard.next();
            System.out.print("\nPassword: ");
            String inputPass=keyboard.next();
            //if inputted password equals the password of the inputted username
            if(inputPass.equals(userPass.get(inputUsr)))
                b=true;
            System.out.println("Either the username or password is incorrect. You have "+(3-tries)+" more attempts.");
            tries++;
            //program quits afte 3 tries
            if(tries>3){
                System.exit(0);
            }
        }
        System.out.println("Welcome "+userFull.get(inputUsr));
    }
}

Answer 1

while 循环内的代码存在两个问题，如下所述:

(1) keyboard.next() 正在读取控制台输出文本，即读取打印文本“密码”，因此将 keyboard.next() 替换为 keyboard.nextLine();

(2) 您没有处理 tries 计数的 else 条件

您可以引用以下带内嵌注释的代码:

while(b==false){
       System.out.print("Login: ");
       inputUsr=keyboard.nextLine();
       System.out.print("\nPassword: ");
       String inputPass=keyboard.nextLine();
       if(inputPass.equals(userPass.get(inputUsr))) {
           b=true;
       } else { 
          System.out.println("Either the username
            or password is incorrect. 
                      You have "+(3-tries)+" more attempts.");
                    tries++;
        }
        if(tries>3){
            System.exit(0);
        }
}