Question

Hey Guys编写了一个程序，其中包含一个服务菜单，就像银行卡一样。问题是我使用了一个名为doLogin的方法并使用了一个布尔值，因此如果answer == true将是doServiceMenu，如果它是假的，我希望它继续获取doLogin。

然而，这不起作用，我不确定这是否是我的逻辑，任何反馈将不胜感激

`enter code here`import java.util.Scanner;
class TopUp{

    //class variable
    static Scanner scan = new Scanner (System.in);
    static String name = "Joe";
    static String cardNumber = "1234 5678 9101 1213";
    static double balance = 0;

    public static void main(String[] args){
        boolean isLoginCorrect = false;
         isLoginCorrect =  doLogin();

    if(isLoginCorrect == true){
        doServiceMenu();
    }
    else if(isLoginCorrect == false){
             System.out.println("Incorrect username or password,try again!");
             System.out.println();
             doLogin();
     }
   }

   public static boolean doLogin(){

    String userName = "joe" ;
    String password = "123456";
    String nameInput;
    String pwdInput;



    System.out.println("Please enter your Username: ");
     nameInput = scan.nextLine();

    System.out.println("Please enter your Password: ");
     pwdInput = scan.nextLine();

    return ((userName.equals(nameInput)) && (password.equals(pwdInput)));

   }

   public static void doServiceMenu(){

    System.out.println("<********************* Services Menu ****************>");
    System.out.println("<**************  Please Select an option: ***********>");
    System.out.println("1> Customer Details");
    System.out.println("2> Customer Balance");
    System.out.println("3> Top-up");
    System.out.println("4> Make A Purchase");
    System.out.println("5> Quit");
    System.out.println("");
    System.out.println("<*************************************************>");

      Scanner keyboard = new Scanner(System.in);
        String menuSelect = keyboard.nextLine();

        switch (menuSelect) {

           case "1":
                    showCustomerDetails();
                    checkIfUserWantsAnotherTransaction();
                    break;
           case "2":

                    printBalance();
                    checkIfUserWantsAnotherTransaction();
                    break;
           case "3":
                    doTopUp();
                    checkIfUserWantsAnotherTransaction();
                    break;
           case "4":
                    makePurchase();
                    checkIfUserWantsAnotherTransaction();
                    break;
           case "5":
                    System.out.println("Goodbye!!!");
                    break;
           default:
                   System.err.println ( "Unrecognized option" );
                   break;
           }
        }

    public static void showCustomerDetails(){
        System.out.println("Name: " + name);
        System.out.println("Card Number : " + cardNumber);
    }

    public static void printBalance(){
        System.out.println("Your balance is : " + balance);
    }

    public static void increaseBalance(double amount){
        balance += amount;
    }

    public static void decreaseBalance(double amount){
        balance -= amount;
    }


    public static void doTopUp(){
        System.out.println("Please enter a Top Up Amount: ");
    double amount = scan.nextDouble();
    double maxTopUp = 1000 - balance;

   if(amount > maxTopUp){
       System.out.println("Amount exceedes Max Top Up: ");
   }
   else{
        increaseBalance(amount);
        printBalance();
   }
}

    public static void makePurchase(){
        System.out.println("Please enter the purchase amount: ");
    double amount = scan.nextDouble();
    double purchase = amount - balance;

    if(amount > balance){
       System.out.println("Sorry Insufficent Funds: ");
    }
    else{
         decreaseBalance(amount);
         printBalance();
    }
  }

    public static void checkIfUserWantsAnotherTransaction() {
        System.out.println("Would you Like another Service: y/n");
        Scanner keyboard = new Scanner(System.in);
        String option = keyboard.nextLine();

     if(option.equals("y")){
         doServiceMenu();
     }
     else if(option.equals("n")){
              System.out.println("Goodbye!!!");
      }
   }
}

Answer 1

如果他们第一次登录失败，程序将进入此栏：

else if(isLoginCorrect == false){
         System.out.println("Incorrect username or password,try again!");
         System.out.println();
         doLogin();
}

在该块结束时，程序退出（无论登录是否成功）。你需要在doLogin（）周围引入一个循环，当它最终成功时，调用doServiceMenu()函数。

我会实现这样的事情：

while(doLogin() != true) {
    System.out.println("Incorrect username or password,try again!");
}
doServiceMenu();

Answer 2

如果您遇到编译错误，则下列代码可能无效：

 String menuSelect = keyboard.nextLine();
 switch (menuSelect) { 
     ...
 }

您无法切换字符串值。您只能切换int或Enums。所以你应该首先将你的String转换为int。

就像那样：

int menuSelect = Integer.valueOf(keyboard.nextLine());

    switch (menuSelect) {

       case 1:
            ...

    }

Answer 3

在main：

中尝试使用此功能

boolean isLoginCorrect = false;
int maxAttempt = 5;

for (int loginAttempt = 1; (isLoginCorrect) || (loginAttempt > maxAttempt); loginAttempt++)
{
    isLoginCorrect = doLogin();
    if ((!isLoginCorrect) && (loginAttempt < maxAttempt))
    {
        System.out.println("Incorrect username or password,try again!");
        System.out.println();
    }
}

if(isLoginCorrect == true){
    doServiceMenu();
}

菜单选择和调用方法

3 个答案: