無法使用方法agian

Question

我在循環我的程序時遇到問題，因此它會一直持續到用戶退出。

在用戶選擇一個選項後，它會在我放置的時候再次顯示菜單，但它不會再次進入其他方法，它只會再次顯示菜單。我認爲我的問題是，選擇不是「重置」，程序已經認爲用戶有輸入？

在此先感謝您的幫助！ （對不起，我把整個程序放在這裏，我不確定需要什麼，什麼不能解決這個問題）。

/*This program simulates a simple ATM machine. 
User can withdraw and deposit money by entering correct acct number and password.*/ 

import java.util.*; 

public class ATM { 

public static Scanner kbd = new Scanner(System.in); 

public static void main(String[] args) 
{ 
    String acctNum, pwd, verifyID; 
    int choice, attempts=0; 
    double acctBal, depositAmount, withdrawAmount; 

    System.out.println("Enter account number: "); 
    acctNum=kbd.next(); 
    System.out.println("Enter password: "); 
    pwd=kbd.next(); 

    verifyID=checkID(acctNum, pwd); 
    //calls checkID method and returns result to verify 

    while(verifyID.equals("error") && attempts<=3) 
     //checkID returns "error" and the attempts are less than or equal to 3. 
    { 
     attempts++; 
     System.out.println("Entered the incorrect account information please try again.\n"); 
     //verifyID=checkID(acctNum, pwd); 

     if (attempts==4) //If Maximum attempts reached display message, then exit. 
     { 
      System.out.print("Maxium attemps reached. Your session has ended."); 
      System.exit(1); 
     } 
     else 
     { 
      System.out.println("Re-enter password: "); 
      pwd=kbd.next(); 
      //verifyID=checkID(acctNum, pwd); 
     } 
    } 
    acctBal=Double.parseDouble(verifyID); 
    //Changing the string from checkID method to double *(acct balance is returned) 

    choice=menu();//Calls menu() method. 

    switch (choice) 
    { 
    case(1)://user enters balance option. 
     displayBalance(acctBal); //Call method displayBalance. 
    break; 
    case(2)://User enters deposit option. 
     System.out.println("Enter deposit amount: "); 
     depositAmount=kbd.nextDouble(); 
     acctBal=deposit(acctBal,depositAmount);//call method deposit(). 
     System.out.printf("Your new current balance is:$ %.2f\n", acctBal); //Print new acctBal to screen. 
    break;  
    case (3)://User enters withdraw option. 
     System.out.println("Enter amout to withdraw: "); 
     withdrawAmount=kbd.nextDouble(); 
     acctBal=withdraw(acctBal, withdrawAmount);//call method withdraw(). 
     System.out.printf("Your new current balance is:$ %.2f\n", acctBal); //Print new acctBal to screen. 
    break; 
    case(4)://User enters log-out 
     System.out.println("You have been logged out."); 
     System.exit(1); 
    } 

    while (choice==1 || choice==2 ||choice==3) 
    { 
     choice=menu(); 
    }  
} 

public static void displayBalance(double acctBal) 
{  
    System.out.printf("Your current balance is :$ %.2f\n", acctBal); //Displays current balance. 
} 

/*The checkID method determines if acctNum is a valid account number 
and pwd is the correct password for the account. If the account information 
is valid, the method returns the current account balance, as a string. 
If the account information is invalid, the method returns the string "error".*/ 

public static String checkID(String acctNum, String pwd) 
{ 
    String result = "error"; 

    /* Strings a, b, and c contain the valid account numbers and passwords. 
    For each string, the account number is listed first, followed by 
    a space, followed by the password for the account, followed by a space, 
    followed by the current balance.*/ 

    String a = "44567-5 mypassword 520.36"; 
    String b = "1234567-6 anotherpassword 48.20"; 
    String c = "4321-0 betterpassword 96.74"; 

    if(acctNum.equals(a.substring(0, a.indexOf(" "))) && 
      pwd.equals(a.substring(a.indexOf(" ")+1, a.lastIndexOf(" ")))) 
    { 
     result=a.substring(a.lastIndexOf(" ") +1); 
    } 
    else if (acctNum.equals(b.substring(0, b.indexOf(" "))) && 
      pwd.equals(b.substring(b.indexOf(" ")+1, b.lastIndexOf(" ")))) 
    { 
     result=b.substring(b.lastIndexOf(" ") +1); 
    } 
    else if (acctNum.equals(c.substring(0, c.indexOf(" "))) && 
      pwd.equals(c.substring(c.indexOf(" ")+1, c.lastIndexOf(" ")))) 
    { 
     result=c.substring(c.lastIndexOf(" ") +1); 
    } 
    return result; 

    // insert code here to determine if acctNum is a valid account number 
    // and pwd is the correct password for the account. 
} 

public static double deposit(double acctBal, double depositAmount) 
{ 
    return acctBal=acctBal + depositAmount; 
} 
public static double withdraw(double acctBal, double withdrawAmount) 
{ 
    if (acctBal<=withdrawAmount) 
    { 
     System.out.println("Insuffienct funds."); 
     return acctBal; 
    } 
    else 
    { 
     return acctBal-withdrawAmount; 
    } 
} 

public static int menu() 
{ 
    int input=0; 
    while (input>=0 || input<=5) //check side 
     //Checking input from user is between 1-4. 
    { 
     System.out.println("\nMain Menu\n1. Display Balance\n\n2. Deposit\n\n" 
       + "3. Withdraw\n\n4. Log Out\n\n(Please enter 1, 2, 3, or 4):"); 
     input=kbd.nextInt(); 

     if (input<=0 ||input>=5) 
      //If input is not between 1-4 print error. 
     { 
      System.out.println("Invaid input."); 
     } 
     else 
     { 
      return input; //Calls whichever method the user selected. 
     } 
    } 
    return input; //Calls whichever method the user selected. 
} 

}

Answer 1

兩個問題。

（1）你做了一個簡單的錯字。該生產線

while (input>=0 || input<=5) 

應該說

while (input <= 0 || input >= 5) 

，因爲你要在循環繼續運行而input值無效。

（2）該部分

while (choice==1 || choice==2 ||choice==3) 
{ 
    choice=menu(); 
} 

是完全錯誤的，因爲你會在收集輸入，而不是作用於它的一個循環結束了。你需要把你的大switch/case聲明放在這個循環中，而不是在外面。