java - 超出范围的字符串索引和使用输入数据的总计

Question

我需要一些关于下面代码的帮助。我尝试循环程序，直到用户选择“N”，然后我想显示以盎司为单位销售的柠檬水总计以及各种 cookies 和衬衫的总计。

我放入了一个 while 循环来循环程序，但出现错误:

线程“main”中的异常 java.lang.StringIndexOutOfBoundsException:字符串索引超出范围:0 在 java.lang.String.charAt(未知来源) 在 edu.kirkland5.SnackStand.main(SnackStand.java:43)

如果有人可以帮助我完成这两件事，我将不胜感激。谢谢!

public static void main(String[] args) 
{
    Scanner input = new Scanner(System.in);

    String userName = "";
    int lemonaid = 0;
    double OZ12_PRICE = 1.50;
    double OZ16_PRICE = 2.00;
    char cookies = 0;
    double COOKIES_OAT= .75;
    double COOKIES_CHOCO= .75;
    char tshirt = 0;
    double TSHIRT_Y = 15.00;
    double TSHIRT_N = 8.00;
    char item;
    char answer = 0;

    System.out.println("Hello. May I ask your name?");
    userName = input.nextLine();



    while (answer != 'N') 
    {
    System.out.println("Welcome " +userName +". Would you like to purchase something? (Y/N) ");
    answer = input.nextLine().charAt(0);
    answer = Character.toUpperCase(answer);

    System.out.println(" ***Lemonaid Stand Program***");
    System.out.println("=======================================");
    System.out.println("Enter purchase item, first letter only.");
    System.out.println("Lemonaid, Cookies, T-shirt.");
    System.out.println("Enter Q to Quit.");
    System.out.println();
    System.out.println("Enter an item or Q to quit (L,C,T,Q)");
    item = input.nextLine().charAt(0);
    item = Character.toUpperCase(item);

    while (item != 'L' && item != 'C' && item != 'T' && item != 'Q')
    {
        System.out.println("Invalid input.");
        System.out.println("Please enter an item, or Q to quit. (L,C,T,Q): ");
        item = input.nextLine().charAt(0);
            item = Character.toUpperCase(item);     
    }

        if (item == 'L')
        {
        System.out.println("What size would you like?");
        System.out.printf("%-10s%10.2f\n", "12oz.", OZ12_PRICE);
        System.out.printf("%-10s%10.2f\n", "16oz.", OZ16_PRICE);
        System.out.println("Input the number only.");
        lemonaid = input.nextInt();

        while (lemonaid != 12 && lemonaid != 16)

        {System.out.println("I'm sorry. Please only input an 16 or 12.");
        lemonaid=input.nextInt();
        }
            if (lemonaid == 12)
            {
                Sales_Header(); 
            System.out.printf("%-10s%10.2f\n", "12oz.", OZ12_PRICE);
            }

            else if (lemonaid == 16)
            {
                Sales_Header();
            System.out.printf("%-10s%10.2f\n", "16oz.", OZ16_PRICE);
            }

            else
            {
            }

        }//end If = L
        else if (item == 'C')
        {
            System.out.println("What type would you like?");
            System.out.printf("%-14s%10.2f\n", "Oatmeal", COOKIES_OAT);
            System.out.printf("%-10s%10.2f\n", "Chocolate Chip", COOKIES_CHOCO);
            System.out.println("Input the first letter only. (O/C)");
            cookies = input.nextLine().charAt(0);
                cookies = Character.toUpperCase(cookies);

            while (cookies != 'O' && cookies != 'C')

            {
            System.out.println("I'm sorry. Please only input an 'O' or 'C'.");
            cookies = input.nextLine().charAt(0);
            cookies = Character.toUpperCase(cookies);
            }

            if (cookies == 'O')
            {
                Sales_Header();
            System.out.printf("%-10s%10.2f\n", "Oatmeal", COOKIES_OAT);
            }

            else if (cookies == 'C')
            {
                    Sales_Header();
            System.out.printf("%-10s%10.2f\n", "Chocolate Chip", COOKIES_CHOCO);
            }

            else
            {
            }

        }// end else if = C

        else if (item == 'T')
            {
            System.out.println("Would you like that shirt autographed?");
            System.out.printf("%-10s%10.2f\n", "With autograph", TSHIRT_Y);
            System.out.printf("%-10s%11.2f\n", "W/O autograph", TSHIRT_N);
            System.out.println("Select Yes or No (Y/N)");
            tshirt = input.nextLine().charAt(0);
            tshirt = Character.toUpperCase(tshirt);

            while (tshirt != 'Y' && tshirt != 'N')
            {
                System.out.println("I'm sorry. Please only input an 'Y' or 'N'.");
                tshirt = input.nextLine().charAt(0);
                tshirt = Character.toUpperCase(tshirt);
            }
                if (tshirt == 'Y')
                {
                    Sales_Header();
                System.out.printf("%-10s%10.2f\n", "With autograph", TSHIRT_Y);
                }

                else if (tshirt == 'N')
                {
                    Sales_Header();
                System.out.printf("%-10s%10.2f\n", "W/O autograph", TSHIRT_N);
                }

                else
                {
                }
        }//end else if T

        else if (item == 'Q')
        {
            System.out.println("Main Menu.");
        }

        else
        {
        }

}//End while loop
}

Answer 1

要从标准输入(a/k/a STDIN a/k/a 键盘)获取单个字符，您可以采用以下两种方法之一:

char tshirt = (char) System.in.read(); //Takes one character, casts to "char"

或者您可以像这样使用 Scanner 中的方法:

char thsirt = scanner.next("."); //Takes exactly one character

这应该确保您不必处理 IndexOutofBounds 错误。