字符串索引超出範圍和使用輸入數據的總數

Question

我需要一些幫助，下面的代碼。我試圖循環這個程序，直到用戶選擇'N'，然後我想要顯示以盎司爲單位銷售的檸檬水和每種類型的總餅乾和襯衫的總數。

我把while循環迴路中的程序，但我得到一個錯誤：在線程

異常「主要」 java.lang.StringIndexOutOfBoundsException：字符串索引超出範圍：0 在java.lang.String中.charAt（Unknown Source） at edu.kirkland5.SnackStand.main（SnackStand.java:43）

如果任何人都可以幫助我完成這兩件事情，我將非常感激。謝謝！

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

異常來自nextInt（）調用，因爲它不會「吃」該行。我已經快速創建了變量，可以讓您總結出售商品的數量，但實際上您需要更好的代碼結構。您可以爲商品創建包含說明，價格和銷售數量的類。在回答問題之前，您在while循環的頂部有一個問題，因爲您正在執行（while answer！= N）。所以解決方法是在循環之前初始化答案，然後在循環結束時重新讀取它。

import java.util.Scanner; 

public class main { 


    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; 

     int numLemonaid = 0; 
     int totalOz = 0; 
     int numCookies = 0; 
     int numTShirts = 0; 

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

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

     while (answer != 'N') { 
      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(); 
       input.nextLine(); 

       numLemonaid++; 

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

       { 
        System.out.println("I'm sorry. Please only input an 16 or 12."); 
        lemonaid = input.nextInt(); 
        input.nextLine(); 
       } 
       totalOz += lemonaid; 
       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); 
       numCookies++; 

       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); 

       numTShirts++ ; 

       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 { 
      } 

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

     System.out.println("Lemonaid: " + numLemonaid + "(" + totalOz +"Oz)") ; 
     System.out.println("Shirts: " + numTShirts) ; 
     System.out.println("Cookies: " + numCookies) ; 
    } 
} 

Answer 2

要想從標準輸入（A/K/A標準輸入A/K/AA鍵盤）單個字符，你可以採取以下兩種方法之一：

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

或者，您可以使用掃描儀的方法，如下所示：

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

這應該可以確保您不必處理IndexOutofBounds錯誤。