在java中使用scanner的問題

Question

我有一項任務，我們假設為書店創建一個程序，幫助他們估算自己的業務。 為此，我們假設要求用戶提供各種輸入，例如書籍的代碼，書籍的單一復制成本，當前的書籍數量，預期的課程注冊等等。 但是，當用戶輸入無效輸入時，我遇到問題，例如當預期注冊無效輸入時，程序開始從開始詢問問題而不是再次詢問相同問題。

任何人都可以幫我找出我做錯了什么？ 這是我的代碼。

提前致謝。

public static void main(String[] args) {

    Scanner sc = new Scanner(System.in);

    System.out.println("Welcome to College Store Sale Class.");
    System.out.println("Please enter all the info below as asked.");
    System.out.println("Write either 'Continue' or 'Exit' to continue or exit program respectively. ");



    double bookCost;
    int bookAvailable;
    String ending = sc.next();
    int prosepectiveEnrollment;
    String rOrO;    
    String nOrU;

    while(!ending.equals("exit")){



        System.out.print("Please enter the cost of book ($>=0). ");
        bookCost = sc.nextDouble();

        if(bookCost >= 0){

            System.out.print("Please enter the number of books available (n>=0). ");
            bookAvailable = sc.nextInt();

            if(bookAvailable >= 0){

                System.out.print("Please enter prospective class enrollement > 0: ");                   
                prosepectiveEnrollment = sc.nextInt();

                if(prosepectiveEnrollment > 0){

                    System.out.print("Is the book Required or Optional (ignoreCase)? ");
                    rOrO = sc.next();

                    if((rOrO.equalsIgnoreCase("Required") || rOrO.equalsIgnoreCase("Optional"))){

                        System.out.print("Is the book New or Used? Enter in 'N' or 'U' format. ");
                        nOrU = sc.next();
                        if((nOrU.equalsIgnoreCase("New") || nOrU.equalsIgnoreCase("Used"))){

                            System.out.println("Thanks for correct info, below is your result");

                        }

                        else{

                            System.out.println("(E) Please enter either 'New' or 'Used'. ");
                        }

                    }
                    else{

                        System.out.println("(D) Please enter either 'Required' or 'Optional'. ");
                    }

                }
                else{

                    System.out.println("(C) Number of prospective class enrollement must be > 0.");
                }
            }
            else{

                System.out.println("(B) Number of books should be >= 0.");
            }

        }

        else{

            System.out.println("(A) Cost should be >= 0. ");
        }
    }

    if(ending.equalsIgnoreCase("exit"))
        System.out.println("See ya later..!! Bbyee..");
    sc.close();
}

Answer 1

你在循環中問問題。 當您的某個條件失敗時，程序將繼續超過所有后續條件（如果它們也不正確）並再次開始LOOP。 要糾正此問題，您可能會在循環內發生每個條件。 就像是

而（錯誤的條件回答）：再問一次

要挑戰自己（並改進），請盡可能少地保留代碼！

祝你的編碼旅程好運:)

Answer 2

我試圖解決這個問題，也許你可以這樣做，讓我知道這是否適合你

    public class Questionaire {

    public static void main(String[] args) {

        double bookCost = 0.0;
        int bookAvailable = 0;
        int prosepectiveEnrollment = 0;
        String rOrO = "";    
        String nOrU = "";

        try (Scanner sc = new Scanner(System.in)){
            System.out.println("Welcome to College Store Sale Class.");
            System.out.println("Please enter all the info below as asked.");
            System.out.println("Write either 'Continue' or 'Exit' to continue or exit program respectively. ");

            String ending = sc.next();
            System.out.println("Your response "+ending);

            while(!ending.equalsIgnoreCase("exit")){

                bookCost = promptQuestion("Please enter the cost of book ($>=0).", param -> {
                    return param >= 0;
                }, bookCost,sc);
                System.out.println("Your response "+bookCost);

                bookAvailable = promptQuestion("Please enter the number of books available (n>=0). ", param -> {
                    return param >= 0;
                }, bookAvailable, sc);
                System.out.println("Your response "+bookAvailable);

                prosepectiveEnrollment = promptQuestion("Please enter prospective class enrollement > 0: ", param -> {
                    return param > 0;
                }, prosepectiveEnrollment, sc);
                System.out.println("Your response "+prosepectiveEnrollment);

                rOrO = promptQuestion("Is the book Required or Optional (ignoreCase)? ", param -> {
                    return param.equalsIgnoreCase("Required") || param.equalsIgnoreCase("Optional");
                }, rOrO, sc);
                System.out.println("Your response "+rOrO);

                nOrU = promptQuestion("Is the book New or Used? Enter in 'N' or 'U' format. ", param -> {
                    return (param.equalsIgnoreCase("New") || param.equalsIgnoreCase("Used")
                            || param.equalsIgnoreCase("N") || param.equalsIgnoreCase("U"));
                }, nOrU, sc);
                System.out.println("Your response "+nOrU);

                System.out.println("Write either 'Continue' or 'Exit' to continue or exit program respectively. ");
                ending = sc.next();
                System.out.println("Your response "+ending);
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    static Integer promptQuestion(String question, Validation<Integer> validation, Integer input, Scanner sc) {
        do {
            System.out.println(question);
            input = sc.nextInt();
        } while(!validation.validate(input));
        return input;
    }

    static Double promptQuestion(String question, Validation<Double> validation, Double input, Scanner sc) {
        do {
            System.out.println(question);
            input = sc.nextDouble();
        } while(!validation.validate(input));
        return input;
    }

    static String promptQuestion(String question, Validation<String> validation, String input, Scanner sc) {
        do { 
            System.out.println(question);
            input = sc.next();
        } while(!validation.validate(input));
        return input;
    }

    @FunctionalInterface
    private static interface Validation<T> {
        boolean validate(T t);
    }
}