在java中跳过输入行

Question

所以我有一个 addItem() 方法，我可以在其中将书籍、磁带或 cd 对象添加到我的库存中。为了存储书籍、磁带或 cd 对象，我从用户那里获取对象的标题、作者和价格。但是，当我运行程序时，它会跳过“请输入标题：”并向右转到“请输入作者：”。然后当我让它显示信息时，标题字段为'null'。

static void addItem(int type) {     

    String title;
    String author;
    Double price;

    System.out.println("Please enter the title");
    title = keyboard.nextLine()

    System.out.println("Please enter the author");
    author = keyboard.nextLine();

    System.out.println("Please enter the price");
    price = keyboard.nextDouble();


        if(type == 0){
            Book BookStoreItem;

                BookStoreItem = new Book(title, author, price);

            System.out.println("You've entered:");
            System.out.println("Title: " + BookStoreItem.getTitle());
            System.out.println("Author: " + BookStoreItem.getAuthor());
            System.out.println("Price: " + BookStoreItem.getPrice());
        }

        if(type == 1){
            Tape BookStoreItem;

            BookStoreItem = new Tape(title, author, price);

            System.out.println("You've entered:");
            System.out.println("Title: " + BookStoreItem.getTitle());
            System.out.println("Author: " + BookStoreItem.getAuthor());
            System.out.println("Price: " + BookStoreItem.getPrice());
        }

        if(type == 2){                  
            CD BookStoreItem;

            BookStoreItem = new CD(title, author, price);

            System.out.println("You've entered:");
            System.out.println("Title: " + BookStoreItem.getTitle());
            System.out.println("Author: " + BookStoreItem.getAuthor());
            System.out.println("Price: " + BookStoreItem.getPrice());
        }


}//end of addItem()

这是一个示例输出：

Press:
    0    To add a book to the inventory
    1    To add a tape to the inventory
    2    To add a Cd to the inventory
Please enter your choice: 0
Please enter the title:
Please enter the author: John Smith
Please enter the price: 55.50

Title: null
Author: John Smith
Price: 55.5

这里是菜单的更新：

static void printMenu() {
    System.out.println("\nPress:");
    System.out.println("\t" + ADD_BOOK + "\tTo add a book to the inventory\n");
    System.out.println("\t" + ADD_TAPE + "\tTo add a tape to the inventory\n");
    System.out.println("\t" + ADD_CD + "\tTo add a CD to the inventory\n");
    System.out.println("\t" + SHOW_ITEM_LIST + "\tTo display a list of available books\n");
    System.out.println("\t" + SEARCH_ITEM + "\tTo search for a specific book\n");
    System.out.println("\t" + QUIT + "\tTo exit\n");
}

还有选择：

static void runBookStoreApplication() {
    int userChoice = QUIT;
    String quitMessage = "\nThank you for using the BookStoreApplication!";
    String invalidOptionMessage = "\nInvalid option!"; 

    do{
        printMenu();
        userChoice = getUserChoice();

        switch (userChoice) {
            case ADD_BOOK:
                addItem(0);
                break;
            case ADD_TAPE:
                addItem(1);
            case ADD_CD:
                addItem(2);
            case SHOW_ITEM_LIST:
                showItemList();
                break;
            case SEARCH_ITEM:
                searchItem();
                break;
            case QUIT:
                System.out.println(quitMessage);
                break;
            default:
                System.out.println(invalidOptionMessage);
        }
    } while(userChoice != QUIT);

}//end of runBookStoreApplication

使用 getUserChoice：

static int getUserChoice() {
    int choice;

    System.out.print("Please enter your choice: ");
    choice = keyboard.nextInt();

    return choice;
}

Answer 1

您没有向我们展示您询问“请输入您的选择：”的代码，但我敢打赌您使用的是 keyboard.nextInt() 或其他东西。此方法不会消耗所有行，只消耗整数0，因此当您随后调用nextLine() 时，它实际上会立即返回该行的其余部分（即使用空字符串）。

要解决这个问题，请在您的方法之前调用keyboard.nextLine()。

编辑：

现在您已经输入了getUserChoice() 方法，您可以看到有一个对keyboard.nextInt() 的调用，正如我推测的那样。只需在它之后调用nextLine()，这样您就可以使用所有线路并且扫描仪已准备好进行下一次输入：

static int getUserChoice() {
    int choice;

    System.out.print("Please enter your choice: ");
    choice = keyboard.nextInt(); // consume just the integer

    // consume the rest of the line
    keyboard.nextLine();

    return choice;
}