如果输入正确或没有JAVA，如何让用户只知道一次

Question

The whole code works almost like I want to but I don't know how to let the user know the error without finishing de whole for loop, so it repeats the error until the loop is over and also repeats the error until it finds the correct answer. If i don't use the for loop i don't know how to iterate inside menu[] to search every match between the elements inside it and the User input... If I write in console "pizza" as an user input it returns:

We have chicken for 10€
We have steak for 15€
We have hamburger for 20€
We have spaghettis for 5€
We have pizza for 12€
What do you want to eat?
pizza
Sorry, we don't have that
Sorry, we don't have that
Sorry, we don't have that
Sorry, we don't have that
You ordered pizza
Want something more? Say YES with 1 and NO with 0

I just want to get returned what I ordered and when i write something wrong then i just want one only advise and not 5! Sorry for my poor english and code knowledge! Thanks!

String[] menu = { "chicken", "steak", "hamburger", "spaghettis", "pizza" };
        int[] price = { 10, 15, 20, 5, 12 };

        for (int i = 0; i < menu.length; i++) {

            System.out.println("We have " + menu[i] + " for " + price[i] + "€");

        }

        boolean wantMore = true;
        int answer = 0;
        int yes = 1;
        int no = 0;

        List<String> Order = new ArrayList<String>();

        List<Integer> TotalPrice = new ArrayList<Integer>();

        Scanner keyboard = new Scanner(System.in);

        System.out.println("What do you want to eat?");

        do {

            String userOrder = keyboard.next().toLowerCase();

            for (int i = 0; i < menu.length; i++) {

                if (userOrder.equals(menu[i])) {

                    Order.add(userOrder);

                    System.out.println("You ordered " + userOrder);

                    TotalPrice.add(price[i]);

                    break;

                } else { 

                    System.out.println("Sorry, we don't have that");

                }

            }

            System.out.println("Want something more? Say YES with 1 and NO with 0");

            answer = keyboard.nextInt();

            if (answer == yes) {

                wantMore = true;

                System.out.println("What else do you want?");

            } else if (answer == no) {

                wantMore = false;

            }

        } while (wantMore);

        int sum = TotalPrice.stream().mapToInt(Integer::intValue).sum();

        System.out.println("Order finished! \nYour order have " + Order);

        System.out.println("The total price is: " + sum);

    }

}

Answer 1

What you want to do is determine if the selected item is within the menu, if it is, order it and ask for more. If it is not within the whole menu, then print the error. If you change your for loop to

//flag to keep track of if the item exists in the menu
boolean exists = false;
for (int i = 0; i < menu.length; i++) {
    //set exists to false at the beginning of the loop
    exists = false;
    if (userOrder.equals(menu[i])) {
        Order.add(userOrder);
        System.out.println("You ordered " + userOrder);
        TotalPrice.add(price[i]);
        //if the item exists in the menu, set the flag to true
        exists = true;
    } 
}
//checks if the item was never found in the menu
if (!exists) { 
    System.out.println("Sorry, we don't have that");
}

See if that gives you any better luck with your program.

Answer 2

First go through the loop to find the matching order. If it is not available, then display the error.

Try this:

boolean validMenuItem = false;
for (int i = 0; i < menu.length; i++) {

    if (userOrder.equals(menu[i])) {

        Order.add(userOrder);

        System.out.println("You ordered " + userOrder);

        TotalPrice.add(price[i]);

        validMenuItem = true;

        break;

    }

}
if (!validMenuItem) {
    // wrong input
    System.out.println("Sorry, we don't have that");
}