Can't get Java do/while to process correctly

Question

I've reviewed several other questions similar to this, but the ones I read didn't help solve my issue. My goal is to print the menu value based on the int user input, and continue offering a selection until the user hits 6 to exit out. Here is my code (I'm new to Java).

class BookCategories {

    public static void main(String args[]) throws java.io.IOException {

        String menu = "MENU: \n1. Science Fiction \n2. Computers and Technology \n3. Cooking \n4. Business \n5. Comics \n6. Exit";

        Map<Integer, String> bookMap = new HashMap<Integer, String>();
        bookMap.put(1, "You selected Science Fiction. This is a fun topic.");
        bookMap.put(2, "You selected Computers and Technology. This is a complex topic.");
        bookMap.put(3, "You selected Cooking. This is a passionate topic.");
        bookMap.put(4, "You selected Business. This is a serious topic.");
        bookMap.put(5, "You selected Comics. This is an entertaining topic.");
        // bookMap.put(6, " ");

        int x;

        do {
            System.out.println(menu);
            System.out.println("Select an item from the Menu, then press Enter: ");

            x = (int) System.in.read();

            if (x == 6)
                System.out.println("You exited the menu.");
            else {
                System.out.println(bookMap.get(x));
                if (x < 1 || x > 6)
                    System.out.println("Invalid entry. Please enter a number from 1 to 6.");
                else
                    System.out.print(menu);
                System.out.println("Select an item from the Menu, then press Enter.");
            }

        } while (x != 6);
    }

}

I'm thinking it has something to do with that, as well, but I'm too new to Java to be sure. When I run the code, it does generate the menu and allows me to enter a number, but regardless as to what number I input, it registers it as the "Invalid entry..." and reloads the menu. I do want the menu to reload until the user hits 6, but I keep getting the same loop regardless as to what number I select, including 6. — , Jun 13 '21 at 16:13
At least for debugging add `System.out.println("You entered: " + x); ` just after reading it - and see first comment, added some more to it — , Jun 13 '21 at 16:14
I added that line for debugging purposes. It makes sense to have it! — , Jun 13 '21 at 16:27

score 1 · Accepted Answer · edited Jun 13 '21 at 16:23

1

As @user15793316 already said, System.in.read() does not read the actual number. You can make use of Scanner instead:

Scanner scanner = new Scanner(System.in);

do {
  // ...
  x = scanner.nextInt();
  scanner.nextLine(); // wait for Enter
  // ...
}

edited Jun 13 '21 at 16:23

Oleg Cherednik

17,377
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answered Jun 13 '21 at 16:14

Daniel

1,426
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Ah! I had that at first, but changed it to what it currently is due to following what was in my reading. I'll try this and report back. Thanks! – Jun 13 '21 at 16:15
Does it matter where I put scanner.close();? – Jun 13 '21 at 16:20
@MameGannon-Luiz Yes. It should be put at the end of your program – Daniel Jun 13 '21 at 16:21
@Daniel Could you please explain why – Seyed Mohammad Amin Atyabi Jun 13 '21 at 16:23
1

@SeyedMohammadAminAtyabi https://stackoverflow.com/questions/24573084/why-we-should-i-close-a-java-util-scanner-variable – Daniel Jun 13 '21 at 16:25
@Daniel it closes out the scanner, so it makes sense to go at the end. – Jun 13 '21 at 16:25
This fixed my issue!! Thank you everyone for taking the time to provide your suggestions! – Jun 13 '21 at 16:26

score 0 · Answer 2 · answered Jun 13 '21 at 16:19

Well, for some reason System.in.read(); was not working properly so I change your code this way :

public static void main(String[] args) throws java.io.IOException{

    String menu = "MENU: \n1. Science Fiction \n2. Computers and Technology \n3. Cooking \n4. Business \n5. Comics \n6. Exit";
    Scanner scanner = new Scanner(System.in); // this line

    Map<Integer, String> bookMap = new HashMap<Integer, String>();
    bookMap.put(1, "You selected Science Fiction. This is a fun topic.");
    bookMap.put(2, "You selected Computers and Technology. This is a complex topic.");
    bookMap.put(3, "You selected Cooking. This is a passionate topic.");
    bookMap.put(4, "You selected Business. This is a serious topic.");
    bookMap.put(5, "You selected Comics. This is an entertaining topic.");
    // bookMap.put(6, " ");

    int x;

    do {
        System.out.println(menu);
        System.out.println("Select an item from the Menu, then press Enter: ");

        x = scanner.nextInt(); // and this line

        if (x == 6)
            System.out.println("You exited the menu.");
        else {
            System.out.println(bookMap.get(x));
            if (x < 1 || x > 6)
                System.out.println("Invalid entry. Please enter a number from 1 to 6.");
            else
                System.out.print(menu);
            System.out.println("Select an item from the Menu, then press Enter.");
        }

    } while (x != 6);

}

Can't get Java do/while to process correctly

2 Answers2