if-Else-if循环不起作用

Question

The requirement is :

• If the user chooses 1 the user will be asked to enter all the required values to create a LibraryItem and add it to the library

• For choices 2 and 3 the user will be asked to enter the title of the LibraryItem

• For choices 4 and 5 the user will be asked to enter the barcode of the item The class InputReader may be used to get the users input.

This is my run method

/**
 * Run the library
 * 
 * @throws InvalidInputException
 */
public void run() throws InvalidInputException {
    InputReader reader = new InputReader();

    System.out.println("1. Add LibraryItem");
    System.out.println("2. Search a Title");
    System.out.println("3. remove a Title");
    System.out.println("4. Borrow an Item");
    System.out.println("5. Return an Item");
    System.out.println("6. Exit");

    if (reader.readInt() == 1) {
        System.out.println("Which catergory are you going to add?");
        System.out.println("1. Music");
        System.out.println("2. AudioBook");
        System.out.println("3. PrintedBook");
        if (reader.readInt() >= 1 && reader.readInt() <= 3) {
            if (reader.readInt() == 1) {
                System.out.print("Please enter a barcode: ");
                String barcode = reader.readString();
                System.out.println("Please enter a title: ");
                String title = reader.readString();
                System.out.println("Is it on loan? ");
                boolean isOnLoan = reader.readBoolean();
                System.out.println("What is the publishing year?");
                int publishingYear = reader.readInt();
                System.out.println("Who is the Artist?");
                String artist = reader.readString();
                System.out.println("What is the Playing Time?");
                double playingTime = reader.readDouble();
                System.out.println("What is the Sound Quality?");
                String soundQuality = reader.readString();
                Music music = new Music(title, barcode, isOnLoan,
                        publishingYear, artist, playingTime, soundQuality);
                addItem(barcode, music);
                System.out.println("Item added");
            } else if (reader.readInt() == 2) {
                System.out.print("Please enter a barcode: ");
                String barcode = reader.readString();
                System.out.println("Please enter a title: ");
                String title = reader.readString();
                System.out.println("Is it on loan? ");
                boolean isOnLoan = reader.readBoolean();
                System.out.println("What is the publishing year?");
                int publishingYear = reader.readInt();
                System.out.println("Who is the Author?");
                String author = reader.readString();
                System.out.println("Who is the publisher?");
                String publisher = reader.readString();
                System.out.println("What is the Playing Time?");
                double playingTime = reader.readDouble();
                AudioBook audioBook = new AudioBook(title, barcode,
                        isOnLoan, publishingYear, author, publisher,
                        playingTime);
                addItem(barcode, audioBook);
                System.out.println("Item added");

            } else {
                System.out.print("Please enter a barcode: ");
                String barcode = reader.readString();
                System.out.println("Please enter a title: ");
                String title = reader.readString();
                System.out.println("Is it on loan? ");
                boolean isOnLoan = reader.readBoolean();
                System.out.println("What is the publishing year?");
                int publishingYear = reader.readInt();
                System.out.println("Who is the Author?");
                String author = reader.readString();
                System.out.println("Who is the publisher?");
                String publisher = reader.readString();
                System.out.println("What is the number of pages?");
                int numberPages = reader.readInt();
                PrintedBook printedBook = new PrintedBook(title, barcode,
                        isOnLoan, publishingYear, author, publisher,
                        numberPages);
                addItem(barcode, printedBook);
                System.out.println("Item added");

            }
        } else if (reader.readInt() == 2) {
            System.out.println("Please enter the Title: ");
            String title = reader.readString();
            searchByTitle(title);
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else if (reader.readInt() == 3) {
            System.out.println("Please enter the Title: ");
            String title = reader.readString();
            removeTitle(title);
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else if (reader.readInt() == 4) {
            System.out.println("Please enter the Barcode: ");
            String barcode = reader.readString();
            borrow(barcode);
            System.out.println("Item Borrowed");
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else if (reader.readInt() == 5) {
            System.out.println("Please enter the Barcode: ");
            String barcode = reader.readString();
            returnItem(barcode);
            System.out.println("Item Returned");
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else {
            return;
        }
    }
}

when i press 1 it always work but when i try to press 2 nothing show up until i have press 2 again then it work

EDIT:

this is the new code i done

public void printMainMenu() {

    System.out.println("1. Add LibraryItem");
    System.out.println("2. Search a Title");
    System.out.println("3. remove a Title");
    System.out.println("4. Borrow an Item");
    System.out.println("5. Return an Item");
    System.out.println("6. Exit");
}

public void printCatergory() {
    InputReader reader = new InputReader();
    int input = reader.readInt();
    System.out.println("Which catergory are you going to add?");
    System.out.println("1. Music");
    System.out.println("2. AudioBook");
    System.out.println("3. PrintedBook");

    if (input >= 1 && input <= 3) {
        if (input == 1){
            System.out.print("Please enter a barcode: ");
            String barcode = reader.readString();
            System.out.println("Please enter a title: ");
            String title = reader.readString();
            System.out.println("Is it on loan? ");
            boolean isOnLoan = reader.readBoolean();
            System.out.println("What is the publishing year?");
            int publishingYear = reader.readInt();
            System.out.println("Who is the Artist?");
            String artist = reader.readString();
            System.out.println("What is the Playing Time?");
            double playingTime = reader.readDouble();
            System.out.println("What is the Sound Quality?");
            String soundQuality = reader.readString();
            Music music = new Music(title, barcode, isOnLoan,
                    publishingYear, artist, playingTime, soundQuality);
            addItem(barcode, music);
            System.out.println("Item added");
        } else if (input == 2) {
            System.out.print("Please enter a barcode: ");
            String barcode = reader.readString();
            System.out.println("Please enter a title: ");
            String title = reader.readString();
            System.out.println("Is it on loan? ");
            boolean isOnLoan = reader.readBoolean();
            System.out.println("What is the publishing year?");
            int publishingYear = reader.readInt();
            System.out.println("Who is the Author?");
            String author = reader.readString();
            System.out.println("Who is the publisher?");
            String publisher = reader.readString();
            System.out.println("What is the Playing Time?");
            double playingTime = reader.readDouble();
            AudioBook audioBook = new AudioBook(title, barcode, isOnLoan,
                    publishingYear, author, publisher, playingTime);
            addItem(barcode, audioBook);
            System.out.println("Item added");

        } else {
            System.out.print("Please enter a barcode: ");
            String barcode = reader.readString();
            System.out.println("Please enter a title: ");
            String title = reader.readString();
            System.out.println("Is it on loan? ");
            boolean isOnLoan = reader.readBoolean();
            System.out.println("What is the publishing year?");
            int publishingYear = reader.readInt();
            System.out.println("Who is the Author?");
            String author = reader.readString();
            System.out.println("Who is the publisher?");
            String publisher = reader.readString();
            System.out.println("What is the number of pages?");
            int numberPages = reader.readInt();
            PrintedBook printedBook = new PrintedBook(title, barcode,
                    isOnLoan, publishingYear, author, publisher,
                    numberPages);
            addItem(barcode, printedBook);
            System.out.println("Item added");
        } 
    }
}

/**
 * Run the library
 * 
 * @throws InvalidInputException
 */
public void run() throws InvalidInputException {
    InputReader reader = new InputReader();
    printMainMenu();
    int input = reader.readInt();
    if (input >= 1 && input <= 6) {
        if (input == 1) {

            printCatergory();

        } else if (input == 2) {
            System.out.println("Please enter the Title: ");
            String title = reader.readString();
            searchByTitle(title);
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else if (input == 3) {
            System.out.println("Please enter the Title: ");
            String title = reader.readString();
            removeTitle(title);
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else if (input == 4) {
            System.out.println("Please enter the Barcode: ");
            String barcode = reader.readString();
            borrow(barcode);
            System.out.println("Item Borrowed");
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else if (input == 5) {
            System.out.println("Please enter the Barcode: ");
            String barcode = reader.readString();
            returnItem(barcode);
            System.out.println("Item Returned");
            System.out.println("Press '1' to return to Main Menu");
            if (reader.readInt() == 1) {
                System.out.println("1. Add LibraryItem");
                System.out.println("2. Search a Title");
                System.out.println("3. remove a Title");
                System.out.println("4. Borrow an Item");
                System.out.println("5. Return an Item");
                System.out.println("6. Exit");
            }
        } else {
            return;
        }
    }
}

Answer 1

this happening because you are trying to take input every single time to fix that you have to change the code in the following manner

System.out.println("1. Add LibraryItem");
System.out.println("2. Search a Title");
System.out.println("3. remove a Title");
System.out.println("4. Borrow an Item");
System.out.println("5. Return an Item");
System.out.println("6. Exit");
**int input =reader.readInt();**// add the input to a variable then            reference this variable 
 if (input == 1)//like this
   {
    System.out.println("Which catergory are you going to add?");
    System.out.println("1. Music");
    System.out.println("2. AudioBook");
    System.out.println("3. PrintedBook");
    if (input) >= 1 && input <= 3) {
        if (input == 1) {
            System.out.print("Please enter a barcode: ");

Answer 2

You're problem is in this line: reader.readInt() >= 1 && reader.readInt() <= 3 . This reads two values. To fix this, you should store the read value.

int category = reader.readInt();
if(category >= 1 && category <= 3) {
//....

You do this quite often - you should store the values that are read and check those. Whenever you write reader.readX() , that's another input from the user.

You should also clean up your code. Make print_menu methods and it'll be a lot easier to debug.

Answer 3

If you are going to individually check for each input value, you don't need

if (input >= 1 && input <= 6) {

And a problem with your updated code is that you prompt for input before you print the options. See here

public void printCatergory() {
    InputReader reader = new InputReader();
    int input = reader.readInt();
    System.out.println("Which catergory are you going to add?");
    System.out.println("1. Music");
    System.out.println("2. AudioBook");
    System.out.println("3. PrintedBook");

You should move the readInt line beneath the System.out

public void printCatergory() {
    InputReader reader = new InputReader();
    System.out.println("Which catergory are you going to add?");
    System.out.println("1. Music");
    System.out.println("2. AudioBook");
    System.out.println("3. PrintedBook");
    int input = reader.readInt();
    // if (input == 1) // do Music stuff
    // else if (input == 2) // do AudioBook stuff
    // ...