如何使switch语句更准确？

Question

We were ask to make a program using the switch statement..

Here is my code:

    double price = 0, totalPrice;

    System.out.print("Enter the number of your choice: ");
    int optionNumber = Integer.parseInt(kb.readLine());

    switch(optionNumber)
    {
        case 1:
            price = 190.00;
            break;
        case 2:
            price = 410.00;
            break;
        default:
            System.out.println("ERROR: Invalid number!");
            break;
    }

    System.out.print("Enter quantity: ");
    int quantity = Integer.parseInt(kb.readLine());

    totalPrice = price * quantity;

So basically, the user will input a certain number and it will have different prices... inside the switch statements. but if the user inputs a wrong number, it will display an error message and i dont want the user to enter the quantity which will be executed after the switch statement. we are not allowed to use any methods or functions and i dont want to code repeatedly like this:

    System.out.print("Enter the number of your choice: ");
    int optionNumber = Integer.parseInt(kb.readLine());

    switch(optionNumber)
    {
        case 1:
            price = 190.00;
            System.out.print("Enter quantity: ");
            int quantity = Integer.parseInt(kb.readLine());
            totalPrice = price * quantity;
            System.out.print("Total price: " + totalPrice);
            break;
        case 2:
            price = 410.00;
            System.out.print("Enter quantity: ");
            int quantity = Integer.parseInt(kb.readLine());
            totalPrice = price * quantity;
            System.out.print("Total price: " + totalPrice);
            break;
        default:
            System.out.println("ERROR: Invalid number!");
            break;
    }

is there any other way not to use if else, methods, functions or coding repeatedly? ANY HELP WILL BE APPRECIATED.

Answer 1

Use as this:

while(!valid option)
   //do this stuff

Use a flag and set it to true if the number entered is valid, so it will go to your next instruction; else ask again for input.

Answer 2

You can use a boolean flag and make it false if invalid option is selected.
Then only ask user further if flag is true.

    System.out.print("Enter the number of your choice: ");
    int optionNumber = Integer.parseInt(kb.readLine());
    boolean flag = true;
    switch (optionNumber) {
        case 1:
            price = 190.00;
            break;
        case 2:
            price = 410.00;
            break;
        default:
            flag = false;
            System.out.println("ERROR: Invalid number!");
            break;
    }
    if (flag) {
        System.out.print("Enter quantity: ");
        int quantity = Integer.parseInt(kb.readLine());
        totalPrice = price * quantity;
        System.out.print("Total price: " + totalPrice);
    }

Answer 3

You could just remove default from the switch statement and check to see if the price is equal to 0 after the switch statement

double price = 0, totalPrice;

System.out.print("Enter the number of your choice: ");
int optionNumber = Integer.parseInt(kb.readLine());

switch(optionNumber)
{
    case 1:
        price = 190.00;
        break;
    case 2:
        price = 410.00;
        break;
}

if (price == 0)
{
     System.out.println("ERROR: Invalid number!");
}
else
{
    System.out.print("Enter quantity: ");
    int quantity = Integer.parseInt(kb.readLine());
    totalPrice = price * quantity;
    System.out.print("Total price: " + totalPrice);
}

This keeps you from adding unnecessary variables (like a boolean flag) when you already have one ( price ) with a default value of 0 that you can check against.

Answer 4

Throw an exception

  default:
            throw new InvalidArgumentException("Invalid number!");

See also InvalidArgumentException vs UnexpectedValueException