根据ArrayList验证用户输入

Question

I am having issues with the following part of my code. when "nn" is entered i get invalid code. when valid code is entered i get invalid code however this only happens once. program doesn't seem to work as intended. Please assist.

    System.out.println("ENTER CODE (nn to Stop) : ");
    ArrayList<Product> list = new ArrayList<Product>();
    .
    .
    .
    .


    ArrayList<Code> codeList = new ArrayList<Code>();


    for (Product product : list) {
        System.out.print("CODE : ");
        String pcode = scan.next();
        if (pcode.equalsIgnoreCase("nn")) {
            break;
        }

        if (!(code.equalsIgnoreCase(product.getCode()))) {
            System.out.println("Invalid code, please enter valid code.");
            System.out.print("CODE : ");
            pcode = scan.next();

        }

        System.out.print("QUANTITY : ");
        int quan = scan.nextInt();
        while (quan > 20) {
            System.out.println("Purchase of more than 20 items are not allowed, please enter lower amount.");
            System.out.print("QUANTITY : ");
            quan = scan.nextInt();
        }
        codeList.add(new Code(pcode, quan));
    }

Answer 1

You want continue instead of break .

Also, you should only call code = scan.next() once inside the loop; otherwise you'll skip over some items.

String code = scan.next();
boolean match = false;
for (Product product : list) {
    if (code.equalsIgnoreCase(product.getCode())) {
        match = true;
        break;
    }
}
// now only if match is false do you have an invalid product code.

Update:

I still can't get this to work. What I am trying to do is test user input to make sure that product code exists, if not prompt that the product code entered is invalid and asks for correct code. I also need to have the condition to stop order when "nn" is entered. I have tried while loops, do-while loops etc. i can't seem to get it right. Please assist. My problem is with writing code for multiple conditions. When one is working correctly the other isn't.

while (true) {
    final String code = scan.next();
    if (isExitCode(code)) {
        break;
    }
    if (!isValidCode(code)) {
        System.out.println("Invalid code, please enter valid code.");
        continue;
    }
    int quantity = -1;
    while (true) {
        quantity = scan.nextInt();
        if (!isValidQuantity(quantity)) {
            System.out.println("bad quantity");
            continue;
        }
        break;
    }
    // if you've got here, you have a valid code and a valid 
    // quantity; deal with it as you see fit.
}

Now you just need to write the methods isExitCode(), isValidCode(), and isValidQuantity().