Do while string validation (with multiple strings)

Question

For some reason, when I have multiple correct strings, the statement keeps repeating

    do {
    System.out.println("Enter Service Code");
    Scanner a = new Scanner(System.in);
    serviceCode = a.nextLine();
} while (!serviceCode.equals("ORB1") || !serviceCode.equals("ORBH") || 
         !serviceCode.equals("ISS5") || !serviceCode.equals("ILLOYDS") || 
         !serviceCode.equals("DLAB") || !serviceCode.equals("LEOM7") || 
         !serviceCode.equals("MOON2"));

However, when there's just one string that the code checks against. The do while statement works fine and will stop looping when the correct input is entered

    do {
    System.out.println("Enter Service Code");
    Scanner a = new Scanner(System.in);
    serviceCode = a.nextLine();
} while (!serviceCode.equals("ORB1"));

Put System.out.println("-"+serviceCode) after you call a.nextLine() and you will know why^^ — Alexander Heim
– Alexander Heim, Commented Sep 19, 2017 at 6:45
take a look at your condition. Let's say you input "ORB1". Then, !serviceCode.equals("ORB1") = False, because they're equal. But, what about the others? They keep returning True, because they're not equal. — Shinra tensei
– Shinra tensei, Commented Sep 19, 2017 at 6:45

dave · Accepted Answer · 2017-09-19 06:46:53Z

1

If you enter "ORB1", "!serviceCode.equals("ORB1")" will return false but the others will return true; and you are using the "OR" operator. So, this sentence :

!serviceCode.equals("ORB1") || !serviceCode.equals("ORBH") || 
     !serviceCode.equals("ISS5") || !serviceCode.equals("ILLOYDS") || 
     !serviceCode.equals("DLAB") || !serviceCode.equals("LEOM7") || 
     !serviceCode.equals("MOON2")

will always be true. You need to use the "AND" operator

!serviceCode.equals("ORB1") && !serviceCode.equals("ORBH") && 
     !serviceCode.equals("ISS5") && !serviceCode.equals("ILLOYDS") &&
     !serviceCode.equals("DLAB") && !serviceCode.equals("LEOM7") && 
     !serviceCode.equals("MOON2")

edited Sep 19, 2017 at 6:46

dave

12k6 gold badges50 silver badges69 bronze badges

answered Sep 19, 2017 at 6:45

Stéphane Ammar

1,45410 silver badges17 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Lachlan Langmead Over a year ago

Thanks. Don't know how I looked over that one

Stultuske · Accepted Answer · 2017-09-19 06:45:16Z

1

Your comparison can never return false. it's either A or B.

so, if you were to say:

if ( !A OR !B ){

--> Input = A => true (because !B returns true) --> Input = B => true (because !A returns true) --> Input = C => true (because !A returns true)

Change your OR (||) by AND (&&)

Also: declare and instantiate your Scanner before your loop.

answered Sep 19, 2017 at 6:45

Stultuske

9,4691 gold badge28 silver badges38 bronze badges

Comments

Naman · Accepted Answer · 2017-09-19 06:57:20Z

1

A better approach would be create a Listof string which includes the valid codes and check if that list contains the provided user input.

List<String> validServiceCodes = Arrays.asList("ORB1", "ORBH", "ISS5", "ILLOYDS", "DLAB", "LEOM7", "MOON2" );

do {
    System.out.println("Enter Service Code");
    Scanner a = new Scanner(System.in);
    serviceCode = a.nextLine();
} while (!validCodes.contains(validServiceCodes));

answered Sep 19, 2017 at 6:57

Naman

32.7k32 gold badges240 silver badges385 bronze badges

Collectives™ on Stack Overflow

Do while string validation (with multiple strings)

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related