Validating Input string with Exceptions in Java

Question

I coded the following java snippet. I want to throw, catch and handle exception if user enters value other than "A","B" or "C". I know this can be done without exception but my task is to implement this with exception. The following code catches exception but the problem is that even if I enter value from A,B or C.It still executes the Catch block. Kindly share where i am wrong.

boolean invalid = false;
    do {
        try {
            System.out.println("Enter:");
            t = in.nextLine();
            invalid=true;
            if(!t.equals("A") || !t.equals("B") || !t.equals("C")){
                invalid=false;
                throw new InputMismatchException("Invalid!");
            }

        }
        catch(InputMismatchException e){
            System.out.println("Enter from options.");
            invalid = false;
            
        }
    }while(!invalid);

Here is another way: if (! List.of("A", "B", "C").contains(t)) { ... } - requires Java SE 9. This is useful in case you have more strings to compare. — prasad_
– prasad_, Commented Aug 24, 2022 at 8:50

prasad_ · Accepted Answer · 2022-08-24 09:44:17Z

1

I want to throw, catch and handle exception if user enters value other than "A","B" or "C"

This can be coded in different ways, and this syntax is useful in case you have more values to compare:

// Using Java 8 Streams
if (Stream.of("A", "B", "C").noneMatch(e -> e == t)) { ...
// Using Java 7 Collections
if (! Arrays.asList("A", "B", "C").contains(t)) { ...
// Using Java 9 Collections
if (! List.of("A", "B", "C").contains(t)) { ...

answered Aug 24, 2022 at 9:44

prasad_

14.4k2 gold badges27 silver badges44 bronze badges

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

Comments

Mammad Yahyayev · Accepted Answer · 2022-08-24 07:20:50Z

0

Your problem is if condition, when you enter A, the first condition will be false, but second condition will be true, because t equals to A not B therefore second condition will be true, if one of the conditions is true, whole if condition will be true because this is OR statement. Therefore, if block will be executed.

try to change it to the following (AND statement)

if(!t.equals("A") && !t.equals("B") && !t.equals("C"))

answered Aug 24, 2022 at 7:20

Mammad Yahyayev

641 silver badge11 bronze badges

Collectives™ on Stack Overflow

Validating Input string with Exceptions in Java

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related