Question

I am looking at the example in How to Program in Java, 7e.
User inputs the data manually into object of class AccountRecord record

AccountRecord record = new AccountRecord();
Scanner input = new Scanner( System.in );
while ( input.hasNext() ) // loop until end-of-file indicator
      {
         try // output values to file
         {
            // retrieve data to be output
            record.setAccount( input.nextInt() ); // read account number
            record.setFirstName( input.next() ); // read first name
            record.setLastName( input.next() ); // read last name
            record.setBalance( input.nextDouble() ); // read balance

         .............................................................

         catch ( NoSuchElementException elementException )
         {
            System.err.println( "Invalid input. Please try again." );
            input.nextLine(); // discard input so user can try again
         } // end catch
      }

I have hard time figuring out how catch ( NoSuchElementException elementException ) works. According to Java Documentation, NoSuchElementException is

Thrown by the nextElement method of an Enumeration to indicate that
there are no more elements in the enumeration.

So, why it would also throw an exception in case type mismatch between expected and what is actually entered, such as for record.setAccount(input.nextInt()), user inputs some text string?

Thanks !

Answer 1

For type mismatch problems, you should catch InputMismatchException. Since it inherits from NoSuchElementException, you will catch it by catching a NoSuchElementException (so the code as it is will catch it and work as expected). To me, that’s a strange inheritance relationship, though…. Certainly does not represent an is-a relationship.

If you really want to differentiate both cases, catch an InputMismatchException before a NoSuchElementException.