Checking if input is correct type java

Question

    System.out.println("What letter should the word begin with?");
        char letter = input.next().charAt(0);
        if(letter != ''){
            throw new InputMismatchException("Please input a letter");
        }

I want to check to see if the user input anything besides a string/char. If they have I want to throw an exception that says the input is wrong. This is my current code but as it stands it does not compile.

Everything the user can enter is a char. There's no way to enter anything other than chars. You need to tell us what your definition of char is. But, have you at least read the javadoc of java.lang.Character? — JB Nizet
– JB Nizet, Commented Apr 14, 2018 at 14:21
Every input can be interpreted as a char because every character, every number and every punctuation sign it's an ascii character. You must tell whats the goal of the program to can give you some advice as @TimBiegeleisen said. — J. Lorenzo
– J. Lorenzo, Commented Apr 14, 2018 at 14:29
@J.Lorenzo actually, most of them are not ASCII characters. ASCII only support 127 characters. — JB Nizet
– JB Nizet, Commented Apr 14, 2018 at 14:31
So, you want the user to enter a letter between 'A' and 'Z'. That's not the same thing as a char. '1' is a char. 'é' is a char. '😊' is a char. So you want if (letter >= 'A' && letter <= 'Z'). — JB Nizet
– JB Nizet, Commented Apr 14, 2018 at 14:59

Sweeper · Accepted Answer · 2018-04-14 15:49:55Z

1

You can check whether letter is a letter like this:

if ((letter >= 'A' && letter <= 'Z') || (letter >= 'a' && letter <= 'z'))

Actually, Scanner has this handy overload of next(String pattern) that throws an InputMismatchException automatically if the input does not match a pattern:

char letter = input.next("[a-zA-Z]").charAt(0);

[a-zA-Z] is the pattern used here. It accepts any character from a to z or from A to Z.

edited Apr 14, 2018 at 15:49

answered Apr 14, 2018 at 15:06

Sweeper

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1 Comment

A.Torres Over a year ago

Thank you so much! I have fixed the issue!

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