How to only allow the user to enter an input of a-z and using an if statement to prompt the correct input

Question

I need to only allow a user to enter a character from the a-z range. I was thinking of using an if statement but its not working out for me.

        System.out.println("Please enter letters of the alphabet");
        String input1 = scnObj.nextLine();
        if (input1 != a-z) {
        System.out.println("Please try again.");
        }  
        else 
        {
        System.out.println("Correct.");
        }

@Spiderman it can be a single character, I also should of included that capital letters would be allowed also! — Nexus_Valentine, Dec 16 '19 at 21:29
@Ivar The entered input from the user must be only a letter or letters from the alphabet. — Nexus_Valentine, Dec 16 '19 at 21:33
Does this answer your question? [Check if String contains only letters](https://stackoverflow.com/questions/5238491/check-if-string-contains-only-letters) — Ivar, Dec 16 '19 at 21:33
@Ivar That method does not prompt the user to enter the correct format. That is why I would like to us the if statement. — Nexus_Valentine, Dec 16 '19 at 21:39
@Nexus_Valentine You already prompt the user. All you need to do is use one of the methods mentioned there, and check if `input1` matches it. — Ivar, Dec 16 '19 at 21:43

score 0 · Answer 1 · answered Dec 16 '19 at 21:30

You could use a regular expression, but a simpler solution might be to take advantage of the fact that the characters in a - z are a in a linear progression within the character set tables and do something like...

    String input1 = scnObj.nextLine();
    if (!input1.trim().isEmpty()) {
        char inputChar = input1.charAt(0);
        if (inputChar >= 'a' && inputChar <= 'z') {
            // Everything is good
        } else {
            // Everything is bad
        }
    }

score 0 · Answer 2 · answered Dec 16 '19 at 21:32

This sounds like the perfect time for a regex implementation. If you have never heard regex I recommend checking out this video. Essentially it is used to match patterns within a string. For java you could simply check whether each character is a lower case letter with:

System.out.println("Please enter letters of the alphabet");
String input1 = scnObj.nextLine();
if (!input1.matches("[a-z]*") {
    System.out.println("Please try again.");
}  else  {
    System.out.println("Correct.");
}

However it might have to add a little more if you want to allow for spaces/hyphens. Good luck!

score 0 · Accepted Answer · answered Dec 16 '19 at 21:38

0

You can use regexp. Your case is simple and something like this:

if(!Pattern.compile("[a-z]*").matcher(line).matches()){
   System.out.println("Please try again.");
}

If you want include also Uppercase, modfy if condition like this:

if(!Pattern.compile("[a-zA-Z]*").matcher(line).matches()){
   System.out.println("Please try again.");
}

If space are allowed:

if(!Pattern.compile("[a-zA-Z\\s]*").matcher(line).matches()){
   System.out.println("Please try again.");
}

In any case and for more complex cases please read the java doc

answered Dec 16 '19 at 21:38

Renato

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Thanks @Renato Do I have to import anything? – Nexus_Valentine Dec 16 '19 at 21:41
Sure: you must have `import java.util.regex.Matcher; ` and `import java.util.regex.Pattern;` but these are part of Java SE – Renato Dec 16 '19 at 21:44
so there is 3 imports with the scanner class as well? Is that right? – Nexus_Valentine Dec 16 '19 at 21:46
If you want read the input string from the standard input or from a file, yes, you can use Scanner and then you have to add the third import – Renato Dec 16 '19 at 21:50
1

Also I had to replace .matcher(line) with .matcher (input1). Other then that your solution works fine. Thanks a lot. – Nexus_Valentine Dec 16 '19 at 21:51

How to only allow the user to enter an input of a-z and using an if statement to prompt the correct input

3 Answers3