Validate Input - String

Question

I am trying to validate input from a textfield so that it only contains characters from a-z. I am using the following method to validate if the input is an int:

//VALIDATE IF INPUT IS NUMERIC.
public static boolean isInt(JFXTextField txtUserInput, String userInput) {
    try {
        int intValidation = Integer.parseInt(userInput);
        txtUserInput.setStyle("-fx-border-color: ; -fx-border-width: 0px ;");
        return true;
    } catch(NumberFormatException exception) {
        showErrorMsg("Invalid Input:", "Please enter a numeric-only value");
        txtUserInput.setStyle("-fx-border-color: RED; -fx-border-width: 1px ;");
        return false;
    }
}

How can I achieve this using a String? I know there is a different way of doing this using an if statement but I was wondering if I can catch an exception like in the example above.

Thanks

Possible duplicate of [Check if String contains only letters](http://stackoverflow.com/questions/5238491/check-if-string-contains-only-letters) — OneCricketeer, May 20 '17 at 14:22
You can throw your own exception. Using an if statement is more performant than try catch — OneCricketeer, May 20 '17 at 14:24

Youcef LAIDANI · Answer 1 · 2017-05-20T14:32:51.633

1

You can use matches with regex so if you want to check your input is an int or not you can use:

String userInput = ...;
if(userInput.matches("\\d+")){
    System.out.println("correct");
}else{
    System.out.println("Not correct");
}

If you want to check if the input contain only alphabetic, you can use :

if(userInput.matches("[a-zA-Z]+")){
    System.out.println("correct");
}else{
    System.out.println("Not correct");
}

If you want to check if your input contains alphanumeric you can use :

if(userInput.matches("[a-zA-Z0-9]+")){
    System.out.println("correct");
}else{
    System.out.println("Not correct");
}

edited May 20 '17 at 14:32

answered May 20 '17 at 14:22

Youcef LAIDANI

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The integers was only an example – OneCricketeer May 20 '17 at 14:23
i don't know @TimBiegeleisen this is sad in the first second dv – Youcef LAIDANI May 20 '17 at 14:24
what did you mean @cricket_007 ? – Youcef LAIDANI May 20 '17 at 14:25
I understand that the OP want to validate if an input is an Integer of not @cricket_007 if i'm wrong explain to me ! – Youcef LAIDANI May 20 '17 at 14:28
2

@YCF_L actually, the OP is contradicting. First says "*contains characters from a-z*" and then "*method to validate if the input is an int*". Not your fault. You're correct in your interpretation of it. – dumbPotato21 May 20 '17 at 14:30
@cricket_007 what about my solution now? – Youcef LAIDANI May 20 '17 at 14:33
The question still only asks for a-z – OneCricketeer May 20 '17 at 18:54
@cricket_007 i do that just for you :) to prove that the question was not clear, for that my first answer was like that :) – Youcef LAIDANI May 20 '17 at 18:55

Bohemian · Answer 2 · 2017-05-20T14:26:40.293

1

Use regex:

if (!userInput.matches("[a-z]+"))
    // Has characters other than a-z

If you want to allow uppercase too:

if (!userInput.matches("[a-zA-Z]+"))
    // Has characters other than a-z or A-Z

edited May 20 '17 at 14:26

answered May 20 '17 at 14:24

Bohemian

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xMarcoGP · Answer 3 · 2017-05-20T15:06:50.790

You could use something like:

if (!userInput.matches(".*[^a-z].*")) { 
    // Do something
}

Alternative solution to @Bohemian♦ to allow uppercase:

if (!userInput.toLowerCase().matches(".*[^a-z].*")) { 
    // Do something
}

A similar method, according to your source:

public static boolean containsAZ(JFXTextField txtUserInput) {
        if (!txtUserInput.getText().toLowerCase().matches(".*[^a-z].*"))
            return true;
        else
            System.err.println("Input is not containing chars between A-Z");

        return false;
}

There your question is, if it's possible to throw/catch an exception, you could do the following:

public static boolean containsAZ(JFXTextField txtUserInput) {
        try {
            if (!txtUserInput.toLowerCase().matches(".*[^a-z].*")) {
                return true;
            } else
                throw new MyException("Something happened");
        } catch (MyException e) {
            e.printStackTrace();
        }
        return false;
    }

Considering that you'll need a class:

class MyException extends Exception {

    public MyException(String e) {
        System.out.println(e);
    }

}

An abstract solution would be:

public class MyException extends Exception {
        // special exception code goes here
}

Throw it as:

 throw new MyException ("Something happened")

Catch as:

catch (MyException e)
{
   // Do something
}

For more info, check this for regex.

Validate Input - String

3 Answers3