How can I not allow the user to type numbers and only text in Java?

Question

I am creating a program about registration in which the user has to put name, password, email, etc. But in the fields such as name I want the user can only put text instead of numbers,and that if he puts a number appears a message to say that he can not put numbers but only type in text. How is it possible to do this ? With a method that checks the length of the field ? If you can help me, I’d appreciate it,.

Here is the code :

String nome,email;
double password,account; 

nome = JOptionPane.showInputDialog("Qual seu nome ? ");
email = JOptionPane.showInputDialog("Qual seu email ?");
account = Double.parseDouble(JOptionPane.showInputDialog("Digite uma account : "));
password = Double.parseDouble(JOptionPane.showInputDialog("Digite um password : "));

Answer 1

Well, it’s simple. By the code you put in and by Joptionpane I see that you are working with Java SE.

You can create a method to validate if the user input contains only text (text is only alphabetic characters) through regex.

Regular Expression (regex) is nothing more than a string of characters that define a search pattern in Strings, you can create expressions to validate a multitude of patterns such as emails, web addresses, cpfs, etc.. to learn more.

I will give you two options of expressions to start your studies on the subject and help you achieve the goal.

1. The first: "[a-za-Z s]+" In this you will validate only lower case letters (a-z), upper case letters (A-Z) and white space ( s). The + character indicates that this combination can occur 1 or more times. Check out the applied example here, as you will notice this expression will not accept special characters or accents and if you want them accepted I will let you search yourself, a link to begin with.

2. The second: "[^\d]+" This expression is easier if you just don’t want to accept number and want to accept any other character type. The character is used to negate the character d that indicates the digits. See the example in practice.

To apply in java you only need a string to call the class’s Matches method, see an example method:

public boolean matchesOnlyText(String text) {
    return text.matches("[^\\d]+"); //Passa para o método matches a regex
    //Se tiver número na string irá retornar falso
    //Note o uso de duas \\, uma sendo obrigatória para servir de caractere de escape
}

Now according to your own example of code, you can do something like:

String nome = JOptionPane.showInputDialog("Qual seu nome ? ");
if(!matchesOnlyText(nome)) {
    JOptionPane.showMessageDialog(null, "Você não pode inserir números no nome.");
}

I hope to have helped, at least to start your studies of regex.

Answer 2

You can monitor what the user is typing through the "Keytyped" event of a jTexfField and there make the proper treatments as example below:

private void tfNomeUsuarioKeyTyped(java.awt.event.KeyEvent evt) {
//Na variável "c" armazenamos o que o usuário digitou    
char c=evt.getKeyChar();

//Aqui verificamos se o que foi digitado é um número, um backspace ou um delete. Se for, consumimos o evento, ou seja, o jTextField não receberá o valor digitado
if((Character.isDigit(c) || (c==KeyEvent.VK_BACK_SPACE) || c==KeyEvent.VK_DELETE)){
        evt.consume();
    }                
}