捕获字符串异常

Question

I'm making a jTextField restrict integer input in netbeans and I don't know what to do. I'm doing it like this:

private void txtNameKeyReleased(java.awt.event.KeyEvent evt) {
    try {
        String j = (String) txtName.getText();
    } catch ("Which Exception to Catch?") {
        if (!txtAge.getText().isEmpty()) {
            jOptionPane1.showMessageDialog(null,
                    "Please enter string values");
            txtAge.setText(txtAge.getText().replaceAll("[^a-z]", ""));
        }
    }
}

What should I put on the catch?

Answer 1

You could just test the input against a regular expression using String.matches() to make sure it's only digits (no need to catch an exception such as a NumberFormatException - it can be considered bad practice to provoke exceptions to validate conditions).

String j = txtAge.getText();
if (!j.matches("\\d+")) { 
    // It is not a number
}

If you just want to try to convert to an Integer directly and catch an exception you should use Integer.parseInt() (it will throw a NumberFormatException if the input can't be parsed as an Integer ):

String j = txtAge.getText();
try { 
    Integer i = Integer.parseInt(txtAge);
}
catch (NumberFormatException e) { 
    // j isn't a number...
} 

EDIT : There seems to be a little confusion with the answer you provided. In your question the error message was Please enter integer values , as if valid input was only digits. In the answer you posted the message was Please enter String values .

If you want to validate the input doesn't have any numbers, you'll have to use another regex, such as .*\\\\d.*" . If it matches, it means it has a digit. Or you could also use \\\\D+ to ensure it has one or more non-digits .

Answer 2

I've solved my problem like this:

private void txtNameKeyReleased(java.awt.event.KeyEvent evt) {
String j = (String)txtName.getText();
if ( j.matches("\\d+") && !txtName.getText().isEmpty()) {
jOptionPane1.showMessageDialog(null, "Please enter String values");
txtName.setText("");
} }

Thanks for the ones who tried to help me :)